CRYSTALLIZATION OF POLY(ARYL ETHER KETONES) .1. CRYSTALLIZATION KINETICS

Isothermal and nonisothermal crystallization kinetics of different poly(aryl ether ketones) (PAEK) were investigated by means of differential scanning calorimetry (DSC). For comparison, a poly(phenylene sulfide) was also included. Systematic relationships between the chemical structure of these materials and their crystallization behavior could be derived. The equilibrium melting temperatures of the different PAEKs were estimated using the extrapolation scheme given by Hoffman and Weeks. Due to the higher flexibility with increasing ether/ketone ratio, the glass transition, crystallization, and melting temperatures decreased, and the melt crystallization was accelerated. The cold crystallization, however, was retarded with more flexible chains relative to that with stiffer chains due to the increased order of stiffer molecules in the quenched amorphous state, which results in a higher nucleation density. Independent of the chemical structure, Avrami exponents of 2.0 less-than-or-equal-to n less-than-or-equal-to 2.8 were found for cold- and melt-crystallized samples. This can be explained by either two-dimensional or three-dimensional diffusion-controlled crystal growth, depending on the amount of thermal or athermal nucleation, respectively. The ranking of the crystallization rates for both cold and melt crystallization could be estimated using simple nonisothermal routine methods based on the temperatures of glass transition, crystallization, and melting.