Isotactic Polymers with Alternating Lactic Acid and Oxetane Subunits from the Endoentropic Polymerization of a 14-Membered Ring

作者：Donghui Zhang, Jianyan Xu, Luis M. Alcazar‐Roman, Loren Greenman, Christopher J. Cramer, Marc A. Hillmyer, William B. Tolman · 发表于：Macromolecules · 年份：2004 · DOI：10.1021/ma049571s · 被引用次数：25 · 研究领域：biodegradable polymer synthesis and properties、Carbon dioxide utilization in catalysis、Advanced Polymer Synthesis and Characterization

A new isotactic, perfectly alternating polymer of ( S )-lactic acid and oxetane was synthesized by the entropically driven ring-opening polymerization of a 14-membered cyclic diester ( S,S - 3 ) mediated by a zinc alkoxide catalyst. The polymer ( S,S -PMOD) was characterized by NMR spectroscopy, size exclusion chromatography, and matrix-assisted laser desorption ionization mass spectrometry. Under polymerization conditions the equilibrium concentration (0.17 ± 0.05 M) of the monomer in toluene was essentially independent of temperature, and the average thermodynamic parameters for the ring-opening polymerization were found to be Δ H p ° = 0.2 ± 0.7 kJ mol -1 and Δ S p ° = +16 ± 2 J mol -1 K -1 (standard state [ S,S - 3 ] = 1.0 M). Theoretical calculations of the standard state enthalpy (Δ H p °) for ring-opening polymerization of various oxocyclics, including S,S - 3, were well-correlated with experimental values. Kinetic studies showed that the polymerization of S,S - 3 was slower ( k p = 0.82 ± 0.04 M -1 s -1 and k dp = 0.12 ± 0.04 s -1 at 25 °C) than that of lactide ( k p = 2.2 M -1 s -1 ) using the same zinc alkoxide catalyst. Differential scanning calorimetry of S,S -PMOD showed a glass transition temperature of −30 °C for samples with molecular weights between 5 and 72 kg mol -1 . In support of the potential utility of S,S -PMOD as a PLA plasticizer, the complete miscibility of the polymeric components was demonstrated by the observation of single T g values for a serie...