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首页> 外文期刊>Macromolecules >Rate Retardation in Reversible Addition-Fragmentation Chain Transfer(RAFT)Polymerization:Further Evidence for Cross-Termination Producing 3-Arm Star Chain
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Rate Retardation in Reversible Addition-Fragmentation Chain Transfer(RAFT)Polymerization:Further Evidence for Cross-Termination Producing 3-Arm Star Chain

机译：可逆加成-断裂链转移（RAFT）聚合中的速率延迟：跨终端生产3臂星形链的进一步证据

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摘要

New pieces of experimental evidence were presented showing that the rate retardation in the polymerization of styrene with polystyryl dithiobenzoate(PSt-SCSPh)at 60 deg C is caused by the irreversible cross-temination between the polystyryl radical(PSt)and the intermediate radical produced by the addition of PSt. to PSt-SCSPh.The polymerization rate R_p 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 crosstermination,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 k_t deduced by this model experiment well agreed with that determined by the kinetic(rate retardation)experiment mentioned above.The 3-arm star was perfactly stable in the time scale of the experiments at 60 deg C,confirming that cross-termination is irreversible at this temperature.
机译：提出了新的实验证据，表明苯乙烯与聚苯乙烯二硫代苯甲酸酯（PSt-SCSPh）在60℃下聚合的速率延迟是由于聚苯乙烯基（PSt）与由聚苯乙烯基产生的中间自由基之间不可逆的交联作用引起的。 PSt的添加。聚合速率R_p随[PSt-SCSPh]的增加而降低，使得1 / R_p〜2 vs [PSt-SCSPh]的图呈线性，这是不可逆交叉终止机理所要求的。终止速率常数k_t估计约为0.5k_t，其中k_t是PSt的自终止速率常数。通过涉及GPC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。 -MALLS（配有多角度激光散射检测器的凝胶渗透色谱法）。3-臂星的浓度相对于通过PSt自终止产生的分子量为两倍的线性直链浓度与[PSt-SCSPh]成正比，并且该模型实验得出的k_t值与上述动力学（速率延迟）实验确定的值完全吻合。三臂星在60℃的实验时间范围内是完全稳定的，证实了终止是不可逆的这个温度。

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