Hydrosilane-Functionalized [2.2]Paracyclophane for Plasma-Etch-Resistant and Post-Modifiable Poly(Para-Xylylene)

Poly(para-xylylene)s (PPXs), or so-called parylenes, have become a well-established polymer class in the conformal coating industry. Due to their transparent nature, low electrical conductivity, and high biocompatibility, they are ideal candidates for coating medical devices and other delicate electronics. However, the crosslinking of PPXs to enhance their durability is still challenging today. Expensive setups need to be used to obtain crosslinked PPXs. Furthermore, the possibility of functionalization post-polymerization is limited. In this work, we present the synthesis of a hydrosilane functionalized [2.2]paracyclophane, which is used to obtain the corresponding hydrosilane functionalized poly(para-xylylene) (PPX-SiH). Through the formation of siloxane bonds during the low-pressure chemical vapor deposition (LP-CVD), which increases internal bonding, PPX-SiH is obtained as a flexible and durable polymer film. The siloxane formation during the LP-CVD is investigated through X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance spectroscopy (NMR), and Fourier-transform infrared spectroscopy (FTIR). Additionally, mechanistic insights into the formation of siloxane bonds are given through quantum chemical calculation. The Si-H bonds in the polymer allow for oxidation to form bridging siloxane moieties which enhances stretchability while also increasing the resistance to organic solvents. Through the passivation of the surface during oxygen plasma treatment, PPX-SiH becomes practically plasma-etch-resistant.