Anuradha Rout

Polymerization of acrylonitrile initiated by Ce4+/thiourea system

Abstract Kinetics of polymerization of acrylonitrile initiated by the Ce4+-thiourea redox system have been investigated at 10°. The rate of monomer disappearance is proportional to (a) (monomer concentration)2, (b) thiourea concentration and, (c) (ceric ion concentration)−1. The rate of ceric disappearance is proportional to the ceric and thiourea concentrations, but independent of monomer concentration. A kinetic scheme has been proposed involving production of initiating radicals from oxidation of thiourea by ceric ions and termination exclusively by the interaction of the chain radicals with ceric ions. The scheme is consistent with experimental findings. The results obtained either in the presence or the absence of the reducing agent have been compared and interpreted in terms of the proposed kinetic scheme.

Rate parameters for transfer reactions of some polymer radicals: in terms of Swain and Lupton's f and r and the unique positional weighting factors of Williams and Norrington

Abstract Rate parameters of the reaction of phenols, deuterated phenols and nitrobenzenes with polyvinylacetate radicals and of aromatic thiols with polymethylmethacrylate radicals have been correlated with Swain and Luptons substituent constants (Fk and Rk) and Williams and Norringtons unique positional weighting factors (fj and rj) by the following equation: P i = α i ƒ j F k + β i r j R k + e i + P 0 i where Pis are the rate parameters, P0i being that for a standard reference state. The correlations were found to be quite satisfactory. The sign and magnitude, and the ratio of the reaction dependent parameters αi and βi throw light on the nature of the transition state and the relative contributions of the mesomeric and inductive effects. The present studies also show that the mesomeric effect of meta-substituents is significantly greater than reported by earlier workers.

Retardation of Cerium(IV)-Initiated Polymerization of Acrylonitrile by Cinnamic Acid

Abstract The kinetics and the mechanism of retarding action of cinnamic acid on the Ce(IV)-initiated polymerization of acrylonitrile were studied in the temperature range 35–45°C. The rate of polymerization Rp was measured with respect to its dependence on time, monomer, metal ion, cinnamic acid, perchloric acid, acetic acid, sodium perchlorate, sodium sulfate, and manganese sulfate. The most significant observation was the rate mechanism. The process of polymerization was initiated by Ce(IV) alone and terminated essentially by the free radical produced by the interaction of Ce(IV) with cinnamic acid, which seems to be a general observation for all retarding substrates.

Ortho Effect and Additivity of Substituent Parameters in the Reaction between Phenols and Poly(vinyl Acetate) Radicals

Abstract The ortho effect and the additivity of substituent parameters in the reaction between phenols and poly(vinyl acetate) radicals have been investigated in the light of theories postulated by Swain and Lupton on substituent constants Fk and Rk and that of Williams and Norrington on the unique positional weighting factors fj and rj. The present correlation studies show that while Chartons theory that the ortho-substituent effect is primarily electrical is true for most of the substituents, some steric considerations have to be invoked while dealing with groups like o-tert-butyl. The additivity of fjFk and rjRk is much less satisfactory than that of Hammetts [sgrave] or Brown-Okamotos electrophilic [sgrave]+ substituent constants.