Polymer A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...

s are chainlike

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 bioch ...

s that are made of the same repetition unit. With a few exceptions such as

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, respo ...

s, a polymer consists of a mix of molecules with different chain lengths. Therefore, average values are given for the

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 ...

like the number average, the weight average or the viscosity average molar mass. A measure for the width of the

molecular weight distribution 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 have ...

is the

polydispersity index In chemistry, the dispersity is a measure of the heterogeneity of sizes of molecules or particles in a mixture. A collection of objects is called uniform if the objects have the same size, shape, or mass. A sample of objects that have an inconsi ...

. The targeted manipulation of the molecular weight distribution of a polymer by removing short and/or long chain material is called polymer fractionation.

Reasons for polymer fractionation

The molecular weight of polymers has a large influence on their properties and therefore determines the applications. Among others the flow behavior, the

solubility In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubil ...

, the mechanical properties but also the lifetime are influenced by the molecular weight. For high duty polymers – polymers that have to fulfill elevated demands – not only the molecular weight but also the molecular weight distribution is important. This especially holds true if low and/or high molecular material disturbs a given task.

Analytical methods

Polymers can be fractionated on an analytical scale by

size exclusion chromatography Size-exclusion chromatography (SEC), also known as molecular sieve chromatography, is a chromatographic method in which molecules in solution are separated by their size, and in some cases molecular weight. It is usually applied to large molecules ...

(SEC),

Matrix-assisted laser desorption/ionization In mass spectrometry, matrix-assisted laser desorption/ionization (MALDI) is an ionization technique that uses a laser energy absorbing matrix to create ions from large molecules with minimal fragmentation. It has been applied to the analysis of ...

(MALDI) or

field flow fractionation Field-flow fractionation, abbreviated FFF, is a separation technique which does not have a stationary phase. It is similar to liquid chromatography as it works on dilute solutions or suspensions of the solute. Separation is achieved by applying ...

(FFF). These methods are used to determine the molecular weight distribution.

Preparative methods

In most cases the fractionation of polymers on a preparative scale is based on chromatographic methods (e.g. preparative SEC or Baker-Williams fractionation). Therefore, the production is normally limited to few grams only. For large scales of several grams up to kg or even tons the “continuous spin fractionation” can be used. F. Francuskiewicz gives an overview about preparative polymer fractionation.

Literature

* M.J.R Cantow ''Polymer Fractionation'' Academic Press, New York (1967) * L.H. Tung ''Fractionation of Synthetic Polymers'' Marcel Dekker, New York (1977) * F. Francuskiewicz ''Polymer Fractionation'' Springer, Berlin (1994) * R. Koningsveld, L.D. Kleintjens, H. Geerissen, P. Schützeichel, B.A. Wolf „Fractionation“ in: ''Comprehensive Polymer Science Volume 1'' Pergamon Press, Oxford (1989) 293-312

External links

* http://www.wee-solve.de - WEE-Solve GmbH: Service provider for polymer fractionation Polymer chemistry Fractionation