(565i) Solventless Synthesis of pH-Responsive Polymer Sponge Coatings

Porous polymer materials are desired for a variety of applications such as catalysis, filtration, sensors, optical devices, and biomaterials. Typically, porous polymer materials are synthesized using solution-phase methods. Solution-phase methods face challenges related to solvent compatibility and surface tension effects. In this work, we develop a solventless method to fabricate stimuli responsive poly(methacrylic acid) (PMAA) polymer sponge coatings The absence of organic solvents renders our process compatible with substrates that may swell or dissolve and also provides a more ecofriendly synthesis route since there is no solvent waste. We synthesize the materials by modifying the initiated chemical vapor deposition (iCVD) process. In the iCVD process, monomer and initiator vapors are introduced into a vacuum chamber and the initiator molecules are broken into free radicals by a hot filament array to begin polymerization. In our modified process, we use a thermoelectric cooler to achieve very low substrate temperatures that lead to freezing of the monomer as solid pillar-like microstructures.[1]^,[2] In our current study, we show that using a higher monomer flow rate and lower reactor pressure results in a sponge-like porous morphology characterized by micrometer size pores, pore interconnectivity, and high surface area to volume ratio. The carboxylic acid functional group in the PMAA sponge coating allows for controlled dissolution in different pH solutions.

[1] Dianat, G.; Movsesian, N.; Gupta, M. Process-Structure-Property Relationships for Porous Membranes Formed by Polymerization of Solid Monomer by a Vapor-Phase Initiator. Macromolecules 2018, 51, 10297-10303

[2] Dianat, G.; Movsesian, N.; Gupta, M. Vapor Deposition of Functional Porous Polymer Membranes. ACS Applied Polymer Materials 2020, 2, 98– 104