Effect of Stereoregularity on Strain-Induced Crystallization and Mechanical Properties of Natural Rubber

Revealing the reason for the performance difference between synthetic isoprene rubber (IR) and natural rubber (NR) has long been pursued but has not yet been achieved. In this paper, a series of isomerized natural rubbers (iNR) with different trans-contents has been prepared by using a thiyl radical-induced isomerization reaction. These iNR samples were used as a model to study the effect of stereoregularity on the strain-induced crystallization (SIC) and mechanical properties of NR. Introducing a low trans-configuration (4%) has little impact on the properties of NR, proving that the performance difference between IR and NR is mainly due to the lack of nonrubber components rather than the effect of stereoregularity. When the trans-content was increased to 10%, the decrease in stereoregularity led to a reduction in crystallinity and an increase in on-set crystallization strain. However, iNR-10% can maintain mechanical properties comparable to NR due to the energy dissipative effect of the pseudonetwork formed by the end groups and nonrubber components. When the trans-content was further increased to 19%, the stereoregularity reduction completely prevented the occurrence of SIC. However, the presence of nonrubber components still makes iNR-19% show a high strength of 15.1 MPa. This paper promotes an understanding of the structure and properties of NR and helps to guide the preparation of high-performance synthetic rubber.