Hill Lawrence, Sims Hunter, Nguyen Ngoc, Collins Christopher, Palmer Jeffery, Wasson Fiona
Department of Chemistry, Western Kentucky University, Bowling Green, KY 42101, USA.
Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA.
Polymers (Basel). 2022 Apr 24;14(9):1733. doi: 10.3390/polym14091733.
Mid-chain degradable polymers can be prepared by atom transfer radical polymerization from difunctional initiators that include triggers for the desired stimuli. While many difunctional initiators can respond to reducing conditions, procedures to prepare difunctional initiators that respond to oxidizing conditions are significantly less available in the literature. Here, a difunctional initiator incorporating an oxidizable boronic ester trigger was synthesized over four steps using simple and scalable procedures. Methyl methacrylate was polymerized by atom transfer radical polymerization using this initiator, and the polymerization kinetics were consistent with a controlled polymerization. The polymer synthesized using the difunctional initiator was found to decrease in molecular weight by 58% in the presence of hydrogen peroxide, while a control experiment using poly(methyl methacrylate) without a degradable linkage showed a much smaller decrease in molecular weight of only 9%. These observed molecular weight decreases were consistent with cleavage of the difunctional initiator via a quinone methide shift and hydrolysis of the methyl ester pendent groups in both polymers, and both polymers increased in polydispersity after oxidative degradation.
中链可降解聚合物可通过原子转移自由基聚合由双官能引发剂制备，这些引发剂包括对所需刺激的触发基团。虽然许多双官能引发剂可对还原条件作出响应，但文献中制备对氧化条件作出响应的双官能引发剂的方法要少得多。在此，使用简单且可扩展的程序，通过四个步骤合成了一种包含可氧化硼酸酯触发基团的双官能引发剂。使用该引发剂通过原子转移自由基聚合使甲基丙烯酸甲酯聚合，聚合动力学与可控聚合一致。发现使用双官能引发剂合成的聚合物在过氧化氢存在下分子量降低了58%，而使用没有可降解连接的聚（甲基丙烯酸甲酯）的对照实验显示分子量仅降低了9%，下降幅度小得多。观察到的分子量下降与双官能引发剂通过醌甲基化物重排以及两种聚合物中甲酯侧基的水解有关，并且两种聚合物在氧化降解后多分散性均增加。
