Chain-length dependent termination in pulsed-laser polymerization, 6. The evaluation of the rate coefficient of bimolecular termination kt for the reference system methyl methacrylate in bulk at 25°C |
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Authors: | Oskar Friedrich Olaj Philipp Vana |
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Abstract: | The values for the rate coefficient of chain termination kt in the bulk polymerization of methyl methacrylate at 25°C were formally calculated (i) from the second moment of the chain-length distribution and (ii) from the rate equation for laser-initiated pseudostationary polymerization (both expressions were originally derived for chain-length independent termination) by inserting the appropriate experimental data including the rate constant of chain propagation kp. These values were treated as average values, k and k , respectively. They exhibited good mutual agreement, even the predicted gradation (k < k by about 20%) was recovered. The log-log plot of kt vs. the average degree of polymerization of the chains at the moment of their termination v′ yielded exponents b of 0.16–0.17 in the power-law k t = A · v′?b, A ranging from 1.1 × 108 to 1.3 × 108 (L · mol?1 · s?1). A 70% contribution of disproportionation to overall termination has been assumed in the calculations. |
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