E. Calahorra

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.

Spherulitic crystallization in blends of poly(ethylene oxide) and poly(methyl methacrylate)

Abstract The crystallization kinetics of binary blends of poly(ethylene oxide) and poly(methyl methacrylate) were investigated. The isothermal spherulitic growth rates were measured by means of a polarized light microscope. The temperature and composition dependence on the growth rates have been analysed. The temperature range studied was from 44° to 58°C. The introduction of poly(methyl methacrylate) into poly(ethylene oxide) resulted in a reduction of the spherulitic growth rate as the proportion of poly(methyl methacrylate) was increased from zero to 40% by weight. Results have been analysed using the theoretical equations of Boon and Azcue for the growth rate of polymer-diluent mixtures. The experimental results are in good agreement with this equation. The temperature coefficient is negative as is the case in the crystallization of bulk homopolymers.

Glass transition behaviour and interactions in poly(p-vinyl phenol)polymethacrylate blends

The glass transition temperatures (Tgs) of binary blends of poly(p-vinyl phenol) with poly(methyl methacrylate), poly(ethyl methacrylate) and poly(ethyl methacrylate-co-methyl methacrylate) have been determined. The experimental Tg-composition data do not obey the Couchman-Karasz equation. However, the Gordon-Taylor, the Kwei and the Schneider equations fit the experimental data quite well. The values of the Gordon-Taylor k parameters, as well as the measurements of the glass transition widths, suggest a similar average intensity of the specific intermolecular interactions in the systems studied here, which is in agreement with the Fourier transform infra-red results. The Kwei and the Schneider equations are able to reflect the additional stabilization due to the dilution of copolymer repulsive interactions in the poly(p-vinyl phenol)poly(ethyl methacrylate-co-methyl methacrylate) blends.

The effect of crosslinking and miscibility on the thermal degradation of an uncured and an amine-cured epoxy resin blended with poly(ε-caprolactone)

The results of an investigation concerning the thermal behaviour of an uncured and an amine-cured diglycidyl ether of bisphenol-A (DGEBA) epoxy resin blended with poly(e-caprolactone) (PCL) are reported. The nature and extent of degradation were analysed by means of integral (TGA) and derivative (DTG) thermogravimetry. The decomposition kinetics of both uncured and cured blends were elucidated by the Coats and Redfern equation. Pure PCL has been seen to be more thermally stable than uncured DGEBA, but more unstable than cured DGEBA. For uncured blends, thermogravimetric curves clearly displayed more than one degradation step, while for the cured blends essentially a single weight loss step was observed. The cured blends showed enhanced thermal stability and char formation when compared to the corresponding uncured ones of identical DGEBA/PCL ratio. Besides, it has also been evidenced that although the uncured blends are miscible and the cured ones are immiscible, both systems exhibited negative deviations of the apparent activation energy from the additivity rule.

Melt behaviour of poly(ethylene oxide)-poly(vinyl acetate) blends

SummaryThe compatibility of blends of poly(vinyl acetate) and poly(ethylene oxide) has been studied by rheological and thermo-optical analysis. Results from experiments point to the conclusion that there is extensive mixing between the segments of the two macromolecules in the blend. The interaction between the two polymers is manifested by a decrease in the melting point and a continuous decrease in viscosity with decreasing POE content in the mixture.