(602c) Vapor Solvent Strategy for Regulating Monomer Reactivity in iCVD

Initiated Chemical Vapor Deposition (iCVD) has revolutionized the preparation of high-quality conformal polymer films with excellent control over composition and properties at the nanoscale. However, iCVD still presents challenges in regulating the polymerization reaction, particularly for monomers with active functional groups, which often exhibit abnormal deposition kinetics, low molecular weight, and low reactivity during copolymerization. Here, we introduce a strategy that utilizes a vapor solvent to modulate monomer reactivity. We focus on 1-vinyl imidazole (1VI), which is known for its uncontrollable deposition rates and low molecular weights due to the formation of "dead radicals" through chain transfer to the imidazole group. By replacing the inert carrier gas, Argon, with acetic acid (AA), we demonstrated a significant increase in molecular weight, from 6.6k to 12.0k, leading to an increased elastic modulus from 3.5 to 4.7 GPa. Meanwhile, we achieved a linear and rapid deposition rate with respect to surface monomer concentration, resulting in a 280% increase. This was due to the enhanced monomer adsorption through molecular complex formation between 1VI and AA while suppressing chain transfer to reactive groups through protonation of AA to the imidazole. We also verified this concept with other monomers, such as amine-containing monomers with rampant chain transfer. We found that the vapor solvent selectively interacted with polar monomers. Therefore, we demonstrated that during copolymerization of 1VI with a reactive and non-polar crosslinker, divinyl benzene (DVB), AA selectively enhanced the adsorption of 1VI molecular complexes and suppressed side reactions, increasing the apparent reactivity of 1VI by an order of magnitude. This approach facilitates the rapid and controllable manufacturing of high-quality polymer films with a high content of functional groups. The use of vapor solvent strategy provides a powerful approach for controlling monomer reactivity, thereby enhancing the control over iCVD polymerization, particularly those containing biologically active groups. The benefits of this technology are wide-ranging, potentially extending to fields such as biomedical devices, antifouling coatings, chemical sensing, and separation.