三氟乙酸溶液中尼龙6链凝聚缠结的NMR弛豫研究

Nuclear Magnetic Resonance Relaxation of Cohesional Entanglement of Nylon 6 Chains in Trifluoroacetic Acid Solution

采用 1 D和 2 D NMR技术 ,归属了三氟乙酸 ( TFA)溶液中尼龙 6链上的主要 1 H NMR共振信号 .不同温度下测定的自旋 -自旋弛豫时间 ( t2 )提供了大分子主链间凝聚缠结及 TFA溶液中尼龙 6链随温度变化的动力学信息 .结果表明 ,尼龙 6主链上亚甲基基团有不同程度的凝聚缠结 ,距离 CO和 NH基团越远 ,凝聚缠结越明显 .与 CO和 NH基团相连的亚甲基基团的缠结不很明显 ,主要是因为尼龙 6链间氢键的存在 .升高温度 ,热运动加快 ,这些凝聚缠结逐渐减弱 .NH质子的 t2 H值几乎不随温度变化 ,TFA质子的 t2 H值随温度升高而快速下降 ,表明尼龙 6链间氢键随温度升高而破坏 ,TFA质子又与因温度升高而从尼龙 6中释放出来的自由 NH和

An unambiguous assignment of the main 1H NMR resonance of nylon 6 in trifluoroacetic acid (TFA) solution was carried out by using a combination of 1D and 2D NMR heteronuclear technique (HMQC). The spin-spin relaxation time measurements at different temperatures provide the information about cohesional entanglements of main chains among the macromolecules and the dynamics of nylon 6 polymer at different temperatures in TFA solution. The results show that the methylene groups of the nylon 6 main chains are cohesionally entangled in different degrees at the ambient temperature. The farther the methylene group from the CO and NH groups,the more intensely entangled they are. The entanglements of the methylene groups adjacent to the CO and NH groups,are less pronounced owning to the formation of interchain hydrogen bonds. These entanglements are gradually weakened by the thermal motion upon increasing temperature. The absence of the variation in t 2H of the NH proton with the charge of temperature and the decrease in t 2H of the TFA protons with the increase in temperature give an evidence about the dissociation of the interchain hydrogen bonds among the nylon 6 molecules and the formation of hydrogen bonds between TFA protons with the NH and CO groups of nylon 6 set free by increasing temperature.