Diffusional Behavior of Poly(diethylsiloxane) in the Liquid Crystalline and Isotropic Phases As Studied by High Field-Gradient NMR

摘要

The diffusion process of poly(diethylsiloxane) (PDES) has been studied by field-gradient NMR at temperatures from 20 to 80 deg C,which is recognized to take the biphasic phase consisting of the liquid crystalline and the isotropic regions at temperatures from 20 to 40 deg C and the isotropic phase at temperatures from 50 to 80 deg C by solid-state ~(29)Si NMR.The diffusion coefficients (D) of PDES in the liquid crystalline region of the biphasic phase have been measured at 20 and 30 deg C by pulse field-gradient stimulated-echo (PGSE) ~(13)C NMR with ~1H CW decoupling as designed by us,and also those in the isotropic region of the biphasic phase and in the isotropic phase have been determined by conventional PGSE ~1H NMR.From these experimental results,it is found that the diffusion coefficient of PDES in the liquid crystalline region is much larger than that for the PDES in the isotropic region.This shows that the smaller diffusion coefficient of PDES chains in the isotropic region (approx = 10~(-10)-10~(-11) cm~2/s) compared with that in the liquid crystalline region (approx 10~(-8) cm~2/s) comes from the entanglements effect between the polymer chains.