Fine Tuning of Thermal Activation and C,H-Insertion Crosslinking of Phenyl Diazo Ester Polymers

We describe the synthesis and crosslinking of polymers containing substituted phenyl diazo ester moieties. The diazo groups, which are dormant at room temperature, can be thermally activated to generate carbenes by releasing nitrogen. This subsequently causes C−H insertion crosslinking (CHic) of the polymers. The rates of carbene formation and crosslinking can be controlled by appropriate choice of the substituents at the phenyl ring. The Hammett equation can be used to predict how electron-donating or electron-withdrawing groups on the aromatic ring influence the activation and crosslinking behavior of the polymer, which allows tailoring of the process to a specific application. With the appropriate substitution pattern, diazo polymers can be designed to undergo thermal crosslinking under mild conditions. Thermally induced crosslinking of polymer films can be performed (gel content >80%) at temperatures as low as 40 °C within hours, or at 110 °C within seconds.