Kinetic investigations of reversible addition fragmentation chain transfer polymerizations: Cumyl phenyldithioacetate mediated homopolymerizations of styrene and methyl methacrylate
Kinetic investigations of reversible addition fragmentation chain transfer polymerizations: Cumyl phenyldithioacetate mediated homopolymerizations of styrene and methyl methacrylate
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DOI：
10.1021/ma010349m
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发表时间：
2001-10-23
期刊：
影响因子：
5.5
通讯作者：
Davis, TP
中科院分区：
文献类型：
--
作者：
Barner-Kowollik, C;Quinn, JF;Davis, TP
使用PREDICI模拟程序对可逆加成断裂链转移(RAFT)过程进行模拟和数据拟合的方法已扩展到苯基二硫代乙酸异丙酯催化的苯乙烯和甲基丙烯酸甲酯(MMA)本体均聚合。实验得到的苯乙烯体系的分子量分布(MWD)是窄的单峰分布，并且随着单体转化率向更高的分子质量线性移动。MMA系统表现出传统链转移和生活行为的混合，导致双峰MWD。在60℃下对苯乙烯体系进行了实验和模拟相结合的研究，得到了聚合物RAFT试剂与游离大分子物质加成反应的速率系数k(β)约为5.6×10(-5)L摩尔(-1)S(-1)和大分子RAFT物种的分解速率系数k-(β)约为2.7×10(-1)S(-1)。对异丙基苯基二硫代乙酸异丙酯的转移速率系数接近2.2×10(5)L摩尔(-1)S(-1)。在25-60℃的温度范围内对MMA体系进行了研究。利用在MMA聚合中观察到的杂化行为(在低单体转化率下)执行Mayo分析，从而确定转移到异丙基苯基二硫代乙酸酯反应的温度依赖性。该过程的活化能接近26kJ·mol(-1)。与苯乙烯体系不同，PREDICI模拟程序不能成功地应用于苯基二硫代乙酸异丙酯催化的MMA聚合，从而推导出k(β)和k-(β)。这种无能为力是由于异丙基苯基二硫代乙酸酯-MMA体系的杂化性质，导致对k(β)和k(-beta)的敏感性显著降低。
A previously published simulation and data fitting procedure for the reversible addition fragmentation chain transfer (RAFT) process using the PREDICI simulation program has been extended to cumyl phenyldithioacetate mediated styrene and methyl methacrylate (MMA) bulk homopolymerizations. The experimentally obtained molecular weight distributions (MWDs) for the styrene system are narrow and unimodal and shift linearly with monomer conversion to higher molecular weights. The MMA system displays a hybrid of conventional chain transfer and living behavior, leading to bimodal MWDs. The styrene system has been subjected to a combined experimental and modeling study at 60 degreesC, yielding a rate coefficient for the addition reaction of free macroradicals to polymeric RAFT agent, k(beta), of approximately 5.6 x 10(-5) L mol(-1) s(-1) and a decomposition rate coefficient for macroradical RAFT species, k-(beta), of about 2.7 x 10(-1) s(-1). The transfer rate coefficient to cumyl phenyldithioacetate is found to be close to 2.2 x 10(5) L mol(-1) s(-1). The MMA system has been studied over the temperature range 25-60 degreesC. The hybrid behavior observed in the MMA polymerizations has been exploited (at low monomer conversions) to perform a Mayo analysis allowing the determination of the temperature dependence of the transfer to cumyl phenyldithioacetate reaction. The activation energy of this process is close to 26 kJ mol(-1). In contrast to the styrene system, the PREDICI simulation procedure cannot be successfully applied to cumyl phenyldithioacetate mediated MMA polymerizations for the deduction of k(beta) and k-(beta). This inability is due to the hybrid nature of the cumyl phenyldithioacetate-MMA system, leading to a significantly reduced sensitivity toward k(beta) and k(-beta).