The dielectric behaviour of isocyanate-terminated polymers is reported in this paper as a function of frequency (100 Hz-100 kHz), temperature (30-90 degrees C) and the concentration of the curing agent, 4,4'-methylene bis(ortho-chloroaniline) (MOCA) (1.2, 3.5 and 4.7%) which was used in preparing the polymer from the toluene di-isocyanate and castor oil. The dielectric constant and the loss were found to decrease as the MOCA concentration was increased. Distinct loss peaks were obtained. The influence of the curing agent on the dielectric properties of the polymer is discussed in detail. The most probable relaxation times were calculated from the complex arc plots of epsilon 'and epsilon ". From these arc plots it is established that the distribution of relaxation times becomes more and more symmetric with the increasing temperature. Activation energies were calculated. Maxwell-Wagner-Sillars interfacial polarisation is proposed as the probable mechanism.

No abstract

The optical properties of an isotropic optically active medium at oblique incidence have been investigated. It was found that the amount of transmitted light converted from p polarization to s polarization and vice versa, through an isotropic optically active medium, is independent of the state of incident polarization. Though the optical rotation through the optically active medium is same for p and s polarization at normal incidence, it becomes different at oblique incidences.

A new method involving an elegant computer curve fitting technique is discussed for evaluating E ' and E", for dilute solutions at X-and Q-bands, with a greater accuracy. Four compounds with rigid (chlorobenzene) and nonrigid (anisole, phenol, and guaiacol) molecules have been tested with this method. The important advantage of the present method is that it involves no mathematical assumptions. The error involved in evaluating E' and E" is estimated to be 1% and 1-2% respectively.On discute une methode nouvelle, comportant une technique elegante d'ajustement de courbe par ordinateur, pour I'evaluation de E ' et E" avec une precision amelioree, dans des solutions diluees, aux frequences des bandes X et Q. On a fait I'essai de cette methode avec quatre composes, a molCcule rigide (chlorobenzene) et a moltcule non rigide (anisole, phenol et guiacol). L'avantage le plus important de cette methode est qu'elle ne fait intervenir aucune hypothese mathematique. Les erreurs que comporte 1'Cvaluation de E ' et E" sont estimees a 1% et 1-2% 1,esnectivement. . . r ---Can.

The dielectric permittivity and dielectric loss of solutions of four unsaturated triple-bonded compounds were measured as a function of frequency (10 kHz, 8.43, 11.3 and 35.6GHz), temperature (33-70 "C) and concentration (0.07-0.01 weight fraction). The data are analysed in terms of a double relaxation process. The most probable relaxation time, the overall molecular relaxation time and the group relaxation time were calculated. The dipole moments were also calculated along with the thermodynamic parameters. The results are discussed in terms of association effects in these compounds and the dielectric data are correlated with the infrared spectral data.