Sunlight-induced crosslinking of 1,2-polybutadienes: access to fluorescent polymer networks

The efficient sunlight-induced crosslinking of 1,2-polybutadienes to generate fluorescent patterns with spatial resolution is reported. The employed photochemical conjugation method is based on a nitrile imine-mediated tetrazole-ene cycloaddition (NITEC), which proceeds under UV-light irradiation ([small lambda]max = 312 nm) at ambient temperature in the absence of any catalyst. The NITEC reaction between 1-pentene and a newly designed di-linker consisting of two photosensitive diaryl-substituted tetrazoles joined by a tetraethylene glycol spacer was investigated in an initial study. Detailed characterization of the small molecule model study was performed by size exclusion chromatography (SEC), UV-Vis and fluorescence spectroscopy, as well as electrospray-ionization mass spectrometry (ESI-MS), which is also employed for monitoring the reaction kinetics (100 % conversion in 20 min). Finally, light-triggered crosslinking is accomplished with two 1,2-polybutadienes of different molar masses. The crosslinking reaction parameters, such as concentration, di-linker fraction and reaction time were optimized via a SEC analysis and gravimetric determination of gel fractions. The applicability of the novel crosslinking technology for generating spatially controlled highly fluorescent gel patterns is demonstrated in a solvent-free reaction in 2 h in sunlight. The current study, in summary, thus introduces an efficient light-triggered technology platform for crosslinking polymers carrying non-activated double bonds.