Polymerization Kinetics of rac-Lactide Initiated with Alcohol/Stannous Octoate Using In Situ Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy: An Initiator Study

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Polymers and High Performance Materials


rac-Lactide polymerization kinetics in THF at 72 degrees 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 degrees 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 x 10(2) M, and [Sn(Oct)(2)]-2.5 x 10(2) M, the first-order rate constant, k(upp) was measured as 1.8 x 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)/d[ROH](0) << 1, where IROHIO represents the initial concentration of initiating hydroxyl groups. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 797-803, 2009.

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Journal of Polymer Science Part A-Polymer Chemistry





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