异戊橡胶微观序列结构与结晶性能研究

天然橡胶特有的应变诱导结晶能力赋予其优异的力学性能.异戊橡胶作为唯一能够替代天然橡胶的合成橡胶品种,其应变诱导结晶能力受到关注.本文对3种异戊橡胶的微观序列结构进行了分析,并研究了其结晶性能.核磁分析结果表明:3种异戊橡胶的顺-1,4-结构含量差别不大;从1,4-结构单元的键接方式(序列结构)看,SKI-5和YS-IR分子链中顺-1,4-结构单元均以头-尾相接的方式沿分子链排列,不存在头-头键和尾-尾键接方式;SKI-3中约有0.4%~0.5%的1,4-单元采取头-头键接方式,约有0.3%~0.6%的1,4-单元采取尾-尾键接方式;根据定量计算结果,从分子链上1,4-结构单元的序列分布来看,SKI-3的规整性与SKI-5、YS-IR相近或略高.XRD研究结果表明:炭黑填充的天然橡胶硫化胶拉伸至400%以上时发生取向结晶;而炭黑填充的异戊橡胶硫化胶需拉伸至500%以上时才发生取向结晶.基本物理机械性能研究表明:3种异戊橡胶的性能相当,拉伸强度和撕裂强度明显低于天然橡胶;由于结构和组成上的差异,异戊橡胶的结晶能力较天然橡胶差.

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 1H 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.