亲核试剂在正离子聚合反应中的作用及其作用机理的研究

EFFECT OF NUCLEOPHILES ON ISO BUTYLENE CARBOCATIONIC POLYMERIZATION

研究了亲核试剂对IB 1 ,3 二 (2 氯异丙基 )苯 (DiCumCl) TiCl4体系正离子聚合反应的规律 ,亲核试剂与增长的碳正离子作用的紫外光谱图 ;采用分子模拟 ,利用量子力学半经验方法计算了亲核试剂与质子反应的活化能 ,确定了不同亲核试剂与质子的作用能力 ;利用分子力学方法计算了在增长碳正离子末端的不同位置亲核试剂与之络合的稳定化能 ,根据能量最低原则确定了亲核试剂在碳正离子链端的作用位置 ;利用分子力学方法进行构象优化后 ,借助QEq方法得到了聚异丁烯碳正离子和聚苯乙烯碳正离子的电荷数值 .

Isobutylene(IB) cationic polymerization by DiCumCl/TiCl4 was studied, and the effects of nucleophiles on PIB growing end were analyzed by UV spectroscopy. Using molecular simulation, the activation energy for reaction of nucleophiles with H+ was calculated by Molecular orbital package(MOPAC) method in semi-experiential quantum dynamics, and the change value of carbonic atoms of the growing species of isobutylene reacting with N-containing nucleophile reagent was obtained by QEq method after conformation optimization by using molecular dynamics. It was found that nucleophiles can complex with protons and so prevent chain transfer and chain termination reactions related with protons, and can also stabilize carbocations by reducing their charges. There are different reaction abilities between nucleophiles and protons or carbocations. Piperidine and 2, 6-diter-butyl pyridine are strong nucleophiles which may complex with protons. 2, 6-Diter-butyl pyridine can only trap protons and cannot complex with carbocations because of its big molecular volume. Piperidine is a good proton trap agent that can complex with carbocations to reduce their charge and increase their stabilization.