Heterogeneous Nature of Reaction in Radiation-Induced Solid-State Polymerization of Acrylamide

Abstract

It has been suggested that the radiation-induced solid-state polymerization of acrylamide is a heterogeneous reaction, that is, it goes by a two-phase mechanism [G. Adler, J. Chem. Phys. 31, 848 (1959) and B. Baysal, G. Adler, D. Ballantine, and P. Colombo, J. Polymer Sci. (to be published)]. According to this concept, the reaction procedes at definite sites within the crystal. After the first few reaction steps, it forms regions of pure or nearly pure polymer imbedded in pure monomer. Further reaction would take place at the interface between the two. The polymer and monomer regions would remain segregated until the crystal is completely polymerized. It has been shown previously that the reaction can take place without the crystal breaking up. The alternative to this scheme seems to be that the reaction takes place within the crystal lattice and is directed by it. This requires a more homogeneous reaction mechanism. It seems feasible, in principle to distinguish between the two mechanisms by x-ray diffraction. A single crystal technique that allows us to look at all the reflections simultaneously appeared to be most promising. It was therefore decided to run a series of rotation diagrams on a crystal in various stages of polymerization.