Temperature modulated DSC studies of melting and recrystallization in poly(oxy-1,4-phenyleneoxy-1,4-phenylenecarbonyl-1,4-phenylene) (PEEK)

The thermal and crystal morphological properties of amorphous and melt crys tallized poly(oxy-1,4-phenyleneoxy-1,4-phenylenecarbonyl-1,4-phenylene) (PE EK) were investigated. Two different molecular weights were studied by Temp erature Modulated DSC (TMDSC) over a broad range of annealing times and tem peratures. The lower molecular weight PEEK under all crystallization condit ions was found to exhibit secondary crystal melting in the low endotherm re gion, followed by melting of primary crystals superimposed with a large rec rystallization contribution. Primary crystal melting broadly overlapped wit h melting of the recrystallized species and contributed to the broad highes t endotherm. Recrystallization contributions and the interpretation of TMDS C were partially confirmed by independent rapid heating rate melting point determinations and variable heating rate DSC. The higher molecular weight P EEK showed many similarities but generally had smaller levels of reorganiza tion above the annealing temperature under most higher temperature crystall ization conditions. TMDSC provides excellent resolution of recrystallizatio n and related events compared to standard DSC. The broad and substantial ex othermic recrystallization in amorphous samples was also examined, showing that recrystallization continues through the final melting region.