DIPOLE-MOMENTS OF ISOTACTIC AND SYNDIOTACTIC POLY(METHYL METHACRYLATE) AND THEIR TEMPERATURE-DEPENDENCE

Dipole moments of isotactic (iso) and syndiotactic (syn) poly(methyl m ethacrylate) (PMMA) samples were determined from measurements of diele ctric constants and densities in dilute benzene solution over the temp erature range from 25 to 55-degrees-C. The dipole moments and their te mperature coefficients showed marked tacticity dependence. It was foun d that the iso-PMMA gives greater values of the dipole moment than tho se for the syn-PMMA; e.g., 1.457 D (= mu, dipole moment per constituti onal repeating unit) was obtained for the iso-PMMA, and 1.323 D for th e syn-PMMA at 25-degrees-C. With increasing temperature, the dipole mo ment of the iso-PMMA showed little change and remained nearly constant , while that of the syn-PMMA increased continuously, giving 1.399 D at 55-degrees-C. Experimental dipole moment ratios, D(r) = [m2]/nnu0(2) = [mu2]/mu0(2), (m, dipole moment of polymer; mu0, dipole moment of th e constitutional unit; n, the number of units;) were compared with the calculated ones, which leads to the conclusion that rotational condit ions regarding the orientation of polar side groups in the PMMA chains are highly restricted.