The mechanisms of radiation‐induced changes in vinyl polymers

Abstract

Abstract An investigation has been made to discover why some polymers degrade while others predominantly crosslink on exposure to high‐energy radiation. All the work was carried out on pure vinyl polymers prepared under controlled conditions, and the irradiations were conducted in vacuo. The volatile irradiation products were analyzed by mass spectrography, and the polymer residues were examined by solubility tests, viscosity measurements, and radioactive assay of 14 C‐labeled polymers. The results confirmed that vinyl polymers containing a qunternary carbon atom degraded while the rest became crosslinked. Polymethyl methacrylate underwent random main‐chain scission with the elimination of rather less than one. COOCH 3 side group for each main‐chain fracture. Some of the polymers which crosslinked lost side groups but this was not related directly to the crosslinking reaction. Free radical mechanisms are proposed to explain the occurrence and the observed features of the radiation‐induced degradation and crosslinking reactions.