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本工作用核磁共振研究了甲基丙烯酸甲酯住甲苯中以n-BuLi为引发剂的阴离子聚合反应产物的空间构型规整性。结果如下: 1.在聚合过程中,单体转化率增大,产物中全同中心单元的浓度增加。2.将合成的PMMA进行沉淀分级之后,不同的级分具有不同的构型规整度。特性粘数大的级分,全同中心单元含量亦大。3.我们设想在所研究的反应体系中存在三种活性中心,它们之间存在一定的络合平衡和相互转化关系,从而合理地解释了各种实验现象,例如分子量分布很平宽和具有双峰,以及产物的构型规整度在反应过程中的变化等等。4.反应温度降低,产物中全同结构增加,但其影响不如溶剂或单体转化率等因素的影响大。测得全同键接和间同键接的活化热焓差及活化熵差分别为:-0.75±0.05千卡和0.27±0.05熵单位。
In this work, the spatial configurational regularity of anionic polymerization products of n-BuLi as initiator in methyl methacrylate-toluene was studied by NMR. The results are as follows: 1. During the polymerization, the monomer conversion increases, and the concentration of concentric central units in the product increases. 2. After fractionating the synthesized PMMA by precipitation, the different fractions have different configuration regularities. Inherently large viscosity fractions, the same center unit content is also large. 3. We envisage that there are three active centers in the reaction system under study. There is a certain complex equilibrium and mutual transformation between them, so that various experimental phenomena can be rationally explained. For example, the distribution of molecular weight is very broad and has double Peak, and product configuration regularity changes in the reaction process and so on. 4. The reaction temperature decreases, the product of the same structure increases, but its impact is not as good as solvent or monomer conversion and other factors. The measured enthalpy difference and activation entropy difference of all-bond and inter-bond were -0.75 ± 0.05 kcal and 0.27 ± 0.05 entropy units, respectively.