Microfluidic stack reactors for the mass synthesis of polymer brushes

Polymer brush (PB) coatings represent a powerful method of tuning surface physicochemical properties in a broad number of fields including biosensing, which require PB synthesis onto 10-100 or more substrates per day. Typically, PBs are synthesized by surface-initiated atom transfer radical polymerization (SI-ATRP) in Schlenk reactors that need large volumes of solutions, imposing substantial economic challenges for mass synthesis, as typically only 0.1% or less of monomers are polymerized. Microfluidic synthesis offers a promising alternative for reducing chemical consumption; however, questions remain on how to perform such synthesis on a mass scale and furthermore, if PBs are of similar quality like those prepared via standard means. Here we present a microfluidic stack reactor designed for an efficient and user-friendly mass synthesis of PBs onto planar substrates. This reactor, 3D printed via stereolithography, consists of repeating units that are easy to fabricate and when stacked together, create a single fluidic pathway connecting an adjustable number of substrates, enhancing polymerization efficiency by over 100-fold. We employed the stack reactors to synthesize various PB structures (homogenous, random copolymer, block copolymer) combining two monomers commonly used in biosensing known for their antifouling properties: zwitterionic poly(carboxybetaine methacrylamide) (pCBMAA) and non-ionic poly[N-(2-hydroxypropyl) methacrylamide] (pHPMAA). Characterization by IRRAS, ellipsometry, XPS, contact angle, and SPR, confirmed that PBs synthesized in stack reactors are comparable, if not superior, to those synthesized via standard SI-ATRP methods. These reactors are thus a promising tool for efficient, large-scale production of PB coatings and have potential for many applications.