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The solid‐state polymerization of acrylamide, both in a radiation field and after removal from the field, is shown to proceed by an unusual kinetic mechanism. The usual steady state assumption is found to be inadequate because there seems to be no free radical termination (in the normal sense) involved. These results are consistent with the view that the solid‐state polymerization proceeds by a nucleation mechanism in which the free radicals are probably trapped by overlapping of the reactive sites.

Trapped free radicals are formed when polyethylene is irradiated with cobalt‐60 gamma rays in the absence of any reactive species‐oxygen, monomer, etc. The net free radical population formed increases with increasing total dose, decreasing temperature of irradiation, and increasing crystallinity of the polymer. Upon addition of a monomer to these vacuum‐irradiated films, the monomer will graft copolymerize. Graft coplymers produced by this technique are the most homogeneous, compared to those formed using other radiation‐induced techniques. If oxygen is present during the irradiation many of the free radicals formed are consumed in reaction with the oxygen to produce peroxides, hydroperoxides, and other oxygen‐containing groups. The ratio of trapped free radicals to those reacted with oxygen increases with increasing crystallinity of the polyethylene. When films irradiated in air are subsequently contacted with monomer, grafting occurs, even at room temperature, and increases in rate at higher tamperatures. It is believed that the initiation of grafting in these films is accomplished by trapped radicals and peroxide decomposition. The graft copolymers formed by this technique are not as homogeneous as those formed in the vacuum irradiation technique, but are far more homogeneous than those formed in either of the simultaneous irradiation‐grafting techniques.

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