Solid-state NMR studies for DC 745: April--May 2000

Stephens, T. ; Labouriau, A.

Los Alamos National Laboratory

关键词: Magnetization;    Protons;    Decay;    Polymers;    36 Materials Science;   

DOI  :  10.2172/768914
RP-ID  :  LA-UR-00-3592
RP-ID  :  W-7405-ENG-36
RP-ID  :  768914

美国|英语

来源: UNT Digital Library

【 摘 要 】

Powles et al. reported in 1961 that pdydimethyl siloxane melts exhibit a transverse decay of nuclear spin magnetization (T{sub 2}) that is nonexponential. This observation was interpreted in terms of the proton NMR signal from the melt having characteristics of a broad line. Since then, similar findings were obtained for other polymer melts too. Accordingly to Powles et al. this peculiar proton line shape was the result of an intramolecular direct dipole-dipole interaction between a pair of protons. They also suggested that this dipolar interaction was weak because the dipolar interaction was motionally averaged since the orientation-dependent local dipolar field is modulated by molecular dynamics. In sum, the consequences and the origins of nuclear spin correlations in viscous polymer melts were recognized almost 4 decades ago. In the 1970s, Cohen-Addad suggested that these weak proton dipolar interactions could be used to characterize polymer melts and networks. In this work, we have used some of these ideas to probe the effects of thermal treatments on the proton spin-spin relaxation times for DC745.