H. Block

Polymerization of methyl methacrylate photosensitized by benzophenones

Abstract Polymerization of methyl methacrylate ( mma ) in tetrahydrofuran ( thf ) may be photosensitized with benzophenone, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride ( btda ) and 3,3′,4,4′-tetramethoxy carbonyl benzophenone ( tmcb ) with an efficiency comparable to that of azodiisobutyronitrile as a photosensitizer. The reactions show conventional chain kinetics for radical polymerizations in which initiation involves hydrogen abstraction from thf by triplet excited sensitizer, i.e. Ar 2 C = O hv →( Ar 2 C = O )( S 1 )→( Ar 2 C = O )(T 1 )→ Ar 2 C − OH + THF . The semipinacol radicals Ar 2 COH do not initiate (at 30°C) but act as terminating agents with an apparent efficiency increasing in the series bdta tmcb « Ph 2 C = O . However, a detailed kinetic analysis suggests that this order results from decreasing rates (in the given order) of self dimerization of the semipinacol radicals.

Dielectric relaxation in polymaleimide and N-substituted polymaleimides

Abstract 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 10 6 Hz 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.

Structure and molecular relaxation of alternating copolymers of styrene and N-substituted maleimides

Abstract The dielectric relaxations of twelve differing styrene N- 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.

A Couette cell with fixed stator alignment for the measurement of flow modified permittivity and electroviscosity

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 <or approximately=105 s-1, and also of measuring viscosity are presented. The provision of both macro- and micro-measuring electrodes enables the equipment to be used for low- and high-permittivity liquids including aqueous systems, at selected and well controlled temperatures.

Molecular motion in a copolymer of styrene and maleic anhydride

Abstract 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.

Flow-modified permittivity of solutions of poly(n-butyl isocyanate) and poly(n-hexyl isocyanate)

Abstract 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 dielectric properties of poly(hexylisocyanate) solutions in electric fields

Abstract 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.

Copolymerization of phenylethyne with maleic anhydride

Abstract 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.

Molecular motions in poly(N-vinylsuccinimide)

Abstract 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 reported 1–4 .

Nuclear magnetic relaxation in poly(N-amyl maleimide) and poly(N-dodecyl) maleimide

Abstract Longitudinal relaxation times in the laboratory ( T 1 ) and rotating ( T 1 ρ ) 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 T 1 data in the dodecyl derivative to theoretical equations is described.