Abstract
Eleven di- and trifunctional compounds based on a core-pyrene π structure (Co_Py) were synthesized and investigated for the formation of free radicals. The application of two- and three-component photoinitiating systems (different Co_Pys with the addition of iodonium or sulfonium salts, alkyl halide or amine) was investigated in detail for cationic and radical photopolymerization reactions under near-UV–vis light. The proposed compounds can behave as new photocatalysts. Successful results in terms of rates of polymerization and final conversions were obtained. The strong MO coupling between the six different cores and the pyrene moiety was studied by DFT calculations. The different chemical intermediates are characterized by ESR and laser flash photolysis experiments. The mechanisms involved in the initiation step are discussed, and relationships between the core structure, the Co_Py absorption property, and the polymerization ability are tentatively proposed.
Highlights
Free radical sources are encountered in various areas such as organic chemistry, biochemistry and polymer chemistry
They are usable in free radical polymerization (FRP), where the PIs work as either cleavable type I PIs or uncleavable type II PIs in dependence of couples formed by the PI and hydrogen or electron donors (r1 in Scheme 1)
PIs may be used in free-radical-promoted cationic polymerization (FRPCP), in which the produced radical R is oxidized by an onium salt, e.g., Ar2I+, to form Ar2I and a cation R+ suit
Summary
Free radical sources are encountered in various areas such as organic chemistry, biochemistry and polymer chemistry. In the field of polymer photochemistry applied to photopolymerization reactions, they are referred to as photoinitiators (PI) [1]. These PIs are usable in two scenarios, both of which are light induced. They are usable in free radical polymerization (FRP), where the PIs work as either cleavable type I PIs or uncleavable type II PIs in dependence of couples formed by the PI and hydrogen or electron donors (r1 in Scheme 1). PIs may be used in free-radical-promoted cationic polymerization (FRPCP), in which the produced radical R is oxidized by an onium salt, e.g., Ar2I+, to form Ar2I and a cation R+ suit-.
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