溶液中尼龙11的NMR弛豫研究

用 2DNMR(HMQC)技术归属了溶液中尼龙 11分子的主要1H和13 C NMR共振信号 ,并通过变温和变浓度 1H NMR弛豫时间的测定 ,得到了尼龙 11溶液中氢键结构变化的动力学信息 .结果表明 ,溶液中尼龙 11分子的弛豫行为与一般高聚物不同 ,随着温度升高 ,尼龙链间相互作用逐渐减弱 ,尼龙分子与溶剂小分子间相互作用逐渐增强 ,尼龙链间氢键逐渐离解 ,而离解出来的自由NH和CO基团又与溶剂小分子间生成氢键 .尼龙 11链卷曲堆积成无规线团状 ,一部分溶剂被包裹在内部并和α CO质子成为一个整体而一起运动 .变浓度实验弛豫过程呈现双指数特性 ,快弛豫部分随体系浓度增加而增多 ,表明聚合物溶液中凝聚缠结含量的增大 ,这种凝聚缠结是由溶液中氢键引起分子链物理交联成网而形成的 .随着浓度增加 ,溶液逐渐变成局部粘度较大的类似软固体

NUCLEAR MAGNETIC RESONANCE RELAXATION STUDIES OF NYLON 11 SOLUTION

An unambiguous assignment of the main 1H and 13 C NMR resonances of nylo n 11 in trifluoroacetic acid solutions has been carried out by using a combinati on of 1D and 2D NMR heteronuclear techniques(HMQC).The spin spin relaxation ti m e measurements at different temperatures and different concentrations provide in formation about the detailed structure and the relative arrangement of the nylon chains in solution.The r esults show that the temperature dependence of the relaxation behavior of nylon 11 solution is obviously different from that of ordinary polymer solutions.With increasing temperature,the solvation is strengthened,i.e.the interaction between nylon 11 chain segments and solvent molecules is gradually strengthened.This le ads to the dissociation of the hydrogen bonding among the nylon 11 chain segment s ,and the interaction among main chain of nylon 11 is then weakened.As a result the phenomenon of cohesional entan glement of the main chains due to hydrogen bonding among them gradually disappea red.In these cases the solvent molecules come to bind the dissociated free CO an d NH groups of nylon 11 m olecules.The main chains are coiled and aggregated with a shape of random clew with a part of the solvent molecules included,making the motions restricted alo ng with the α methylene protons of the CO groups staying in the interior of thi s random clew structure.The dependence of the relaxation process of nylon 11 so lution on concentrations shows biexponential behavior,which suggests the existe nce of two states of the polymer.The fast relaxation component rapidly increase s with increasing concentration,it corresponds to the increase of the cohesional entanglement of the main chain due to hydrogen bonding among the nylon 11 chain s.This behaviour is related to the increase of the cohesional entangleme nt points in a unit volume.With the increase of the concentration,the nylon 11 solution gradually becomes soft solid like.