Study of the kinetics of radiation graft polymerization from the vapour phase on mineral powders

Abstract

IT HAS been shown previously that the method of polymerization by irradiation of solid materials in the presence of monomers in the vapour state extends the possibilities of this process considerably and enables graft polymerization to be achieved not only on organic, but also on mineral substrates [1-2]. :New organo-mineral ion-exchange materials [3] and mechanically strong semiconductors [4] have been produced by this means. A process of a similar nature, based on irradiation of mineral powders in the presence of a two-component gas mixture has been applied to the synthesis of higher carboxylic acids [5]. The process of polymerization from the vapour phase on mineral surfaces has however not been studied sufficiently, in particular the fundamental kinetic relationships have not been elucidated, and knowledge of these is necessary both for selection of the optimal technological conditions and for understanding the peculiarities and mechanism of the process. From the kinetic point of view this process is of particular interest because essentially we have here a new case of heterogeneous polymerization with the distinctive feature that active eentres initiating polymerization are generated continuously during the course of the reaction throughout the entire volume of the solid phase, both in the original mineral particles and in the newly formed surface layer of polymer. This investigation is devoted to elucidation of the main kinetic relationships of radiation graft polymerization from the vapour phase on mineral surfaces. The materials selected for study were methyl methacrylate (MMA) and styrene (St) polymerized on magnesium oxide and Aerosi]. With the four systems a study was made of the dependence of the reaction rate on dose rate, temperature, vapour pressure of monomer and the degree of adsorption of the latter on the irradiated substrate. We also studied the dependence of the reaction rate on the quantity of polymer formed on the mineral powder up to formation on the mineral particles of fairly thick polymer layers, corresponding to the thickness of the grafted layers in the organo-mineral graft materials mentioned above.