The segmental motions of stereoregular poly(methyl methacrylates), PMMAs, in a homologous series of n-alkyl acetate solvents as well as the molecular motion of solvents themselves were investigated by the $^{13}$C spin-lattice relaxation time($T_1$) measurements at 40℃. Not only the segmental motion of polymer but also the molecular motion of solvents are mobile in isotactic PMMA solutions than in syndiotactic PMMA solutions. As the molecular size of solvents increases, the mobilities of all the carbon groups in isotactic polymer solutions decrease. However, in syndiotactic PMMA solutions, the mobilities of quaternary, carbonyl, and methoxy carbons increase with the increase of molecular size of solvents while the mobilities of the methylene and α-methyl carbons decrease. These results are considered to be due to the much stronger polymer-solvent interactions in syndiotactic PMMA solutions than in isotactic PMMA solutions.
By relating the solvent dependences of the $T_1$ 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 $T_1$ values of those carbon groups in which the polymer-solvent interaction is not significant, e.g., methylene and α-methyl carbon groups, were consistent with the solvnet dependence of the dissolution rate of polymer. This result suggested that the dissolution dynamics of polymer is significantly affected by the free volume and segmental motion of polymer. Thus the $^{13}$C NMR spin-lattice relaxation experiments will be expected to be useful for a preliminary estimation of the dissolution rate of polymer.
