Alastair M. North

Dielectric properties of phase separated polymer solids: 1. Styrene-butadiene-styrene triblock copolymers

Abstract Theories currently applicable to the description of the low frequency dielectric loss, associated with trapping of charge carriers at interphase boundaries in polymers, are presented. Experimental observations on styrene-butadiene-styrene triblock copolymers are compared with theory. The interfacial polarization process in a film-cast copolymer with 30 wt % styrene was found to be in reasonable agreement with predictions for a morphology of parallel cylinders oriented at random, whereas that for a 50 wt % styrene copolymer was compatible with prediction for a random arrangement of partly parallel lamellae. These structures correspond to morphologies observed by electron microscopic observation. No evidence was found for a dielectric effect specifically requiring a diffuse conducting interfacial zone between the polystyrene and polybutadiene domains. The bulk d.c. conductivity also correlated with predictions made using the same parameters as those involved in calculation of the relaxation effects.

High frequency ultrasonic studies of polyethylene

Abstract Ultrasonic measurements, covering the frequency range 5 MHz to 1 GHz, are reported on linear and branched polyethylene. At the lower frequencies the temperature dependence of the velocity and the amplitude of the absorption loss are consistent with observation of the familiar beta (β) and gamma (γ) relaxation processes. Studies as a function of the thermal history of the samples indicate that the detailed attenuation profile and the magnitude of the velocity are sensitive to crystallinity, reflecting changes in the branched chain content and lamella thickness. Data are also reported illustrating how the morphological changes of drawing and annealing influence the acoustic propagation parameters. The high frequency attenuation is due to the γ-macromolecular conformational relaxation, crystalline spherulite-amorphous region thermoelastic heat flow and spherulite-phonon scattering.

Compressibility studies of benzene + hexafluorobenzene mixtures

Abstract The excess isentropic compressibility and the excess thermal-pressure coefficient have been measured over a small range of temperature for benzene + hexafluorobenzene mixtures. The results are discussed in the light of the different types of molecular structure known to exist in the two pure liquids and in the mixture.

Dielectric properties of phase separated polymer solids: 2. Butanediol terephthalate-poly(tetramethylene oxide terephthalate) copolymers

Abstract The low frequency dielectric behaviour of copolymers of butanediol terephthalate with poly(tetramethylene oxide terephthalate) is reported. Comparison of the theories for interfacial polarization with experimental dielectric observations highlights the role of domain boundary conduction in such polar polymers.

Kinetic matrix effects (response and density distribution functions): ring closure. Reaction of indolinobenzospiropyrans in glassy poly(alkyl methacrylates)

The ring closure (bleaching) reaction of photochromic indolinobenzospirans is a fast unimolecular process with a finite activation volume. When the reagent is immobilised in a rigid matrix, the isomerization is controlled by the amount of free volume in the neighbourhood of the reacting molecule and so the distribution of reaction rates reflects the density distribution in the matrix. The theory of such kinetic matrix effects is presented and methods of evaluating the reagent response and matrix density distribution functions are discussed. Ring closure reactions of three such compounds in four polymeric matrices are reported and the complete functions evaluated for 8-bromo-2′,2′-dimethyl-6-nitro-1′-phenyl-(2H-[1]benzospiropyran-2,2′indoline) in poly(methyl methacrylate).

Ultrasonic investigations of morphology and stress relaxation in drawn polypropylene

Abstract The effects of annealing on ultrasound propagation in drawn samples of polypropylene are reported. Below 373K the attenuation is dominated by scattering associated with voids generated during the drawing process. Above 383K the void content changes significantly with an associated decrease in the ultrasonic attenuation. Shrinkage, changes in optical clarity and changes in density of the drawn samples are discussed in terms of possible modification of the polymer structure.

Ultrasonic relaxation in dilute polystyrene solutions: 1. Normal mode and conformational processes

Abstract Ultrasonic relaxation data are reported on solutions of polystyrene in toluene, dioxan, m-xylene and p-xylene over a frequency range of 1–1000 MHz and a temperature range of 293–353K. The data are analysed in terms of two components, a viscoelastic contribution associated with the normal mode relaxations and a more local conformational change of the polymer backbone. The solvent, molecular weight and temperature dependence of the relaxation processes are discussed. An anomalous increase in the amplitude of the acoustic absorption at high temperatures is ascribed to the occurrence of a pseudo helix-coil transition. A picture of the dynamic processes now emerges which rationalizes the apparently disparate earlier studies into a coherent self-consistent description.

Ultrasonic studies of solid poly(alkyl methacrylates)

Abstract The attenuation and velocity of ultrasonic longitudinal waves of frequencies 5–35 MHz in poly (methyl methacrylate), poly(ethyl methacrylate), poly (n-butyl methacylate) and poly(isobutyl methacrylate) between 233 and 363K are reported. The methyl and ethyl polymers showed evidence of a single relaxation process (associated with cooperative main chain and ester group motions), but the butyl polymers showed also a second relaxation at about 200–230K. This is associated with conformational rearrangement of the alkyl group, and the acoustic energetics are in line with theoretical predications for this process. The velocity data show the expected decreases due to the main glass transition (and cooperative processes) and to reduction of the intermolecular interaction force constant with increasing size of the alkyl group. Attempts to calculate an acoustic low temperature specific heat yielded values lower than expected from calorimetric observations, showing that the acoustic modes are capable of greater energy storage than is involved in the longitudinal perturbation, and/or that calculation based on a Debye T 3 law are invalid for these glassy polymers.

Infrared and Raman studies of phenyl substituted ethanes

Abstract The infrared and Raman spectra of meso-1,2-dicyano-1,2-diphenyl ethane, 1,2-diphenyl ethane and 1-chloro-2-phenyl ethane are reported. A tentative assignment of the characteristic vibrational frequencies is proposed and the barriers restricting internal rotation are calculated.

Adiabatic compressibility of binary liquid mixtures

Adiabatic compressibility, density and some viscosity measurements are reported on a series of mixtures of aromatic compounds with cyclic saturated rings and carbon tetrachloride. The magnitudes and signs of the excess functions are discussed in terms of the intermolecular interactions expected in these systems.