Chain Scission and Cross-Linking in the Radiation Degradation of Polymers: Limitations on the Utilization of Theoretical Expressions and Experimental Results in the Pregel Region

Abstract

An appraisal is made of current methods of determining radiation-chemical yields for main-chain scission and cross-linking of a polymer from measurements of molecular size distributions and average molar masses after high-energy radiation doses D below the gel dose D. Calculation of molecular size distributions by a single cycle of successive scission and cross-linking is shown to give significant errors. A multicycle procedure that uses iterative, numerical solutions of the fundamental scission and cross-linking equations is developed and shown to be superior. On the basis of theoretical calculations of likely experimental errors in measurements of M and M it is recommended that radiation doses be restricted to the region D < 0.4D for evaluation of scission and cross-linking yields from the dose dependence of average molar masses.