Copolymer

[1] Copolymers can be characterized by a variety of techniques such as NMR spectroscopy and size-exclusion chromatography to determine the molecular size, weight, properties, and composition of the material.

[2] Commercial copolymers include acrylonitrile butadiene styrene (ABS), styrene/butadiene co-polymer (SBR), nitrile rubber, styrene-acrylonitrile, styrene-isoprene-styrene (SIS) and ethylene-vinyl acetate, all of which are formed by chain-growth polymerization.

[12] A block index has been proposed as a quantitative measure of blockiness or deviation from random monomer composition.

Statistical copolymers are dictated by the reaction kinetics of the two chemically distinct monomer reactants, and are commonly referred to interchangeably as "random" in the polymer literature.

[18] Copolymerization is particularly useful in tuning the glass transition temperature, which is important in the operating conditions of polymers; it is assumed that each monomer occupies the same amount of free volume whether it is in a copolymer or homopolymer, so the glass transition temperature (Tg) falls between the values for each homopolymer and is dictated by the mole or mass fraction of each component.

[17] A number of parameters are relevant in the composition of the polymer product; namely, one must consider the reactivity ratio of each component.

Free radical polymerization is less expensive than other methods, and produces high-molecular weight polymer quickly.

Anionic polymerization can be used to create random copolymers, but with several caveats: if carbanions of the two components do not have the same stability, only one of the species will add to the other.

Additionally, anionic polymerization is expensive and requires very clean reaction conditions, and is therefore difficult to implement on a large scale.

For example, polystyrene chains may be grafted onto polybutadiene, a synthetic rubber which retains one reactive C=C double bond per repeat unit.

The growing chains can add across the double bonds of rubber molecules forming polystyrene branches.

The graft copolymer is formed in a mixture with ungrafted polystyrene chains and rubber molecules.

In the example cited, the rubbery chains absorb energy when the substance is hit, so it is much less brittle than ordinary polystyrene.

The material was made by living polymerization so that the blocks are almost monodisperse to create a regular microstructure.

Blocks of similar length form layers (often called lamellae in the technical literature).

[26] Block copolymers are sometimes used as a replacement for phospholipids in model lipid bilayers and liposomes for their superior stability and tunability.

[32] In thin films, block copolymers are of great interest as masks in the lithographic patterning of semiconductor materials for applications in high density data storage.

In particular, NMR can indicate the tacticity and configuration of polymeric chains while IR can identify functional groups attached to the copolymer.

[35] Differential scanning calorimetry is a thermoanalytical technique used to determine the thermal events of the copolymer as a function of temperature.

[36] It can indicate when the copolymer is undergoing a phase transition, such as crystallization or melting, by measuring the heat flow required to maintain the material and a reference at a constantly increasing temperature.

Thermogravimetric analysis is another thermoanalytical technique used to access the thermal stability of the copolymer as a function of temperature.

This provides information on any changes to the physicochemical properties, such as phase transitions, thermal decompositions, and redox reactions.

[37] Size-exclusion chromatography can separate copolymers with different molecular weights based on their hydrodynamic volume.

The collected material is commonly detected by light scattering methods, a refractometer, or a viscometer to determine the concentration of the eluted copolymer.

[2] Styrenic TPEs entered the market later, and are used in footwear, bitumen modification, thermoplastic blending, adhesives, and cable insulation and gaskets.

[39] Due to this property, amphiphilic block copolymers have garnered much attention in research on vehicles for drug delivery.

[39][40] Similarly, amphiphilic block copolymers can be used for the removal of organic contaminants from water either through micelle formation[2] or film preparation.

[41] The styrene-maleic acid (SMA) alternating copolymer displays amphiphilicity depending on pH, allowing it to change conformations in different environments.

[42] SMA has been used as a dispersing agent for dyes and inks, as drug delivery vehicles, and for membrane solubilization.

Elastomeric phases within a rigid matrix act as crack arrestors, and so increase the energy absorption when the material is impacted for example.