Ring-opening polymerization of l, l -lactide with various amounts of catalyst, 2-ethylhexanoic acid tin(II) salt, and cocatalyst, 1-dodecanol, at 130 °C in bulk is examined. Monomer-to-catalyst and cocatalyst-to-catalyst molar ratios were changed from 500 to 4000 and from 1 to 600, respectively. In agreement with previous literature, the catalyst concentration is affecting the reaction rate, whereas OH-bearing species (such as cocatalyst and impurities) are controlling both reaction rate and polymer molecular weight. A model implementing a living kinetic scheme is first developed and validated by comparison with the experimental results. The rate coefficients of the main reactions (activation, propagation, and reversible chain transfer) have been evaluated. Finally, to predict with accuracy the broadening of the molecular weight distribution, we introduce ester interchange reactions, so-called “transesterifications”, into the kinetic scheme, and the corresponding rate coefficient is evaluated.
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Yu et al. (2009) studied this question.