Pulsed NMR Study of Network Formation in the Course of Bulk Polymerization of Methyl Acrylate
Pulsed NMR Study of Network Formation in the Course of Bulk Polymerization of Methyl Acrylate
复制标题
丙烯酸甲酯本体聚合过程中网络形成的脉冲核磁共振研究
DOI：
10.2116/analsci.21.315
复制
发表时间：
2005
影响因子：
1.6
通讯作者：
Takuzo Kurotsu
中科院分区：
文献类型：
--
作者：
H. Kimoto;A. Fukuda;A. Asano;Takuzo Kurotsu
测定了不同温度下丙烯酸甲酯本体聚合过程中质子自旋-自旋弛豫时间（t_2）随聚合时间的变化。随着聚合的进行，得到了三种类型的t_2 （t_2l（长）、t_2s（短）和t_2m（中间））。在一定的反应时间内，t_2s （F _S）的分数显著增加，而t_2l （F _L）的分数则呈下降趋势。前者对应于分子量足够高的聚合物的量，其分子量足以引起产生瞬态网络结构的紧密缠结；后者反映了单体混合物的减少和聚合物的低分子量。t_2m被认为产生于纠缠的一个相对可移动的区域。发现t_2s + t_2m分数与聚合物收率之间呈线性关系，这使得我们可以在聚合过程中实时监测聚合物收率。测量了^13C DD（偶极解耦）/MAS（魔角旋转）核磁共振谱，以监测聚合过程中主链和侧链在形成网络结构中的分子运动。^13C DD/MAS核磁共振谱表明，当观察到“Trommosdorff效应”（凝胶效应）时，侧链运动和主链运动都受到限制，部分单体被困在网络结构中。
The proton spin-spin relaxation time ( T _2) during the bulk polymerization of methyl acrylate was measured as a function of the reaction time at various temperatures. Three kinds of T _2 ( T _2L (long), T _2S (short) and T _2M (intermediate)) were obtained as the polymerization proceeded. The fraction of T _2S ( F _S) increased sigmoidally at a certain reaction time, while that of T _2L ( F _L) decreased reciprocally. The former corresponded to the amount of a polymer whose molecular weight was sufficiently high enough to cause a tight entanglement that produced a transient network structure; the latter reflected a decrease in the mixture of the monomer and the low molecular weight of the polymer. T _2M is considered to arise from a relatively mobile region of the entanglement. The relationship between the fractions of T _2S + T _2M and the polymer yield was found to be linear, which led us to monitor the polymer yield in real time during the polymerization in a non-distractive manner. ^13C DD (dipolar decoupling)/MAS (magic angle spinning) NMR spectra were also measured to monitor the polymerization process in terms of the molecular motions between the main chain and the side chain in the formation of a network structure. The ^13C DD/MAS NMR spectra show that the side chain motion became restricted as well as the main chain when the “Trommosdorff effect” (gel effect) was observed, and a part of the monomers were trapped in the network structure.