Polymerization kinetics of rac -lactide initiated with alcohol/stannous octoate using in situ attenuated total reflectance-fourier transform infrared spectroscopy: An initiator study

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 COOC 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, kapp 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. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 797–803, 2009