Metal alkyl catalysts for cationic polymerization of vinyl monomers

New catalyst systems consisting of, e.g., metal alkyl—H2O—cocatalyst for the polymerizations of styrene, vinyl ether and α‐methylstyrene were found. Metal alkyls were Al(C2H5)3 or Zn(C2H5)2 and active chlorine compounds such as α‐chlorodimethyl ether, acetyl chloride or tert.‐butyl chloride were cocatalysts. A mechanism of cationic polymerization was proposed in which AlEt3 behaves as LEWIS acid and forms a carbonium ion complex with the cocatalyst. The function of water was assumed to convert Al(C2H5)3 into another LEWIS acid and the ternary systems of Al(C2H5)3—H2O—cocatalyst were regarded as LEWIS acid‐cocatalyst systems. In the polymerization of styrene with Al(C2H5)3—H2O—CH3COCl, the mechanism of cationic polymerization initiated by acetyl cation was established by the end group analysis.