Segmented block copolymers of natural rubber and bisphenol A-toluene diisocyanate oligomers

摘要

Segmented block copolymers were synthesized from hydroxyl-terminated liquid natural rubber and polyurethane oligomers based on Bisphenol A and toluene diisocyanate by one-shot and two-shot processes in solution. Structural features were characterized by infrared and nuclear magnetic resonance spectroscopic analysis. The spectra of the one-shot materials were identical with those of the two-shot materials, indicating their chemical identity. The soft segment T_g was well defined and almost invariant around -64°C, but the hard segment T_g varied from 75 to 105°C as the hard segment content increased from 30 to 60 wt %. Two relaxation temperatures were observed for each sample in dynamic mechanical analysis (DMA). These observations and the two-stage thermal decomposition by random nucleation mechanism, as investigated in thermogravimetric analysis unambiguously confirmed complete phase segregation in these materials. The scanning electron microscopy and optical micrographs showed well-defined domains dispersed in a matrix, indicating the two-phase morphology. Systematic changes in hardness and tensile properties with hard segment content were also observed. The samples behaved like soft elastomers at lower hard segment content, toughened plastics at high hard segment content, and rigid elastomers at intermediate compositions. Variations in hardness and tear strength were consistent with this behavior.