STEREOCHEMISTRY OF POLYMERIZATION OF TRIPHENYLMETHYL AND DIPHENYLMETHYL METHACRYLATE UNDER GROUP-TRANSFER CONDITIONS

The polymerization of triphenylmethyl and diphenylmethyl methacrylate (TrMA and DMA, respectively) was investigated using group-transfer polymerization (GTP) initiators and various catalysts at temperatures varying from +50 to -97-degrees-C. The catalysts found to be effective were tris(dimethylamino)-sulfonium trimethyldifluorosiliconate ((TAS)Me3SiF2) and the bifluoride TAS catalyst ((TAS)HF2). Furthermore, the polymerizations required relatively large quantities of catalyst. The fluoride and acetate catalysts were found to be ineffective. The molecular weight control is relatively poor, presumably as a result of side reactions involving the GTP initiator. The stereochemistry of the PTrMA was highly isotactic (70-90%), the isotactic content increasing at higher temperatures. Furthermore, a plot of the log (k(r)/k(m)) vs 1/T where k(r) and k(m) denote the rate constants for racemic and meso placements shows a pronounced curvature. These and other observations suggest a mechanism of TrMA polymerization involving TAS enolates that equilibrate with other species. In contrast, the stereochemistry of polymerization of DMA resembles that of MMA in that mostly syndiotactic polymers are formed. In this case, the stereoregularity decreases with increasing temperature and Bernoullian statistics prevails, suggesting the intermediacy of a single propagating species. This is supported by a linear plot of log(r/m) vs 1/T.