Solid and Hollow Poly(p‑xylylene) Particles Synthesis via Metal−Organic Framework-Templated Chemical Vapor Polymerization
Begum, S. / Behboodi-Sadabad, F. / Pramudya, Y. / Dolle, C. / Kozlowska, M. / Hassan, Z. / Mattern, C. / Gorji, S. / Heißler, S. / Welle, A. / Koenig, M. / Wenzel, W. / Eggeler, Y.M. / Bräse, S. / Lahann, J. / Tsotsalas, M.
Chemistry of Materials
- Date: Juli 2022
Poly(para-xylylene)s are a unique class of chemical vapor deposition (CVD)-based polymers, generally referred to their trade-name “parylenes”, widely used as a protective coating and insulating layer in electronics, especially in printed circuit boards and optical and biomedical devices. Due to their unique synthesis via CVD polymer-
ization, parylene coating conforms to a surface; however, molecularly controlled structuring of parylene particles with precise spatial arrangements over multiple hierarchical levels, tailored shapes, sizes, and porosities has not been realized. Here, we report metal−organic framework (MOF)-templated cyclophane-based CVD polymerization with morphology and porosity transcription of the host framework. This catalyst- and initiator-free template approach forms a CVD polymer in three-dimensional (3D) confined nanospaces. The paraxylene diradicals (monomers) formed during CVD polymerization using [2.2]paracyclophane (PCP) as a precursor molecule (Gorham process) diffuse into confined nanochannels of the crystalline 3D HKUST-1 MOF and spontaneously polymerize to generate parylene@MOF composites. Here, MOF confined geometries can act as a sacrificial template and, upon removal of the coordinating metal ions, facilitate the formation of templated parylene particles with the transcription of the parent crystal HKUST-1 morphology and porosity. The templated morphologies depend on subtle changes of the chemical composition of the CVD precursors as indicated by clear morphological differences observed for parylene particles synthesized from pristine and chlorosubstituted PCPs. Atomistic ab initio and classical molecular dynamics simulations and energy barrier calculations using the density functional theory−nudged elastic band method of the poly(para-xylylene) precursors in an HKUST-1 confinement were performed to study the mechanism of the molecularly controlled structuring of parylenes. The structuring process is driven by the differences in the diffusion properties of diradicals precursors inside the HKUST-1 MOF. MOF-templated CVD polymerization with implementation of 3D spatial arrangements establishes a new platform for the synthesis of functional parylene polymer particles with structurally controlled morphologies, where molecularly imprinted structuring is modulated by the choice of both the template and the CVD precursor.