ma062405v_si_001.pdf (131.61 kB)
Chain Length Dependent Termination Rate Coefficients of Methyl Methacrylate (MMA) in the Gel Regime: Accessing kti,i Using Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerization
journal contribution
posted on 2007-04-17, 00:00 authored by Geoffrey Johnston-Hall, Martina H. Stenzel, Thomas P. Davis, Christopher Barner-Kowollik, Michael J. MonteiroThe termination rate coefficient, kti,i, for propagating chains of near equal length, i, was evaluated
using the RAFT−CLD−T method over a wide range of chain lengths and up to a conversion of 70% for MMA
polymerizations carried out in the presence of the RAFT agent, CPDB, at 80 °C. We found that the conversion
for the gel onset corresponded to the conversion at which polymer chains begin to overlap (i.e., c*), and was
found to range from 15 to 30% conversion depending on the Mn. It was further shown that c* also corresponded
with the gel onset conversions for vinyl acetate and methyl acrylate. The chain length dependence of kt in the gel
regime scaled as αgel(x) = 1.8x + 0.056, suggesting that reptation alone does not play a role in our system. A
composite model was then derived to accurately describe kti,i for chain lengths up to 3200 and conversions up to
70%. The kti,i profiles for well-known termination models were tested and most gave unsatisfactory agreement
with our experiments. Our model can be readily applied to any monomer provided accurate kti,i(x) data can be
determined.