Propriétés physiques et mécaniques d'un copolymère séquencé polystyrène-polyisoprène-polystyrène hydrogéné

Differential scanning calorimetry (DSC) and stress-strain measurements have been made on a polyisoprene hydrogenated polystyrene-polyisoprene-polystyrene (SIS) elastomeric block copolymer and compared with those of the corresponding nonhydrogenated copolymer. The SIS copolymer was prepared by anionic polymerization with butyllithium in benzene. Both polymers are two-phase amorphous elastomeric materials displaying two glass transition temperatures. The transition temperature of the hydrogenated polyisoprene phase is only 4°C higher than that of the polyisoprene phase in the unhydrogenated material. Stress-strain curves measured on solvent cast films before and after hydrogenation show identical behaviors at low elongation. Both the tensile strength and elongation at break are smaller for the hydrogenated polymer. Comparison between the stress-strain curves measured in successive extension cycles shows that this polymer does not exhibit the “leathery” behavior generally observed for SIS elastomeric block copolymers, but behaves more like a typical vulcanized elastomer. This would indicate more rigid and much better separated polystyrene particles in the hydrogenated system.