Charge-Transfer Complexes as New Inhibitors/Photoinitiatorsfor On-Demand Amine/Peroxide Redox Polymerization

摘要

Redox free-radical polymerizations have widespread applications but still clearly suffer from poor time control of the reaction. Currently, the workability (delay of the gel time) in redox polymerization after mixing is possible thanks to two main types of inhibitors (radical scavengers): phenols and nitroxides. Out of this trend, we propose in this work an alternative strategy for time delaying of the redox polymerization, which is based on charge-transfer complexes (CTCs). Thanks to iodonium salt complexation, the amine (here 4-N,N-trimethylaniline) is proposed to be stored in a CTC equilibrium and is slowly released over a period of time (as a result of the consumption of free amines by peroxides). This alternative strategy allowed us to double the gel time (e.g., from 60 to 120 s) while maintaining a high polymerization efficiency (performance comparable to reference nitroxides). More interestingly, the CTCs involved in this retarding strategy are photoresponsive under visible LED@405 nm and can be used on demand as photoinitiators, allowing (i) spectacular increases in polymerization efficiencies (from 50 °C withoutlight to 120 °C under mild irradiation conditions); (ii) drasticreduction of the oxygen-inhibited layer (already 45% C=C conversionat a 2 μm distance from the top surface) compared to the nonirradiatedsample (thick inhibited layer of more than 45 μm); and (iii)external control of the redox polymerization gel time due to the possiblelight activation.