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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 develo ...
'', "many" + '' -mer'', "part") is a
substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composition * Matter, anything that has mass and takes up space * Substance th ...
or
material Material is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composition * Matter, anything that has mass and t ...

material
consisting of very large
molecule A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion I ...

molecule
s, or
macromolecule macromolecule A macromolecule is a very large molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neu ...
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 plastic Plastics are a wide range of syntheticA synthetic is an artificial material produced by organic chemistry, organic chemical synthesis. Synthetic may also refer to: In the sense of both "combination" and "artificial" * Synthetic chemical or sy ...
s such as
polystyrene Polystyrene (PS) is a synthetic aromatic forms of benzene (top) combine to produce an average structure (bottom) In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, com ...

polystyrene
to natural
biopolymer Biopolymers are natural polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Repeat unit ...
s such as
DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral gro ...

DNA
and
protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a No ...

protein
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, monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks.Clayden, J ...
of many small molecules, known as
monomer In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during a ...

monomer
s. Their consequently large
molecular mass The molecular mass (''m'') is the mass of a given molecule: it is measured in dalton Dalton may refer to: Science * Dalton (crater), a lunar crater * Dalton (program), chemistry software * Dalton (unit) (Da), the atomic mass unit Entertainment ...
, relative to
small moleculeWithin the fields of molecular biology Molecular biology is the branch of biology that seeks to understand the molecule, molecular basis of biological activity in and between Cell (biology), cells, including biomolecule, molecular synthesis, modi ...
compound Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above fortified with defensive structu ...
s, produces unique
physical properties A physical property is any property Property (''latin: Res Privata'') in the Abstract and concrete, abstract is what belongs to or with something, whether as an attribute or as a component of said thing. In the context of this article, it is on ...
including
toughness In materials science The Interdisciplinarity, interdisciplinary field of materials science, also commonly termed materials science and engineering, covers the design and discovery of new materials, particularly solids. The intellectual origin ...
, high
elasticity Elasticity often refers to: *Elasticity (physics), continuum mechanics of bodies that deform reversibly under stress Elasticity may also refer to: Information technology * Elasticity (data store), the flexibility of the data model and the clu ...

elasticity
,
viscoelasticity In and , viscoelasticity is the property of that exhibit both and characteristics when undergoing . Viscous materials, like water, resist and linearly with time when a is applied. Elastic materials strain when stretched and immediately ret ...
, and a tendency to form
amorphous In condensed matter physics Condensed matter physics is the field of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science th ...

amorphous
and
semicrystalline Crystallinity refers to the degree of structural order in a solid Solid is one of the four fundamental states of matter (the others being liquid, gas and plasma). The molecules in a solid are closely packed together and contain the le ...
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, macrosco ...

crystal
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 Robert Boyle (; 25 January 1627 – ...

Jöns Jacob Berzelius
, 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 that represents chemists in individual countries. It is a member of the International Science Council (ISC). IUPAC ...
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 macromolecule macromolecule A macromolecule is a very large molecule File:Pentacene on Ni(111) STM.jpg, A scanning tu ...

Hermann Staudinger
, who spent the next decade finding experimental evidence for this hypothesis. Polymers are studied in the fields of
polymer science Polymer science or macromolecular science is a subfield of materials science The interdisciplinary field of materials science, also commonly termed materials science and engineering, covers the design and discovery of new materials, particular ...
(which includes
polymer chemistry Polymer chemistry is a sub-discipline of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior ...
and
polymer physicsPolymer physics is the field of physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entiti ...
),
biophysics uses protein domain dynamics on nanoscale Image:Protein translation.gif, 300px, A ribosome is a biological machine that utilizes nanoscale protein dynamics The nanoscopic scale (or nanoscale) usually refers to structures with a length scale ...
and
materials science and engineering ''Materials Science and Engineering'' may refer to several journals in the field of materials science and engineering: * '' Materials Science and Engineering A'' * '' Materials Science and Engineering B'' * ''Materials Science and Engineering ...
. Historically, products arising from the linkage of repeating units by
covalent A covalent bond is a chemical bond A chemical bond is a lasting attraction between atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes ...

covalent
chemical bond A chemical bond is a lasting attraction between atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday ...
s have been the primary focus of
polymer science Polymer science or macromolecular science is a subfield of materials science The interdisciplinary field of materials science, also commonly termed materials science and engineering, covers the design and discovery of new materials, particular ...
. An emerging important area now focuses on supramolecular polymers formed by non-covalent links.
Polyisoprene Polyisoprene is a collective name for polymers A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or material consisting of very large molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy imag ...

Polyisoprene
of
latex Latex is a stable dispersion (emulsion An emulsion is a mixture of two or more liquids that are normally Miscibility, immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class o ...

latex
rubber Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymer A polymer (; Greek ''poly- Poly, from the Greek :wikt:πολύς, πολύς meaning "many" or "much" ...

rubber
is an example of a natural polymer, and the
polystyrene Polystyrene (PS) is a synthetic aromatic forms of benzene (top) combine to produce an average structure (bottom) In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, com ...

polystyrene
of
styrofoam Styrofoam is a trademark A trademark (also written trade mark or trade-markThe styling of ''trademark'' as a single word is predominantly used in the United States and Philippines only, while the two-word styling ''trade mark'' is used in ...
is an example of a synthetic polymer. In biological contexts, essentially all biological
macromolecule macromolecule A macromolecule is a very large molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neu ...
s—i.e.,
protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a No ...

protein
s (polyamides),
nucleic acid Nucleic acids are biopolymers, macromolecules, essential to all Organism, known forms of life. They are composed of nucleotides, which are the monomers made of three components: a pentose, 5-carbon sugar, a phosphate group and a nitrogenous base. ...

nucleic acid
s (polynucleotides), and polysaccharides—are purely polymeric, or are composed in large part of polymeric components.


Common examples

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


Natural

Natural polymeric materials such as
hemp Hemp, or industrial hemp, is a botanical class of ''Cannabis sativa ''Cannabis sativa'' is an annual herbaceous flowering plant The flowering plants, also known as Angiospermae (), or Magnoliophyta (), are the most diverse group of Embry ...
,
shellac Shellac () is a resin In polymer chemistry and materials science, resin is a solid or highly Viscosity, viscous substance of plant or synthetic origin that is typically convertible into polymers. Resins are usually mixtures of organic co ...
,
amber Amber is fossil A fossil (from Classical Latin Classical Latin is the form of Latin language Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was ...

amber
,
wool Wool is the textile A textile is a flexible material made by creating an interlocking bundle of yarn Yarn is a long continuous length of interlocked fibres, suitable for use in the production of textiles, sewing, crocheting, knitti ...
,
silk Silk is a natural fiber, natural protein fiber, some forms of which can be weaving, woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form cocoon (silk), cocoons. The be ...

silk
, and natural
rubber Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymer A polymer (; Greek ''poly- Poly, from the Greek :wikt:πολύς, πολύς meaning "many" or "much" ...

rubber
have been used for centuries. A variety of other natural polymers exist, such as
cellulose Cellulose is an organic compound with the chemical formula, formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of glycosidic bond, β(1→4) linked glucose, D-glucose units. Cellulose is an important stru ...

cellulose
, 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 (incorrectly) polythene (abbreviated PE; IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents chemists in individual countr ...

polyethylene
,
polypropylene Polypropylene (PP), also known as polypropene, is a thermoplastic A thermoplastic, or thermosoftening plastic, is a plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling. Most the ...

polypropylene
,
polystyrene Polystyrene (PS) is a synthetic aromatic forms of benzene (top) combine to produce an average structure (bottom) In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, com ...

polystyrene
,
polyvinyl chloride Polyvinyl chloride (colloquial Colloquialism or colloquial language is the style (sociolinguistics), linguistic style used for casual (informal) communication. It is the most common functional style of speech, the idiom normally employed in ...
,
synthetic rubber A synthetic rubber is any artificial elastomer An elastomer is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or mac ...
,
phenol formaldehyde resin Phenol formaldehyde resins (PF) or phenolic resins are synthetic polymers obtained by the reaction of phenol or substituted phenol with formaldehyde. Used as the basis for Bakelite, PFs were the first commercial synthetic resins (plastics). They h ...
(or
Bakelite Bakelite ( ; sometimes spelled Baekelite) or polyoxybenzylmethylenglycolanhydride was the first plastic made from synthetic components. It is a thermosetting polymer, thermosetting phenol formaldehyde resin, formed from a condensation reaction o ...

Bakelite
),
neoprene Neoprene (also polychloroprene) is a family of synthetic rubber A synthetic rubber is any artificial elastomer An elastomer is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substan ...
,
nylon Nylon is a generic designation for a family of s composed of s ( linked by links).The polyamides may be or . Nylon is a -like , generally made from , that can be melt-processed into fibers, , or shapes. Nylon polymers can be mixed with a w ...

nylon
,
polyacrylonitrile Polyacrylonitrile (PAN), also known as polyvinyl cyanide and Creslan 61, is a synthetic, semicrystalline organic polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or ma ...

polyacrylonitrile
,
PVB
PVB
,
silicone A silicone or polysiloxane is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many R ...

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 (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
atoms. A simple example is polyethylene ('polythene' in British English), whose repeat unit or monomer is
ethylene Ethylene (IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Science C ...

ethylene
. Many other structures do exist; for example, elements such as silicon form familiar materials such as silicones, examples being
Silly Putty Silly Putty is a toy based on silicone polymers that have unusual physical properties. It bounces, but it breaks when given a sharp blow, and it can also flow like a liquid. It contains a viscoelasticity, viscoelastic liquid silicone, a type of ...
and waterproof plumbing sealant.
Oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

Oxygen
is also commonly present in polymer backbones, such as those of
polyethylene glycol Polyethylene glycol (PEG; ) is a polyether Ethers are a class of organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bo ...

polyethylene glycol
,
polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant found in . They are long chain carbohydrates composed of units bound together by . This carbohydrate can react with water () using as catalyst, which produces constituent sugars ...
s (in
glycosidic bond A glycosidic bond or glycosidic linkage is a type of covalent bond A covalent bond is a chemical bond A chemical bond is a lasting attraction between atoms, ions or molecules that enables the formation of chemical compounds. The bond may ...
s), and
DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral gro ...

DNA
(in
phosphodiester bond A phosphodiester bond occurs when exactly two of the hydroxyl groups A hydroxy or hydroxyl group is a functional group with the chemical formula -OH and composed of one oxygen atom Chemical bond , covalently bonded to one hydrogen atom. In or ...
s).


History

Polymers have been essential components of commodities since the early days of humankind. The use of
wool Wool is the textile A textile is a flexible material made by creating an interlocking bundle of yarn Yarn is a long continuous length of interlocked fibres, suitable for use in the production of textiles, sewing, crocheting, knitti ...
(
keratin Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin Alpha-keratin, or α-keratin, is a type of keratin Keratin () is one of a family of fibrous structural proteins known as Scleroprot ...

keratin
),
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. Under natural condition ...

cotton
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 h ...

linen
fibres (
cellulose Cellulose is an organic compound with the chemical formula, formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of glycosidic bond, β(1→4) linked glucose, D-glucose units. Cellulose is an important stru ...

cellulose
) for garments,
paper reed
paper reed
(
cellulose Cellulose is an organic compound with the chemical formula, formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of glycosidic bond, β(1→4) linked glucose, D-glucose units. Cellulose is an important stru ...

cellulose
) for
paper Paper is a thin sheet material Material is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composition ...

paper
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 polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, ...

natural rubber
) reached Europe in the 16th century from South America long after the
Olmec The Olmecs () were the earliest known major Mesoamerica Mesoamerica is a historical region and cultural area in North America North America is a continent entirely within the Northern Hemisphere and almost all within the Western ...
,
Maya Maya may refer to: Civilizations * Maya peoples The Maya peoples () are an ethnolinguistic group of indigenous peoples Indigenous peoples, also referred to as First people, Aboriginal people, Native people, or autochthonous people, are cu ...
and
Aztec The Aztecs () were a Mesoamerican culture that flourished in central Mexico in the post-classic period from 1300 to 1521. The Aztec peoples included different Indigenous peoples of Mexico, ethnic groups of central Mexico, particularly those g ...

Aztec
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
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 Celluloids are a class of materials produced by mixing nitrocellulose Nitrocellulose (also known as cellulose nitrate, flash paper, flash cotton, guncotton, pyroxylin and flash string, depending on form) is a highly flammable compound formed ...

celluloid
, galalith,
parkesine Celluloids are a class of material A material is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composition ...
,
rayon Rayon is a synthetic fiber Synthetic fiber or synthetic fibre (in British English British English (BrE) is the standard dialect A standard language (also standard variety, standard dialect, and standard) is a language variety that ...

rayon
, vulcanised rubber and, later,
Bakelite Bakelite ( ; sometimes spelled Baekelite) or polyoxybenzylmethylenglycolanhydride was the first plastic made from synthetic components. It is a thermosetting polymer, thermosetting phenol formaldehyde resin, formed from a condensation reaction o ...

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,
Hermann Staudinger Hermann Staudinger (; 23 March 1881 – 8 September 1965) was a German organic chemist who demonstrated the existence of macromolecule macromolecule A macromolecule is a very large molecule File:Pentacene on Ni(111) STM.jpg, A scanning tu ...

Hermann Staudinger
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 economical drive and it was supported by a wide academic community that contributed with innovative synthesis of monomers from cheaper raw materials, more efficient polymerisation processes, improved techniques for polymer characterisation and advanced theoretical understanding of polymers. Since 1953, six Nobel prizes were awarded in the area of polymer science, excluding those for research on biological macromolecules. This further testifies its impact on modern science and technology. As Lord Todd summarised it 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
small moleculeWithin the fields of molecular biology Molecular biology is the branch of biology that seeks to understand the molecule, molecular basis of biological activity in and between Cell (biology), cells, including biomolecule, molecular synthesis, modi ...
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 . The monomers are
terephthalic acid Terephthalic acid is an organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reaction ...

terephthalic acid
(HOOCC6H4COOH) and
ethylene glycol Ethylene glycol (IUPAC name In chemical nomenclatureA chemical nomenclature is a set of rules to generate systematic names for chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecula ...

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 In polymer chemistry, a repeat unit or repeating unit is a part of a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or ...
or monomer residue. Synthetic methods are generally divided into two categories,
step-growth polymerization Step-growth polymerization refers to a type of polymerization In polymer chemistry, polymerization (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set ...

step-growth polymerization
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
polystyrene Polystyrene (PS) is a synthetic aromatic forms of benzene (top) combine to produce an average structure (bottom) In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, com ...

polystyrene
, whereas in step-growth polymerization chains of monomers may combine with one another directly, such as in
polyester Polyester is a category of polymers that contain the ester functional group in every repeat unit of their main chain. As a specific material, it most commonly refers to a type called polyethylene terephthalate (PET). Polyesters include natural ...
. Step-growth polymerization can be divided into
polycondensation Condensation polymers are any kind of polymers formed through a condensation reaction—where molecules join together—''losing'' small molecules as byproducts such as water or methanol. Condensation polymers are formed by polycondensation, when ...

polycondensation
, in which low-molar-mass by-product is formed in every reaction step, and
polyadditionA polymerization reaction that forms polymers via individual independent addition reaction, addition reactions. Polyaddition occurs as a reaction between functional groups on molecules with low degrees of polymerization, such as dimers, trimers and ...

polyaddition
. Newer methods, such as
plasma polymerization Plasma polymerization (or glow discharge polymerization) uses plasma sources to generate a gas discharge that provides energy to activate or fragmentation (chemistry), fragment gaseous or liquid monomer, often containing a vinyl group, in order to ...
do not fit neatly into either category. Synthetic polymerization reactions may be carried out with or without a
catalyst that utilizes a low-temperature oxidation catalyst to convert carbon monoxide to less toxic carbon dioxide at room temperature. It can also remove formaldehyde from the air. Catalysis () is the process of increasing the reaction rate, rate of a ...

catalyst
. Laboratory synthesis of biopolymers, especially of
proteins Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a No ...
, is an area of intensive research.


Biological synthesis

There are three main classes of biopolymers:
polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant found in . They are long chain carbohydrates composed of units bound together by . This carbohydrate can react with water () using as catalyst, which produces constituent sugars ...
s,
polypeptide Peptides (from Greek language πεπτός, ''peptós'' "digested"; derived from πέσσειν, ''péssein'' "to digest") are short chains of amino acids linked by peptide bonds. Chains of fewer than ten or fifteen amino acids are called oligope ...
s, and
polynucleotide A polynucleotide molecule is a biopolymer Biopolymers are natural polymers produced by the cells of Organism, living organisms. Biopolymers consist of monomeric units that are Covalent_bond, covalently bonded to form larger molecules. There are th ...
s. 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 enzyme Enzymes () are s that act as s (biocatalysts). Catalysts accelerate . The molecules upon which enzymes may act are called , and the enzyme converts the substrates into different molecules ...

DNA polymerase
. The synthesis of proteins involves multiple enzyme-mediated processes to
transcribe Transcription refers to the process of producing a copy of something piece by small piece, including: Genetics * Transcription (biology) Transcription is the process of copying a segment of DNA into RNA. The segments of DNA transcribed into ...
genetic information from the DNA to
RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Re ...
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 ...

translate
that information to synthesize the specified protein from
amino acid Amino acids are organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, a ...

amino acid
s. The protein may be modified further following translation in order to provide appropriate structure and functioning. There are other biopolymers such as
rubber Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymer A polymer (; Greek ''poly- Poly, from the Greek :wikt:πολύς, πολύς meaning "many" or "much" ...

rubber
,
suberin Suberin, cutin and lignins are complex, higher plant Epidermis (botany), epidermis and periderm cell-wall macromolecules, forming a protective barrier. Suberin, a complex polyester biopolymer, is lipophilic, and composed of long chain fatty acids ...

suberin
,
melanin Melanin (; from el, μέλας ''melas'', "black, dark") is a broad term for a group of natural pigments found in most organisms. Melanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the ami ...

melanin
, and
lignin Lignin is a class of complex organic polymer 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 s ...

lignin
.


Modification of natural polymers

Naturally occurring polymers such as cotton, starch, and rubber were familiar materials for years before synthetic polymers such as polyethene and
perspex Poly(methyl methacrylate) (PMMA), also known as acrylic, acrylic glass, or plexiglass, as well as by the trade names Crylux, Plexiglas, Acrylite, Astariglas, Lucite, Perclax, and Perspex, among several others ( see below), is a transparent th ...
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 and cellulose to form
nitrocellulose Nitrocellulose (also known as cellulose nitrate, flash paper, flash cotton, guncotton, pyroxylin and flash string, depending on form) is a highly flammable compound formed by nitrating In organic chemistry, nitration is a general class of chem ...

nitrocellulose
and the formation of
vulcanized rubber Vulcanization (British: Vulcanisation) refers to a range of processes for hardening rubbers. The term originally referred exclusively to the treatment of natural rubber with sulfur Sulfur (in traditional laity, lay Commonwealth English ...
by heating natural rubber in the presence of
sulfur Sulfur (in nontechnical British English: sulphur) is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: th ...

sulfur
. Ways in which polymers can be modified include
oxidation Redox (reduction–oxidation, pronunciation: or ) is a type of chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter ...

oxidation
,
cross-link In chemistry and biology a cross-link is a bond or a short sequence of bonds that links one polymer A polymer (; Greek ''poly- Poly, from the Greek :wikt:πολύς, πολύς meaning "many" or "much", may refer to: Businesses * Chin ...
ing, and
endcapping In chromatography In chemical analysis, chromatography is a laboratory technique for the Separation process, separation of a mixture into its components. The mixture is dissolved in a fluid solvent (gas or liquid) called the ''mobile phase'', ...
.


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 of polymers, crystallization, the glass transition or Copolymer#Microphase separation, 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 In polymer chemistry, a repeat unit or repeating unit is a part of a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or ...
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 is composed only of styrene-based repeat units, and is classified as a homopolymer. Polyethylene terephthalate, even though produced from two different
monomer In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during a ...

monomer
s (
ethylene glycol Ethylene glycol (IUPAC name In chemical nomenclatureA chemical nomenclature is a set of rules to generate systematic names for chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecula ...

ethylene glycol
and
terephthalic acid Terephthalic acid is an organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reaction ...

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,
polynucleotide A polynucleotide molecule is a biopolymer Biopolymers are natural polymers produced by the cells of Organism, living organisms. Biopolymers consist of monomeric units that are Covalent_bond, covalently bonded to form larger molecules. There are th ...
s such as DNA are composed of four types of nucleotide subunits. : A polymer containing ionizable subunits (e.g., pendant carboxylic acid, 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 elastomers have a wide-meshed cross-linking between the "main chains". Close-meshed crosslinking, on the other hand, leads to thermosets. 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 branching (polymer chemistry), branched polymer molecule is composed of a main chain with one or more substituent side chains or branches. Types of branched polymers include star polymers, comb polymers, polymer brushes, dendronized polymers, ladder polymers, and dendrimers. There exist also two-dimensional polymers (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, 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.


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. 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 (''M''n) and weight-average molecular weight (''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 (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 reptation, 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 (Tg). This is a result of the increase in chain interactions such as Van der Waals force, van der Waals attractions and reptation, 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 unit In polymer chemistry, a repeat unit or repeating unit is a part of a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or ...
s. : *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 of chirality (chemistry), 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 (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 (polymer chemistry), branching and random copolymers form Amorphous solid, amorphous (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, freely-jointed-chain model. In the Solid, solid state, the respective Protein conformation, conformations of the molecules are frozen. Hooking and entanglement of chain molecules lead to a "mechanical bond" between the chains. Intermolecular force, 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 (Chemiker), 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 (polymer physics), 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 bonds, as in the case of Aramid, ''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 elastomers and cannot be molten (unlike thermoplastics); heating cross-linked polymers only leads to Thermal decomposition, decomposition. Thermoplastic elastomers, 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. For example, the structure of a crystalline protein or polynucleotide, such as a sample prepared for x-ray crystallography, may be defined in terms of a conventional unit cell composed of one or more polymer molecules with cell dimensions of hundreds of angstroms 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, reduced crystallinity may also be associated with increased 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, 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 basis. Many physical and chemical properties describe how a polymer behaves as a continuous macroscopic material. They are classified as bulk properties, or Intensive and extensive properties#Intensive properties, intensive properties according to thermodynamics.


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 cross-link, crosslinking of polymer chains.


Young's modulus of elasticity

Young's modulus quantifies the elasticity (physics), elasticity of the polymer. It is defined, for small deformation (mechanics)#Strain, 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 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 phenomena, Transport properties such as mass diffusivity, 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 In and , viscoelasticity is the property of that exhibit both and characteristics when undergoing . Viscous materials, like water, resist and linearly with time when a is applied. Elastic materials strain when stretched and immediately ret ...
.


Phase behavior


Crystallization and melting

Depending on their chemical structures, polymers may be either semi-crystalline or amorphous. Semi-crystalline polymers can undergo crystallization of polymers, 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 plasticizers. Whereas crystallization and melting are first-order phase transitions, 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
small moleculeWithin the fields of molecular biology Molecular biology is the branch of biology that seeks to understand the molecule, molecular basis of biological activity in and between Cell (biology), cells, including biomolecule, molecular synthesis, modi ...
materials. This effect results from the fact that the driving force for mixing is usually entropy, 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 Paul J. Flory, 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 Tg and increase polymer flexibility. Addition of the plasticizer will also modify dependence of the glass-transition temperature Tg 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 reduced 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 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 or carbonyl groups can form hydrogen bonds 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 carbamate, urethane or urea linkages. Polyesters have intermolecular force#Dipole-dipole interactions, 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's (Twaron), but polyesters have greater flexibility. Polymers with non-polar units such as polyethylene interact only through weak Van der Waals forces. 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 poly(methyl methacrylate), 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 laser linewidth, 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 Insulator (electricity), electrical insulators, but the development of polymers containing Conjugated system, π-conjugated bonds has led to a wealth of polymer-based semiconductors, 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 Polymer matrix composite, composites. Their application allows to save energy (lighter cars and planes, thermally insulated buildings), protect food and drinking water (packaging), save land and reduce 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#Uses and applications, polyester and PVC clothing, spandex, sneakers, sport shoes, wetsuits, Ball (association football), footballs and Billiard ball#Snooker, billiard balls, skis and snowboards, Racket (sports equipment), rackets, parachutes, sailcloth, sails, tent, tents and shelters. * Electronic and photonic technologies: organic Organic electronics, field effect transistors (OFET), OLED#Polymer light-emitting diodes, light emitting diodes (OLED) and organic solar cell, solar cells, Television set, television components, compact discs (CD), photoresists, holography. * Packaging and containers: Plastic film, films, Plastic bottle, bottles, food packaging, barrels. * Insulation: Insulator (electricity), electrical and thermal insulation, spray foams. * Construction and structural applications: garden furniture, polyvinyl chloride, PVC windows, flooring, seal (mechanical), sealing, Plastic pipework, pipes. * Paints, glues and lubricants: varnish, adhesives, dispersants, anti-graffiti coatings, Biofouling#Non-toxic coatings, antifouling coatings, non-stick surfaces, lubricants. * Car parts: tires, Bumper (car), bumpers, windshields, windscreen wipers, fuel tanks, car seats. * Household items: buckets, kitchenware, toys (e.g., construction sets and Rubik's cube). * Medical applications: Blood transfusion, blood bag, syringes, rubber gloves, surgical suture, contact lenses, prosthesis, Drug carrier, controlled drug delivery and release, Growth medium, matrices for cell growth. * Personal hygiene and healthcare: diapers using superabsorbent polymers, toothbrushes, cosmetics, shampoo, condoms. * Security: personal protective equipment, bulletproof vests, space suits, ropes. * Separation technologies: synthetic membranes, Fuel cell#Proton-exchange membrane fuel cells (PEMFCs), fuel cell membranes, filtration, ion-exchange resins. * Money: polymer banknotes and payment cards. * 3D printing.


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 (ACS) and
IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Science Council (ISC). IUPAC ...
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 Repeat unit, 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), sometimes coupled with static light scattering, can used to determine the number-average molecular weight, weight-average molecular weight, and polydispersity, 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 polymers, 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 FTIR, Fourier-transform infrared spectroscopy, Raman spectroscopy, 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 viscosity, elastic modulus, 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, shape, or molecular weight—of a polymer or polymer-based product under the influence of one or more environmental factors, such as heat, light, and the presence of certain chemicals, 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, they may be intended to prevent environmental pollution. 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. Polymers containing an Saturated and unsaturated compounds, unsaturated backbone degrade via ozone cracking. Carbon based polymers are more susceptible to thermal degradation than inorganic polymers 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 atoms 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 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 molding, 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 devices. One of the oldest known failure modes is ozone cracking caused by chain scission when ozone gas attacks susceptible elastomers, such as
natural rubber Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, ...

natural rubber
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 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 6,6, 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 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 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.


See also

*Biopolymer *Ideal chain *Inorganic polymer *List of important publications in chemistry#Polymer chemistry, Important publications in polymer chemistry *Oligomer *Polymer adsorption *Polymer classes (disambiguation), Polymer classes *Polymer engineering *Polymerization *Merosity, Polymery (botany) *Reactive compatibilization *Sequence-controlled polymer *Shape-memory polymer *Sol–gel process *Supramolecular polymer *Thermoplastic *Thermosetting polymer


References


Bibliography

* * * *


External links


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