Crystallization of poly(ethylene oxide) in binary blends containing poly( p-vinyl phenol)

Abstract

Blends of poly(ethylene oxide) (PEO) with an amorphous polymer, poly( p-vinyl phenol) (PVPh), showed a single, composition-dependent, glass transition temperature as a consequence of the miscibility between components. X-ray diffraction and differential scanning calorimetry (d.s.c.) results indicated a strong reduction of blend crystallinity with increasing PVPh content. Observation of melting point depression allowed the determination of the interaction energy density, B, between the two polymers in the melt. To obtain equilibrium melting point data, the Hoffman—Weeks procedure was employed to take into account the influence of crystal morphology. The values of B obtained by d.s.c. and by thermal optical microscopy were −7.1 and −8.8 cal cm −3, respectively. Analysis of the isothermal crystallization by means of the Avrami equation led to average values of the Avrami index of 2.5 for both pure PEO and a PEO/PVPh 90/10 blend, and 3.1 for the remaining compositions analysed. The temperature and composition dependence of the growth rates were analysed using an expression incorporating both the diffusion mechanism and the nucleation tendency. A discontinuity in the temperature coefficient of the growth rate curve was found for PEO/PVPh blends with 90 and 80 wt% PEO. The experimental results indicate that the rate of crystallization, the degree of crystallinity and the equilibrium melting temperature are strongly dependent on the composition of the blends.