Simultaneous Scission and Gelation Reactions in Photocrosslinkable Polymers

Polymers used in medical devices, lithographic patterning, and other applications are often exposed to ultraviolet, e-beam, or gamma irradiation to obtain a sterile and/or crosslinked polymer. Since these stimuli can produce free radical intermediates on the polymer backbone, simultaneous gelation and scission reactions will occur. These reaction rates underlie the resulting mechanical properties, % oxidation, and % leachables, but in practice these reactions are challenging to directly quantify. To establish a simple approach for extracting stoichiometric likelihoods of scission or gelation reactions resulting from irradiation, we have adapted the Miller-Macosko statistical model to account for these effects. The simple, closed form expressions that result provide a means to quantitatively analyze sol fraction vs. dose data and gain mechanistic insight into these reactions. Here we will describe our approach in detail and apply it a model photopolymer, poly(styrene sulfonyl azide-alt-maleic anhydride).