It has recently been reported' that the gamma-ray irradiation of several monomer-polymer combinations produces graft copolymers. This paper is concerned with the mechanism of the grafting process and application of four different types of copolymers. The solution property behavior of various graft copolymers will be described elsewhere.2 EXPERIMENTAL PROCEDUREAll experiments were performed with polymer h s having limited swelling by the monomer employed. The technique generally involved suspension of the polymer film in a large excess of monomer enclosed within a 1 X 12 inch Pyrex ampule. The ampules were sealed under nitrogen and placed in cobalt-60 gamma sources of varying intensities. Dose rates of 200,000 rep per hour were employed for routine operations and, for kinetic measurements, dose rates ranging from 20,000 to 300,000 rep per hour were used. (The dose rates were measured using a high level ionization chamber.) All irradiations were performed at room temperature. Initially, distilled monomer was employed, but it was later found that commercial, undistilled monomer containing inhibitor could be employed, The inhibitor caused a short induction period which was followed by a rate of grafting identical to that obtained with distilled monomer. In grafting experiments with acrylonitrile, saturated aqueous solutions were found to be more advantageous than bulk acrylonitrile, because of the rapid homopolymerization rate of the latter. Grafting exeriments with vinylcarbazole were performed with 20 weight per cent solutions of the monomer in toluene.

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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