Abstract rac ‐Lactide polymerization kinetics in THF at 72 °C were monitored in real‐time using mid‐infrared ATR‐FTIR spectroscopy, with diamond composite insertion probe and light conduit technology. Monomer concentration as a function of time was acquired using the 1240 cm −1 resonance associated with the COOC stretch. Polymerizations were initiated with either n ‐propanol (PrOH), ethylene glycol (EG), trimethylol propane (TMP), or pentaerythritol (PENTA) with the coinitiator stannous octoate (Sn(Oct) 2 ). Polymerizations were found to be reversible at high monomer conversions, with a residual monomer concentration at 72 °C (345 K) of 0.081 M. The polymerizations were internally first‐order with respect to monomer, indicating a constant concentration of propagating centers. For a typical reaction with [ rac ‐LA] 0 = 1.0 M, [PENTA] 0 = 1.3 × 10 −2 M, and [Sn(Oct) 2 ] = 2.5 × 10 −2 M, the first‐order rate constant, k app was measured as 1.8 × 10 −4 s −1 . First‐order rate constants were determined to be independent of polymer architecture (i.e., initiator functionality) and proportional to [Sn(Oct) 2 ] for [Sn(Oct) 2 ] 0 /[ROH] 0 ≪ 1, where [ROH] 0 represents the initial concentration of initiating hydroxyl groups.
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Moravek et al. (2008) studied this question.
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