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Proton spin–lattice and spin–spin relaxation times in isotactic polypropylene. I. Effects of crystallinity and atactic fraction
Author(s) -
Tanaka Hiroshi
Publication year - 1982
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1982.070270630
Subject(s) - crystallinity , tacticity , amorphous solid , materials science , relaxation (psychology) , polypropylene , spin–lattice relaxation , polymer chemistry , condensed matter physics , polymer , nuclear magnetic resonance , crystallography , chemistry , polymerization , physics , composite material , psychology , social psychology , paramagnetism
Spin–lattice relaxation time T 1 and spin–spin relaxation time T 2 were measured at 40°C on the isotactic polypropylene films of varying preparations and thermal history. T 1 increases with increasing crystallinity and two T 1 's appear for the samples annealed at elevated temperatures (>120°C). These variations in T 1 are well interpreted in terms of the spin diffusion and decoupling of the mobile protons with immobile ones. A free induction decay following a 90° pulse is the superposition of three different decay curves, one of which is exponential and other two are nonexponential. There is an increase in T 2a with increasing crystallinity, which is indicative of the enhancement of the chain mobility in the amorphous region. There are differences between the crystallinity calculated from density and the fraction of crystalline region, F c , obtained by the NMR method, which can be explained by the existence of the microparacrystals and the stress imposed on the amorphous chains on rapid cooling. On the other hand, there is a gradual lowering in T 1 and a considerable increase in T 2a as an atactic fraction is increased. The increase in atactic fraction also results in a decrease in the amount of the isotactic amorphous chains in the amorphous region.