Dielectric properties of stereoregular poly(methyl methacrylates)

To obtain more useful information about the effect of the degree of stereoregularity on the motion of the polymer chain, the dielectric and dilatometric measurements were made for a series of stereoregular poly(methyl methacrylates) (PMMA). The α- and β-absorptions were observed in each sample, of which the dielectric behaviors of the α-process are discussed. The temperature dependence of the relaxation time of the α-process was sufficiently represented by the WLF equation and the resulting values of the parameters f_g and B in the modified WLF equation were found smaller for isotactic-rich PMMA than those values for syndiotactic PMMA. It may be deduced from these results that the chain mobility of the isotactic PMMA is larger than that of the syndiotactic. The dielectric increment of the α-process in the isotactic PMMA is much larger than that in the syndiotactic PMMA, increasing rapidly with temperature, and taking its maximum in the temperature range of 55 to 60°C. The dielectric transition was clearly observed in the case of isotactic-rich PMMA.