Synthesis and photopolymerization kinetics of benzophenone piperazine one‐component initiator

A one‐component type II photoinitiator (PDBP), based on 4‐hydroxybenzophenone (HBP), acryloyl chloride, and piperazine, was synthesized and its structure was confirmed by ¹H‐NMR. The photopolymerization kinetics of the photoinitiator was studied by real‐time Infrared spectroscopy (FT‐IR). It indicated that PDBP was a more effective photoinitiator than that of BP/triethylamine (TEA). The rate of polymerization, final conversion increased and the induction period shortened with increase in PDBP concentration, light intensity, and amine concentration. The kinetics of photopolymerization for TPGDA incorporating PDBP in the presence of different tertiary amines as the initiating system indicated that the PDBP/TEA combination exhibited the highest polymerization rates among the PDBP/amine combinations. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis and photopolymerization of novel multifunctional vinyl esters

Novel mono‐ and multifunctional vinyl ester monomers containing thioether groups were synthesized via an amine‐catalyzed Michael addition reaction between vinyl acrylate and multifunctional thiols. Using photo‐differential scanning calorimetry and real‐time Fourier transform infrared (RTIR) spectroscopy, the polymerization kinetics and oxygen inhibition of the homopolymerizations of the vinyl ester monomers were investigated. The effect of the vinyl ester and thioether group on acrylate/vinyl ester and thiol/vinyl ester copolymerizations was determined using real‐time IR spectroscopy to monitor polymerization rates of acrylate, vinyl, and thiol groups simultaneously. Polymerization of the vinyl esters used was found to be relatively insensitive to oxygen inhibition. We propose that the thioether group is responsible for reducing oxygen inhibition by a series of chain transfer/oxygen‐scavenging reactions. In polymerization of a acrylate/vinyl ester mixture both in nitrogen and in air, the vinyl ester monomer significantly enhances the polymerization rates and the conversion of the acrylate double bonds via plasticization of the crosslinked matrix and reduction of inhibition by oxygen. Ultimately, the vinyl ester monomer is incorporated into the polymer network. Thiol/vinyl ester free‐radical copolymerization is much faster than either thiol/allylether copolymerization or vinyl ester homopolymerization. The electron‐rich vinyl ester double bonds ensure rapid copolymerization with thiol. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4424–4436, 2004     

Synthesis of oligomeric urethane dimethacrylates with carboxylic groups and their testing in dental composites

Carboxyl urethane dimethacrylate oligomers with poly(ethylene oxide) sequences in the structure were synthesized and examined in photopolymerizable resins that could better adhere to various kinds of materials, including tooth substrates. Aspects of the morphogenesis of dental composites formed through a photochemically initiated radical copolymerization of the carboxylic derivatives, in addition to other partners encountered frequently in such materials, were studied comparatively with the corresponding urethane dimethacrylate monomer. The effect of a small quantity of a carboxylic macromer (ca. 10%) on the formation of a network with a non‐carboxyl urethane dimethacrylate oligomer (90%) as a potential substitute for diglycidyl methacrylate of bisphenol A and a filler (1/1 70% Aerosil/glass) was visualized by fluorescence spectroscopy with a pyrene methanol probe. The results showed the following: (1) the degree of conversion in the formulations into which carboxyl urethane dimethacrylate was incorporated decreased with increasing poly(ethylene oxide) chain length, (2) the formation of excimers was inhibited in the derived composites, and (3) an important quenching of the monomer fluorescence emission with the UV–vis irradiation time was observed in the formulation containing a filler (Aerosil+Zr/Sr glass). Preliminary testing of the resin composites suggested that all urethane oligomers containing carboxylic acid could lead to dental materials with reduced polymerization shrinkage and good mechanical properties. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1956–1967, 2007     

Factors affecting the sensitivity to acid inhibition in novel acrylates characterized by secondary functionalities

Here we demonstrate that acrylates exhibit significant rate reductions in the presence of small concentrations of protic acids (0.1–0.5 wt %) compared with the bulk monomer concentration. Dramatically different sensitivities to acid inhibition, differing by up to 2 orders of magnitude, are exhibited for various acrylates. This study examines the various factors that cause enhanced sensitivity toward acid inhibition in novel acrylates characterized by carbamate and cyclic carbonate secondary functionalities. Acid inhibition studies conducted in the presence of a highly polar solvent, such as propylene carbonate, have been performed to determine the impact of overall medium polarity and the extent of acid dissociation on the sensitivity to acid inhibition. The studies depict only a twofold increase in the parameters associated with acid inhibition, upon the addition of 70 wt % propylene carbonate, in comparison with an increase of 2 orders of magnitude for the novel acrylates. These studies indicate that the susceptibility to acid inhibition is primarily determined by the stability of the hypothesized radical–acid complex as well as its propensity to terminate with other species in the system and not by the extent of acid dissociation in the system. Furthermore, it is implied that the stability of the radical–acid complex and its propensity to terminate with other species in the system are dominated by intramolecular interactions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1287–1295, 2007     

Novel photocurable multifunctional acrylate monomers containing perfluorinated aromatic units and their copolymers for photonic applications

We designed and synthesized novel UV‐curable multifunctional acrylate monomers with perfluorinated aromatic units and their copolymers. The UV‐curable multifunctional acrylate monomers with perfluorinated aromatic units were synthesized as follows. Perfluorinated aromatic methylmethane derivatives were prepared through the reaction of pentaerythritol with hexafluorobenzene and decafluorobiphenyl in the presence of sodium hydride. They were sequentially substituted with 2,2,3,3,4,4,5,5‐octafluoro‐6‐(tetrahydropyran‐2‐yloxy)‐hexan‐1‐ol, and this yielded hydroxy‐functional compounds after tetrahydropyran deprotection. Finally, the reaction of the resultant hydroxy compounds with acryloyl chloride generated the perfluorinated multifunctional acrylate monomers in high yields of greater than 85%. The novel photocrosslinked and perfluorinated copolyacrylates, obtained after the UV and thermal curing of these monomers, satisfied the material requirements for photonic devices. Most of these copolymers were thermally stable over 370 °C, and their glass‐transition temperatures were not detected because of their highly crosslinked nature. The refractive indices of the copolymers ranged from 1.410 to 1.441. The refractive indices of the photocrosslinked and perfluorinated copolyacrylates were easily tuned by the variation of the copolymer composition. Some of these copolymers exhibited a birefringence of less than 0.0003. This was much lower than the birefringence of fluorinated polyacrylate‐based materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6375–6383, 2004     

Photopolymerization of acrylates without photoinitiators with short‐wavelength UV radiation: A study with real‐time fourier transform infrared spectroscopy

This article reports on the UV photopolymerization of acrylates without photoinitiators. Initiation of the reaction was achieved by direct excitation of the acrylates during irradiation with short‐wavelength UV light by use of the 222‐nm emission of a KrCl^* excimer lamp. The reactivity of various acrylates was studied by real‐time Fourier transform infrared–attenuated total reflection spectroscopy. The rate and the extent of the reaction within the layer were strongly dependent on the depth of penetration of UV light, which was determined by the molar extinction coefficient of the acrylate. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 894–901, 2004     

Polymerization kinetics and volume relaxation behavior of photopolymerized multifunctional monomers producing highly crosslinked networks

Multifunctional monomers (trimethylol propane trimethacrylate, trimethylol propane triacrylate, pentaerythritol tetraacrylate, and dipentaerythritol monohydroxy pentaacrylate) were photopolymerized with 2,2-dimethoxy-2-phenylacetophenone as the photoinitiator to produce highly crosslinked networks. The volume shrinkage behavior and the reaction kinetics were studied under various reaction conditions. The volume shrinkage and maximum functional group conversion were dependent on the number of functional groups, type of functional group, and the curing conditions. The maximum functional group conversion was also dependent on the reaction temperature. All the polymerized systems exhibited a strong coupling between the volume relaxation and the reaction kinetics. The kinetic constants were also determined as a function of conversion, and the termination mechanism was found to be reaction diffusion dominated even at low conversions. The importance of these results on the prediction of the reaction behavior for multifunctional monomers producing highly crosslinked polymers is discussed. © 1994 John Wiley & Sons, Inc.     

Synthesis and characteristics of novel chelate fiber containing amine and amidine groups

A polyacrylonitrile (PAN) fiber was adopted for the backbone of a chelate polymer and poly(acrylo‐amidino ethylene amine) (PAEA) was prepared through a one‐step reaction between the PAN fiber and ethylenediamine (EDA). The maximum removal capacity and degree of substitution were 7.8 meq per gram of dried PAEA and 98%, respectively. The PAEA was tested as an adsorbent in single and two‐component metal aqueous solutions under changing pH. The Cu²⁺ ion accomplished maximum adsorption amount at pH 3 and the order of maximum adsorbed amounts on PAEA is Cu²⁺ > Ag⁺ > Zn²⁺ > Ni²⁺ > Pb²⁺ in molar basis. FT‐IR spectroscopy was employed to characterize the chemical bonding in metal aqueous solutions and surface morphology was examined using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Copyright © 2004 John Wiley & Sons, Ltd.     

Castor oil based hyperbranched urethane acrylates and their performance as UV-curable coatings

Castor oil (CO) based hyperbranched urethane acrylates (HBUAs), namely C10-IH and C20-IH, were synthesized by modifying the hydroxyl groups of first (C10)- and second (C20)-generation of CO-based hyperbranched polyesters with isocyanate-bearing semi-adducts (IPDI-HEA). Herein, the C10 and C20 polyesters were prepared using the renewable CO as a B₃ core molecule and dimethylolpropionic acid as an AB₂ monomer via a pseudo-one-pot condensation procedure. For comparison, a CO-based urethane acrylate (CO-IH) was synthesized by directly modifying the hydroxyl groups of CO with IPDI-HEA. The structure-property relationship of the UV-cured films was investigated in detail. Consequently, the number of terminal urethane acrylates greatly influenced their final properties. The tensile strength of the C20-IH based UV-cured sample could be improved by 129% in comparison with the CO-IH based sample, and its pencil hardness reached up to 7H. Furthermore, the chemical resistance tests and the morphology study proved that the C20-IH based UV-cured coatings exhibited excellent chemical stability and superb microstructure. These improvements can be attributed to the unique oligomer architecture that combined the structural features of hyperbranching, castor oil chains and multiple urethane acrylates.     

Relevance of linked dye‐coinitiator in visible three‐component photoinitiating systems: Application to red light photopolymerization

A new visible light photoinitiating system (PIS) containing a linked dye‐coinitiator dyad and a nondissociative electron donor was evaluated and compared with unlinked three components systems. Our results show that in the physical mixture of the three component PIS, addition of the nondissociative donor decreased the Rp to a great extent, whereas in combination with the dyads an increase in Rp is observed. The results were explained based on faster intramolecular electron transfer in linked pairs and point out the importance of linked initiator in three‐component PIS for the first time. This system is the first example of three‐components system with a nondissociative donor that would be useful for long life coating formulation. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4325–4330     

Near‐infrared spectroscopy investigation of water effects on the cationic photopolymerization of vinyl ether systems

Real‐time Fourier transform near‐infrared spectroscopy has been used to monitor monomer and water concentrations simultaneously during cationic vinyl ether photopolymerization. The use of near‐infrared peak area methods allows the water content to be conveniently and nondestructively determined in any monomer or polymer for which the water peak has previously been calibrated by gravimetric analysis. Although the shape of the absorption band due to absorbed water in a monomer changes with the quantity of water, the integrated intensity from about 5350 to 4900 cm^?1 can be correlated directly to the water concentration, and this region is well removed from the vinyl‐based absorption at approximately 6190 cm^?1. This approach provides a highly informative, dynamic technique for examining the influence of moisture on polymerization reactions. Significant differences have been observed in the effects of absorbed water on the cationic photopolymerization kinetics of vinyl ether monomers with or without an ? OH group. Along with the rapid consumption of water coupled to vinyl ether polymerization, acid‐catalyzed hydrolysis reactions have also been spectroscopically observed, giving rise to the formation of aldehyde groups. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1985–1998, 2004     

The influence of a radical structure on the kinetics of photopolymerization

A radical initiation ability of new initiating systems in photopolymerization of 2‐ethyl‐2‐(hydroxymethyl)‐1,3‐propanediol triacrylate has been investigated and presented. The evaluation of alkyltriphenyl‐ and tetraalkylborates, iodonium salts, N‐alkoxypyridinium salts, maleimides, phthalimides, 1,3,5‐triazine derivatives and others as a free radical source in combination with suitable photosensitizer for radical polymerization of triacrylate is described. It is assumed that the photochemical decomposition of a coinitiator molecule results in formation of free radicals, which further initiate polymerization. The order of activity of free radical sources on kinetic of photopolymerization was also presented. Different initiator activity can be explained by the difference in the decomposition rate constant and the reactivity of radicals formed toward the double bond of monomer. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1575–1589     

Visible light photopolymerization: Synthesis of new fluorone dyes and photopolymerization of acrylic monomers using them

Several 3-alkoxy-5, 7-diiodo-6-fluorones (λ_max ≈ 470 nm) have been synthesized and evaluated as initiators for photopolymerization triggered with the 515.5 nm line of an Ar⁺ laser. 2-Acyl- and 2-alkyl-4,5,7-triiodo-3-hydroxy-6-fluorones were also tested at 515.5 nm. 9-Cyano-2-Acyl- and 9-cyano-2-alkyl-4,5,7-triiodo-3-hydroxy-6-fluorones were studied and could be excited with the 632 nm line of a He–Ne laser. Dyes with long linear carbon chain alkoxy groups at C-6 showed larger molar extinction coefficients and formed polymers with better mechanical properties than did compounds with shorter carbon chains, or did the corresponding C-6 phenols. The optimum side chain length of the C-6 ether alkyl group is between 4–7 carbon atoms. With longer carbon chain alkoxy groups at C-8, e.g., octyl, the mechanical properties of the formed polymers are inferior to systems formed with the butyl isomer as photoinitiator. In the case of alkoxy groups with branched alkyl groups (e.g., 2-ethylbutyl), the relationship between dye structure and the properties of the polymers formed is less straightforward. Though the dyes react from their triplet state, the fluorescence quantum yields of the dyes and the performance of the dyes as photoinitiators appear directly related. © 1995 John Wiley & Sons, Inc.     

Synthesis and photopolymerization kinetics of lower odor benzophenone derivative photoinitiators

Seven lower odor benzophenone (BP) derivatives (2a, 2b, 2c, 2d, 3a, 3b, 3c) based on 4‐hydroxybenzophenone(1) were synthesized and characterized by ¹H NMR, Mass, UV–Vis absorption spectroscopy. electron spin resonance (ESR) spectroscopy was carried out to research the photopolymerization mechanism. The kinetics of photopolymerization was studied by differential scanning photocalorimetry (photo‐DSC). The results showed that 2a–d with uni‐BP moiety were more effective photoinitiators (PIs) than 3a–c with bi‐BP moieties, and 2c was the most effective one which could be a promising candidate for BP alternative in practical application. Copyright © 2009 John Wiley & Sons, Ltd.     

Obtaining of hybrid nanocomposites by simultaneous photopolymerization of some urethane monomers and photoinduced formation of gold nanoparticles

Urethane–urea dimethacrylates were synthesized and used in the preparation of nanocomposites containing gold nanoparticles (Au NPs) in situ photogenerated during the UV‐curing process in the absence of reducing agent. A study of the photopolymerization kinetics showed that the photoreactivity of the monomers alone or in combination with a dual urethane benzophenone (BP) macromer is dependent on the nature of photoinitiator (Irgacure819, BP/amine) and the formulation composition. It was found that the addition of 1 wt % AuBr₃ in monomers slightly improved the polymerization rate and the degree of conversion. The formation of Au NPs into the network was confirmed through UV–vis, XRD, EDX, SAXS, and TEM analyses, the last indicating the existence of NPs with size around 8.5 nm and spherical/triangle shapes. On addition of 10 wt % 2[N‐methacryloyloxyethyl‐(N'‐2‐thioethyl)] (urea) in formulation, the Au NPs (200 nm) became predominantly cubic/hexagonal in shape. The composite films emit fluorescence at 575 nm, and this property could be exploited in the field of fluorescent bio/sensors. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 728–738     

A New Model and Measurement Technique for Dynamic Shrinkage during Photopolymerization of Multi‐Acrylates

Summary: A novel experimental set‐up has been devised to measure simultaneously, in real time, the conversion and shrinkage of multi‐acrylates during photopolymerization. The data show that the current practice of assigning the excess volume entirely as excess free volume is inappropriate as this leads to an increasing fractional free volume with conversion. We propose to partition the excess volume into free and occupied volume components. The new model produces satisfactory results.

Experimental set‐up for the simultaneous collection of shrinkage and conversion data.     

Real‐time Fourier transform infrared study of the free‐radical ultraviolet‐induced polymerization of a hybrid sol–gel. II. The effect of physicochemical parameters on the photopolymerization kinetics

Free‐radical photocurable hybrid sol–gel materials have gained special interest during the last decades. Compared to thermally processed materials, they present the advantages of fast curing, low energy consumption, and spatiotemporal control of the reaction. Although comprehension of the photochemical step is fundamental, little is known about the characteristic of photochemistry in this kind of material. Real‐time Fourier transform infrared spectroscopy was used to study the photopolymerization of a hybrid sol–gel upon ultraviolet irradiation. Various photoinitiator systems were tested for their efficiency in inducing the polymerization of pendant polymerizable moieties anchored on a partially condensed silicate network. The presence of O₂ and the nature of the polymerizable function were shown to be crucial factors in the photoinduced process. The effects of the photoinitiator concentration and light intensity were also studied. These results were explained in terms of classical kinetic models developed for all‐organic photopolymers to point out the distinctive aspects related to the use of photoinitiated polymerization in hybrid sol–gel materials. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 831–840, 2003     

Influence of the alkene structure on the mechanism and kinetics of thiol–alkene photopolymerizations with real‐time infrared spectroscopy

The effect of the chemical structure on the reactivity of alkenes used in thiol–ene photopolymerizations has been investigated with real‐time infrared spectroscopy. Model studies of thiol–ene photoreactions with various monofunctional hydrocarbon alkenes and the monofunctional thiol ethyl‐3‐mercaptopropionate have been performed to identify and understand structure–reactivity relationships. The results demonstrate that terminal enes react very rapidly with thiol, achieve complete conversion, and are independent of the aliphatic hydrocarbon substituent length. Disubstitution on a single carbon of a terminal ene significantly reduces the reactivity, whereas substitution on the carbon α to the terminal ene has a minimal influence on the reactivity. Internal trans enes display reduced reactivity and a lower overall conversion and deviate from the standard thiol–ene reaction mechanism because of steric strain induced by 1,3‐interactions. The reactivity and conversion of internal trans enes decrease as the substituents on the ene become larger, reaching a minimum when the substituent size is greater than or equal to that of propyl groups. Internal cis enes react rapidly with thiol; however, they undergo a fast isomerization–elimination reaction sequence generating the trans ene, which proceeds to react at a reduced rate with thiol. The reactivity of cyclic enes is dictated by ring strain, stereoelectronic effects, and hydrogen abstractability. The reactivity trends in the model studies have been used to explain the photopolymerization mechanism and kinetics of a series of multifunctional thiol–ene systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6283–6298, 2004     

Synthesis and polymerization of phosphorus‐containing acrylates

Novel phosphorus‐containing acrylate monomers were synthesized by two different routes. The first involved the reaction of ethyl α‐chloromethyl acrylate and t‐butyl α‐bromomethyl acrylate with diethylphosphonoacetic acid. The monomers were bulk‐ and solution‐polymerized at 56–64 °C with 2,2′‐azobisisobutyronitrile. The ethyl ester monomer showed a high crosslinking tendency under these conditions. The selective hydrolysis of the ethyl ester phosphonic ester compound was carried out with trimethylsilyl bromide, producing a phosphonic acid monomer. In the second route, ethyl α‐hydroxymethyl acrylate and t‐butyl α‐hydroxymethyl acrylate were reacted with diethylchlorophosphate. The bulk homopolymerization and copolymerization of these monomers with methyl methacrylate and 2,2′‐azobisisobutyronitrile gave soluble polymers. The attempted hydrolysis of the monomers was unsuccessful because of the loss of the diethylphosphate group. The relative reactivities of the monomers in the photopolymerizations were also compared. The ethyl α‐hydroxymethyl acrylate/diethylphosphonic acid monomer showed higher reactivity than the other monomers, which may explain the crosslinking during the polymerization of this monomer. The reactivities of other derivatives were similar, but the rates of polymerization were slow in comparison with those of methyl methacrylate. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3221–3231, 2002