Carbocationic Polymerization in the Presence of Sterically Hindered Bases. VII. The Polymerization of α-Methylstyrene with the Pentamethyl Benzyl Chloride/SnCl4Initiating System

The polymerization of α-methylstyrene by the Me5C6 CH2C1/ SnCl4 nonprotic initiating system has been studied in the presence and absence of 2,6-di-tert-butylpyridine (DtBP) in CH2C12 in the −30 to −80°C temperature range. Model experiments demonstrate that initiation involves direct carbocationation of the olefin by Me5C6C⊕H2. According to kinetic studies, polymerizations in the absence of DtBP are very rapid (no induction) and terminationless, and molecular weights are determined by chain transfer to monomer. In the presence of DtBP, polymerizations do not go to completion due to terminative proton entrapment. Reducing the temperature increases the yields and molecular weights. Evidently a decrease in temperature reduces the rate of proton expulsion and thus the rate of terminative proton entrapment is also reduced. That chain transfer to monomer is absent in the presence of DtBP is demonstrated by the constancy of the number of polymer molecules formed and initiator efficiencies obtained under a variety of experimental conditions, and by Mayo plots. In addition to being an initiator, Me5C6 CH2C1 is also an efficient chain transfer agent. The chain transfer activity of Me5C6 CH2Cl has been quantitatively determined in the -30 to -66°C range. The effect of temperature on poly(α-methylstyrene) molecular weights has been investigated and the Arrhenius plot yielded ΔH[Dbar][Pbar]n = −2.15 ± 0.2 kcal/mol.