EFFECT OF THE HETEROGENEOUS DISTRIBUTION OF LAMELLAR STACKS ON AMORPHOUS RELAXATIONS IN SEMICRYSTALLINE POLYMERS

Polymers crystallized at high temperatures, such as poly(aryl ether et her ketone) (PEEK), poly(ethylene terephthalate) and a thermoplastic p olyimide, exhibit well developed lamellar stacks. We have obtained sma ll angle X-ray scattering (SAXS) and wide angle X-ray diffraction data at 290 degrees C and 25 degrees C for PEEK and have also utilized lit erature SAXS data taken at 25 degrees C for the other materials. To mo del these systems we assume that the interlamellar 'amorphous' or non- crystalline species do not contribute to the glass transition and use the SAXS parameters to calculate a total rigid fraction. Using this as sumption it is shown that we can qualitatively describe the strength o f glass transitions measured directly by thermal analysis. No other ri gid 'amorphous' fractions (RAFs) are needed to model the data under th ese crystallization conditions. The results suggest that conventionall y measured glass transitions originate from the broad amorphous gaps b etween lamellar stacks in these space-filling spherulitic systems. In situations of very high crystallinities or systems with other crystal morphologies such as defective or high surface area lamellar stack mor phologies, the model does not work and the conventional analysis assum ing an RAF associated with crystal surfaces is more appropriate.