PMMA: A key macromolecular component for dielectric low-κ hybrid inorganic–organic polymer films

Linear dynamic viscoelasticity of miscible polymer blends with hydrogen bonding has been investigated. The polymer blend systems investigated are (1) blends of poly(vinylphenol) (PVPh) and poly(vinyl acetate) (PVAc), (2) blends of PVPh and poly(vinyl methyl ether) (PVME), (3) blends of PVPh and poly(2-vinylpyridine) (P2VP), and (4) blends of PVPh and poly(4-vinylpyridine) (P4VP). Fourier transform infrared (FTIR) spectroscopy was employed to find that both the intraassociation (self-association) of the phenolic −OH groups in PVPh and interassociation (intermolecular interactions) between the constituent components in each blend system have profound influence on the frequency dependence of dynamic moduli in the terminal region of the PVPh-based miscible blend systems. It has been found further that time−temperature superposition (TTS) is applicable to all four PVPh-based miscible blend systems forming hydrogen bonds, including the PVPh/PVME blends having the difference in component glass transition tempera...

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Rheology of Miscible Polymer Blends with Hydrogen Bonding

Thermally stimulated creep and depolarization current measurements have been carried out in a temperature range between −180 and 120 °C, on a pure commercial poly(vinyl chloride). Mechanical and dielectric relaxation times involved in α and β relaxations are obtained by fractional stresses/polarizations procedure. The distribution of the Arrhenius‐like kinetic parameters, deduced from the relaxation times, is interpreted in terms of compensation laws. From the obtained results, a same molecular origin can be assumed for the mechanical and dielectric behavior in both α and β relaxations. Moreover, the compensation law analysis leads to two different relaxations modes, likely associated to two kinds of thermally activated molecular motions, in β relaxation. In the α region, the values of found kinetic parameters point out a high degree of cooperativeness of the involved molecular motions. Depolarization curve in this region shows a high temperature peak, not found in the mechanical one, whose evolution with the poling field allows us to assign it to a nondipolar process associated to the movement of free charge carriers.

Study of the α and β relaxations on a commercial poly(vinyl chloride) by thermally stimulated creep and depolarization current techniques

Inhomogeneous media present an interesting class of materials for dielectric research. Differences in conductivity of the phases of an inhomogeneous medium give rise to interfacial polarization, the build-up of space charges near the interfaces between the various phases. Such a polarization usually occurs at frequencies lower than the time scales typical of dipolar polarizations. Moreover, the contribution of interfacial polarization to the dielectric properties of a material is often much larger than the dipolar contributions.

Dielectric Properties of Inhomogeneous Media

A series of polycarbonate-poly(butylene terephthalate) (PC-PBT) blends has been formed via reactive melt-blending in a torque rheometer. The degree of transesterification between the two homopolymers was controlled by the incorporation of an alkyl titanium catalyst. Resultant materials were characterised using DSC, DMA, FTIR and SEM. As the degree of transesterification increased composition of the blends became increasingly complex, comprising mixtures of the homopolymers and various AB-type block copolymers of PC-PBT, with concomitant changes in their thermal behaviour. A corresponding transformation in materials morphology was observed: the relatively coarse structure characteristic of essentially two-phase blends, developed into a more refined structure exhibited by blends containing significant volumes of interphase material. This morphological change was due to the formation of increasing concentrations of random block copolyesters.

The effects of transesterification on structure development in PC-PBT blends

Measurements of the dielectric constant and loss factor of polyvinyl chloride (PVC) have been made over a wide range of temperature and frequency. Maxima in dielectric loss were observed at a temperature corresponding to the α or glass transition temperature and secondary β transition temperature. The sensitivity of these maxima to both frequency and thermal pretreatment was investigated. It was found that the position of the β peak on the temperature axis changed markedly with frequency, while the glass transition or α peak showed only small variations. Neither the α nor the β peak were very sensitive to thermal pretreatment, but interesting changes in the minimum between these peaks were observed. In quenched samples a distinct shoulder peak at Tβ < Ts < Tα was observed; it was possible to eliminate it by a slow cooling of the samples. The effect of plasticizer content was also studied.

Dielectric studies of poly(vinyl chloride)

The behavior of PVC changes drastically with the temperature and the method of sample preparation. In the steady-state shear mode, upon a decrease of the rate of deformation, the data may show either a steady increase of the shear viscosity or a leveling off to a Newtonian plateau. In the dynamic test mode, both the storage modulus, G′, and the loss modulus, G″, show an effect of the yield stress. Only at temperatures above 210°C are flow curves normal for polymer melts obtained. Rigid and nonrigid PVC formulations have been tested in Weissenberg Rheogoniometer, using steady-state or dynamic test modes at temperatures from 140 to 220°C. It was observed that yield affects elasticity more (measured by the first normal stress difference or the storage modulus) than viscosity (expressed by the shear stress or the loss modulus). The corrected for yield plots of elastic vs. viscous parameter can be easily interpreted in terms of a composite flow.

Rheology of PVC. Part 5: Melt elasticity

The behavior of polyvinyl chloride, (PVC), formulation changes drastically with the temperature and the method of sample preparation. In the steady state shear mode, upon a decrease of the rate of deformation, the data may show either a steady increase of the shear viscosity or leveling off to a Newtonian plateau. In the dynamic test mode, the storage modulus, G′, shows a viscoelastic behavior, whereas the loss modulus, G″, shows the yield. Only at temperatures above 210°C are normal flow curves for polymer melts obtained. Rigid PVC wire coating formulation was examined at 140 to 220°C using serrated parallel plates, 2.5 cm in diameter. The data at frequencies ω = 10−2 to 102 rads/s were recorded. The results were analyzed in terms of the relation, derived for polymeric composites, in which the yield stress was explicitly incorporated. It was found that G″ (but not G*) could be easily understood in terms of the model, provided that the yield stress was allowed to vary with the temperature. Three distinct flow zones were observed with the two border-temperatures at about 180 and 210°C, assigned respectively as due to gel and crystalline melting. These findings were supported by earlier results of the dielectric measurements. In conclusion, treating PVC as a composite provides a simple and effective means of data interpretation.

L. A. Utracki

Papers

Dielectric studies of poly(vinyl chloride)

Rheology of PVC. Part 5: Melt elasticity

Rheology of PVC; part IV: Particulate flow