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 surface plasmon resonance, confirmed that PBs synthesized in stack reactors are comparable to, 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.聚合物刷（Polymer Brush, PB）涂层是一种可有效调控表面物理化学性质的强大手段，其应用领域涵盖生物传感等诸多方向，而这类应用每日需要在10至100片乃至更多基底上合成PB。通常而言，PB通过表面引发原子转移自由基聚合（Surface-Initiated Atom Transfer Radical Polymerization, SI-ATRP）在施兰克反应器中合成，这类反应器需要消耗大量溶液，且单体聚合转化率通常仅为0.1%甚至更低，这给规模化合成带来了沉重的经济成本压力。微流控合成是降低化学品消耗的一种极具潜力的替代方案，但目前仍存在两大待解问题：一是如何实现该合成方式的规模化量产，二是通过微流控合成得到的PB是否能达到传统方法制备产物的同等质量水平。 本研究设计了一款微流控堆叠反应器，可实现平面基底上PB的高效、易操作规模化合成。该反应器采用立体光刻技术3D打印而成，由多个易于加工的重复单元组成，堆叠后可形成一条可连接任意数量可调基底的单一流体通道，将聚合效率提升了100倍以上。我们利用该堆叠反应器合成了多种PB结构，包括均聚物、无规共聚物与嵌段共聚物，所用的两种单体均为生物传感领域常用的抗污型单体：两性离子型聚（甲基丙烯酰胺基羧酸甜菜碱）（pCBMAA）以及非离子型聚[N-(2-羟丙基)甲基丙烯酰胺]（pHPMAA）。通过红外反射吸收光谱（Infrared Reflection-Absorption Spectroscopy, IRRAS）、椭偏仪、X射线光电子能谱（X-ray Photoelectron Spectroscopy, XPS）、接触角测试以及表面等离子体共振（Surface Plasmon Resonance, SPR）对产物进行表征后证实：在堆叠反应器中合成的PB，即便未达到传统SI-ATRP方法制备产物的水平，也至少与其相当，部分性能甚至更优。因此，该反应器是实现PB涂层高效规模化生产的极具潜力的工具，具备广阔的应用前景。