Crystallization of poly(aryl-ether-ether-ketone)s blends

Abstract

The crystallization and melting behaviour of poly(aryl-ether-ether-ketone) (PEEK) in blends with another polymer of the same family containing a bulky pendant phenolphthalein group (PEK-C) have been investigated by thermal methods. The small interaction energy density of the polymer pair ( B = −8.99 J/cm 3), evaluated from equilibrium melting point depression, is consistent with the T g data that indicate partial miscibility in the melt. Two conjugated phases are in equilibrium at 430°C: one is crystallizable and contains about 35 wt% of PEK-C; the other, containing only 15 wt% of PEEK, does not form crystals upon cooling and it interferes with the development of spherulites in the sample. The analysis of kinetic data according to nucleation theories shows that crystallization of PEEK in the explored temperature range takes place in Regime III and that a transition to Regime II might be a consequence of an increase in the amount of non-crystallizable molecules in the PEEK-rich phase. A composition independent value of the end surface free energy of PEEK lamellae has been derived from kinetic data ( ρ e = 40 ± 4 erg cm 2 ) in excellent agreement with previous thermodynamic estimates. A new value for the equilibrium melting temperature of PEEK ( T° m = 639 K) has been obtained; it is about 30°C lower than the commonly accepted value and it explains better the “memory effect” in the crystallization from the melt of this high performance polymer.