SCATTERING FUNCTION OF SYNDIOTACTIC POLY(METHYL METHACRYLATE) IN DILUTE-SOLUTION

The scattering function was measured for a syndiotactic poly(methyl methacrylate)(s-PMMA) sample with the fraction of racemic diads f, = 0.92 and weight-average molecular weight M(W) = 3.76 X 10(4) in acetonitrile at 44.0-degrees-C (0) for the magnitude k of the scattering vector smaller than 1 ansgtrom-1 by the use of the same point-focusing small-angle X-ray scattering (SAXS) camera as used in a previous SAXS study of atactic (a-)PMMA samples with f(r) = 0.79. Supplementary measurements were also carried out on the same s-PMMA sample in benzene at 25.0-degrees-C. As in the case of a-PMMA, the Kratky plots of the present data for s-PMMA in the two solvents do not exhibit the second maximum and minimum, or oscillation, as observed by Kirste and Wunderlich in the range of k greater than or equal to 0.4 angstrom-1, being consistent with the theoretical prediction on the basis of the helical wormlike chain. A rather detailed comparison of the present data for s-PMMA in acetonitrile with the previous corresponding ones for a-PMMA shows that the relative value of the first maximum of the Kratky plot compared to the first minimum is larger for the former than for the latter. This may be regarded as arising from the fact that the helical nature of PMMA chains becomes more remarkable with increasing f(r).