Silylation as a tool to extend the initiated chemical vapor deposition to hydrophilic monomers: an experimental study using 2-hydroxyethyl methacrylate

Initiated Chemical Vapor Deposition (iCVD) is a powerful tool for the deposition of polymer thin films. It allows the solvent-free deposition of conformal coatings on sensitive substrates as well as on complex geometries using a variety of different monomers. However, the need to evaporate the contributing monomers limits its use, for example in the synthesis of hydrogels. Strong polar intermolecular interactions result in low vapor pressure of potential monomers, rendering them unsuitable for iCVD. In this study, silylation was used to increase the hydrophobicity and thus the vapor pressure of an important monomer used in hydrogel preparation, 2-hydroxyethyl methacrylate (HEMA). Silylated HEMA (sHEMA) was successfully copolymerized with 1,2-ethanediol dimethacrylate (EGDMA) and subsequently converted back to hydrophilic p(HEMA-co-EGDMA) under mild acidic conditions. This exemplary study suggests that by using a silylation process in combination with e.g., hydrochloric acid (HCl) post-treatment, the monomer toolbox available for polymer deposition via iCVD can be significantly extended to include monomers with initially lower vapor pressures due to hydrophilicity. • iCVD was utilized to produce sHEMA based polymer thin films. • sHEMA is a silylated counterpart to 2-hydroxyethylmethacrylate (HEMA). • Silylation increases volatility leading to reduced energy input and valve clogging. • Desilylation by mild acid post-treatment restores hydrophilicity of the polymer.