Lower critical solution temperature phase behavior of natural rubber/polybutadiene blend

Abstract

The lower critical solution temperature (LCST) phase behavior of the blend of natural rubber (NR) with polybutadiene (PB) having 32.3% 1,2 unit was investigated by measuring Tg through DSC after annealing the blend. NR was separated with toluene into branched polymer and crosslinked one as a soluble fraction (NR-sol) and gel fraction (NR-gel), respectively, followed by mixing with PB. Coexistence composition of NR-sol/PB and NR-gel/PB blends was determined by a method proposed in this work using DSC. The LCST of the NR-sol/PB blend was 328 K, being identical to the reported LCST of synthetic cis-1,4-polyisoprene/PB blend in our previous paper. The LCST of NR-gel/PB blend was quite similar to that of NR-sol/PB blend despite that NR-gel was crosslinked rubber (v = 1.5 × 10-6). Molecular weight was proved to produce no effect on the LCST phase behavior for high molecular weight polymer-polymer blend.