Abstract
In this work, the use of fluorescent molecular rotors such as 9-(2,2-dicyanovinyl)julolidine (DCVJ) and 2,3-bis(4-(phenyl(4-(1,2,2-triphenylvinyl) phenyl)amino)phenyl)fumaronitrile (TPETPAFN) was proposed for the real-time monitoring of polyurethane (PU) formation in a solution of dimethylacetamide starting with 4,4′-methylenediphenyl diisocyanate (MDI) and different polyethylene glycols (PEG400 and PEG600) as diols. Notably, relative viscosity variations were compared with fluorescence changes, recorded as a function of the polymerization progress. The agreement between these two parameters suggested the innovative use of a low-cost fluorescence detection system based on a LED/photodiode assembly directly mountable on the reaction apparatus. The general validity of the proposed experiments enabled the monitoring of polyurethane polymerization and suggested its effective applications to a variety of industrial polymers, showing viscosity enhancement during polymerization.
Highlights
Global demand for polyurethanes (PUs) is continuously growing, representing one of the main markets of polymeric materials
Their emission characteristics are often attributed to the formation of an equilibrium between a nonemissive twisted intramolecular charge transfer (TICT) state that occurs in solutions and a strongly emissive locally excited (LE) state, which is favored in molecular aggregates or viscous environments [10,15,21,22]
We proposed the use of AIEgens as fluorescent probes (i.e., 9-(2,2dicyanovinyl)julolidine (DCVJ) and 2,3-bis(4-(phenyl(4-(1,2,2-triphenylvinyl) phenyl)amino) phenyl)fumaronitrile (TPETPAFN)) for monitoring the polymerization of PU in a dimethylacetamide solution starting with 4,40 -methylenediphenyl diisocyanate (MDI) and polyethylene glycol (PEG) as diols (Figure 1)
Summary
Global demand for polyurethanes (PUs) is continuously growing, representing one of the main markets of polymeric materials. The fluorescent probes utilized in these studies belong to the category of fluorescent molecular rotors (FMR), which have recently received much attention due to their easy applicability as nonmechanical viscosity sensors and local microviscosity imaging [10,11,12,13,14,15,16,17,18,19,20] Their emission characteristics are often attributed to the formation of an equilibrium between a nonemissive twisted intramolecular charge transfer (TICT) state that occurs in solutions and a strongly emissive locally excited (LE) state, which is favored in molecular aggregates or viscous environments [10,15,21,22].
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