Living Carbocationic Polymerization of α-Methylstyrene Using Tin Halides as Coinitiators

The polymerization of α−methylstyrene (αMeSt) was studied in conjunction with the (CH 3 ) 3 CCH 2 C(CH 3 ) 2 CH 2 C(Ph) 2 Cl (1,1-diphenylethylene-capped 2,4,4-trimethyl-2-chloropentane)/SnBr 4 or SnCl 4 initiating systems. Using SnBr 4, living polymerization was obtained in methyl chloride (MeCl)/hexane (Hex) 60/40 to 40/60 v/v at −80 or −60 °C. The polymers exhibited theoretical molecular weights and narrow molecular weight distributions ( M w / M n ∼ 1.1). The low polymerization rate obtained in MeCl/Hex 40/60 v/v more than doubled when the solvent polarity was increased to 60/40 v/v. A similar ca. twofold increase in rate was also observed when the temperature was raised from −80 to −60 °C. Living polymerization and high rates were obtained using SnCl 4; however, theoretical molecular weight and therefore 100% initiator efficiency were only achieved at [SnCl 4 ] ∼ 0.5[chain end]. Mechanistic studies indicated that the initiator is fully ionized at this ratio, giving rise to SnCl 6 2- counteranions. The polymer chain end, however, is not fully ionized, and propagation involves SnCl 5 - counteranions.