Determination of gel point during atom transfer radical copolymerization with cross-linker
Determination of gel point during atom transfer radical copolymerization with cross-linker
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DOI：
10.1021/ma071324b
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发表时间：
2007-10-30
期刊：
影响因子：
5.5
通讯作者：
Matyjaszewski, Krzysztof
中科院分区：
文献类型：
--
作者：
Gao, Haifeng;Min, Ke;Matyjaszewski, Krzysztof
以丙烯酸甲酯（MA）和乙二醇二丙烯酸酯（EGDA）为单体，采用原子转移自由基聚合（ATRP）方法，通过改变交联剂与引发剂的初始摩尔比，合成了一系列支化和交联的聚（MA-co-EGDA）共聚物。与Flory-Stockmayer理论一致，当反应的侧链乙烯基的浓度大于主链时，发生凝胶化。这个临界点取决于引发效率和交联剂和单体中乙烯基的反应性。实验凝胶化点发生在总溶胶中支化聚合物的分子量和重量分数（f（分支））达到最大值时，如通过在不同转化率下的溶胶的GPC测量所确定的。基于实验结果和Predici模拟的动力学研究表明，所有丙烯酸酯基团具有相似的反应活性。在所有反应中，基于MA和EGDA的转化率（conV（MA），（凝胶）和conV（EGDA），（凝胶）），通过Predici模拟理论上预测的凝胶点仅略低于实验结果。这些结果表明，由ATRP合成的凝胶具有更均匀的结构，并含有较少量的环化产物相比，由传统的自由基聚合合成的凝胶。
Atom transfer radical polymerization (ATRP) of methyl acrylate (MA) and ethylene glycol diacrylate (EGDA) provided a series of poly(MA-co-EGDA) branched and cross-linked copolymers using various initial molar ratios of cross-linker to initiator. In agreement with the Flory -Stockmayer theory, the gelation occurred when the concentration of reacted pendant vinyl groups was larger than that of primary chains. This critical point depends on the initiation efficiency and the reactivity of vinyl groups in both cross-linker and monomer. The experimental gelation point occurred when both the molecular weight and the weight fraction of branched polymers among the total sols (f(branch)) reached the maximum, as determined by GPC measurement of the sols at different conversions. The kinetic study based on experimental results and Predici simulation demonstrated that all acrylate groups had a similar reactivity. In all reactions, the gel points theoretically predicted by Predici simulation, based on the conversions of MA and EGDA (conV(MA),(gel), and conV(EGDA),(gel)), were only slightly lower than the experimental results. These results indicate that the gels synthesized by ATRP have a more homogeneous structure and contain a smaller amount of cyclization products in contrast to gels synthesized by conventional free radical polymerization.