During August of 1955 while preparing some samples for an irradiation exhibit some post irradiation effects were observed. A 1:1 mixture of acrylonitrile and styrene and of methacrylic acid and styrene were placed in 6 by 12 in. 3-mil polyester film bags, the air bubbles removed, the bags heat sealed, and the contents irradiated to a slightly viscous consistency. The bags were then placed on a peg board in a room with northern exposure for a few weeks; following this exposure it was observed that the mixture had changed from a slightly viscous consistency to a firm, solid mass. Inasmuch as the dilfusion of the monomer through the plastic film had been previously determined to be very low, it was inferred that postirradiation effects had completed the polymerization.