Investigation of Lewis photobase-catalysed oxa-Michael addition for hot lithography

Abstract

In lithography-based additive manufacturing, step-growth polymerization is a highly desired mode as the resulting polymer networks are usually more homogenous and therefore tougher than ones obtained by free radical chain growth polymerization. Therefore, thiol-ene chemistry sees widespread use, however, the employed thiols are accompanied by strong odor, limited availability and limited storage stability of the formulation. Replacing the thiols with alcohols resolves these problems as a wide variety of odorless alcohols is available. The oxa-ene reaction presented here is a base-catalysed Michael-type reaction for which a highly active Lewis base catalyst is known. Our work shows the preparation of photocaged Lewis base catalysts for this oxa-Michael addition, its implementation into photochemistry and the accompanying new mechanism compared to the regular thermal catalysis. Additionally, the storage stability of such formulation was investigated at different temperatures. Finally, the developed system is applied in additive manufacturing using hot lithography approaches with both linear and non-linear absorption of light.