Photochemistry of 2,6‐di(4′‐azidobenzylidene)‐methylcyclohexanone in polymer matrices

Abstract

2,6-Di(4 0 -azidobenzylidene)-methylcyclohexanone (ABC) was one of the most used photoinitiators in negative photoresists industry, rendering insolubility of the resist films at short UV exposure times (several minutes). Although the photodecomposition of aromatic azides is very well established, the peculiarities of the irradiation medium impose specific reaction pathways for arylnitrenes. In this study, photoreactions of arylnitrenes resulted from ABC photolysis were applied in the photoinitiated crosslinking of 1,2-polybutadiene (1,2-PB), under soft monochromatic UV irradiation (365 nm). To elucidate the crosslinking mechanism, studies on a model compound were performed. 3-Methyl-1-butene was chosen to simulate the monomeric unit of 1,2-PB. As a support in photoproducts identifying and with the purpose of a deeper investigation of the ABC photochemistry alone, ABC was photolysed in a rigid matrix of poly(methyl methacrylate).

Degradable multi(aryl azide) star copolymer as universal photo-crosslinker for elastomeric scaffolds

“…The BA concentrations tested (2wt% and 5wt%) were chosen based on the data found in literature [20]. Gel fractions results (Fig This lack of crosslinking despite aryl-azide photoactivation was attributed to the formation of azo-dimers and termination reactions that do not allow crosslinking [21]. Furthermore, molecular weight of the PLA50PLU copolymer did not influence significantly the crosslinking efficiency compared to nature of the UV-bulb used (metal halide bulb versus mercury bulb) and BA concentration.…”

“…Only at a 50/50 ratios, a slightly lower gel fraction was obtained for the PLA50PLU50 compared to PLA50PLU100 or PLA50PLU200. This result might be due to a lower chain entanglement combined with higher chain mobility that partly prevent reaction between the active nitrene species and the polymeric chains [21]. It is to note that this independence of crosslinking efficiency over the molecular weight of the polymer is a unique feature considering the fact that most degradable elastomers are obtained from low molecular weight pre-polymers.…”

“…The main advantages of this approach are i) that any polymer containing CH bonds can potentially be crosslinked and ii) that crosslinking efficiency should be largely independent of the polymer molecular weight. Besides PHBV, this UV-reactive crosslinker has been recently employed with other polymers including poly(methyl methacrylate) (PMMA) or polybutadiene (PB) [21][22][23][24]. However, the outcome of the cited studies is unclear with results that do not corroborate.…”

“…Another limiting point to consider in the search for photo-crosslinked degradable elastomers for soft tissues scaffolding, is the spatial limitation of photo-crosslinking. According to Avadenei et al [21], azide cross-linking agent is restricted to micro-scale materials. Among a wide range of process to build architected materials dedicated to soft-tissue reconstruction [27][28][29][30], electrospinning process that produces micro/nano-scale fibers appears therefore as the most appropriate choice to build scaffolds using aryl-azide crosslinker.…”