Thermoplastic elastomers

化学的特性The characteristic properties of the styrene-butadiene thermoplastic elastomers stem from the inherent incompatibility of the polystyrene and polybutadien blocks. In the bulk material the two different blocks aggregate into separate domains leading to a dispersion of polystyrene domains (as the lesser component) in a continuous matrix of polybutadiene. At ordinary temperatures the polystyrene domains are rigid and immobilize the ends of the polybutadiene segments, in effect serving both as cross-links and filler particles. Thus the system has the strength of a filler-reinforced vulcanized amorphous elastomer. At temperatures above the glasstransition temperature of polystyrene (l00°C), the polystyrene domains are readily disrupted and the material may be melt-processed. The maximum service temperature of components fabricated from the copolymers is about 60°C. The chemical properties of the block copolymers are similar to those of unvulcanized styrene-butadiene rubber. Thus the block copolymers are soluble in a range of solvents, including chlorinated and aromatic hydrocarbons, esters and ketones.