Abstract
A vapor-phase process, involving the sublimation of an ice substrate/template and the vapor deposition of a maleimide-functionalized poly-p-xylylene, has been reported to synthesize an advanced porous material, with readily clickable chemical interface properties, to perform a Michael-type addition of a maleimide functionality for conjugation with a thiol group. In contrast to the conventional chemical vapor deposition of poly-p-xylylenes on a solid surface that forms thin film coatings, the process reported herein additionally results in deposition on a dynamic and sublimating ice surface (template), rendering the construction of a three-dimensional, porous, maleimide-functionalized poly-p-xylylene. The process seamlessly exploits the refined chemical vapor deposition polymerization from maleimide-substituted [2,2]paracyclophane and ensures the preservation and transformation of the maleimide functionality to the final porous poly-p-xylylene products. The functionalization and production of a porous maleimide-functionalized poly-p-xylylene were completed in a single step, thus avoiding complicated steps or post-functionalization procedures that are commonly seen in conventional approaches to produce functional materials. More importantly, the equipped maleimide functionality provides a rapid and efficient route for click conjugation toward thiol-terminated molecules, and the reaction can be performed under mild conditions at room temperature in a water solution without the need for a catalyst, an initiator, or other energy sources. The introduced vapor-based process enables a straightforward synthesis approach to produce not only a pore-forming structure of a three-dimensional material, but also an in situ-derived maleimide functional group, to conduct a covalent click reaction with thiol-terminal molecules, which are abundant in biological environments. These advanced materials are expected to have a wide variety of new applications.
Highlights
Porous materials, owing to their remarkable interface properties, have been widely applied in sensing, catalysis, biomedical, drug delivery, adsorption/desorption applications, etc. [1,2,3,4]
To fabricate the proposed maleimide-functionalized poly-p-xylylene materials, ice templates were first constructed, and a reported mechanism showed that the vapor deposition of polychloro-p-xylylene on a dynamic substrate of the sublimating ice can result in a final porous and three-dimensional polychloro-p-xylylene material [17]
Other poly-p-xylylene systems, such as its functionalized derivatives [15] and the maleimide-functionalized poly-p-xylylene proposed which have been deposited using the same conventional chemical vapor deposition (CVD) polymerization, should be extendable and applied on an ice substrate. In this experiment, the preparation of the ice substrates/templates was enabled by using a polydimethylsiloxane (PDMS) mold, with the dimensions of 300 μm × 300 μm × 300 μm, and resulted in ice cubes with the same dimensions, analogous to how ice cubes are made
Summary
Porous materials, owing to their remarkable interface properties, have been widely applied in sensing, catalysis, biomedical, drug delivery, adsorption/desorption applications, etc. [1,2,3,4]. Many bio-orthogonal reactions have been developed that enable the efficient formation of a specific product in complex environments, which is beneficial for biological research [11] These fascinating chemistries, have seldom been exploited during the fabrication of porous materials and are sporadically seen using complicated synthetic approaches [12] or by post-modification attempts, which involve using harsh solvents or potentially harmful chemicals during the modification process [13,14]. Compared to the maleimide-functionalized coating prepared previously [33], the current monolith poly-p-xylylene comprised (i) porous and structural information in three dimensions and (ii) a maleimide functionality that exhibits specific reactivity toward thiol-terminated biomolecules This unique fabrication process, and the resultant polymer product, combines interface properties from its surface porosity, topology, and specific chemical reactivity and provides a robust tool with enhanced synergistic ability for biointerface engineering. Depending on the feed amount of the starting material, the deposition rate was adjusted to approximately 0.5 to 1.0 Å/s and monitored by a real-time quartz crystal microbalance (QCM) sensor (STM-100/MF, East Syracuse, NY, USA) mounted in the deposition chamber
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