Precisely Controlled Microsphere Design via Visible‐Light Cross‐Linking of Functional Prepolymers

A new strategy for particle synthesis is enabled by utilizing modern synthetic, polymer, and photochemical techniques to facilitate the synthesis of highly narrow–disperse multifunctional microspheres from visible‐light induced crosslinking of prepolymers in both a single and dual polymer system. The approach requires no stabilizers, bases, or initiators, and proceeds at ambient temperature to yield microspheres with a tunable size range (0.25–5 µm) in less than 4 h, depending largely on solvent composition, but also polymer concentration (2–10 mg mL^?1), ratio, and irradiation intensity (3–20 W). Critically, the visible‐light induced dimerization reaction exploited herein enables simple functional particle syntheses via a single polymer system. Underpinned by an in‐depth kinetic analysis of the particle formation as well as a detailed small molecule study, the mechanism for particle formation is also elucidated. Importantly, inherent advantages of the system are exploited for surface functionalization of residual acrylate and hydroxyl groups (generating inherently fluorescent particles).     

Cover Picture: Three‐Dimensional SiCN Ceramic Microstructures via Nano‐Stereolithography of Inorganic Polymer Photoresists (Adv. Funct. Mater. 9/2006)

An inorganic polymer photoresist was successfully synthesized for the first time with high photosensitivity and a high ceramic yield. Furthermore, it is shown by Kim, Yang, and co‐workers on p. 1235 that a nano‐stereolithography process linked with careful pyrolysis of this resin paves the way for the fabrication of 2D and 3D ceramic microstructures (examples of which are shown on the cover) with high spatial resolution. We report a newly synthesized inorganic polymer photoresist with a high ceramic yield by the functionalization of polyvinylsilazane (KiON VL20) with 2‐isocyanatoethyl methacrylate via linkage or insertion reaction routes. The chemistry of the synthesis and the pyrolytic conversion as well as the mechanical evaluation were investigated by using various analytical instruments. We show for the first time that this photosensitive resin is a novel precursor for the fabrication of complex 3D SiCN ceramic microstructures with a 210 nm resolution via a two‐photon absorbed crosslinking process and subsequent pyrolysis at 600 °C under a nitrogen atmosphere. Moreover, the dimensional deformation during pyrolysis was significantly reduced by adding silica nanoparticles as a filler. In particular, the ceramic microstructures containing 40 wt % silica nanoparticles exhibited a relatively isotropic shrinkage owing to its sliding free from the substrate during pyrolysis.