1,2-聚丁二烯^(13)C-NMR弛豫的溶剂效应

SOLVENT EFFECT ON THE 13C-NMR RELAXATION OF 1,2-POLYBUTADIENE

本文测定了一系列具有不同微观结构的1,2-聚丁二烯样品在四种溶剂的50.3MHz ^(13)C自旋-晶格弛豫时间(T_1)和核Overhauser效应(NOE)值。并用Schaefer logx^2相关时间分布模型对实验数据进行了拟合。研究了1,2-聚丁二烯在溶液中的^(13)C-NMR弛豫的溶剂效应及其与结构的关系。发现聚合物与溶剂的溶解度参数之差△δ越大,聚合物在溶液中协同链段运动趋向越明显,^(13)C自旋-晶格弛豫速率(1/T_1)越大;1,2-链节较少,分子链较柔顺时,^(13)C-NMR弛豫受溶剂影响较显著。NMR弛豫参数对结构变化的反应在良溶剂中比在不良溶剂中敏感。

Carbon-13 spin-lattice relaxation time (T1) and nuclear Overhauser factor (NOE) series of 1,2-polybutadiene samples with different microstructures in four different solvents were measured at 50.3 MHz. The data were fit by using Schaefer's asymmetrical logx2 distribution. The relationship between solvent effect on 13C NMR relaxation and the structure of 1,2-polybudiene was studied. It was found that with the increase of the difference of solubility parameters between polymer and solvent (A S), the extent of cooperative segmental motion of the polymer in solution tends to be easier and spin-lattice relaxation rate (1/T1) becomes greater. When 1, 2-unit content decreases and main chain becomes more flexible, the effect of solvent on 13C-NMR relaxation becomes more considerable. NMR relaxation parameters are more sensitive to the variation of structure in good than in poor solvents.