Substituent effects in the catalytic chain transfer polymerization of 2-hydroxyethyl methacrylate

The catalytic chain transfer behavior of 2-hydroxyethyl methacrylate (HEMA) was studied in bulk at 40 and 60 °C. The chain transfer constant of cobaloxime boron fluoride (COBF) was found to be 6×102 at 40 and 60 °C, which corresponds to chain transfer rate coefficients of about 1.2×106 and 2.0×106 l mol−1 s−1, respectively. These values are about 10–15 times lower than those found previously for methyl methacrylate (MMA) and this decrease can be conceivably ascribed to the combination of a monomer viscosity effect, which lowers the rate coefficient by a factor of 6–8, and the complexation of the hydroxyl group with the catalyst, which causes an additional lowering by a factor of about two. The latter effect was studied by UV/Vis spectroscopy and additional kinetic studies of the COBF-mediated polymerization of MMA in the presence of ethanol. Similar UV/Vis spectra as in the case of HEMA and a reduction in chain transfer constant by a factor of two were observed.