Segmented block copolymers of natural rubber and 1, 3-butanediol–toluene diisocyanate oligomers

Abstract

A series of segmented block copolymers of NR and 1,3-butanediol–toluene diisocyanate oligomers have been synthesized with varying hard segment content. The synthesis has been carried out by one-shot and two-shot processes in solution. The products were characterized by spectral analysis, thermal and mechanical analysis, SEM and optical microscopy. They are found to be amorphous materials having no potential for hydrogen bonding between the `hard' and `soft' segments. Their two-phase morphology has been deduced from SEM and optical micrographs and established by DMA and thermal studies. DSC analysis shows a soft segment glass transition temperature at −62±2°C and hard segment glass transitions between 70° and 100°C, depending on the polyurethane content. The T g values determined by the dynamic mechanical analysis are significantly higher than these values. The thermogravimetric analysis indicates a two-stage thermal decomposition of the materials by random nucleation mechanism and corresponds to the two phases present in the block copolymer. Depending on the proportion of the continuous and dispersed phases, the block coolymers behave like quasi-elastomers at lower hard segment concentrations and brittle plastics at higher hard segment contents. This variation in mechanical behaviour is consistent with the sample morphology. Materials synthesized by the two-shot process are found to possess better mechanical properties than the one-shot products, presumably due to a more systematic ordering of the different segments in the former.