Abstract
The frequency dependences of 13C spin-lattice relaxation times (T1) and nuclear Overhauser enhancements (NOE) of poly(methyl methacrylate) (PMMA) in CDCl3 solution have been analyzed in terms of different models describing the motions of the C-H internuclear vector. Box-type and log−χ2 distribution models of correlation times as well as the 2τ model assuming two independent motions are inadequate to explain simultaneously the frequency dependences of T1 and NOE values for backbone CH2, α-CH3, and OCH3 carbons. In contrast, those frequency dependences can be well interpreted by the 3τ model in which three superimposed motions with correlation times of the orders of 10−12, 10−10, and 10−9 s are assumed. This indicates that the backbone motion of PMMA should be described in terms of at least three types of superimposed motion and thus one or two additional motions may be overlapped for the side-group carbons.
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