Configurational-conformational statistics of stereoirregular poly(methyl methacrylate)s

The mean-square radius of gyration of poly(methyl methacrylate) (PMMA) with Bemoullian statistics was theoretically investigated utilizing the method of periodic condition. The dependent curve of the characteristic ratio of mean-square end-to-end distance on periodic microstructure length increases monotonously with the length and goes gradually to its asymptotic value for atactic PMMA chains (P _m = 0.5). Conformational energies E _α ～1.3 kcal mol^?1 and E _β ～-0.6 kcal mol^?1 of the two-state scheme are acceptable, from which the derived meansquare end-to-end distance and mean-square radius of gyration conform to the experimental data. The ratio ?S²?/χ of atactic PMMA (P _m = 0.2) as a function of the degree of polymerization χ first increases with increasing chain length, then passes through a maximum at χ = 30, and finally decreases to its asymptotic value, which is in reasonable agreement with the experimental measurements reported elsewhere. The ratio ?S²?/χ as a function of stereochemical composition indicates that theoretical and experimental data are in accord for isotactic and atactic PMMA, but small-angle neutron scattering (SANS) measurements are higher than the calculated values for syndiotactic PMMA.