Gradient copolymer

[4][5] In the gradient copolymer, as a result of the gradual compositional change along the length of the polymer chain less intrachain and interchain repulsion are observed.

[6] The development of controlled radical polymerization as a synthetic methodology in the 1990s allowed for increased study of the concepts and properties of gradient copolymers because the synthesis of this group of novel polymers was now straightforward.

[6] In the gradient copolymer, there is a continuous change in monomer composition along the polymer chain (see Figure 2).

This second equation identifies the average composition over all present polymer chains at a given position,

The resulting change in composition throughout the polymerization creates an inconsistent gradient along the polymer.

Forced gradient polymerization involves varying the comonomer composition of the feed being throughout the reaction time.

In general, the glass transition temperature (Tg) is broad in comparison with the homopolymers.

[9] The composition can be determined by gel permeation chromatography(GPC) and nuclear magnetic resonance (NMR).

Generally the composition has a narrow polydispersity index (PDI) and the molecular weight increases with time as the polymer forms.

[10] The compatibilization has been tested by reduction in interfacial tension and steric hindrance against coalescence.

This application is not available for block and graft copolymer because of its very low critical micelle concentration (cmc).

However, the gradient copolymer, which has higher cmc and exhibits a broader interfacial coverage, can be applied to effective blend compatibilizers.

[11] A small amount of gradient copolymer (i.e.styrene/4-hydroxystyrene) is added to a polymer blend (i.e. polystyrene/polycaprolactone) during melt processing.

The resulting interfacial copolymer helps to stabilize the dispersed phase due to the hydrogen-bonding effects of hydroxylstyrene with the polycaprolactone ester group.

This broad glass transition is one of the important features for vibration and acoustic damping applications.

The glass transition breadth can be adjusted by selection of monomers with different degrees of reactivity in their controlled radical polymerization (CRP).

The strongly segregated styrene/4-hydroxystyrene (S/HS) gradient copolymer is used to study damping properties due to its unusual broad glass transition breadth.

[6] There are many possible applications for gradient copolymer like pressure-sensitive adhesives, wetting agent, coating, or dispersion.

[12][6] Recent studies have evaluated gradient copolymers as potential drug delivery carriers.