Abstract
AbstractThe growth rate of high melt form spherulites in trans‐1,4‐polyisoprene was found to be Inversely proportional to the molecular weight up to Mn = 150,000. At higher molecular weights the dependence virtually ceases. The growth is given by: Where ED is the free energy required to transport a crystallizing segment across the liquid‐crystal interface and ΔF2* is the free energy required to form a stable crystal nucleus. The relationship between molecular weight and spherulitic growth rate was not accounted for by the dependence of Tg on molecular weight, expressing ED by the WLF equation, nor by the dependence of ΔF2* on the molecular weight. The product of the end and lateral interfacial free energies of the crystallites is constant to M̄n = 40,000, above which it Increases with molecular weight. This has been attributed to a change in the crystallization mechanism near M̄n = 40,000, perhaps from a mechanism where most molecules crystallize within a single cyrstallite to one where each molecule is involved in several crystallites and the amorphous regions between them.
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