Cold crystallization of natural rubber and its synthetic analogues: The influence of chain microstructure

Abstract

The crystalizabilities of eight synthetic high cis-1,4-polyisoprene rubbers have been compared with that of purified natural rubber by differential scanning calorimetry measurements. The detailed microstructure of the rubbers as determined by 13C and 1H nuclear magnetic resonance have also been studied. Whereas natural rubber is characterized by an essentially sterically pure main chain of 100% cis-1,4 content, the structure of the synthetic rubbers spans the range 90.9 to 99.1 mol% cis-1,4 content with varying amounts of trans-1,4 and 3,4 units. The study shows that the purified natural rubber samples undergo cold crystallization more readily than the synthetic analogues and this is attributable to the more perfect microstructure of the natural product. Generally the crystallizability of the rubbers correlates with the average cis sequence lengths of the polymer main chain.