EFFECT OF MOLECULAR-WEIGHT ON THE SPHERULITIC GROWTH-RATE OF POLY(ARYL ETHER ETHER KETONE)

This study examines the change in spherulitic growth rate of poly(aryl ether ether ketone) (PEEK) as a function of molecular weight in the range of M(n) = 6900 to 60 200 and for temperatures varying between 250 and 300-degrees-C. Optical microscopy using polarized light was used to follow the growth of the spherulites. Detailed analysis of the temperature dependence of the growth rates indicates that, within this relatively narrow range of molecular weight and temperature, both the pre-exponential factor and the exponential factor involving the free energy for nucleation are affected by molecular weight. Values of K(g) increase with molecular weight from almost-equal-to 0.8 x 10(6) K2 to 1.82 x 10(6) K2. Values of sigma-e, the end surface free energy, increase likewise from 41 to 101 erg cm-2 with increasing molecular weight. The results of the microscopy study and the differential scanning calorimetry study are compared and discussed in terms of the relevance of either a thermodynamic model or a kinetic model with regime behaviour for the kinetics of crystallization of PEEK.