Abstract
Diaryliodonium salts are well-established compounds in free radical chemistry and are already used as photoinitiators (free radical or cationic polymerization), but the presence of counter anions is a strong drawback. Indeed, a counter anion is always required (e.g., SbF6−) leading to potential toxicity issues or release of HF. In the present paper, counter anion-free and fluoride-free aryliodonium salts are proposed, that is, aryliodonium ylides (AY) are studied here as new and efficient additives for radical chemistry and an example is provided for the camphorquinone (CQ)/amine based photoinitiating systems (PISs) for the polymerization of thick (1.4 mm) and thin (20–13 µm) methacrylates under air and blue light irradiation. The newly proposed PISs, for example, CQ/amine/AY, presented excellent polymerization performances and good bleaching properties were obtained after polymerization. Real-time Fourier transform infrared spectroscopy (RT-FTIR) was used to monitor the photopolymerization profiles. The chemical mechanisms involved were investigated using electron spin resonance (ESR).
Highlights
Photoinitiated polymerization has been widely used in the past decades and has found many industrial applications, such as 3D printing, coatings, inks, adhesives, and so on
Two types of polymerization can be distinguished depending on the nature of the photoinitiator used; free radical photopolymerization and cationic polymerization [1,2]
The cationic part of the diphenyliodonium salt is responsible for light absorption whereas the nature of the counter anion governs the strength of the acid formed during photolysis [1]
Summary
Photoinitiated polymerization has been widely used in the past decades and has found many industrial applications, such as 3D printing, coatings, inks, adhesives, and so on. Two types of polymerization can be distinguished depending on the nature of the photoinitiator used; free radical photopolymerization and cationic polymerization [1,2]. The latter presents numerous advantages compared to the former, such as insensitivity to oxygen, low shrinkage during curing, dark polymerization after the removal of the light source, and so on [3] Two families of cationic photoinitiators are generally used: iodonium and sulfonium salts [1,4,5]. The cationic part of the diphenyliodonium salt is responsible for light absorption whereas the nature of the counter anion governs the strength of the acid formed during photolysis [1].
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