Rate retardation in reversible addition-fragmentation chain transfer (RAFT) polymerization: Further evidence for cross-termination producing 3-arm star chain
Rate retardation in reversible addition-fragmentation chain transfer (RAFT) polymerization: Further evidence for cross-termination producing 3-arm star chain
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DOI：
10.1021/ma030434p
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发表时间：
2004-02-24
期刊：
影响因子：
5.5
通讯作者：
Fukuda, T
中科院分区：
文献类型：
--
作者：
Kwak, Y;Goto, A;Fukuda, T
新的实验证据表明，在60℃时，聚苯乙烯与聚二硫代苯甲酸酯(PST-SCSPh)聚合的速度减慢是由于聚苯乙烯基(PST(.)以及由PST(.)至PST-SCSPh。聚合速率R随[PSt-SCSPh]的增加而降低，1/R-p(2)与[PSt-SCSPh]的关系曲线呈线性，符合不可逆交叉终止机理的要求。交叉终止速率常数k(T)‘约为0.5k(T)，其中k(T)为PSt(.)的自终止速率常数。由GPC-MALLS(配有多角度激光散射检测器的凝胶渗透色谱)分析的模型实验证明了三臂星的形成，这可能是交叉终止的产物。由PST(.)自终止产生的三臂星相对于双分子量线性链的浓度。与[PST-SCSPh]成正比，由该模型实验得到的kt‘值与上述动力学(减速)实验测得的kt’值吻合较好。三臂星在60摄氏度的实验时间范围内非常稳定，证实了在这个温度下交叉终止是不可逆的。
New pieces of experimental evidence were presented showing that the rate retardation in the polymerization of styrene with polystyryl dithiobenzoate (PSt-SCSPh) at 60 degreesC is caused by the irreversible cross-termination between the polystyryl radical (Pst(.)) and the intermediate radical produced by the addition of PSt(.) to PSt-SCSPh. The polymerization rate R, decreased with an increase of [PSt-SCSPh] such that a plot of 1/R-p(2) VS [PSt-SCSPh] was linear, as the irreversible cross-termination mechanism demands. The cross-termination rate constant k(t)' was estimated to be about 0.5k(t), where k(t) is the self-termination rate constant of PSt(.). The formation of a 3-arm star, a possible product of cross-termination, was evidenced by a model experiment involving the analysis by GPC-MALLS (gel permeation chromatography equipped with a multiangle laser-light scattering detector). The concentration of the 3-arm star relative to that of the doubled molecular weight linear chain produced by self-termination of PSt(.) was proportional to [PSt-SCSPh], and the value of kt' deduced by this model experiment well agreed with that determined by the kinetic (rate retardation) experiment mentioned above. The 3-arm star was perfectly stable in the time scale of the experiments at 60 degreesC, confirming that cross-termination is irreversible at this temperature.