Branching in free radical polymerization due to chain transfer, 2. Theory of the effect of polyfunctional transfer reagents
Branching in free radical polymerization due to chain transfer, 2. Theory of the effect of polyfunctional transfer reagents
复制标题
自由基聚合中由于链转移而支化，2.多官能转移试剂的作用理论
DOI：
10.1002/macp.1977.021780516
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发表时间：
1977
影响因子：
2.5
通讯作者：
W. Burchard
中科院分区：
文献类型：
--
作者：
B. Ullisch;W. Burchard
多官能团链转移剂在自由基聚合中的应用对聚合物分子量有两方面的影响。在单官能调节剂的情况下，链长减少;然而，转移试剂的多官能度导致支化，从而增加分子量。在级联理论的基础上发展了描述聚合物结构与单体转化率关系的一般理论。该理论利用了有向图的图论概念，通过该有向图可以适当地表示定向链式反应。导出了重均分子量Mw、z均方回转半径<$S2 <$z和平均粒子散射因子Pz（μ）的解析式。此外，还给出了一个简单的凝胶化条件方程。特别关注的是在聚合过程中形成的支化和线性聚合物的馏分。推导出的方程进行了讨论的动力学常数已知的聚苯乙烯。甘精胰岛素被证明是可能的链转移常数Ctr = 22，如果每个转移分子的官能团的数量超过至少一个值为7。
Polyfunctional chain transfer reagents applied in free radical polymerization have two effects on the polymer molecular weight. As in the case of monofunctional regulators the chain length is reduced; the polyfunctionality of the transfer reagents causes, however, branching and thus an increase in molecular weight. A general theory is developed on the basis of Cascade Theory to describe the polymer structure in dependence on the monomer conversion. The theory takes advantage of the graph theoretical concept of digraphs by which the directed chain reaction can be properly represented. Analytic equations are derived for the weight average molecular weight Mw, z-average mean square radius of gyration 〈S2〉z and the average particle scattering factor Pz(μ). Furthermore, a simple equation is given for the condition of gelation. Special concern is given to the formation of fractions of branched and linear polymers during the polymerization process. The derived equations are discussed in terms of kinetic constants known for polystyrene. Gelation is shown to be possible for a chain transfer constant of Ctr = 22 if the number of functional groups per transfer molecule exceeds at least a value of 7.