Mechanism and kinetics of RAFT-based living radical polymerizations of styrene and methyl methacrylate
Mechanism and kinetics of RAFT-based living radical polymerizations of styrene and methyl methacrylate
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DOI：
10.1021/ma0009451
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发表时间：
2001-01-30
期刊：
影响因子：
5.5
通讯作者：
Thang, SH
中科院分区：
文献类型：
--
作者：
Goto, A;Sato, K;Thang, SH
研究了以模型聚合物-二硫代碳酸酯加合物为介质、过氧化苯甲酰（BPO）为引发剂的苯乙烯和甲基丙烯酸甲酯本体聚合动力学。聚合速率，以及因此聚合物自由基P-的浓度，与[BPO]（1/2）成正比。用GPC峰分辨法和多分散性分析法测定了拟一级活化速率常数k（act）。结果表明，k（act）与[P-.]成正比，表明可逆加成-断裂链转移（RAFT）是唯一重要的活化机制。汇率常数k（ex）的大小（= k（act）/[P-.]）强烈依赖于二硫代碳酸酯基团和聚合物的结构。在这项工作中检查的三个RAFT系统的k（ex）值都非常大，这解释了为什么这些系统可以提供低多分散性聚合物从聚合的早期阶段。聚苯乙烯二硫代乙酸酯（PSt-SCH 3）的活化能k（ex）为21.0 kJ mol（-1），这对于快速加成反应是合理的。
The bulk polymerizations of styrene and methyl methacrylate in the presence of model polymer-dithiocarbonate adducts as mediators and benzoyl peroxide (BPO) as a conventional initiator were kinetically studied. The polymerization rate, and hence the concentration of polymer radical P-., was proportional to [BPO](1/2), The pseudo-first-order activation rate constants k(act) were determined by the GPC peak-resolution and the polydispersity-analysis methods. The results showed that k(act) is directly proportional to [P-.], indicating that reversible addition-fragmentation chain transfer (RAFT) is the only important mechanism of activation. The magnitude of the exchange rate constant k(ex) (= k(act)/[P-.]) was strongly dependent on both the structures of the dithiocarbonate group and the polymer. The k(ex) values for the three RAFT systems examined in this work were all very large, which explains why these systems can provide low-polydispersity polymers from an early stage of polymerization. The activation energy of k(ex) for a polystyryl dithioacetate (PSt-SCSCH3) was 21.0 kJ mol(-1), which is reasonable for a fast addition reaction.