吡啶类试剂调节H_2O/TiCl_4引发苯乙烯正离子聚合研究

1988年,Kennedy等1~3]首先实现了由BCl3共引发的苯乙烯(St)及其衍生物活性正离子聚合,但所得到聚合产物的分子量分布宽(Mw/Mn=5~6).苯乙烯活性正离子聚合的共引发剂由BCl3扩展到SnCl4、TiCl44~7]和TiCl3(OiPr).对于TiCl4共引发的St活性正离子聚合,所用引发剂为2,4,4-三甲基-2

CARBOCATIONIC POLYMERIZATION OF STYRENE WITH H2O/TiCl4 INITIATING SYSTEM IN THE PRESENCE OF PYRIDINE AND ITS DERIVANTS

The carbocationic polymerization of styrene(St) initiated by H_2O/TiCl_4 system was conducted at-60℃ in dichloromethane(CH_2Cl_2)/hexane(n-Hex)(50/50 V/V) in the presence of pyridine(Py),2-methyl pyridine(MPy) and 2,6-dimethyl pyridine(DMPy).A desirable polymerization process with a relative slow polymerization rate and PS products with relatively narrow molecular weight distribution(MWD,M_w/M_n ca.1.8) were obtained.Py and its derivants and/or their complexes with Lewis acid TiCl_4 interact with the growing chain end to reduced its "cationicity" and thus to decrease the polymerization rate,suppress chain transfer and termination reactions and narrow MWD.The experimental results also show that the monomer conversion as well as the molecular weight of polymer products increased but MWD almost kept unchanged with polymerization time.The number-average molecular weight of polymer increased linearly with monomer conversion but the line did not pass through the origin.