| Abstract: | Melting-point and spherulite growth rate measurements for a sample of syndiotactic polypropylene (S = 0.716 and η = 0.356) were analyzed for the parameters characterizing crystal formation and growth: Tm = 159 ± 2°C, σe = 47 erg cm ?2, σ = 4.4 erg cm?2, and q = 5.6 kcal per mole of folds. The q and σe values place syndiotactic polypropylene in the group of “unhindered” polymers. Failure of the isotactic-polypropylene spherulite growth rate data to follow current theories of crystal growth precluded a comparison of crystal parameters of the two stereoisomers. At comparable degrees of supercooling, the absolute growth rates for the two forms are of the same order of magnitude and exhibit one or more crossover(s) in relative position. |
