Modulating Solubility and Enhancing Reactivity ofPhoto-Cross-Linkable Poly(styrene sulfonyl azide-alt-maleic anhydride) Thin Films.

To formalize our understanding ofindiscriminate grafting chemistriesas they pertain to cross-linkable polymers and emerging patterningtechnologies, we designed a new polymer, poly(styrene sulfonyl azide-alt-maleic anhydride) (PSSMA). By modulating its solubility,it can be deposited into smooth, ultrathin films atop polar and nonpolarpolymers. Upon heating above 120 °C or exposure to UV light,highly reactive nitrene intermediates are generated from the azidegroups which form covalent adducts and cross-link the PSSMA. Azidephotolysis and polymer gelation were studied in the context of a statisticalmodel to gain insight into the network outcomes of nitrenes in a polymerfilm. For every azide group converted to a nitrene in ambient atmosphere,it has an 11% likelihood of grafting to another chain and a 5% chanceof causing a scission. These values can be increased over 3-fold byreducing the O2content by 85%. Alternatively, the effectsof quenching by ground-state O2can be mitigated by addingMichler’s ketone (MK) to the film. PSSMA/MK blend films possessa 39% (±13) likelihood for grafting and 29% (±10) for scission.The higher ratio of scission to grafting is a consequence of the sensitizedazides producing triplet-state nitrenes, which favor hydrogen abstraction.These broadly generalizable considerations will be useful to otherswho wish to maximize light sensitivity in related polymer systems. [ABSTRACT FROM AUTHOR]