C. Wang, M.M. Zieger, A. Schenzel, M. Wegener, J. Willenbacher, C. Barner-Kowollik, and C.N. Bowman 

Adv. Funct. Mater. 27, 1605317 (2017)

Abstract:

We report the preparation of tetrazole-containing step-growth microparticles and the subsequent use of photoinduced nitrile imine-mediated tetrazole-ene cycloaddition (NITEC) reactions on the particles with spatiotemporal control. Microparticles with an average diameter of 4.1 µm and with inherent tetrazole-ene dual functionality are prepared by a one-pot off-stoichiometric thiol-Michael addition dispersion polymerization. The NITEC reaction is performed efficiently in the solid phase by UV irradiation, leading to the formation of fluorescent pyrozoline adducts, with an estimated quantum yield of 0.7. Particle concentration-independent reaction kinetics are observed and full conversion is reached within 10 min of UV exposure at an intensity of 8 mW cm^-2. Temporal control is demonstrated with either UV or rooftop sunlight irradiation of variable duration. By using two-photon writing with a laser centered around 700 nm wavelength, spatial control is demonstrated with micrometer-scale resolution via surface patterning of the microparticles. Further, microparticles with exclusive tetrazole functionality are prepared by a one-pot, two-step thiol-Michael addition dispersion polymerization. The NITEC reaction between tetrazole-functional particles and acrylates in solution is examined at various tetrazole/alkene molar ratios, and a 10:1 excess of alkenes in solution is found necessary for efficient functionalization.