衰减链转移(DT)聚合醋酸乙烯酯的动力学

在醋酸乙烯酯的普通自由基聚合体系中加入少量碘（质量分数为0.57%～0.86%），用偶氮二异丁腈作引发剂合成聚醋酸乙烯酯，对其聚合反应的动力学及反应机理进行了研究。 考察了碘质量分数对聚合反应速率、聚合物分子量及分子量分布的影响，发现随着碘浓度的增加，聚合物分子量及分子量分布得到更好的控制；对聚合过程进行了核磁跟踪，考察了聚合过程中几种化合物的变化情况，特别是初级自由基与碘生成的加合物A-I（A来自引发剂分裂后产生的自由基）及单体加合物A-Mn-I（M代表单体单元）的变化情况；对聚合物结构作了详细的1H NMR分析，结果表明，聚合过程中分子量随时间延长而逐渐增大，分子量分布随单体转化率增加而变窄，聚合终期，单体转化率达到80%左右时，所得聚合物分子量分布窄（Mw/Mn≤1.41），且含有碘端基。该方法的自由基聚合具有活性/可控的性质。

Kinetics of Degenerative Transfer Radical Polymerization of Vinyl Acetate

Controlled/living polymerization kinetics of vinyl acetate(VAc) was studied. Poly(vinyl acetate)(PVAc) with predetermined molecular mass and relatively low polydispersity was successfully synthesized from vinyl acetate(VAc) by a degenerative transfer radical polymerization with the presence of iodine（0.57%～0.86% mass fraction of the system） using 2,2′-azobis(isobutyronitrile)(AIBN) as the initiator. The effects of iodine concentration on reaction speed and relative molecular mass and relatively polydispersity were investigated. The results indicated that the increasing speed of molecular mass was successfully controlled and relatively polydispersity was narrowed with increasing iodine concentration. The polymerization was monitored by an on-line 1H NMR spectroscopy to investigate the evolution of several compounds in the reaction medium, especially the adduct between primary radicals and iodine(A-I, where A stands for the radical fragment from the initiator), and the monoadduct A-Mn-I(where M stands for the monomer unit). The structure of the poly(vinyl acetate) iodo-terminated chain end groups by this method was proved using 1H NMR spectrum. Molecular masses increase linearly with conversion and molecular polydispersities decrease gradually with improving monomer conversion of vinyl acetate, and polymers with relatively narrow molecular polydispersities(Mw/Mn≤1.41) are obtained when the monomer conversion of vinyl acetate reaches up to 80%, indicating that the process of degenerative transfer polymerization efficiently controls the number-average molecular mass and molecular polydispersities in the presence of molecular iodine(I2), therefore the process is a controlled/living radical polymerization.