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New High‐Power LEDs Open Photochemistry for Near‐Infrared‐Sensitized Radical and Cationic Photopolymerization
Author(s) -
Schmitz Christian,
Pang Yulian,
Gülz André,
Gläser Marina,
Horst Joachim,
Jäger Martin,
Strehmel Bernd
Publication year - 2019
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201813696
Subject(s) - cationic polymerization , photopolymer , photochemistry , chemistry , polymerization , cyclopentene , moiety , polymer chemistry , radical polymerization , polymer , organic chemistry , catalysis
Cyanines derived from heptamethines were investigated in combination with iodonium salts as initiators of the radical polymerization of tripropylene glycol diacrylate and epoxides derived from bisphenol‐A‐diglycidylether. A new near‐infrared (NIR) LED prototype emitting at 805 nm with an exposure intensity of 1.2 W cm −2 facilitated initiation of both radical and cationic polymerization using sensitizers derived from cyanines. This new light‐emitting device has brought new insight into the photochemistry of cyanines with the general structure 1 because a combination of photonic and thermal processes strongly influences reaction pathways. In particular, cationic cyanines comprising a cyclopentene moiety and diphenylamino group in the center initiated the cationic polymerization of epoxides. Selective oxidation of this unit explains why specifically these derivatives may function as initiators for cationic polymerization. In contrast, when the diphenylamino group was replaced by a barbital group at the meso ‐position cationic polymerization of epoxides was not initiated.