Ring-opening polymerization of L,L-lactide with various amounts of catalyst, 2-ethylthexanoic acid tin(II) salt, and cocatalyst, 1-dodecanol, at 130 degrees C m bulk is examined. Monomer-to-catalyst and cocalalyst-to-catalyst molar ratios were changed frorn 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 reactors (activation, propagation, and reversible chain transfer) have been evaluated. Finally. to predict with accuracy the bioadening of the molecular weight distribution, we introduce ester interchange reactions, so-called "transesterifications", into the kinetic scheme, and the corresponding rate coefficient is evaluated.