Observations during crystallisation of poly(ethylene-co-butylene naphthalene-2,6-dicarboxylate)s

The crystallisation behaviour of poly(ethylene-co-butylene naphthalene-2,6-dicarboxylate)s (PEBN copolyesters) was studied by means of differential scanning calorimetry (DSC). A eutectic behaviour was found, and the composition related with the lower melting point was about 50/50 mol%. On the other hand, the crystallisation kinetics was faster for copolymers with high butylene-naphthalate content, while the slower crystallisation rates were observed for the PEEN 70/30. Crystallisation and melting of PEEN 50/50 and PEEN 70/30 copolymers are of special interest. Despite its composition, the PEEN 50/50 copolyester exhibited significant crystallinity and fast crystallisation rates. Cooling from the melt resulted in crystallisation at T-c = 106 degreesC, quite close to the glass transition temperature (T-g = 92 degreesC). On isothermal crystallisation at temperatures near T-c region, double exothermic peaks in the heat flow vs, time plot were observed. For amorphous samples, in the DSC traces on heating, a sharp cold-crystallisation peak (T-cc 125 degreesC), followed by a second exothermal peak, was observed. The relatively low melting point (T-m = 196 degreesC), comparing with those of the other PEEN copolymers was attributed to limited crystal lamellar thickness. For the PEEN 70/30, crystallisation was very slow. Even after prolonged crystallisation times, a quadruplicate melting peak was observed which was attributed to melting of metastable crystalline phases initially formed. (C) 2001 Published by Elsevier Science Ltd.