SEGMENTED BLOCK-COPOLYMERS OF NATURAL-RUBBER AND 1,3-BUTANEDIOL TOLUENE DIISOCYANATE OLIGOMERS

A series of segmented block copolymers of NR and 1,3-butanediol-toluen e diisocyanate oligomers have been synthesized with varying hard segme nt content. The synthesis has been carried out by one-shot and two-sho t processes in solution. The products were characterized by spectral a nalysis, thermal and mechanical analysis, SEM and optical microscopy. They are found to be amorphous materials having no potential for hydro gen bonding between the 'hard' and 'soft' segments. Their two-phase mo rphology has been deduced from SEM and optical micrographs and establi shed by DMA and thermal studies. DSC analysis shows a soft segment gla ss transition temperature at -62 +/- 2 degrees C and hard segment glas s transitions between 70 degrees and 100 degrees C, depending on the p olyurethane content. The T-g values determined by the dynamic mechanic al analysis are significantly higher than these values. The thermograv imetric analysis indicates a two-stage thermal decomposition of the ma terials by random nucleation mechanism and corresponds to the two phas es 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 behaviou r is consistent with the sample morphology. Materials synthesized by t he two-shot process are found to possess better mechanical properties than the one-shot products, presumably due to a more systematic orderi ng of the different segments in the former. (C) 1998 Elsevier Science Ltd. All rights reserved.