Light-scattering study of the molecular weight distribution of polypropylene

A light-scattering study is presented of two isotactic polypropylene samples with broad molecular weight distributions (M _w/M _n = 8.1 and 8.7, respectively) dissolved in α-chloronaphthalene at 147°C. Incident radiation of 5460, 4358, and 3650 A. was used. The reciprocal intramolecular scattering function, P^?1(u) is expressed as a function of the variable sin(θ/2)/λ′]². This provides a wider range of experimental values of the variable u = 16π²(b²/6) sin(θ/2)/λ′]² than is accessible by the usual technique of using only one wavelength. The shape of the function P^?1(u) is closer to that predicted theoretically if the weight distribution function f(N) in the equation is given by the log-normal distribution rather than the distribution function of Schulz and Zimm. The method is applicable to polymer samples for which the average molecular weights are too low to be measured by the light-scattering method of Benoit and Loucheux.