The effect of large electric fields (≤0.8 MV m−1) on solutions of poly(n-hexylisocyanates) of differing molecular weights is described. Non-linear dielectric effects are observed and their magnitudes are in fair agreement with those predicted theoretically for inflexible dipolar molecules of low polarizability. Small enhancements of relaxation frequencies are also caused by the application of large electric fields.

The dielectric behaviour of solutions of poly(n-butyl isocyanate) and poly(n-hexyl isocyanate) in flow have been examined, including, for the latter polymer, fractions of differing molecular weight. The data are analysed in terms of established theories for changes in the permittivity of solutions of rigid macromolecules undergoing shear and are critically compared to dielectrically based information obtained from studies of still solutions. Rotational diffusion coefficients and dipole moments have been measured and the influence of heterogeneity in molecular weight on flow-modified permittivity is examined. The results obtained support the view that the theories for the flow-modified permittivity of rigid macromolecules are generally satisfactory in providing rotational diffusion coefficients and resolved dipoles, but that the influence of molecular shape on the effect is not simply obtained when polydisperse material is involved.

The design features required for the construction of a Couette shear cell with fixed stator-rotor alignment to measure the permittivity of liquids in flow is discussed. Details of the construction of such a cell having the capability of measuring permittivities of liquids from rest to flow rate

Electrical and dielectric behaviour of polymers reflect macromolecular structure and motion, both in solution and the solid state. Some polymers which have special electrical properties may have commercial potential. Mention need only be made of polymer electrets, pyro-electric polymers, photo-conductive polymers as used in electro-imaging, and conductive polymers to indicate the expansion of use over that of insulators. The separation of electrical behaviour into ‘dielectric’ and ‘bulk conductive’ properties is convenient and has been followed in this review.

A study into the photoconductance of poly( N -vinyl carbazole) partly oxidized to introduce cation radicals is described (mole fraction < 4 × 10 −3 ). These materials are shown to be photoconductors whose response to illumination is time dependent. Their photoconductive behaviour has been studied as a function of extent of oxidation, field strength, temperature, light intensity and irradiating wavelength. The observed response is discussed in terms of a model for the amorphous state in which there are accessible levels in the forbidden gap for interaction with photopromoted electrons or holes. Variation in the role of level as trap or recombination centre with external conditions is shown to form, in part, an adequate model for behaviour. However, light intensity and temperature dependence does indicate that there is a significant change of the distribution of levels in the for-bidden gap as the temperature is reduced to ∼ −20°C, possibly due to a change in structure or mode of motion.

AbstractMeasurements of the increase in the relative permittivity for solutions of polystyrenes, poly(p‐ethoxystyrene), poly(methyl methacrylate), and poly(N‐vinyl carbazole) when subjected to shear gradients are reported. The influences of such factors as shear rate, concentration, viscosity, solvent permittivity, polymer dipole moment, and polymer molecular weight on the phenomenon are described. An empirical correlation for the diverse data obtained with polystyrenes and poly(p‐ethoxystyrene) has been established, but this relation does not entirely match the theoretically predicted effects. We discuss the various physical processes which may have an influence on the observed phenomenon.

The important design features of a Couette cell capable of measuring birefringence, viscosity and permittivity changes in shear are discussed. Described are the details of construction of such a cell which can perform one or all of these functions. The cell is capable of operating in the range of shear rates up to about 3*105 s-1 for dielectric and viscosity determinations and up to about 104 s-1 for double-refraction measurements. This paper concentrates primarily on the details pertinent to dielectric measurements.

A study into the photoconductance of poly(N-vinyl carbazole) partly oxidized to introduce cation radicals is described (mole fraction < 4 × 10−3). These materials are shown to be photoconductors whose response to illumination is time dependent. Their photoconductive behaviour has been studied as a function of extent of oxidation, field strength, temperature, light intensity and irradiating wavelength. The observed response is discussed in terms of a model for the amorphous state in which there are accessible levels in the forbidden gap for interaction with photopromoted electrons or holes. Variation in the role of level as trap or recombination centre with external conditions is shown to form, in part, an adequate model for behaviour. However, light intensity and temperature dependence does indicate that there is a significant change of the distribution of levels in the for-bidden gap as the temperature is reduced to ∼ −20°C, possibly due to a change in structure or mode of motion.

CERTAIN polymer solutions have been shown using a Couette shear dielectric cell1 to exhibit changes in dielectric properties when subjected to a shear field2,3. For polar polymers which lack flexibility, the qaction of a rotational shear field alters the time-dependent distribution of dipole orientation which results in changes of permittivity, loss magnitude and relaxation frequency2. In quantitative terms these changes seem to correspond well with the theoretical treatment due to Barisas4. A distinct difference in the situation occurs when flexible polymers such as poly(styrenes) or poly(p-ethoxystyrenes) are subjected to such shear fields. The changes are inconsistent with the magnitude of the polymer dipole and solvent relative permittivity takes on a rather dominant role3. To test the importance of variation of the internal field term on shape changes due to polymer coil distortions, we have studied an organic colloid system: cross-linked poly(ethylacrylate) dispersed in heptane and stabilised with a ‘comb’ graft copolymer [poly-(12-hydroxy stearic acid) terminated with glycidyl methacrylate and then copolymerised (1:1) with methyl methacrylate]5.

Spin—lattice and rotating frame relaxation measurements have been made on nine copolymers of styrene with N -n-alkyl maleimides in which the alkyl groups are CH 3 , C 2 H 5 , C 5 H 11 , C 7 H 15 , C 9 H 19 , C 12 H 25 , C 14 H 29 , C 16 H 33 and C 18 H 37 . Five relaxations have been detected which are correlated with existing relaxation work. The highest temperature (αβ) relaxation is associated with the glass transition and the γ-relaxation results from ring twisting in the ordered (helical) parts of the structure. The δ-relaxation occurs only in the C 1 –C 7 polymers and reflects movement in helical stacking within the ordered phase while the ε-relaxation occurs only in the C 7 –C 18 homologues and arises from motion of the pendant alkyl chain in both ordered and disordered regions. The lowest temperature minimum in T 1 is associated in all polymers with methyl rotation. Spin diffusion plays a prominent role in the relaxations and this is used to interpret further the morphology of the samples.

The dielectric and pulsed n.m.r. relaxation of poly(N-vinyl succinimide) has been investigated as a function of frequency and temperature. Five loss processes (α to ϵ) have been observed and assigned to main chain motion (α, β) and ring deformations (γ, δ, ϵ) on the basis of comparative work with chemically analogous polymers previously reported1–4.

Partial oxidation of poly(N-vinyl carbazole) (PNVC) to produce crosslinked PNVC containing dimeric carbazylium cation radicals is shown to produce material with significant semiconductivity (σ) up to ∼10−5ohm−1cm−1 at 293K. The synthesis of these materials (including partly ring-chlorinated analogues) is described and their semiconductivities and activation energies for conductance (Ea) examined as a function of cation-radical content. It is demonstrated that the extent of reaction essentially determines the semiconduction of these materials, provided homogeneous conditions are maintained. The starting molecular weight of the PNVC, and whether or not it is partly chlorinated, have minimal effect on σ.

The dielectric relaxations of twelve differing styreneN-substituted maleimide alternating copolymers are reported. Five processes common to most member copolymers have been observed, and their molecular origins are discussed. Supplementary evidence based on measured X-ray structural factors and differential scanning calorimetry, together with comparative literature data on N-substituted polymaleimides and a styrene-maleic anhydride copolymer is presented as further evidence supporting the suggested origins for loss peaks in these structurally related polymers.

Longitudinal relaxation times in the laboratory (T1) and rotating (T1ρ) frames have been measured for poly(N-amyl maleimide) and poly(N-dodecyl maleimide). The results are compared with information previously published using dielectric relaxation techniques. A total of three relaxation processes have been detected corresponding to methyl rotation, motion within the substituent alkyl chain and out-of-plane deformation of the maleimide ring. An attempt to fit the T1 data in the dodecyl derivative to theoretical equations is described.

Onsager's theory of dipole moments is modified for radially inhomogeneous permittivity [form ϵ(r)=ϵBexp(—κ/r)] arising at the cavit Calculations show more consistent agreement between gaseous and liquid dipole moments with the modified theory.

Dielectric and mechanical relaxation techniques have been applied to the study of the molecular motions exhibited by an alternating copolymer of styrene and maleic anhydride. Three major relaxations were detected by these techniques and shown to correspond to motions already defined in homopolymers of substituted maleimides. A fourth relaxation was detected but insufficient evidence for assignment was obtained. The α relaxation is attributed to gross main chain motion ( T g ∼475K), the β relaxation (activation energy 103kJ) to local motion about the backbone and the δ relaxation (activation energy 51kJ) to deformation of the substituted succinic anhydride ring.

We report a satisfactory method for the direct conversion of step-response (transient) data (such as is obtained from the rate of discharge of a capacitor) into the frequency dependence of the complex relative permittivity. This computer-based method has no a-priori restriction on the shape of the loss peak or functional dependence of the decay response. In this it differs from a number of approaches described in the literature.1–4 The method herein described is compared to such other techniques for converting step-response data, and assessed in relation to the predicted behaviour for single and unresolved double Debye relaxations. The dielectric relaxation behaviour of a sample of poly(vinyl acetate) is also investigated using the described method of data analysis.

We report a study on the dielectric relaxation of polymaleimide and selected N-alkyl and N-aryl polymaleimides covering the frequency range 10−5 to 106Hz and the temperature range −80° to +230°C. In most instances three relaxations are observable and these have been assigned to the glass to rubber transition, a local chain motion and an in-plane deformation of the maleimide ring. Activation energies for these processes are reported. Secondary factors such as crystallinity and, in polymaleimide and poly(N-methyl maleimide), thermal reactions are demonstrated to affect the individual relaxations.

We report the successful free radical copolymerization of phenylethyne with maleic anhydride to give a high molecular weight (up to ∼ 105), alternating copolymer. Some of the chemical and physical properties of this material are described. The possibility of converting this and allied copolymers to conjugated polymers is discussed.