Sol-gel processing of alkoxysilanes is plagued by shrinkage due to evaporation of solvent, loss of alkoxide groups and water, and collapse of intermonomer distances to intramolcular distances in the final gel. The result is that netshape casting by sol-gel is virtually impossible. Furthermore stress-induced cracking of monolithic structures and films becomes an additional limiting factor in applying sol-gel processing. In this research we have designed a hybrid organic-inorganic sol-gel system that avoids shrinkage by 1) eliminating the alkoxysilane step growth polymerization process with its condensation products 2) providing a single phase system with no need for a solvent, and 3) using an acid or base catalyzed ring opening polymerization reaction to compensate for volume loss due to covalent bond formation. The Non-Shrinking Sol-Gel system is based on the ring opening polymerization of monomers bearing two strained disilaoxacyclopentane groups to afford a siloxane network gel. An organic bridging group between the two rings can be systematically varied to permit mechanical properties such as the coefficent of thermal expansion and glass transition temperature to be tailored to fit applications. We have successfully used this chemistry to encapsulate electronic test chips. Efforts are currently underway to develop photolithographic processing.

Loy, Douglas A.; Rahimian, Kamyar; Samara, Michael. Phenylene-bridged cyclic siloxanes as precursors to nonshrinking sol-gel systems and their use as encapsulants. Angew. Chem., Int. Ed. (1999), 38(4), 555-557.

Contact: Doug Loy