Cationic polymerization of 1

3-pentadiene initiated by trimethylsilyl compounds

trimethysilyl trifluoromethanesulfonate (TMSOTf) or trimethysilyl chloride (TMSCl)

in combination with TiCl4

SbCl3 or AlCl3

was carried out in n-hexane or in toluene．The polymer yields are greatly increased by the addition of TMSOTf or TMSCl．However

the introduction of TMSOTf or TMSCl gives a drop of polymer molecular weight．Kinetic results demonstrate that the polymerization initiated by the composite initiating systems is faster than that induced by Lewis acids alone．Various electron donors (such as ethers

ketones) were used to mediate the initiating systems．Adding diphenyl ether could increase both polymer yield and molecular weight．Structural evidences illustrate that the polymerization is initiated by Lewis acid in combination with HCl or HOTf

which are resulted from hydrolysis of TMSCl or TMSOTf by water contained in the system．