SEGMENTAL MOTION OF STEREOREGULAR POLY(METHYL METHACRYLATES) IN A HOMOLOGOUS SERIES OF N-ALKYL ACETATE SOLVENTS BY NMR RELAXATION MEASUREMENTS

Abstract

The C-13 spin-lattice relaxation times, T1s, of both stereoregular poly(methyl methacrylates) (PMMA) and homologous series of n-alkyl acetate solvents in solution have been measured at 40-degrees-C. It was observed that the motion of polar side-chains was highly affected by the degree of interaction with solvent molecules. The stronger polymer-solvent interactions in predominantly syndiotactic PMMA solutions than in isotactic PMMA solutions were shown from the T1 values for the carbonyl, methoxy, and quaternary carbons in polymer segments and also from the carbonyl T1s of solvent molecules. By relating the solvent dependences of the T1 data in syndiotactic polymer solutions to that of the known dissolution rate data of atactic PMMA, it was found that the solvent dependences of the T1 values of those carbon groups in which the polymer-solvent interaction is not significant, e.g., methylene and alpha-methyl carbon groups, were consistent with the solvent dependence of the dissolution rate of polymer. This result suggested that the dissolution of polymer is mainly governed not by the sorption process related to the polymer-solvent interaction but by the transport process related to the local motions of polymer segments and solvent molecules.