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

The mean-square radius of gyration of poly(methyl methacrylate) (PMMA) with Bernoullian 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 fo r atactic PMMA chains (P-m = 0.5). Conformational energies E-alpha similar to 1.3 kcal mol(-1) and E-beta similar to -0.6 kcal mol(-1) of the two-stat e scheme are acceptable, from which the derived mean-square end-to-end dist ance and mean-square radius of gyration conform to the experimental data. T he ratio [S-2]/x of atactic PMMA (P-m = 0.2) as a function of the degree of polymerization x first increases with increasing chain length, then passes through a maximum at x = 30, and finally decreases to its asymptotic value , which is in reasonable agreement with the experimental measurements repor ted elsewhere, The ratio [S-2]/x as a function of stereochemical compositio n indicates that theoretical and experimental data are in accord for isotac tic and atactic PMMA, but small-angle neutron scattering (SANS) measurement s are higher than the calculated values for syndiotactic PMMA.