Solid and Hollow Poly(p-xylylene) Particles SynthesisviaMetal–Organic Framework-Templated Chemical Vapor Polymerization

Abstract

Poly(para-xylylene)s are a unique class of chemical vapor deposition (CVD)-based polymers, generally referred to their tradename "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 polymerization, 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.

The Chemistry of Metal Organic Framework Materials

“…They made hydrogels modelled into films, tablets, and pellets, which retained the intrinsic porosity of the MOF. Begum et al engaged MOFs as a template for chemical vapor deposition in a process wherein para -xylene diradicals (monomers) diffused into the HKUST pores and spontaneously polymerized to generate parylene@MOF composites . After removing the coordinating metal ions, they obtained templated parylene particles with the transcription of the parent HKUST-1 morphology and porosity.…”

“…More recently, MOF glasses, a disordered form of MOFs, are finding niche applications. This virtual collection catalogues recent MOF advances featured in Chemistry of Materials from 2022 to 2023, − with an accompanying editorial by Laura Gagliardi and Omar Yaghi that outlines three critical future directions for MOFs …”

Chemical and Topological Control of Surfaces Using Functional Parylene Coatings

“…In a recent work by Tsotsalas and co-workers, crystal-controlled CVD polymerization using metal–organic frameworks (MOFs) as the template was used to create porous microparticles ( Figure 6 ). 74 They used PPX and PPX-C for the deposition and HKUST-1 as a sacrificing MOF crystal. After CVD deposition, PPX@MOF composites were formed and then placed in a basic solution in order to remove the template and create monolithic PPX particles.…”

Design Strategies for Structurally Controlled Polymer Surfaces via Cyclophane‐Based CVD Polymerization and Post‐CVD Fabrication

“…[ 75 ] Employing the crystalline 3D HKUST‐1 MOF as a sacrificial template, we have demonstrated parylenes particle synthesis with morphology and porosity transcription inside the host 3D framework. [ 76 ] The para ‐xylene diradicals formed during CVD polymerization 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 dissolution/removal of the coordinating metal ions, facilitate the formation of templated hollow and solid parylene particles with the transcription of the parent crystals HKUST‐1 morphology and porosity.…”

“…A) Schematic illustration of poly(p-xylylene)s polymerization via CVD using MOF crystals as a template; EDTA stands for ethylenediaminetetraacetic acid. B) Crystal shape and cross section of the parylene particles PPX and PPX-Cl before and after the focused ion beam (FIB-cuts).A,B) Reproduced with permission [76]. Copyright 2022, American Chemical Society.…”