M. Cortázar

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.

Ester exchange reactions in polyarylate/poly(ethylene terephthalate) blends

Abstract Blends coagulated by a solution/precipitation procedure of a polyarylate (PAr) based on bisphenol A and tere/isophthalates with poly(ethylene terephthalate) (PET) have been studied by a variety of experimental methods. Differential scanning calorimetry experiments have shown that in blends containing more than 30% PET, conditioning of the blends at high temperatures required for calorimetric measurements resulted in progressive ester exchange reactions. The 10% and 20% PET mixtures, in which this extreme conditioning was not required, showed a single glass transition, contrary to the behaviour of the other PET compositions. These differences may be attributed to the shape of the spinodal curve, which has been simulated according to the McMaster model for polymer mixtures. The progression of the interchange reactions has been followed by solvent extraction of the resulting products and subsequent Fourier transform infra-red spectroscopy analysis. A parallel decrease in the PET heat and temperature of fusion in the insoluble fractions was observed. In our opinion this was due to the incorporation of PAr units in the PET chains, which caused a decrease in their crystallizable segment length.

Isothermal crystallisation of iPP/Vectra blends by DSC and simultaneous SAXS and WAXS measurements employing synchrotron radiation

Abstract The isothermal crystallisation behaviour and morphology of blends of isotactic polypropylene, iPP, and a liquid crystal polymer, Vectra A950, has been studied using differential scanning calorimetry, optical microscopy and simultaneous WAXS and SAXS in real-time measurements using synchrotron radiation. It has been observed that Vectra domains act as sites for the nucleation of iPP, and the rate of crystallisation is enhanced with increasing Vectra content in the blend. The presence of the α crystalline form in pure iPP, and both α and β forms for iPP in iPP/Vectra blends has been found. The SAXS patterns for iPP/Vectra blends containing β iPP are characterized by two different long period values that were related to the α and β lamellae. The secondary crystallisation mechanism has been investigated by SAXS/WAXS experiments. It is shown that, in contrast to primary crystallisation, secondary crystallisation of iPP is not affected by the presence of the thermotropic liquid crystalline polymer. As already known from pure iPP, the main process of secondary crystallisation is the growth of new lamellar stacks within remaining amorphous regions in the iPP spherulites.

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.

Miscibility and Crystallization of an Amine-Cured Epoxy Resin Modified with Crystalline Poly(ε-caprolactone)

Blends of diglicidyl ether of bisphenol-A, DGEBA, and poly(e-caprolactone), PCL, were cured with 4,4′-diaminodiphenyl sulfone, DDS, and analyzed by differential scanning calorimetry, DSC, in order to study the effect of curing on the miscibility and crystallization behavior of the crystallizable component. The spherulitic morphology of PCL was investigated by thermal microscopy. The results indicate a change in the miscibility state resulting from curing. Likewise, at all the temperatures studied a marked difference in crystallization behavior and morphology between the uncured and the cured systems was observed. These differences are attributed to the multiphase nature of the cured blends versus the homogeneous character of the uncured ones.

A study of the degradation of uncured DGEBA/PVP blends by thermogravimetry and their miscibility state*

Poly(N-vinyl pyrrolidone) was blended with an epoxy resin to give a miscible blend. The thermal stability of DGEBA/PVP blends was studied by dynamic thermogravimetry. The kinetic parameters of the degradation were calculated. The results indicated that the presence of one component influences the stability of the other. In general, PVP has a stabilizing effect on DGEBA, but PVP is destabilized by DGEBA. The chemical interactions between PVP and DGEBA on the one hand, and the viscosity of the medium, on the other hand, seem to be the factors governing the degradation behavior of the blend.

Compositional variation of glass-transition temperature in miscible polymer blends involving weak and strong specific interactions

The miscibilities of some styrene derivatives (polystyrene (PS), poly(p-methylstyrene) (PPMS) and poly(p-vinyl phenol) (PVPh)) with poly(cyclohexyl methacrylate) (PCHMA) have been compared by studying their compositional variation of glass-transition temperatures (T g ). The mixtures of PS and PPMS with PCHMA were found to be miscible over the full composition range whereas PVPh)PCHMA blends showed two phas behaviours.. Only when S was copolymerized with VPh at high styrene content (P(S 75 -co-VPh 25 )) was miscibility observed with PCHMA. All the blends studies exhibited a non-additive composition dependence, showing both negative (PS/PCHMA and PPMS/PCHMA blends) and positive (PVPh/PMMA and (P(S 75 -co-VPh 25 )/PCHMA blends) deviations from additivity. Positive deviations indicate the presence of significant specific interactions between the two polymers. The lattice-fluid theory was combined with the Gibbs-DiMarzio approach to study the compositional variation of T g and an extension of this last theory to hydrogen bonding was applied to mixtures with strong specific intermolecular interactions. The flex energy values and their compositional variation, as well as the hydrogen bonding contribution have been used to study the T g s.

Glass transition temperatures of plasticized polyarylate

SummaryGlass transition temperatures of different Polyarylate/plasticizer systems with plasticizer concentrations limited to 30 wt.% have been determined by Differential Scanning Calorimetry. Experimental results have been compared to the predictions of three different expressions: the logarithmic rule of mixtures, the Fox equation and the Couchman-Karasz equation. The degree of homogeneity of the different systems has been related to the width of the simple Tg. The data for the different PAr/plasticizer mixtures seem to fit the Fox equation more closely than the other equations tested.