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 PEBN 70/30. Crystallisation and melting of PEBN 50/50 and PEBN 70/30 copolymers are of special interest. Despite its composition, the PEBN 50/50 copolyester exhibited significant crystallinity and fast crystallisation rates. Cooling from the melt resulted in crystallisation at Tc=106°C, quite close to the glass transition temperature (Tg=92°C). On isothermal crystallisation at temperatures near Tc 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 (Tcc=125°C), followed by a second exothermal peak, was observed. The relatively low melting point (Tm=196°C), comparing with those of the other PEBN copolymers was attributed to limited crystal lamellar thickness. For the PEBN 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.