Polymerization of sterically congested α-alkylacrylates under high pressure

A series of alpha-alkylacrylates, including methyl ethacrylate (MEA), methyl alpha-propylacrylate, methyl alpha-isopropylacrylate (MiPA), methyl alpha-butylacrylate (MnBA), and methyl alpha-isobutylacrylate (MiBA), were successfully polymerized at 65 degreesC under high pressure (1-9 kbar). In contrast to results obtained at ambient pressure, all monomers yielded high molecular weight polymers (number-average molecular weight = 4-18 X 10(4)), except for MiPA (number-average molecular weight = 8 X 10(3)), probably because of the high steric hindrance of the isopropyl group. Polymerization kinetics under high pressure were obtained for MEA, MnBA, and MiBA. Overall activation volumes were estimated to be - 14.9, - 17.0, and - 11.6 mL mol(-1) for MEA (3-7 kbar), MnBA (3-7 kbar), and MiBA (5-9 kbar), respectively. Extrapolation to ambient pressure provided rates of polymerization for these monomers unaffected by the ceiling temperature effect. These values were further used to quantitatively assess the steric influence exerted by the alpha-substituent on the polymerizability of these sterically congested acrylates with Meyer's steric parameter. (C) 2002 Wiley Periodicals, Inc.