Crystallization kinetics and morphological features of star-branched nylon-6: effect of branch-point functionality

Bulk crystallization rates, nucleation density, general morphological features, equilibrium melting point and absolute crystalline percentage of linear and star-branched nylon-6 have been studied as a function of branch-point functionality and temperature. Overall bulk crystallization rates were described in terms of the Avrami equation and crystallization half-times. No significant differences in bulk crystallization rates as a function of crystallization temperature or absolute crystalline percentage were observed between linear, three-arm and six-arm samples with identical thermal history. Equilibrium melting points obtained by Hoffman Weeks analysis were reduced in star-branched nylon-6 compared to the linear polymer of comparable molecular weight. In order to deconvolute the effects of a decreased thermodynamic driving force for formation of crystals of branched polymers, crystallization half-times were measured as a function of supercooling. The crystallization half-times of star-branched nylon-6 as a function of supercooling were reduced compared to those of linear nylon-6 of comparable molecular weight. The general spherulitic superstructure appeared unaffected by increasing branch-point functionality up to six. However, irregularities in lamellar structure were implied by SAXS experiments on samples with branch-point functionality as low as three.