Synthesis, photochemistry and cross-linking of visibly sensitised photopolymers of PVA based on (E)-2-(4-Formylstyryl)-3,4-dimethylthiazolium Methylsulfate

Abstract

The synthesis and cross-linking of new, visibly sensitive high-speed water-soluble photoresists are reported. Attempts to sensitise our existing poly(viny1 alcohol) (PVA)-based photopolymer into the visible region with various additives at between 1 and 5 mol% have been unsuccessful. The additives may disrupt the formation or configuration of the dimeric aggregates previously found to be a prerequisite for cross-linking or have a screening effect absorbing some or all of the photonic energy, thereby preventing excitation of any aggregated chromophore groups.Synthetic modification of the original (€)-2-(4-forrnylstyryI)-3,4-dimethylthiazolium methylsulfate produces chromophores which, when grafted onto PVA, generate photopolymers absorbing in the visible region. (€)-2-[4-(2-Ethylbutoxy)-styryl]-3-methylbenzothiazolium methylsulfate forms a photopolymer with A , , , at 400 nm ; while (€)-2-[2-(2,2-diethoxyethoxy)-4-(N,~-diethylamino)styryl]-3,4-dimethylthiazolium methylsulfate forms a photopolymer with A , , , at 495 nm.Step-wedge analysis, UV absorption and FT-NMR spectroscopy indicate that the thiazolium and benzothiazolium photopolymers cross-link by a [2 + 2lcycloaddition reaction generating interchain cross-links via cyclobutane units. However, the amine photopolymer does not show any evidence of cross-linking, with the stencil being completely washed out during step-wedge analysis. Molecular modelling indicates that the diethoxyethoxy group prevents formation of the aggregates normally formed by electrostatic attractions.This theoretical prediction is confirmed by fluorescence spectroscopy. In high-concentration solutions the thiazolium and benzothiazolium models show significant emission bands relating to excimer or higher-order aggregate species. Upon dilution these bands are blue shifted to wavelengths comparable to those observed for photopolymer films. At very dilute concentrations they are lost and monomer bands appear while for thin films they are lost upon dimerisation. The amine photopolymer shows very weak emission bands unaffected upon exposure. This confirms that very few aggregates are formed, suggesting they are in non-reactive configurations.

Synthesis and transport abilities of new membrane materials incorporating bipyrazolic tripods

“…Cockburn et al described that PVA‐SbQ exhibits fluorescence emitting at about 450 nm in concentrated solutions, while a hypsochromic shift down to about 420 nm occurs upon dilution 33,34. Detailed studies were carried out by Allen et al for PVAs having styrylthiazolium side chains, which are very close to SbQ, to present their peculiar aspect of fluorescence spectra 36. They reported an extraordinarily bathochromic shift of fluorescence down to 530 nm and the corresponding excitation spectra having λ max at 445 nm in concentrated solutions.…”

“…They attempted to detect the presence of the corresponding band through the noisy second derivative spectrum, whereas no band was observable in the corresponding wavelength region of a fundamental absorption spectrum. Nevertheless, they assigned the strange band to a ground‐state dimer acting as a precursor for photocrosslinking, though no data were presented for the fluorescence in film 36…”

Preparation of a Water-Based Photoreactive Azosulphonate-Doped Poly(Vinyl Alcohol) and the Investigation of Its UV Response

“…For example, modern photoresist materials are, in general, formulated in organic solvents, developed in strong alkaline aqueous solutions, and used for the production of circuit boards, flat panel displays, television screens and semiconductor devices [1,2]. In recent years, the development of water-based photoresist has gained more and more attention [3,4,5,6]. The advantage of this system is that it can simplify the imaging process while being more environmentally desirable.…”