Photo-curing kinetics of hydroxyethyl acrylate (HEA): synergetic effect of dye/amine photoinitiator systems

International Journal of Industrial Chemistry https://doi.org/10.1007/s40090-019-00197-7 RESEARCH Photo‑curing kinetics of hydroxyethyl acrylate (HEA): synergetic effect of dye/amine photoinitiator systems Nouria Bouchikhi1,2 · Manel Bouazza2 · Salah Hamri1,2 · Ulrich Maschke3 · Djahida Lerari1 · Faycal Dergal1 · Khaldoun Bachari1 · Lamia Bedjaoui‑Alachaher2 Received: 27 September 2018 / Accepted: 3 December 2019 © The Author(s) 2019 Abstract The aim of this study is to examine and evaluate several dye/amine systems as photoinitiators for photopolymerization of 2-hydroxyethyl acrylate (HEA) monomer under visible light conditions. For this purpose, a series of dye/amine photoinitiators were formed using methylene blue (MB) or acridine orange (AO) as photosensitizers, and triethanolamine (TEOA), ethyl 4-(dimethylamino) benzoate (EDMAB), trioctylamine (TOA), and N,N-diméthylallylamine (DMAA) as co-initiators. The photopolymerization kinetic of the HEA monomer in the presence of proposed dye/amine systems was performed using Fourier-transform infrared spectroscopy (FTIR) analysis and the synergetic effect of the dye/amine photoinitiators systems on the photopolymerization efficiency was examined. Interestingly, (MB/EDMAB) system shows the better reactivity with a total conversion of HEA monomer. Keywords Dye · Amine · Visible light · Phototransformation · Photopolymerization Introduction Visible light-activated photoinitiators (VALP’s) have received considerable attention owing to their involvement in visible light-induced polymerization. The attractiveness and potential use of visible light in material science steam essentially from its harmless character and higher penetration ability as compared for example with UV light [1, 2]. Indeed, from a polymer chemistry perspective, photopolymerization using visible light offers a plethora of advantages encompassing solvent-free formulation, rapid curing at ambient temperature and appealing cost-effective bias that have led to broad application in industrial fields such as * Nouria Bouchikhi 1 Centre de Recherche Scientifique et Technique en Analyses Physico-chimiques, BP 384, Zone Industrielle Bou‑ismail, RP 42004 Tipaza, Algeria 2 Laboratoire de Recherche sur les Macromolécules, Faculté des Sciences, Université de Tlemcen, BP119, 13000 Tlemcen, Algeria 3 Unité Matériaux et Transformations UMET (UMR CNRS N_8207) Bâtiment C6, Université Lille 1-Sciences et Technologies, 59655 Villeneuve d’Ascq, France pigmented coatings, paints, dental adhesives, holographic records, inks and electronics [3–5]. As far as photopolymerization is concerned, a careful selection of the photoinitiator (PI) is crucial to this process. Two types of PI are currently used. TypeI photoinitiator, in which a hemolytic cleavage of its species is taking place, triggers the free radical formation and hence, the initiation of the photopolymerization. In type II, where in the generally accepted mechanism more than two species are involved, the radicals are formed by an electron transfer reaction succeeded by hydrogen transfer between a photosensitizer (PS) and a co-initiator [6]. As a typical example of typeII photoinitiator, VALP’s are generally based on a combination of a carbogenic dye acting as PS and an amine-bearing compound as co-initiator [7–9]. In some cases, addition of electron acceptors such as iodonium or sulfonium salts to the mixture has been reported in the literature [10–12]. In as much, the photosensitization step is determining for subsequent evolution of the polymerization process as whole, practical requirements ought to be implemented for achieving high conversion rates. These include: (i) good miscibility of PI with monomers, (ii) maximum light absorption, (iii) high quantum yield coupled to long lifetime of the triplet state and, (iv) excellent hydrogen-donating character of 13 Vol.:(0123456789) International Journal of Industrial Chemistry the co-initiator. In other words, of the four above-mentioned requirements, three are of physical nature and only (iv) is chemically driven parameter [13, 14]. As application of these concepts, photopolymerization using LED’s as visible light source has been recently reported. A remarkable enhancement of light absorbance as well as improved efficiency of VALP’s was achieved through the use of panchromatic visible light irradiation [15, 16]. In a forward move, high monomer conversion rates for both cationic and radical photopolymerization were reported by a subtle combination of LED’s and redox systems [6, 17]. However, chemical hazards inherent to the use of powerful oxidizing agents in polymerization processes have severely limited the generalization of this option, even though a soft redox system based on copper complex–phosphine interaction was introduced for methacrylate polymerization [18]. From a literature survey, notwithstanding the impressive efforts that were devoted to implement a safe and efficient photopolymerization using visible laser or LED’s, all of which are grouped in physical type strategies, a reliable chemical approach based on a careful selection of dye/amine (PS system) deserves to be considered. In an attempt to investigate the efficiency of dye/amine couple as PI system in the photopolymerization of hydroxyl ethyl acrylate (HEA) under visible light irradiation in soft condition (halogen lamp, air atmosphere), we have prepared five PI couples, namely MB/TEOA, AO/TEOA, MB/ DMAA, MB/TAO and MB/EDMAB. The photochemical behavior of MB and AO were first evaluated by UV–Visible spectroscopy. In the next task, we turned our attention to the selection of PI, by focusing on the synergistic effect between PS and its amine co-initiator partner. In each case, HEA polymerization was monitored by FTIR. The conversion yield is discussed in terms of PI system chemical combination. Materials and methods O OH (a) O N S+ N (b) Cl- N Instrumentation and characterization Absorption spectra of dyes and photoinitiator systems (dye/ amine) were recorded on Agilent Cary 60 UV–Visible 13 N N (c) OH (d) N HO OH N (e) (f) Reagents and chemicals All the reactants were used as received and are shown in Fig. 1. 2-Hydroxyethyl acrylate (HEA), methylthioninium chloride (methylene blue MB), 3-N,3-N,6-N,6-N tetramethylacridine-3,6 diamine (acridine orange AO), triethanolamine (TEOA), N,N-dimethylallylamine (DMAA), trioctylamine (TOA) and ethyl 4- (dimethylamino) benzoate (EDMAB) were purchased from Aldrich. N O O N (g) Fig. 1  Chemical structures of reagents. a HEA, b MB, c AO, d TEOA, e DMAA, f TOA, g EDMAB International Journal of Industrial Chemistry Conv (%) = A0 − At × 100, A0 (1) where A0 is the initial absorbance at 1635 cm−1 and At the absorbance value at irradiation time t. A DSC Q2000 from TA Instruments was used for differential scanning calorimetry (DSC) analyses under nitrogen atmosphere. Samples of 5–7 mg were sealed in aluminum pans and placed in th (...truncated)