The empirical dielectric decay function +(t) = exp -( t / ~~) f i , O< p 9 1 has been transformed analytically and numerically into the frequency dependent complex dielectric permittivity. It is shown that empirical curves give a very satisfactory representation of the dielectric a relaxations observed in polyethyl acrylate, polyvinyl acetate, polyvinyl octanoate, polymethyl acrylate, polypropylene oxide and amorphous polyethylene terephthalate. It is suggested that the present empirical representation is far more satisfactory than existing functions for non-symmetrical loss curves. It is also suggested that the success of the empirical representation may imply that the dipole moment correlation function is a non exponential decay function of time rather than arising from a weighted sum of exponential decay functions. In addition the accuracy of the transformation of transient data into frequency domain data-via the Hamon approximation, is examined for the empirical representation, and it is shown that the transform is accurate for log m0 >0, but significant corrections may have to be applied for / 3 >0.5 and log wz0< 0.

No abstract

No abstract

No abstract

No abstract

Five new carbazole-containing polymers have been synthesized. With poly(N-vinylcarbazole) these form two series in which (a) the nitrogen atom of the chromophore is attached to the polymer backbone with an increasingly flexible linking moiety, PNVK, I, -II, -III, and (b) a series in which the backbone is attached to the 9-, 2-and 3-ring positions, I, IV, V. The molecular weights of the polymers have been characterized by membrane osmometry and gel permeation chromatography. These polymers are susceptible to photochemical degradation which causes both scission of the chain backbone and diminution of carbazole chromophore fluorescence. Sensitive viscosity measurements made on samples undergoing this main-chain scission have been used to obtain the intrinsic viscosity-molecular weight K, a values of the resulting fragments. Comparison of the absorption and emission spectra shows that appreciable excimer emission occurs only in the case of poly(lV-vinylcarbazole) (PNVK) and poly [2-(9-ethyl)carbazolylmethyl methacrylate] (IV). Excimer emission from the latter is weakest in polar fluid solvents and strongest in a rigid glassy matrix. Luminescence decay measurements in the presence and absence of anthracene quencher suggest that down-chain energy migration is virtually absent in the sterically unhindered polymers I, II, III, and V, and this is confirmed by steady state analysis of collisional quenching. Collisional quenching of monomer excitation from IV indicates that the excitation is effectively immobilized in the region of not more than three neighboring chromophores. These

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-l'-phenyl-(2H-[l]bspiropyran-2,2'~doline) in poly(methy1 methacrylate).The non-homogenous structure of amorphous solid polymers has been shown to influence both the kinetics and mechanism of a variety of photochemical reactions occurring in low molecular weight compounds homogenously dispersed throughout the matrix. This topic has recently been reviewed by Williams and Da1y.l Kinetic matrix effects are easily observed in thermal isomerization reactions of photochromic systems, ie., hv kT

A kinetic equation for the rate of copolymerization has been developed when the rate of termination depends not on the nature of the last monomer unit added to the growing polymer chain, but on the composition of the whole growing chain (and hence on the monomer feed composition). The termination reaction in the copolymerization of methyl methacrylate and vinyl acetate at 30°C has been shown to be diffusion-controlled, and the termination rate coefficient has been evaluated using the equation, The termination rate coefficient decreases slightly as vinyl acetate is added to methyl methacrylate, and passes through a minimum at 92 mole % vinyl acetate in the monomer feed. At this temperature the termination rate so calculated has decreased to a third of the value for pure methyl methacrylate.The same equation has been applied to published results for the same copolymerization at 60°C. The values obtained for k t ( ~) lie very close to an " ideal " case defined by k t ( ~~) = ktaaxa+ktbbxb, where kt,, krbb are the termination rate constants for the respective homopolymerizations, and xa, Xb are the mole fractions of units A,B in the polymer chain. It is suggested that in this system, and probably in others, the conventional application of a 4 factor describing relative rates of radical interaction is invalid.