超临界CO_2中左旋丙交酯的开环聚合反应

Ring-Opening Polymerization of L -Lactide in Supercritical CO_2

以辛酸亚锡为催化剂,用超临界CO2作溶剂,实现了左旋丙交酯的开环聚合,系统地研究了催化剂用量、单体浓度、聚合时间、聚合温度、CO2纯度和压力等因素对单体转化率、聚合产物相对分子质量及其分布的影响。研究结果表明,在超临界状态下聚合温度、催化剂用量和CO2纯度是影响聚合的几个最重要的因素。超临界状态下的丙交酯开环聚合与本体丙交酯开环聚合相似,聚合过程符合配位插入聚合反应的机理。

Ring-opening polymerization of L -lactide was conducted in supercritical carbon dioxide using stannous octoate as catalyst. A relatively high relative molecular mass polymer, Mw≥ 80 000, with a polydispersity index (PDI) of 2.5 measured by gel permeation chromatography (GPC) was obtained. Various effects such as polymerization temperature,time,pressure,concentration of monomer (L -lactide) .monomer to catalyst mole ratio and purity of supercritical carbon dioxide on relative molecular mass of poly(L-lactide) and its distribution as well as monomer conversion monitored with 1H NMR spectroscopy were systematically investigated. Polymerization temperature, monomer to catalyst mole ratio and purity of carbon dioxide where key factors. The relative molecular mass of polymer had a maximum value as a monomer /catalyst mole ratio of 500,being close to the value in solution polymerization of polylactides. The efficiency of catalyst indicated that a single SnOct2 molecule seemed able to initiate a number of polymer chains. The experimental results were consistent with the coordination-insertion polymerization mechanism of formation of alkoxide initiator in situ via reaction between stannous octoate and traces of water present in carbon dioxide and catalyst.