Acenaphthoquinoxaline Derivatives as Dental Photoinitiators of Acrylates Polymerization.

Ilona Pyszka,Beata Jędrzejewska

doi:10.3390/ma14174881

Abstract

A series of dyes based on the acenaphthoquinoxaline skeleton was synthesized. Their structure was modified by introducing electron-withdrawing and electron-donating groups, increasing the number of conjugated double bonds and the number and position of nitrogen atoms, as well as the arrangement of aromatic rings (linear or angular). The dyes were investigated as a component in the photoinitiating systems of radical polymerization for a potential application in dentistry. They acted as the primary absorber of visible light and the acceptor of an electron, which was generated from a second component being an electron donor. Thus, the radicals were generated by the photoinduced intermolecular electron transfer (PET) process. Electron donors used differed in the type of heteroatom, i.e., O, S and N and the number and position of methoxy substituents. To test the ability to initiate the polymerization reaction by photoinduced hydrogen atom transfer, we used 2-mercaptobenzoxazole as a co-initiator. The effectiveness of the photoinitiating systems clearly depends on both the modified acenaphthoquinocaline structure and the type of co-initiator. The lower amount of heat released during the chain reaction and the polymerization rate comparable to this achieved for the photoinitiator traditionally used in dentistry (camphorquinone) indicates that the studied dyes may be valuable in this field.

Highlights

The most versatile and implemented polymerization method is radical polymerization
The structures of acenaphthoquinoxaline derivatives have been modified to adjust their spectroscopic properties, especially absorption properties, so as to obtain compounds suitable to effectively initiate polymerization upon visible light irradiation. They differ in the number of conjugated double bonds as well as the type of substituent, i.e., an electron acceptor (–COOH) and electron donor (–OCH3 ) groups
The acenaphthoquinoxaline (AN1–AN8) derivatives were synthesized by the condensation of the appropriate diamines with acenaphthoquinone in glacial acetic acid according to the method described in literature [58,59,60] and shown in Schemes 5 and 6

Summary

Introduction

The most versatile and implemented polymerization method is radical polymerization. Free radicals are formed by a number of different mechanisms They can be generated directly from an initiator that undergoes thermal or photolytic dissociation or may be formed in bimolecular processes following a photoinduced intermolecular electron (or proton) transfer [1,2,3]. Depending on the type and position of the functional groups, the unimolecular fragmentation of the precursor occurs within the bond located at position α (α-photodissociating initiators) [8,9,10,11] or β (β-photodissociating initiators) in relation to the carbonyl group [12] This group of photoinitiators includes organic compounds with weak O–O, S–S, N–S and C–N bonds in the molecule [13,14,15,16]

Methods

Results

Conclusion