Li Chuanqing

Microstructure of polyisoprene and its effect on crystallization behavior

It is widely accepted that the outstanding mechanical properties of nature rubber (NR) are partly attributed to the strain-induced crystallization. The strain-induced crystallization of isoprene rubber should also attract our attention because it is the only alternative for NR. The microstructure and crystallization of three grades of polyisoprene rubber has been studied by 13 C and 1 H NMR. There exists slightly difference of cis -1,4 configuration among the three polyisoprene samples. According to the sequential structure of 1,4-configuration, the cis -1,4 units of SKI-5 and YS-IR adopt only head-to-tail arrangement. However, the 1,4-units of SKI-3 consist of head-to-head (about 0.4%~0.5%), tail-to-tail (about 0.3%~0.6%) and head-to-tail arrangement. According to the quantitative measurements, the regularity of the three samples are similar. The crystalizability of polyisoprene rubber have been studied through X-ray diffraction (XRD) method. The NR vulcanizates filled with carbon black crystallize above 400% elongation. But the crystallization of polyisoprene vulcanizates occurs when it is stretched above 500%. According to the mechanical tests, SKI-3, SKI-5 and YS-IR show comparative mechanical properties. The strain-induced crystallization performance of isoprene rubber is inferior to nature rubber because of the differences in the structure and composition.