Temperature modulated DSC studies of melting and recrystallization in polyethylene-2,6-naphthalene dicarboxylate) (PEN) and blends with poly(ethylene terephthalate) (PET)

The thermal properties of amorphous and melt crystallized poly(ethylene-2,6-naphthalene dicarboxylate) (PEN) and its blends with poly(ethylene terephthalate) (PET) were investigated. Temperature modulated DSC (TMDSC) was used over a broad range of annealing times and temperatures. PEN under all moderate temperature crystallization conditions was found to exhibit secondary crystal melting in the low endotherm region, followed by melting of primary crystals superimposed with a large endotherm due to melting of DSC scan-induced recrystallized species. The exothermic signal due to recrystallization was separated into the TMDSC non-reversing signal. Annealing time had a small effect on thermal properties at moderate annealing temperatures, and varying the annealing temperature had a larger effect on the recrystallization properties above the annealing temperature. The results show that TMDSC provides excellent resolution of recrystallization and related events compared to standard DSC. Blends of PEN and PET were evaluated as a function of melt blending time, and the phase properties were studied at 260 and 285 degreesC and related to transesterification reactions. The evolution from a phase separated mixture to a single phase but still crystallizable copolymer, to finally a non-crystallizable copolymer with a higher degree of randomness was studied. The crystallization properties measured using TMDSC were contrasted with those of PEN. (C) 2001 Elsevier Science Ltd. All rights reserved.