Min Xin, Fan Xiaodong, Liu Jie
Northwestern Polytechnical University, Xi'An, Shannxi 710000, People's Republic of China.
R Soc Open Sci. 2018 May 30;5(5):180156. doi: 10.1098/rsos.180156. eCollection 2018 May.
A novel alkyl lithium-based initiator with relatively large steric hindrance, -butyldimethylsiloxydimethylpropyl lithium (TBDMSODPrLi), was designed and synthesized. By using TBDMSODPrLi, hydroxyl-terminated polybutadiene (HTPB) was prepared via anionic polymerization. The macromolecular structure of HTPB was characterized and verified by FTIR and H-NMR. It was found that 1,4 unit content in HTPB initiated by TBDMSODPrLi was significantly higher (over 90%) compared to a HTPB (1,4 unit content of 70%) initiated with another initiator possessing smaller steric hindrance. The possible mechanism, which was based on initiator steric hindrance affecting monomer chain addition behaviour, was deduced. It was that the initiator's larger steric hindrance blocked lithium's intermolecular association during anionic polymerization; as a result, it could effectively increase the 1,4 unit content in HTPB. To further study how to obtain higher and stable 1,4 unit content, the optimal anionic polymerization technique for HTPB was explored including polymerization temperature, time and the amount of initiator used. The study concluded that utilization of an initiator with larger steric hindrance and reducing the polymerization temperature were two important factors to raise the 1,4 unit content in HTPB.
设计并合成了一种具有较大空间位阻的新型烷基锂引发剂——叔丁基二甲基硅氧基二甲基丙基锂（TBDMSODPrLi）。通过使用TBDMSODPrLi，采用阴离子聚合法制备了端羟基聚丁二烯（HTPB）。利用傅里叶变换红外光谱（FTIR）和氢核磁共振（H-NMR）对HTPB的大分子结构进行了表征和验证。结果发现，与用另一种空间位阻较小的引发剂引发的HTPB（1,4-单元含量为70%）相比，由TBDMSODPrLi引发的HTPB中1,4-单元含量显著更高（超过90%）。推导了基于引发剂空间位阻影响单体链加成行为的可能机理。即引发剂较大的空间位阻在阴离子聚合过程中阻碍了锂的分子间缔合；因此，它可以有效提高HTPB中1,4-单元的含量。为了进一步研究如何获得更高且稳定的1,4-单元含量，探索了HTPB的最佳阴离子聚合工艺，包括聚合温度、时间和引发剂用量。研究得出结论，使用空间位阻较大的引发剂和降低聚合温度是提高HTPB中1,4-单元含量的两个重要因素。
