Studies of Radical Polymerization by Using Long-lived Propagating Polymer Radicals

衣康酸衍生物和一些相关单体虽然有两个大的取代基，但它们很容易被自由基引发剂聚合。在实际聚合条件下，观察到聚合体系中存在esr可检测的聚合物自由基。利用ESR测定的聚合物自由基浓度，我们成功地估计了这些单体的增殖速率常数k_p和终止速率常数k_t。二烷基酸酯的k_p和k_t值随着烷基链的变长而减小。烷基的位阻效应对终止反应的抑制作用远大于对增殖反应的抑制作用，使得烷基越长单体的聚合速率越高。在极性较强的溶剂中，衣康酸二辛酯的k_p值较小。可观的溶剂效应可以用聚合物自由基对所用溶剂的亲和力来解释。SnCl_4的存在降低了衣康酸二乙酯的k_p和k_t值，这似乎是由于熵因子的作用。α -苯甲酰氧甲基丙烯酸乙酯（EBMA）的k_p （990 l/mol, 60 C）远大于itacon酸酯（约2倍），k_t （2.9 × 10^6 l/mols）是itacon酸酯的10倍。n -苯丙酮酸甲酯的k_p值（8.2 l/mol s）和k_t值（1.9 ~ 4.2 l/mol s）与邻苯丙酮酸甲酯相似。N-（2.6-二甲苯基）itaconimide的k_p （24 ~ 27 l/mols）与单体浓度无关，而kt （3.8 × 10^4 ~ 2.0 × 10^5l/mols）随单体浓度的增加而减小，这是由于k_t与聚合物长度的关系。获得了衣康酸二丁酯与n -环己基马来酰亚胺自由基共聚的二次效应的ESR光谱和动力学证据。

Itaconic acid derivatives and some related monomers were found to be easily polymerized by radical initiators in spite of their two bulky alpha -substituents. The polymerization systems were observed to involve ESR-detectable propagating polymer radicals under the actual polymerization conditions. Using the polymer radical concentration determined by ESR, we succeeded in estimating the rate constants of propagation (k_p) and termination (k_t) of these monomers. The k_p and k_t values of dialkyl itaconates decrease as the alkyl chain becomes longer. The steric effect due to the alkyl group suppresses much more termination than propagation, leading to the fact that the monomer with longer alkyl group shows a higher polymerization rate. The k_p value of dioctyl itaconate is smaller in a more polar solvent. The considerable solvent effect is explicable in terms of affinity of the propagating polymer radical for the solvent used. The presence of SnCl_4 reduces both the k_p and k_t values of diethyl itaconate, which seems to be due to an entropy factor. k_p (990 l/mols, 60ﾟC) of ethyl alpha -benzoyloxymethylacrylate (EBMA) is much larger (about two factors) than those of itaconates, and k_t (2.9x10^6 l/mol s) of EBMA is ten times those of itaconates. Methyl N-phenylitaconamate shows the k_p (8.2 l/mol s) and k_t (1.9-4.2 l/mol s) values 55ﾟC similar to those of itaconates. k_p (24-27 l/mol s) of N- (2.6-dimethylphenyl) itaconimide at 50ﾟC is almost independent of the monomer concentration, while kt (3.8x10^4-2.0x10^5l/mols) decreases with the monomer concentration which is ascribable to dependence of k_t on the polymer chai n length. ESR spectroscopic and kinetic evidences for penultimate effect were obtained in the radical copolymerization of dibutyl itaconate with N-cyclohexylmaleimide.