A polymer (; Greek ''

poly- Poly, from the Greek :wikt:πολύς, πολύς meaning "many" or "much", may refer to: Businesses * China Poly Group Corporation, a Chinese business group, and its subsidiaries: ** Poly Property, a Hong Kong incorporated Chinese property devel ...

'', "many" + '' -mer'', "part") is a substance or

material Material is a substance or mixture of substances that constitutes an object. Materials can be pure or impure, living or non-living matter. Materials can be classified on the basis of their physical and chemical properties, or on their geolo ...

consisting of very large

molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bio ...

s called

macromolecule A macromolecule is a very large molecule important to biophysical processes, such as a protein or nucleic acid. It is composed of thousands of covalently bonded atoms. Many macromolecules are polymers of smaller molecules called monomers. ...

s, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic and natural polymers play essential and ubiquitous roles in everyday life. Polymers range from familiar synthetic plastics such as

polystyrene Polystyrene (PS) is a synthetic polymer made from monomers of the aromatic hydrocarbon styrene. Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin per unit weight. It is ...

to natural

biopolymer Biopolymers are natural polymers produced by the cells of living organisms. Like other polymers, biopolymers consist of monomeric units that are covalently bonded in chains to form larger molecules. There are three main classes of biopolymers ...

s such as DNA and

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respon ...

s that are fundamental to biological structure and function. Polymers, both natural and synthetic, are created via

polymerization In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many fo ...

of many small molecules, known as monomers. Their consequently large

molecular mass The molecular mass (''m'') is the mass of a given molecule: it is measured in daltons (Da or u). Different molecules of the same compound may have different molecular masses because they contain different isotopes of an element. The related quant ...

, relative to

small molecule Within the fields of molecular biology and pharmacology, a small molecule or micromolecule is a low molecular weight (≤ 1000 daltons) organic compound that may regulate a biological process, with a size on the order of 1 nm. Many drugs are ...

compounds, produces unique physical properties including

toughness In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing.elasticity, viscoelasticity, and a tendency to form

amorphous In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid, glassy solid) is a solid that lacks the long-range order that is characteristic of a crystal. Etymology The term comes from the Greek language ...

and semicrystalline structures rather than

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macr ...

s. The term "polymer" derives from the Greek word πολύς (''polus'', meaning "many, much") and μέρος (''meros'', meaning "part"). The term was coined in 1833 by

Jöns Jacob Berzelius Baron Jöns Jacob Berzelius (; by himself and his contemporaries named only Jacob Berzelius, 20 August 1779 – 7 August 1848) was a Swedish chemist. Berzelius is considered, along with Robert Boyle, John Dalton, and Antoine Lavoisier, to be ...

, though with a definition distinct from the modern

IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...

definition. The modern concept of polymers as covalently bonded macromolecular structures was proposed in 1920 by

Hermann Staudinger Hermann Staudinger (; 23 March 1881 – 8 September 1965) was a German organic chemist who demonstrated the existence of macromolecules, which he characterized as polymers. For this work he received the 1953 Nobel Prize in Chemistry. He is also ...

, who spent the next decade finding experimental evidence for this hypothesis. Polymers are studied in the fields of polymer science (which includes polymer chemistry and

polymer physics Polymer physics is the field of physics that studies polymers, their fluctuations, mechanical properties, as well as the kinetics of reactions involving degradation and polymerisation of polymers and monomers respectively.P. Flory, ''Principles of ...

biophysics Biophysics is an interdisciplinary science that applies approaches and methods traditionally used in physics to study biological phenomena. Biophysics covers all scales of biological organization, from molecular to organismic and populations. ...

and materials science and engineering. Historically, products arising from the linkage of repeating units by covalent

chemical bond A chemical bond is a lasting attraction between atoms or ions that enables the formation of molecules and crystals. The bond may result from the electrostatic force between oppositely charged ions as in ionic bonds, or through the sharing o ...

s have been the primary focus of polymer science. An emerging important area now focuses on

supramolecular polymer The term "polymer" refers to large molecules whose structure is composed of multiple repeating units and the prefix "supra" meaning "beyond the limits of". Supramolecular polymers are a new category of polymers that can potentially be used for mat ...

s formed by non-covalent links. Polyisoprene of

latex Latex is an emulsion (stable dispersion) of polymer microparticles in water. Latexes are found in nature, but synthetic latexes are common as well. In nature, latex is found as a milky fluid found in 10% of all flowering plants (angiosper ...

rubber Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds. Thailand, Malaysia, a ...

is an example of a natural polymer, and the

styrofoam Styrofoam is a trademarked brand of closed-cell extruded polystyrene foam (XPS), commonly called "Blue Board", manufactured as foam continuous building insulation board used in walls, roofs, and foundations as thermal insulation and water barrier ...

is an example of a synthetic polymer. In biological contexts, essentially all biological

s—i.e., proteins (polyamides),

nucleic acid Nucleic acids are biopolymers, macromolecules, essential to all known forms of life. They are composed of nucleotides, which are the monomers made of three components: a 5-carbon sugar, a phosphate group and a nitrogenous base. The two main ...

s (polynucleotides), and polysaccharides—are purely polymeric, or are composed in large part of polymeric components. Polymer chain SPT

Common examples

Polymers are of two types: naturally occurring and synthetic or ''man made''.

Natural

Natural polymeric materials such as hemp,

shellac Shellac () is a resin secreted by the female lac bug on trees in the forests of India and Thailand. It is processed and sold as dry flakes and dissolved in alcohol to make liquid shellac, which is used as a brush-on colorant, food glaze and ...

amber Amber is fossilized tree resin that has been appreciated for its color and natural beauty since Neolithic times. Much valued from antiquity to the present as a gemstone, amber is made into a variety of decorative objects."Amber" (2004). In M ...

wool Wool is the textile fibre obtained from sheep and other mammals, especially goats, rabbits, and camelids. The term may also refer to inorganic materials, such as mineral wool and glass wool, that have properties similar to animal wool. ...

silk Silk is a natural protein fiber, some forms of which can be woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form cocoons. The best-known silk is obtained from the ...

, and natural

have been used for centuries. A variety of other natural polymers exist, such as

cellulose Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...

, which is the main constituent of wood and paper.

Synthetic

The list of synthetic polymers, roughly in order of worldwide demand, includes

polyethylene Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and containers including ...

polypropylene Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications. It is produced via chain-growth polymerization from the monomer propylene. Polypropylene belongs to the group of polyolefins an ...

, polyvinyl chloride,

synthetic rubber A synthetic rubber is an artificial elastomer. They are polymers synthesized from petroleum byproducts. About 32-million metric tons of rubbers are produced annually in the United States, and of that amount two thirds are synthetic. Synthetic rubbe ...

phenol formaldehyde resin Phenol formaldehyde resins (PF) or phenolic resins (also infrequently called phenoplasts) are synthetic polymers obtained by the reaction of phenol or substituted phenol with formaldehyde. Used as the basis for Bakelite, PFs were the first comm ...

(or Bakelite),

neoprene Neoprene (also polychloroprene) is a family of synthetic rubbers that are produced by polymerization of chloroprene.Werner Obrecht, Jean-Pierre Lambert, Michael Happ, Christiane Oppenheimer-Stix, John Dunn and Ralf Krüger "Rubber, 4. Emulsion R ...

nylon Nylon is a generic designation for a family of synthetic polymers composed of polyamides ( repeating units linked by amide links).The polyamides may be aliphatic or semi-aromatic. Nylon is a silk-like thermoplastic, generally made from pet ...

, polyacrylonitrile, PVB, silicone, and many more. More than 330 million tons of these polymers are made every year (2015). Most commonly, the continuously linked backbone of a polymer used for the preparation of plastics consists mainly of

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...

atoms. A simple example is polyethylene ('polythene' in British English), whose repeat unit or monomer is

ethylene Ethylene ( IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds). Ethylene ...

. Many other structures do exist; for example, elements such as silicon form familiar materials such as silicones, examples being Silly Putty and waterproof plumbing sealant.

Oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as we ...

is also commonly present in polymer backbones, such as those of

polyethylene glycol Polyethylene glycol (PEG; ) is a polyether compound derived from petroleum with many applications, from industrial manufacturing to medicine. PEG is also known as polyethylene oxide (PEO) or polyoxyethylene (POE), depending on its molecular w ...

polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with ...

s (in

glycosidic bond A glycosidic bond or glycosidic linkage is a type of covalent bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate. A glycosidic bond is formed between the hemiacetal or hemiketal gr ...

s), and DNA (in phosphodiester bonds).

History

Polymers have been essential components of commodities since the early days of humankind. The use of

(

keratin Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, ...

cotton Cotton is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus '' Gossypium'' in the mallow family Malvaceae. The fiber is almost pure cellulose, and can contain minor p ...

and

linen Linen () is a textile made from the fibers of the flax plant. Linen is very strong, absorbent, and dries faster than cotton. Because of these properties, linen is comfortable to wear in hot weather and is valued for use in garments. It also ...

fibres (

) for garments, paper reed (

) for

paper Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, Textile, rags, poaceae, grasses or other vegetable sources in water, draining the water through fine mesh leaving the fibre e ...

are just a few examples of how our ancestors exploited polymer-containing raw materials to obtain artefacts. The latex sap of “caoutchouc” trees (

natural rubber Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds. Thailand, Malaysia, a ...

) reached Europe in the 16th century from South America long after the

Olmec The Olmecs () were the earliest known major Mesoamerican civilization. Following a progressive development in Soconusco, they occupied the tropical lowlands of the modern-day Mexican states of Veracruz and Tabasco. It has been speculated that ...

Maya Maya may refer to: Civilizations * Maya peoples, of southern Mexico and northern Central America ** Maya civilization, the historical civilization of the Maya peoples ** Maya language, the languages of the Maya peoples * Maya (Ethiopia), a popu ...

and

Aztec The Aztecs () were a Mesoamerican culture that flourished in central Mexico in the post-classic period from 1300 to 1521. The Aztec people included different ethnic groups of central Mexico, particularly those groups who spoke the Nahuatl ...

had started using it as a material to make balls, waterproof textiles and containers. The chemical manipulation of polymers dates back to the 19th century, although at the time the nature of these species was not understood. The behaviour of polymers was initially rationalised according to the theory proposed by Thomas Graham which considered them as colloidal aggregates of small molecules held together by unknown forces. Notwithstanding the lack of theoretical knowledge, the potential of polymers to provide innovative, accessible and cheap materials was immediately grasped. The work carried out by Braconnot, Parkes, Ludersdorf, Hayard and many others on the modification of natural polymers determined many significant advances in the field. Their contributions led to the discovery of materials such as celluloid, galalith, parkesine,

rayon Rayon is a semi-synthetic fiber, made from natural sources of regenerated cellulose, such as wood and related agricultural products. It has the same molecular structure as cellulose. It is also called viscose. Many types and grades of viscose ...

vulcanised rubber Vulcanization (British: Vulcanisation) is a range of processes for hardening rubbers. The term originally referred exclusively to the treatment of natural rubber with sulfur, which remains the most common practice. It has also grown to include ...

and, later, Bakelite: all materials that quickly entered industrial manufacturing processes and reached households as garments components (''e.g.'', fabrics, buttons), crockery and decorative items. In 1920,

published his seminal work “Über Polymerisation”, in which he proposed that polymers were in fact long chains of atoms linked by covalent bonds. His work was debated at length, but eventually it was accepted by the scientific community. Because of this work, Staudinger was awarded the Nobel Prize in 1953. After the 1930s polymers entered a golden age during which new types were discovered and quickly given commercial applications, replacing naturally-sourced materials. This development was fuelled by an industrial sector with a strong economic drive and it was supported by a broad academic community that contributed innovative syntheses of monomers from cheaper raw material, more efficient polymerisation processes, improved techniques for polymer characterisation and advanced, theoretical understanding of polymers. Since 1953, six Nobel prizes have been awarded in the area of polymer science, excluding those for research on biological macromolecules. This further testifies to its impact on modern science and technology. As Lord Todd summarised in 1980, “I am inclined to think that the development of polymerization is perhaps the biggest thing that chemistry has done, where it has had the biggest effect on everyday life”.

Synthesis

Polymerization is the process of combining many

s known as monomers into a covalently bonded chain or network. During the polymerization process, some chemical groups may be lost from each monomer. This happens in the polymerization of PET polyester. The monomers are terephthalic acid (HOOCC₆H₄COOH) and ethylene glycol (HOCH₂CH₂OH) but the repeating unit is OCC₆H₄COOCH₂CH₂O, which corresponds to the combination of the two monomers with the loss of two water molecules. The distinct piece of each monomer that is incorporated into the polymer is known as a repeat unit or monomer residue. Synthetic methods are generally divided into two categories,

step-growth polymerization Step-growth polymerization refers to a type of polymerization mechanism in which bi-functional or multifunctional monomers react to form first dimers, then trimers, longer oligomers and eventually long chain polymers. Many naturally occurrin ...

and chain polymerization. The essential difference between the two is that in chain polymerization, monomers are added to the chain one at a time only, such as in

, whereas in step-growth polymerization chains of monomers may combine with one another directly, such as in polyester. Step-growth polymerization can be divided into polycondensation, in which low-molar-mass by-product is formed in every reaction step, and polyaddition. Styrene radical chain polymerization

Newer methods, such as plasma polymerization do not fit neatly into either category. Synthetic polymerization reactions may be carried out with or without a

catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

. Laboratory synthesis of biopolymers, especially of proteins, is an area of intensive research.

Biological synthesis

There are three main classes of biopolymers:

polypeptide Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides ...

s, and polynucleotides. In living cells, they may be synthesized by enzyme-mediated processes, such as the formation of DNA catalyzed by

DNA polymerase A DNA polymerase is a member of a family of enzymes that catalyze the synthesis of DNA molecules from nucleoside triphosphates, the molecular precursors of DNA. These enzymes are essential for DNA replication and usually work in groups to create ...

. The synthesis of proteins involves multiple enzyme-mediated processes to transcribe genetic information from the DNA to

RNA Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...

and subsequently

translate Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transla ...

that information to synthesize the specified protein from

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...

s. The protein may be modified further following translation in order to provide appropriate structure and functioning. There are other biopolymers such as

, suberin, melanin, and

lignin Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity ...

Modification of natural polymers

Naturally occurring polymers such as

starch Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diets ...

, and rubber were familiar materials for years before synthetic polymers such as polyethene and perspex appeared on the market. Many commercially important polymers are synthesized by chemical modification of naturally occurring polymers. Prominent examples include the reaction of

nitric acid Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available ni ...

and

to form nitrocellulose and the formation of

vulcanized rubber Vulcanization (British: Vulcanisation) is a range of processes for hardening rubbers. The term originally referred exclusively to the treatment of natural rubber with sulfur, which remains the most common practice. It has also grown to inclu ...

by heating natural rubber in the presence of

sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...

. Ways in which polymers can be modified include

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...

, cross-linking, and end-capping.

Structure

The structure of a polymeric material can be described at different length scales, from the sub-nm length scale up to the macroscopic one. There is in fact a hierarchy of structures, in which each stage provides the foundations for the next one. The starting point for the description of the structure of a polymer is the identity of its constituent monomers. Next, the microstructure essentially describes the arrangement of these monomers within the polymer at the scale of a single chain. The microstructure determines the possibility for the polymer to form phases with different arrangements, for example through crystallization, the glass transition or microphase separation. These features play a major role in determining the physical and chemical properties of a polymer.

Monomers and repeat units

The identity of the repeat units (monomer residues, also known as "mers") comprising a polymer is its first and most important attribute. Polymer nomenclature is generally based upon the type of monomer residues comprising the polymer. A polymer which contains only a single type of repeat unit is known as a homopolymer, while a polymer containing two or more types of repeat units is known as a copolymer. A terpolymer is a copolymer which contains three types of repeat units.

Polystyrene Polystyrene (PS) is a synthetic polymer made from monomers of the aromatic hydrocarbon styrene. Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin per unit weight. It is ...

is composed only of styrene-based repeat units, and is classified as a homopolymer. Polyethylene terephthalate, even though produced from two different monomers ( ethylene glycol and terephthalic acid), is usually regarded as a homopolymer because only one type of repeat unit is formed. Ethylene-vinyl acetate contains more than one variety of repeat unit and is a copolymer. Some biological polymers are composed of a variety of different but structurally related monomer residues; for example, polynucleotides such as DNA are composed of four types of

nucleotide Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecul ...

subunits. : A polymer containing ionizable subunits (e.g., pendant carboxylic groups) is known as a polyelectrolyte or ionomer, when the fraction of ionizable units is large or small respectively.

Microstructure

The microstructure of a polymer (sometimes called configuration) relates to the physical arrangement of monomer residues along the backbone of the chain. These are the elements of polymer structure that require the breaking of a covalent bond in order to change. Various polymer structures can be produced depending on the monomers and reaction conditions: A polymer may consist of linear macromolecules containing each only one unbranched chain. In the case of unbranched polyethylene, this chain is a long-chain ''n''-alkane. There are also branched macromolecules with a main chain and side chains, in the case of polyethylene the side chains would be alkyl groups. In particular unbranched macromolecules can be in the solid state semi-crystalline, crystalline chain sections highlighted red in the figure below. While branched and unbranched polymers are usually thermoplastics, many

elastomer An elastomer is a polymer with viscoelasticity (i.e. both viscosity and elasticity) and with weak intermolecular forces, generally low Young's modulus and high failure strain compared with other materials. The term, a portmanteau of ''elastic ...

s have a wide-meshed cross-linking between the "main chains". Close-meshed crosslinking, on the other hand, leads to

thermosets In materials science, a thermosetting polymer, often called a thermoset, is a polymer that is obtained by irreversibly hardening ("curing") a soft solid or viscous liquid prepolymer ( resin). Curing is induced by heat or suitable radiation an ...

. Cross-links and branches are shown as red dots in the figures. Highly branched polymers are amorphous and the molecules in the solid interact randomly. :

Polymer architecture

An important microstructural feature of a polymer is its architecture and shape, which relates to the way branch points lead to a deviation from a simple linear chain. A

branched polymer In polymer chemistry, branching is the regular or irregular attachment of side chains to a polymer's backbone chain. It occurs by the replacement of a substituent (e.g. a hydrogen atom) on a monomer subunit by another covalently-bonded ch ...

molecule is composed of a main chain with one or more substituent side chains or branches. Types of branched polymers include

star polymer Star-shaped polymers are the simplest class of branched polymers with a general structure consisting of several (at least three) linear chains connected to a central core. The core, or the center, of the polymer can be an atom, molecule, or macr ...

s, comb polymers, polymer brushes, dendronized polymers, ladder polymers, and dendrimers. There exist also

two-dimensional polymer A two-dimensional polymer (2DP) is a sheet-like monomolecular macromolecule consisting of laterally connected repeat units with end groups along all edges. This recent definition of 2DP is based on Hermann Staudinger's polymer concept from the 1 ...

s (2DP) which are composed of topologically planar repeat units. A polymer's architecture affects many of its physical properties including solution viscosity, melt viscosity, solubility in various solvents, glass-transition temperature and the size of individual polymer coils in solution. A variety of techniques may be employed for the synthesis of a polymeric material with a range of architectures, for example

living polymerization In polymer chemistry, living polymerization is a form of chain growth polymerization where the ability of a growing polymer chain to terminate has been removed. This can be accomplished in a variety of ways. Chain termination and chain transfer ...

Chain length

A common means of expressing the length of a chain is the degree of polymerization, which quantifies the number of monomers incorporated into the chain.Rubinstein, p. 3 As with other molecules, a polymer's size may also be expressed in terms of

molecular weight A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...

. Since synthetic polymerization techniques typically yield a statistical distribution of chain lengths, the molecular weight is expressed in terms of weighted averages. The

number-average molecular weight The molar mass distribution (or molecular weight distribution) describes the relationship between the number of moles of each polymer species (Ni) and the molar mass (Mi) of that species. In linear polymers, the individual polymer chains rarely h ...

(''M''_n) and

weight-average molecular weight The molar mass distribution (or molecular weight distribution) describes the relationship between the number of moles of each polymer species (Ni) and the molar mass (Mi) of that species. In linear polymers, the individual polymer chains rarely hav ...

(''M''_w) are most commonly reported.Rubinstein, pp. 23–24 The ratio of these two values (''M''_w / ''M''_n) is the dispersity (''Đ''), which is commonly used to express the width of the molecular weight distribution. The physical properties of polymer strongly depend on the length (or equivalently, the molecular weight) of the polymer chain.Rubinstein, p. 5 One important example of the physical consequences of the molecular weight is the scaling of the

viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...

(resistance to flow) in the melt. The influence of the weight-average molecular weight (

M_w

) on the melt viscosity (

\eta

) depends on whether the polymer is above or below the onset of entanglements. Below the entanglement molecular weight,

\eta \sim ^

, whereas above the entanglement molecular weight,

\eta \sim ^

. In the latter case, increasing the polymer chain length 10-fold would increase the viscosity over 1000 times. Increasing chain length furthermore tends to decrease chain mobility, increase strength and toughness, and increase the glass-transition temperature (T_g). This is a result of the increase in chain interactions such as van der Waals attractions and entanglements that come with increased chain length. These interactions tend to fix the individual chains more strongly in position and resist deformations and matrix breakup, both at higher stresses and higher temperatures.

Monomer arrangement in copolymers

Copolymers are classified either as statistical copolymers, alternating copolymers, block copolymers, graft copolymers or gradient copolymers. In the schematic figure below, Ⓐ and Ⓑ symbolize the two repeat units. : *Alternating copolymers possess two regularly alternating monomer residues:Painter, p. 14 . An example is the equimolar copolymer of styrene and maleic anhydride formed by free-radical chain-growth polymerization.Rudin p.18-20 A step-growth copolymer such as Nylon 66 can also be considered a strictly alternating copolymer of diamine and diacid residues, but is often described as a homopolymer with the dimeric residue of one amine and one acid as a repeat unit.Cowie p.104 *Periodic copolymers have more than two species of monomer units in a regular sequence. *Statistical copolymers have monomer residues arranged according to a statistical rule. A statistical copolymer in which the probability of finding a particular type of monomer residue at a particular point in the chain is independent of the types of surrounding monomer residue may be referred to as a truly random copolymer.Painter, p. 15 For example, the chain-growth copolymer of vinyl chloride and vinyl acetate is random. *Block copolymers have long sequences of different monomer units. Polymers with two or three blocks of two distinct chemical species (e.g., A and B) are called diblock copolymers and triblock copolymers, respectively. Polymers with three blocks, each of a different chemical species (e.g., A, B, and C) are termed triblock terpolymers. *Graft or grafted copolymers contain side chains or branches whose repeat units have a different composition or configuration than the main chain. The branches are added on to a preformed main chain macromolecule. Monomers within a copolymer may be organized along the backbone in a variety of ways. A copolymer containing a controlled arrangement of monomers is called a sequence-controlled polymer. Alternating, periodic and block copolymers are simple examples of sequence-controlled polymers.

Tacticity

Tacticity describes the relative

stereochemistry Stereochemistry, a subdiscipline of chemistry, involves the study of the relative spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focuses on the relationships between stereo ...

of chiral centers in neighboring structural units within a macromolecule. There are three types of tacticity: isotactic (all substituents on the same side), atactic (random placement of substituents), and

syndiotactic Tacticity (from el, τακτικός, taktikos, "relating to arrangement or order") is the relative stereochemistry of adjacent chiral centers within a macromolecule. The practical significance of tacticity rests on the effects on the physical ...

(alternating placement of substituents). :

Morphology

Polymer morphology generally describes the arrangement and microscale ordering of polymer chains in space. The macroscopic physical properties of a polymer are related to the interactions between the polymer chains. * Disordered polymers: In the solid state, atactic polymers, polymers with a high degree of branching and random copolymers form

(i.e. glassy structures).Bernd Tieke: ''Makromolekulare Chemie.'' 3. Auflage, Wiley-VCH, Weinheim 2014, S. 295f (in German). In melt and solution, polymers tend to form a constantly changing "statistical cluster", see freely-jointed-chain model. In the

solid state Solid state, or solid matter, is one of the four fundamental states of matter. Solid state may also refer to: Electronics * Solid-state electronics, circuits built of solid materials * Solid state ionics, study of ionic conductors and their u ...

, the respective conformations of the molecules are frozen. Hooking and entanglement of chain molecules lead to a "mechanical bond" between the chains. Intermolecular and intramolecular attractive forces only occur at sites where molecule segments are close enough to each other. The irregular structures of the molecules prevent a narrower arrangement. * Linear polymers with periodic structure, low branching and stereoregularity (e. g. not atactic) have a semi-crystalline structure in the solid state. In simple polymers (such as polyethylene), the chains are present in the crystal in zigzag conformation. Several zigzag conformations form dense chain packs, called crystallites or lamellae. The lamellae are much thinner than the polymers are long (often about 10 nm). Wolfgang Kaiser: ''Kunststoffchemie für Ingenieure.'' 3. Auflage, Carl Hanser, München 2011, S. 84. They are formed by more or less regular folding of one or more molecular chains. Amorphous structures exist between the lamellae. Individual molecules can lead to entanglements between the lamellae and can also be involved in the formation of two (or more) lamellae (chains than called tie molecules). Several lamellae form a superstructure, a spherulite, often with a diameter in the range of 0.05 to 1 mm. :The type and arrangement of (functional) residues of the repeat units effects or determines the crystallinity and strength of the secondary valence bonds. In isotactic polypropylene, the molecules form a helix. Like the zigzag conformation, such helices allow a dense chain packing. Particularly strong intermolecular interactions occur when the residues of the repeating units allow the formation of

hydrogen bond In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing ...

s, as in the case of ''p''-aramid. The formation of strong intramolecular associations may produce diverse folded states of single linear chains with distinct circuit topology. Crystallinity and superstructure are always dependent on the conditions of their formation, see also: crystallization of polymers. Compared to amorphous structures, semi-crystalline structures lead to a higher stiffness, density, melting temperature and higher resistance of a polymer. * Cross-linked polymers: Wide-meshed cross-linked polymers are

s and cannot be molten (unlike

thermoplastic A thermoplastic, or thermosoft plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling. Most thermoplastics have a high molecular weight. The polymer chains associat ...

s); heating cross-linked polymers only leads to

decomposition Decomposition or rot is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is ...

Thermoplastic elastomer Thermoplastic elastomers (TPE), sometimes referred to as thermoplastic rubbers, are a class of copolymers or a physical mix of polymers (usually a plastic and a rubber) that consist of materials with both thermoplastic and elastomeric propertie ...

s, on the other hand, are reversibly "physically crosslinked" and can be molten. Block copolymers in which a hard segment of the polymer has a tendency to crystallize and a soft segment has an amorphous structure are one type of thermoplastic elastomers: the hard segments ensure wide-meshed, physical crosslinking.

Crystallinity

When applied to polymers, the term ''crystalline'' has a somewhat ambiguous usage. In some cases, the term ''crystalline'' finds identical usage to that used in conventional

crystallography Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids. Crystallography is a fundamental subject in the fields of materials science and solid-state physics (condensed matter physics). The wo ...

. For example, the structure of a crystalline protein or polynucleotide, such as a sample prepared for

x-ray crystallography X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angle ...

, may be defined in terms of a conventional unit cell composed of one or more polymer molecules with cell dimensions of hundreds of

angstrom The angstromEntry "angstrom" in the Oxford online dictionary. Retrieved on 2019-03-02 from https://en.oxforddictionaries.com/definition/angstrom.Entry "angstrom" in the Merriam-Webster online dictionary. Retrieved on 2019-03-02 from https://www.m ...

s or more. A synthetic polymer may be loosely described as crystalline if it contains regions of three-dimensional ordering on atomic (rather than macromolecular) length scales, usually arising from intramolecular folding or stacking of adjacent chains. Synthetic polymers may consist of both crystalline and amorphous regions; the degree of crystallinity may be expressed in terms of a weight fraction or volume fraction of crystalline material. Few synthetic polymers are entirely crystalline. The crystallinity of polymers is characterized by their degree of crystallinity, ranging from zero for a completely non-crystalline polymer to one for a theoretical completely crystalline polymer. Polymers with microcrystalline regions are generally tougher (can be bent more without breaking) and more impact-resistant than totally amorphous polymers. Polymers with a degree of crystallinity approaching zero or one will tend to be transparent, while polymers with intermediate degrees of crystallinity will tend to be opaque due to light scattering by crystalline or glassy regions. For many polymers, crystallinity may also be associated with decreased transparency.

Chain conformation

The space occupied by a polymer molecule is generally expressed in terms of radius of gyration, which is an average distance from the center of mass of the chain to the chain itself. Alternatively, it may be expressed in terms of

pervaded volume Pervaded volume is a measure of the size of a polymer chain in space. In particular, it is "the volume of solution spanned by the polymer chain". Scaling The pervaded volume V scales as the cube of the chain size V \approx R^3 R is some lengt ...

, which is the volume spanned by the polymer chain and scales with the cube of the radius of gyration. The simplest theoretical models for polymers in the molten, amorphous state are ideal chains.

Properties

Polymer properties depend of their structure and they are divided into classes according to their physical bases. Many physical and chemical properties describe how a polymer behaves as a continuous macroscopic material. They are classified as bulk properties, or intensive properties according to

thermodynamics Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws o ...

Mechanical properties

The bulk properties of a polymer are those most often of end-use interest. These are the properties that dictate how the polymer actually behaves on a macroscopic scale.

Tensile strength

The tensile strength of a material quantifies how much elongating stress the material will endure before failure. This is very important in applications that rely upon a polymer's physical strength or durability. For example, a rubber band with a higher tensile strength will hold a greater weight before snapping. In general, tensile strength increases with polymer chain length and crosslinking of polymer chains.

Young's modulus of elasticity

Young's modulus Young's modulus E, the Young modulus, or the modulus of elasticity in tension or compression (i.e., negative tension), is a mechanical property that measures the tensile or compressive stiffness of a solid material when the force is applied ...

quantifies the elasticity of the polymer. It is defined, for small strains, as the ratio of rate of change of stress to strain. Like tensile strength, this is highly relevant in polymer applications involving the physical properties of polymers, such as rubber bands. The modulus is strongly dependent on temperature. Viscoelasticity describes a complex time-dependent elastic response, which will exhibit

hysteresis Hysteresis is the dependence of the state of a system on its history. For example, a magnet may have more than one possible magnetic moment in a given magnetic field, depending on how the field changed in the past. Plots of a single component of ...

in the stress-strain curve when the load is removed. Dynamic mechanical analysis or DMA measures this complex modulus by oscillating the load and measuring the resulting strain as a function of time.

Transport properties

Transport properties Transport (in British English), or transportation (in American English), is the intentional movement of humans, animals, and goods from one location to another. Modes of transport include air, land ( rail and road), water, cable, pip ...

such as diffusivity describe how rapidly molecules move through the polymer matrix. These are very important in many applications of polymers for films and membranes. The movement of individual macromolecules occurs by a process called reptation in which each chain molecule is constrained by entanglements with neighboring chains to move within a virtual tube. The theory of reptation can explain polymer molecule dynamics and viscoelasticity.

Phase behavior

Crystallization and melting

Depending on their chemical structures, polymers may be either semi-crystalline or amorphous. Semi-crystalline polymers can undergo crystallization and melting transitions, whereas amorphous polymers do not. In polymers, crystallization and melting do not suggest solid-liquid phase transitions, as in the case of water or other molecular fluids. Instead, crystallization and melting refer to the phase transitions between two solid states (''i.e.'', semi-crystalline and amorphous). Crystallization occurs above the glass-transition temperature (''T''_g) and below the melting temperature (''T''_m).

Glass transition

All polymers (amorphous or semi-crystalline) go through glass transitions. The glass-transition temperature (''T''_g) is a crucial physical parameter for polymer manufacturing, processing, and use. Below ''T''_g, molecular motions are frozen and polymers are brittle and glassy. Above ''T''_g, molecular motions are activated and polymers are rubbery and viscous. The glass-transition temperature may be engineered by altering the degree of branching or crosslinking in the polymer or by the addition of

plasticizer A plasticizer ( UK: plasticiser) is a substance that is added to a material to make it softer and more flexible, to increase its plasticity, to decrease its viscosity, and/or to decrease friction during its handling in manufacture. Plasticiz ...

s. Whereas crystallization and melting are first-order

phase transition In chemistry, thermodynamics, and other related fields, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states ...

s, the glass transition is not. The glass transition shares features of second-order phase transitions (such as discontinuity in the heat capacity, as shown in the figure), but it is generally not considered a thermodynamic transition between equilibrium states.

Mixing behavior

In general, polymeric mixtures are far less miscible than mixtures of

materials. This effect results from the fact that the driving force for mixing is usually

entropy Entropy is a scientific concept, as well as a measurable physical property, that is most commonly associated with a state of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodyna ...

, not interaction energy. In other words, miscible materials usually form a solution not because their interaction with each other is more favorable than their self-interaction, but because of an increase in entropy and hence free energy associated with increasing the amount of volume available to each component. This increase in entropy scales with the number of particles (or moles) being mixed. Since polymeric molecules are much larger and hence generally have much higher specific volumes than small molecules, the number of molecules involved in a polymeric mixture is far smaller than the number in a small molecule mixture of equal volume. The energetics of mixing, on the other hand, is comparable on a per volume basis for polymeric and small molecule mixtures. This tends to increase the free energy of mixing for polymer solutions and thereby making solvation less favorable, and thereby making the availability of concentrated solutions of polymers far rarer than those of small molecules. Furthermore, the phase behavior of polymer solutions and mixtures is more complex than that of small molecule mixtures. Whereas most small molecule solutions exhibit only an upper critical solution temperature phase transition (UCST), at which phase separation occurs with cooling, polymer mixtures commonly exhibit a lower critical solution temperature phase transition (LCST), at which phase separation occurs with heating. In dilute solutions, the properties of the polymer are characterized by the interaction between the solvent and the polymer. In a good solvent, the polymer appears swollen and occupies a large volume. In this scenario, intermolecular forces between the solvent and monomer subunits dominate over intramolecular interactions. In a bad solvent or poor solvent, intramolecular forces dominate and the chain contracts. In the theta solvent, or the state of the polymer solution where the value of the second virial coefficient becomes 0, the intermolecular polymer-solvent repulsion balances exactly the intramolecular monomer-monomer attraction. Under the theta condition (also called the Flory condition), the polymer behaves like an ideal random coil. The transition between the states is known as a coil–globule transition.

Inclusion of plasticizers

Inclusion of plasticizers tends to lower T_g and increase polymer flexibility. Addition of the plasticizer will also modify dependence of the glass-transition temperature T_g on the cooling rate. The mobility of the chain can further change if the molecules of plasticizer give rise to hydrogen bonding formation. Plasticizers are generally small molecules that are chemically similar to the polymer and create gaps between polymer chains for greater mobility and fewer interchain interactions. A good example of the action of plasticizers is related to polyvinylchlorides or PVCs. A uPVC, or unplasticized polyvinylchloride, is used for things such as pipes. A pipe has no plasticizers in it, because it needs to remain strong and heat-resistant. Plasticized PVC is used in clothing for a flexible quality. Plasticizers are also put in some types of cling film to make the polymer more flexible.

Chemical properties

The attractive forces between polymer chains play a large part in determining the polymer’s properties. Because polymer chains are so long, they have many such interchain interactions per molecule, amplifying the effect of these interactions on the polymer properties in comparison to attractions between conventional molecules. Different side groups on the polymer can lend the polymer to ionic bonding or

hydrogen bonding In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing ...

between its own chains. These stronger forces typically result in higher tensile strength and higher crystalline melting points. The intermolecular forces in polymers can be affected by dipoles in the monomer units. Polymers containing

amide In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula , where R, R', and R″ represent organic groups or hydrogen atoms. The amide group is called a peptide bond when it is ...

carbonyl In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups. A compound containin ...

groups can form

s between adjacent chains; the partially positively charged hydrogen atoms in N-H groups of one chain are strongly attracted to the partially negatively charged oxygen atoms in C=O groups on another. These strong hydrogen bonds, for example, result in the high tensile strength and melting point of polymers containing

urethane Urethane may refer to: * Ethyl carbamate, a chemical compound which is an ester of carbamic acid * Polyurethane, a polymer composed of a chain of organic units joined by carbamate (urethane) links *Carbamate In organic chemistry, a carbamate is ...

or urea linkages. Polyesters have dipole-dipole bonding between the oxygen atoms in C=O groups and the hydrogen atoms in H-C groups. Dipole bonding is not as strong as hydrogen bonding, so a polyester's melting point and strength are lower than

Kevlar Kevlar (para-aramid) is a strong, heat-resistant synthetic fiber, related to other aramids such as Nomex and Technora. Developed by Stephanie Kwolek at DuPont in 1965, the high-strength material was first used commercially in the early 1970s ...

's ( Twaron), but polyesters have greater flexibility. Polymers with non-polar units such as polyethylene interact only through weak

Van der Waals force In molecular physics, the van der Waals force is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical electronic bond; they are comparatively weak and t ...

s. As a result, they typically have lower melting temperatures than other polymers. When a polymer is dispersed or dissolved in a liquid, such as in commercial products like paints and glues, the chemical properties and molecular interactions influence how the solution flows and can even lead to self-assembly of the polymer into complex structures. When a polymer is applied as a coating, the chemical properties will influence the adhesion of the coating and how it interacts with external materials, such as superhydrophobic polymer coatings leading to water resistance. Overall the chemical properties of a polymer are important elements for designing new polymeric material products.

Optical properties

Polymers such as PMMA and HEMA:MMA are used as matrices in the gain medium of solid-state dye lasers, also known as solid-state dye-doped polymer lasers. These polymers have a high surface quality and are also highly transparent so that the laser properties are dominated by the laser dye used to dope the polymer matrix. These type of lasers, that also belong to the class of organic lasers, are known to yield very narrow linewidths which is useful for spectroscopy and analytical applications. An important optical parameter in the polymer used in laser applications is the change in refractive index with temperature also known as dn/dT. For the polymers mentioned here the (dn/dT) ~ −1.4 × 10⁻⁴ in units of K⁻¹ in the 297 ≤ T ≤ 337 K range.

Electrical properties

Most conventional polymers such as polyethylene are

electrical insulators An electrical insulator is a material in which electric current does not flow freely. The atoms of the insulator have tightly bound electrons which cannot readily move. Other materials—semiconductors and conductors—conduct electric current ...

, but the development of polymers containing π-conjugated bonds has led to a wealth of polymer-based

semiconductor A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...

s, such as polythiophenes. This has led to many applications in the field of organic electronics.

Applications

Nowadays, synthetic polymers are used in almost all walks of life. Modern society would look very different without them. The spreading of polymer use is connected to their unique properties: low density, low cost, good thermal/electrical insulation properties, high resistance to corrosion, low-energy demanding polymer manufacture and facile processing into final products. For a given application, the properties of a polymer can be tuned or enhanced by combination with other materials, as in composites. Their application allows to save energy (lighter cars and planes, thermally insulated buildings), protect food and drinking water (packaging), save land and lower use of fertilizers (synthetic fibres), preserve other materials (coatings), protect and save lifes (hygiene, medical applications). A representative, non-exhaustive list of applications is given below. * Clothing, sportswear and accessories: polyester and PVC clothing, spandex, sport shoes, wetsuits, footballs and billiard balls, skis and snowboards, rackets, parachutes,

sail A sail is a tensile structure—which is made from fabric or other membrane materials—that uses wind power to propel sailing craft, including sailing ships, sailboats, windsurfers, ice boats, and even sail-powered land vehicles. Sails ma ...

s, tents and shelters. * Electronic and photonic technologies: organic field effect transistors (OFET), light emitting diodes (OLED) and solar cells, television components,

compact disc The compact disc (CD) is a digital optical disc data storage format that was co-developed by Philips and Sony to store and play digital audio recordings. In August 1982, the first compact disc was manufactured. It was then released in Octo ...

s (CD), photoresists,

holography Holography is a technique that enables a wavefront to be recorded and later re-constructed. Holography is best known as a method of generating real three-dimensional images, but it also has a wide range of other applications. In principle, i ...

. * Packaging and containers:

films A film also called a movie, motion picture, moving picture, picture, photoplay or (slang) flick is a work of visual art that simulates experiences and otherwise communicates ideas, stories, perceptions, feelings, beauty, or atmospher ...

, bottles, food packaging, barrels. * Insulation: electrical and

thermal insulation Thermal insulation is the reduction of heat transfer (i.e., the transfer of thermal energy between objects of differing temperature) between objects in thermal contact or in range of radiative influence. Thermal insulation can be achieved with ...

, spray foams. * Construction and structural applications:

garden furniture Garden furniture, also called patio furniture or outdoor furniture, is a type of furniture specifically designed for outdoor use. It is typically made of weather-resistant materials such as aluminium which is rust-proof. History The oldes ...

, PVC windows, flooring, sealing, pipes. * Paints, glues and lubricants:

varnish Varnish is a clear transparent hard protective coating or film. It is not a stain. It usually has a yellowish shade from the manufacturing process and materials used, but it may also be pigmented as desired, and is sold commercially in vario ...

, adhesives,

dispersant A dispersant or a dispersing agent is a substance, typically a surfactant, that is added to a suspension of solid or liquid particles in a liquid (such as a colloid or emulsion) to improve the separation of the particles and to prevent their set ...

s, anti-graffiti coatings, antifouling coatings, non-stick surfaces, lubricants. * Car parts:

tire A tire (American English) or tyre (British English) is a ring-shaped component that surrounds a wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide traction on the surface over which t ...

s, bumpers,

windshield The windshield (North American English) or windscreen (Commonwealth English) of an aircraft, car, bus, motorbike, truck, train, boat or streetcar is the front window, which provides visibility while protecting occupants from the elements. ...

s, windscreen wipers,

fuel tank A fuel tank (also called a petrol tank or gas tank) is a safe container for flammable fluids. Though any storage tank for fuel may be so called, the term is typically applied to part of an engine system in which the fuel is stored and propel ...

s, car seats. * Household items: buckets,

kitchenware :'' For a record label, see Kitchenware Records'' Kitchenware are the tools, utensils, appliances, dishes, and cookware used in food preparation, or the serving of food. Kitchenware can also be used in order to hold or store food before or af ...

, toys (e.g., construction sets and

Rubik's cube The Rubik's Cube is a 3-D combination puzzle originally invented in 1974 by Hungarian sculptor and professor of architecture Ernő Rubik. Originally called the Magic Cube, the puzzle was licensed by Rubik to be sold by Pentangle Puzzles in t ...

). * Medical applications:

blood bag Whole blood (WB) is human blood from a standard blood donation. It is used in the treatment of massive bleeding, in exchange transfusion, and when people donate blood to themselves. One unit of whole blood (~517 mls) brings up hemoglobin level ...

syringe A syringe is a simple reciprocating pump consisting of a plunger (though in modern syringes, it is actually a piston) that fits tightly within a cylindrical tube called a barrel. The plunger can be linearly pulled and pushed along the inside o ...

s, rubber gloves, surgical suture, contact lenses, prosthesis, controlled drug delivery and release, matrices for cell growth. * Personal hygiene and healthcare: diapers using

superabsorbent polymer A superabsorbent polymer (SAP) (also called slush powder) is a water-absorbing hydrophilic homopolymers or copolymers that can absorb and retain extremely large amounts of a liquid relative to its own mass. Water-absorbing polymers, which are cl ...

toothbrush A toothbrush is an oral hygiene tool used to clean the teeth, gums, and tongue. It consists of a head of tightly clustered bristles, atop of which toothpaste can be applied, mounted on a handle which facilitates the cleaning of hard-to-reach ...

es,

cosmetics Cosmetics are constituted mixtures of chemical compounds derived from either natural sources, or synthetically created ones. Cosmetics have various purposes. Those designed for personal care and skin care can be used to cleanse or protec ...

shampoo Shampoo () is a hair care product, typically in the form of a viscous liquid, that is used for cleaning hair. Less commonly, shampoo is available in solid bar format. Shampoo is used by applying it to wet hair, massaging the product into th ...

condom A condom is a sheath-shaped barrier device used during sexual intercourse to reduce the probability of pregnancy or a sexually transmitted infection (STI). There are both male and female condoms. With proper use—and use at every act of inte ...

s. * Security:

personal protective equipment Personal protective equipment (PPE) is protective clothing, helmets, goggles, or other garments or equipment designed to protect the wearer's body from injury or infection. The hazards addressed by protective equipment include physical, ...

, bulletproof vests,

space suit A space suit or spacesuit is a garment worn to keep a human alive in the harsh environment of outer space, vacuum and temperature extremes. Space suits are often worn inside spacecraft as a safety precaution in case of loss of cabin pressure ...

rope A rope is a group of yarns, plies, fibres, or strands that are twisted or braided together into a larger and stronger form. Ropes have tensile strength and so can be used for dragging and lifting. Rope is thicker and stronger than similarly ...

s. * Separation technologies: synthetic membranes, fuel cell membranes,

filtration Filtration is a physical separation process that separates solid matter and fluid from a mixture using a ''filter medium'' that has a complex structure through which only the fluid can pass. Solid particles that cannot pass through the filte ...

ion-exchange resin An ion-exchange resin or ion-exchange polymer is a resin or polymer that acts as a medium for ion exchange. It is an insoluble matrix (or support structure) normally in the form of small (0.25–1.43 mm radius) microbeads, usually white or ...

s. * Money: polymer banknotes and payment cards. *

3D printing 3D printing or additive manufacturing is the construction of a three-dimensional object from a CAD model or a digital 3D model. It can be done in a variety of processes in which material is deposited, joined or solidified under computer ...

Standardized nomenclature

There are multiple conventions for naming polymer substances. Many commonly used polymers, such as those found in consumer products, are referred to by a common or trivial name. The trivial name is assigned based on historical precedent or popular usage rather than a standardized naming convention. Both the

American Chemical Society The American Chemical Society (ACS) is a scientific society based in the United States that supports scientific inquiry in the field of chemistry. Founded in 1876 at New York University, the ACS currently has more than 155,000 members at all ...

(ACS) and

have proposed standardized naming conventions; the ACS and IUPAC conventions are similar but not identical. Examples of the differences between the various naming conventions are given in the table below: In both standardized conventions, the polymers' names are intended to reflect the monomer(s) from which they are synthesized (source based nomenclature) rather than the precise nature of the repeating subunit. For example, the polymer synthesized from the simple alkene ethene is called polyethene, retaining the ''-ene'' suffix even though the double bond is removed during the polymerization process: :→ :However, IUPAC structure based nomenclature is based on naming of the preferred constitutional repeating unit.

Characterization

Polymer characterization spans many techniques for determining the chemical composition, molecular weight distribution, and physical properties. Select common techniques include the following: * Size-exclusion chromatography (also called

gel permeation chromatography Gel permeation chromatography (GPC) is a type of size-exclusion chromatography (SEC), that separates analytes on the basis of size, typically in organic solvents. The technique is often used for the analysis of polymers. As a technique, SEC was f ...

), sometimes coupled with static light scattering, can used to determine the number-average molecular weight, weight-average molecular weight, and dispersity. *Scattering techniques, such as static light scattering and small-angle neutron scattering, are used to determine the dimensions ( radius of gyration) of macromolecules in solution or in the melt. These techniques are also used to characterize the three-dimensional structure of microphase-separated

block polymer In polymer chemistry, a copolymer is a polymer derived from more than one species of monomer. The polymerization of monomers into copolymers is called copolymerization. Copolymers obtained from the copolymerization of two monomer species are some ...

s, polymeric micelles, and other materials. * Wide-angle X-ray scattering (also called wide-angle X-ray diffraction) is used to determine the crystalline structure of polymers (or lack thereof). *Spectroscopy techniques, including Fourier-transform infrared spectroscopy,

Raman spectroscopy Raman spectroscopy () (named after Indian physicist C. V. Raman) is a spectroscopic technique typically used to determine vibrational modes of molecules, although rotational and other low-frequency modes of systems may also be observed. Raman s ...

, and nuclear magnetic resonance spectroscopy, can be used to determine the chemical composition. * Differential scanning calorimetry is used to characterize the thermal properties of polymers, such as the glass-transition temperature, crystallization temperature, and melting temperature. The glass-transition temperature can also be determined by dynamic mechanical analysis. * Thermogravimetry is a useful technique to evaluate the thermal stability of the polymer. * Rheology is used to characterize the flow and deformation behavior. It can be used to determine the

, modulus, and other rheological properties. Rheology is also often used to determine the molecular architecture (molecular weight, molecular weight distribution, branching) and to understand how the polymer can be processed.

Degradation

Polymer degradation is a change in the properties—tensile strength,

color Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are assoc ...

, shape, or molecular weight—of a polymer or polymer-based product under the influence of one or more environmental factors, such as

heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...

light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...

, and the presence of certain

chemical A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., wit ...

s, oxygen, and enzymes. This change in properties is often the result of bond breaking in the polymer backbone ( chain scission) which may occur at the chain ends or at random positions in the chain. Although such changes are frequently undesirable, in some cases, such as biodegradation and

recycling Recycling is the process of converting waste materials into new materials and objects. The Energy recycling, recovery of energy from waste materials is often included in this concept. The recyclability of a material depends on its ability t ...

, they may be intended to prevent environmental

pollution Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the ...

. Degradation can also be useful in biomedical settings. For example, a copolymer of polylactic acid and polyglycolic acid is employed in hydrolysable stitches that slowly degrade after they are applied to a wound. The susceptibility of a polymer to degradation depends on its structure. Epoxies and chains containing aromatic functionalities are especially susceptible to UV degradation while polyesters are susceptible to degradation by

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysis ...

. Polymers containing an unsaturated backbone degrade via ozone cracking. Carbon based polymers are more susceptible to thermal degradation than

inorganic polymer An inorganic polymer is a polymer with a skeletal structure that does not include carbon atoms in the backbone. Polymers containing inorganic and organic components are sometimes called hybrid polymers, and most so-called inorganic polymers are ...

s such as polydimethylsiloxane and are therefore not ideal for most high-temperature applications. The degradation of polyethylene occurs by random scission—a random breakage of the bonds that hold the

atom Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, liquid, gas ...

s of the polymer together. When heated above 450 °C, polyethylene degrades to form a mixture of hydrocarbons. In the case of chain-end scission, monomers are released and this process is referred to as unzipping or depolymerization. Which mechanism dominates will depend on the type of polymer and temperature; in general, polymers with no or a single small substituent in the repeat unit will decompose via random-chain scission. The sorting of polymer waste for recycling purposes may be facilitated by the use of the resin identification codes developed by the Society of the Plastics Industry to identify the type of plastic.

Product failure

Failure of safety-critical polymer components can cause serious accidents, such as fire in the case of cracked and degraded polymer fuel lines. Chlorine-induced cracking of acetal resin plumbing joints and polybutylene pipes has caused many serious floods in domestic properties, especially in the US in the 1990s. Traces of

chlorine Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine is ...

in the water supply attacked polymers present in the plumbing, a problem which occurs faster if any of the parts have been poorly extruded or injection molded. Attack of the acetal joint occurred because of faulty molding, leading to cracking along the threads of the fitting where there is stress concentration. Polymer oxidation has caused accidents involving

medical device A medical device is any device intended to be used for medical purposes. Significant potential for hazards are inherent when using a device for medical purposes and thus medical devices must be proved safe and effective with reasonable assur ...

s. One of the oldest known failure modes is ozone cracking caused by chain scission when

ozone Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...

gas attacks susceptible

s, such as

and nitrile rubber. They possess double bonds in their repeat units which are cleaved during ozonolysis. Cracks in fuel lines can penetrate the bore of the tube and cause fuel leakage. If cracking occurs in the engine compartment, electric sparks can ignite the

gasoline Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organic ...

and can cause a serious fire. In medical use degradation of polymers can lead to changes of physical and chemical characteristics of implantable devices. Nylon 66 is susceptible to acid hydrolysis, and in one accident, a fractured fuel line led to a spillage of diesel into the road. If

diesel fuel Diesel fuel , also called diesel oil, is any liquid fuel specifically designed for use in a diesel engine, a type of internal combustion engine in which fuel ignition takes place without a spark as a result of compression of the inlet air and ...

leaks onto the road, accidents to following cars can be caused by the slippery nature of the deposit, which is like black ice. Furthermore, the

asphalt concrete Asphalt concrete (commonly called asphalt, blacktop, or pavement in North America, and tarmac, bitumen macadam, or rolled asphalt in the United Kingdom and the Republic of Ireland) is a composite material commonly used to surface roads, parkin ...

road surface will suffer damage as a result of the diesel fuel dissolving the asphaltenes from the composite material, this resulting in the degradation of the asphalt surface and structural integrity of the road.

References

Bibliography

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External links

How to Analyze Polymers Using X-ray DiffractionPolymer Chemistry Hypertext, Educational resourceIntroduction to Polymers
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