HES/TiCl_4体系引发异丁烯可控正离子聚合

由六官能团引发剂环氧化角鲨烯(HES)与TiCl4组成引发体系,引发异丁烯(IB)在CH2Cl2/n-Hex(40/60,V/V)混合溶剂中进行正离子聚合,分别探讨了HES和2,6-二甲基吡啶(DMP)用量对IB正离子聚合转化率、产物分子量及其分布的影响.结果表明HES和微量水均可与TiCl4发生络合,并分别形成碳正离子和质子两种引发活性中心,导致聚合产物GPC谱图呈明显双峰分布.增加引发剂HES用量(HES]=2.64mmol/L),可以减少聚合体系中微量水的不可控引发,提高HES引发效率;在聚合体系中引入少量DMP时,可明显地减少微量水的不可控引发和提高HES的引发效率,使得即使在较低HES用量下(HES]=0.084mmol/L),也可达到主要由HES引发IB正离子聚合,制备出官能叔氯末端的六臂星形支化遥爪聚异丁烯,GPC谱图呈现单峰分子量分布,分布指数为1.5左右.

CONTROLLED CATIONIC POLYMERIZATION OF ISOBUTYLENE WITH HES/TiCl4 INITIATING SYSTEM

The cationic polymerization of isobutylene (IB) by utilizing six functional initiator hexaepoxy squalane (HES) in conjunction with TiCl_4 was carried out in CH_2Cl_2/n-Hex (40/60,V/V) solvent mixtures in the absence or in the presence of 2,6-dimethylpyridine (DMP) respectively.The effects of concentrations of HES,DMP on monomer conversion,molecular weight and molecular weight distribution (MWD) of the product polyisobutylene (PIB) were investigated.A small amount of water in the polymerization system in conjunction with TiCl_4 could induce a conventional uncontrolled rapid polymerization of IB and led to polyisobutylene with broad molecular weight distribution.It is found that the GPC trace of resultant polymer obtained by HES/H_2O/TiCl_4 system exhibit a bimodal distribution,which is attributed to the competition of initiation from two different active centers,i.e.,H~+TiCl_4OH~-(A) and HES~+TiCl_4OH~-(B).The initiation from active center (B) increased with an increase in HES concentration.A large dosage of HES (HES]=2.24×10~ -3 mol/L) was needed to decrease the initiation from active center (A) to some extend but it was still difficult to suppress the initiation from (A) and the chain transfer reaction.According to the GPC and NMR characterization results of polymers,the controlled initiation from (B) could almost be achieved and the GPC traces exhibited relatively narrow unimodal MWD by addition of small amount of DMP.The mechanistic role of DMP is suggested to decrease the initiation from (A) and chain transfer to monomer.A desirable cationic polymerization of IB would be achieved with HES/TiCl_4 initiation system in the presence of adequate amount of DMP,and the star-branched telechelic polyisobutylenes with relatively narrow MWD and tert-chloride end-groups could be prepared.