Photobase generators with AIE property used for visual observations of thiol–epoxy near‐UV/visible photopolymerization

Abstract

AbstractPhotopolymerization of thiol–epoxy resins initiated by photobase generators (PBGs) is a very good way to prepare specific polymeric products. However, the lack of near‐UV or visible light emitting diode (LED) light‐sensitive PBGs that can release strong bases to effectively catalyze this reaction and synchronously monitor the polymerization progress still is a problem. In this work, a series of such PBGs are successfully synthesized by modifying common aggregation‐induced emission (AIE) molecules, including triphenylamine and tetraphenylethylene and then neutralizing them with strong bases like 1,8‐diazabicyclo[5.4.0]undec‐7‐ene, 1,5‐diazabicyclo[4.3.0]non‐5‐ene, and 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD). The obtained PBGs show very good light absorption ability from 365 to 405 nm. They can generate free strong bases under near‐UV/visible LED light radiations as a result of photodecarboxylation reaction to catalyze the rapid thiol–epoxy photopolymerization. The TBD‐based PBGs have the best final monomer conversion above 60% due to their strongest alkalinity. Increasing viscosity during the polymerization process can trigger an AIE phenomenon of the PBGs. A linear correlation equation of the AIE intensity with the monomer conversion can be found, which is helpful for quantitatively monitoring the photopolymerization progress. More importantly, qualitative observations of the brightness changes of the resulting AIE lights are very useful to visualize the photopolymerization progress, which may find some applied potential in industry.