A Quantum-Based Test of Chemical Degradation Pathways in Silicones

The study of chemical damage in irradiated silicone polymers (primarily polydimethylsiloxane, PDMS) date to the 1950's, with several works attempting to correlate small-molecule off-gassing with proposed radiation-induced reaction schemes. We develop a general conditional probability analysis approach that tests causal connections between proposed experimental observables to reexamine this chemistry through quantum-based molecular dynamics (QMD) simulations. Analysis of the QMD simulations suggests that the established reaction schemes are qualitatively reasonable but lack strong causal connections between off-gassing and crosslinking. Further assessment of the QMD data uncovers a strong quantitative connection between hard-to-measure chain scission events and formation of silanol (Si-OH) groups. A benefit of the proposed approach is that it enables independent quantum-based tests of assumed connections between experimental observables without the burden of fully elucidating entire reaction networks.