¹³C NMR relaxation of poly(t-butyl crotonate) in solution. Effects of β-substitution on local chain motions

Measurement of ¹³C spin-lattice relaxation times, T₁, and nuclear Overhauser effects, NOE, was made as a function of temperature at two magnetic fields for poly(t-butyl crotonate), PTBC, and poly(t-butyl methacrylate), PTBM, in toluene-d₈ to study the effects of β-substitution on local chain motions. For main chain carbons of PTBC and PTBM, experimental T₁ and NOE data were well reproduced by the Dejean-Laupretre-Monnerie (DLM) model in the entire temperature range. The model parameters thus obtained differed between PTBC and PTBM. For methyl carbons in the t-butyl ester group, the experimental data were analyzed by the models combining the DLM model and multiple internal rotations. The model parameters were almost the same for the two polymers. These results indicate that β-substitution affects the local motion of main chains as well as chain stiffness, but does not significantly affect the local motion of methyl carbons at the ends of side-chains. The correlation between the local dynamics of various polymer chains and chain stiffness is discussed.