The influence of N‐vinyl pyrrolidone on polymerization kinetics and thermo‐mechanical properties of crosslinked acrylate polymers

Polymerization of multifunctional acrylate monomers generates crosslinked polymers that are noted for their mechanical strength, thermal stability, and chemical resistance. A common reactive diluent to photopolymerizable formulations is N‐vinyl pyrrolidone (NVP), which is known to reduce the inhibition of free radical photopolymerization by atmospheric oxygen. In this work, the copolymerization behavior of NVP was examined in acrylate monomers with two to five functional groups. At concentrations as low as 2 wt %, NVP increases the polymerization rate in copolymerization with multifunctional acrylate monomer. The relative rate enhancement associated with adding NVP increases dramatically as the number of acrylate double bonds changes from two to five. The influence of NVP on polymerization kinetics is related to synergistic cross‐propagation between NVP and acrylate monomer, which becomes increasingly favorable with diffusion limitations. This synergy extends bimolecular termination into higher double bond conversion through reaction diffusion controlled termination. Copolymerizing concentrations of 5–30 DB% NVP with diacrylate or pentaacrylate monomer also increases Young's modulus and the glass transition temperature (T_g) in comparison to neat acrylate polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4062–4073, 2007     

Hybrid acrylate‐oxetane photopolymerizable systems

Simultaneous free radical and cationic photopolymerizations of mixtures of multifunctional acrylate and oxetane monomers were carried out to provide hybrid interpenetrating network polymers. The use of “kick‐started” oxetanes in which oxetane monomers are accelerated by the use of small amounts of certain highly substituted epoxides provides dual independent radical and cationic systems with similar rates of photopolymerization leading to homogeneous interpenetrating networks. The combined photopolymerizations are very rapid and afford crosslinked network films that are colorless, hard, and transparent. The networks display no indications of phase separation. The use of this technology in various applications such as coatings, 3D imaging, and for composites is discussed. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 594–601     

Influence of the secondary functionality on the radical‐vinyl chemistry of highly reactive monoacrylates

The impact of secondary functionalities on the radical‐vinyl chemistry of monoacrylates characterized by secondary functionalities that dramatically enhance their polymerization rate was elucidated utilizing experimental and computational techniques. Firstly, bulk interactions affecting the acrylate reactivity towards photopolymerization were removed by polymerizing at 5 wt % monomer in 1,4‐dioxane. Following deconvolution of bulk interactions impacting reactivity towards photopolymerization, a linear correlation between average polymerization rates and Michael addition reaction rate constants was observed on a logarithmic scale. This result indicates that the presence of the secondary functionality intramolecularly alters the monomer chemistry in a manner which impacts both of these distinct reaction types in a similar manner. These monomers exhibited reduced activation energies in both Michael addition and photopolymerization reactions as compared to hexyl acrylate. Reduction up to 20 ± 8 kJ mole^?1was observed for Michael addition reactions and 12 ± 1 kJ mole^?1 for photopolymerization reactions, thereby explaining the higher reactivity of the acrylates characterized by the secondary functionalities. Cyclic voltammetry experiments conducted to investigate the nature of the acrylic double bonds indicated that the rapidly polymerizing acrylates are more readily reduced as compared to traditional acrylates. Further, a distinct monotonic correlation of the irreversible cathodic peak potentials of the (meth)acrylates to photopolymerization and Michael addition reactivity was observed. The computationally estimated acrylic LUMO energies characterized by the secondary functionalities (?2.3 eV to ?2.7 eV) were also found to be lower relative to hexyl acrylate (?2.2 eV). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4859–4870, 2009     

Monitoring photopolymerization reactions with optical pyrometry

This article describes the development of optical pyrometry (OP) as a new analytical technique for the continuous monitoring of the progress of both free‐radical and cationic photopolymerizations. The method is rapid, reproducible, and very easy to implement. A temperature profile of a photopolymerization can be obtained. Preliminary studies have shown that the temperatures of some polymerizing monomers can easily reach temperatures in excess of 250 °C. The effects of the mass and reactivity of the monomer, light intensity, structures, and concentrations of the photoinitiators and monomers as well as the presence or absence of oxygen on various free‐radical and cationic photopolymerizations were examined with this method. Coupling of real‐time infrared spectroscopy with OP provides a convenient method for simultaneously monitoring both the chemical conversion and the temperature of a photopolymerization. This combined technique affords new insights into the effects of temperature‐induced autoacceleration on the course of photopolymerizations. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 579–596, 2003     

Photoinitiating monomers based on di‐ and triacryloylated hydroxylamine derivatives

The purpose of our study was to design a new class of acrylate‐based monomers with an UV‐cleavable heteroatom bond, offering the possibility to initiate radical polymerization upon irradiation with UV‐light. A method to derive the double bond conversion from the ATR‐IR spectra of the monomers and the cured polymers was employed, that enabled us to calculate the theoretical polymerization heats of the new monomers. Their photopolymerization properties were determined by Photo Differential Scanning Calorimetry. Surprisingly, some of these new compounds exhibited high photoinitiation activity, comparable to well‐established Type II photoinitiator systems like benzophenone/triethanolamine. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 392–403, 2009     

Germanes as efficient coinitiators in radical and cationic photopolymerizations

In this article, germanes are presented as new coinitiators for both radical and cationic photopolymerization processes. For the free radical polymerization process, the newly proposed structures are characterized by efficiencies similar or better than the reference amine. Germyl radicals are also found to be excellent initiators for free radical promoted cationic photopolymerization (FRPCP) of an epoxy resin. The associated reactivity is even better under air. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3042–3047, 2008     

Combination of transition metal carbonyls and silanes: New photoinitiating systems

The recently developed silyl radical chemistry is used in combination with transition metal carbonyls MC (dimanganese(0) decacarbonyl; dirhenium decacarbonyl; cyclopentadienyl iron(II) dicarbonyl dimer) for both free radical promoted cationic photopolymerization (FRPCP) and free radical photopolymerization (FRP). The newly developed photoinitiating systems (MC/silane and MC/silane/iodonium salt) are highly efficient under air. Photopolymerization profiles obtained upon a visible light irradiation delivered by a xenon lamp show that high conversion can be easily achieved after a 400 s exposure. Sunlight irradiations under air can also lead to tack free coatings. The processes associated with the metal carbonyl radical/silane interactions are investigated by Laser Flash Photolysis (LFP) and ESR‐Spin Trapping (ESR‐ST) experiments. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1830–1837, 2010     

Living radical photopolymerization induced grafting on thiol–ene based substrates

The formation of reactive substrates with iniferter‐mediated living radical photopolymerization is a powerful technique for surface modification, which can readily be used to facilitate the incorporation of a variety of surface functionalities. In this research, the photopolymerization kinetics of novel bulk thiol–ene systems have been compared with those of typical acrylate and methacrylate systems when polymerized in the presence of the photoiniferter p‐xylene bis(N,N‐diethyl dithiocarbamate) (XDT). In the presence of XDT, the thiol–ene systems photopolymerize more quickly than the traditional acrylate and methacrylate systems by one to two orders of magnitude. Fourier transform infrared spectroscopy has been used to monitor the photografting kinetics of various monomers on dithiocarbamate‐functionalized surfaces. Furthermore, this technique has been used to evaluate surface‐initiation kinetics and to emphasize the influence of bulk substrate properties on grafting kinetics. Finally, photopatterning has been demonstrated on a dithiocarbamate‐incorporated thiol–ene substrate with conventional photolithographic techniques. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2134–2144, 2005     

Kinetic investigations on the photopolymerization of di- and tetrafunctional (meth)acrylic monomers in polymeric matrices. ESR and calorimetric studies. I. Reactions under irradiation

The photopolymerization of several di- and tetrafunctional (meth)acrylic monomers in the presence of a styrene–butadiene–styrene polymeric matrix (SBS) has been studied. Electron spin resonance spectroscopy (ESR) and differential scanning photocalorimetry (photo-DSC) were used as monitoring techniques to identify the photogenerated radicals and analyze photopolymerization profiles, radical environments, and radical secondary reactions. The study of the photopolymerization and/or photocrosslinking reactions of these monomers in the solid media was carried out by taking into consideration different factors, such as the influence of both monomer and photoinitiator structures on the hydrogen abstraction in the binder with formation of benzylic and allylic radicals, the polymerization of the monomers itself and the hydrogen abstraction reaction in the polymerized acrylic chains. Finally, irradiation of the system SBS/photoinitiator in the absence of monomer was also accomplished. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2775–2783, 1998     

Reactivity of oxetane monomers in photoinitiated cationic polymerization

Studies of the onium salt photoinitiated cationic ring‐opening polymerizations of various 3,3‐disubstituted oxetane monomers have been conducted with real‐time infrared spectroscopy and optical pyrometry. The polymerizations of these monomers are typified by an extended induction period that has been attributed to the presence of a long‐lived tertiary oxonium ion intermediate formed by the reaction of the initially formed secondary oxonium ion with the cyclic ether monomer. Because the extended induction period in the photopolymerization of these monomers renders oxetane monomers of limited value for many applications, methods have been sought for its minimization or elimination. Three general methods have been found effective in markedly shortening the induction period: (1) carrying out the photopolymerizations at higher temperatures, (2) copolymerizing with more reactive epoxide monomers, and (3) using free‐radical photoinitiators as synergists. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3205–3220, 2005     

Photopolymerization of ternary thiol–ene/acrylate systems: Film and network properties

Photocurable, ternary‐component mixtures of a 1:1 molar multifunctional thiol–ene (trithiol and triallyl ether) blend and a 16‐functional acrylate based monomer have been photopolymerized, and the final film properties of the ternary crosslinked networks have been measured. The photopolymerization kinetics, morphology, and mechanical and physical properties of the films have been investigated with real‐time infrared, atomic force microscopy, and dynamic mechanical analysis. The photopolymerization process is a combination of acrylate homopolymerization and copolymerizations of thiol with allyl ether and acrylate functionalities. The tan δ peaks of the photopolymerized ternary systems are relatively narrow and tunable over a large temperature range. The morphology is characterized by a distinct phase‐separated nanostructure. The photocured thiol–ene/acrylate ternary systems can be made to exhibit good mechanical properties with enhanced energy absorption at room temperature by the appropriate selection of each component concentration. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 822–829, 2007.     

Full control of polymer properties during the two‐stage on‐demand free‐radical photopolymerization of fiber‐reinforced polymers

The effect of a two‐step free‐radical photopolymerization of an acrylate resin on the polymer properties in the presence of glass fibers is studied. It is found that a first irradiation leading to a partial conversion is effective for the fabrication of a preimpregnated glass‐fiber composite, which can be further processed and fully polymerized through a second irradiation. DMA analysis evidences the formation of a first relatively soft polymer embedding unreacted double bonds during the preirradiation. Further process allows the completion of the photopolymerization together with a reinforcement of the polymer network. This obviously affects the final mechanical properties of the photocomposite. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1440–1447     

Systematic Investigation of the Photopolymerization of Imidazolium-Based Ionic Liquid Styrene and Vinyl Monomers

The use of ionic liquids (ILs) as media in radical polymerizations has demonstrated the ability of these unique solvents to improve both reaction kinetics and polymer product properties. However, the bulk of these studies have examined the polymerization behavior of common organic monomers (e.g., methyl methacrylate, styrene) dissolved in conventional ILs. There is increasing interest in polymerized ILs (poly(ILs)), which are ionomers produced from the direct polymerization of styrene-, vinyl-, and acrylate-functionalized ILs. Here, the photopolymerization kinetics of IL monomers are investigated for systems in which styrene or vinyl functionalities are pendant from the imidazolium cation. Styrene-functionalized IL monomers typically polymerized rapidly (full conversion ≤1 min) in both neat compositions or when diluted with a nonpolymerizable IL, [C₂mim][Tf₂N]. However, monomer conversion in vinyl-functionalized IL monomers is much more dependent on the nature of the nonpolymerizable group. ATR-FTIR analysis and molecular simulations of these monomers and monomer mixtures identified the presence of multiple intermolecular interactions (e.g., π–π stacking, IL aggregation) that contribute to the polymerization behaviors of these systems. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2364–2375     

Synthesis and characteristics of photopolymerized benzophenone

Photopolymerization is extensively used in today's industrial field due to its advantages of rapid reaction, environmental friendly, energy saving and economical. Benzophenone is a most common photoinitiator (PI) using in photopolymerization because of its superior ability to initiate acrylate monomers. However, the intrinsic nature of initiator molecules is that they migrate out of polymer network, which limits its application, especially in the domain of food packaging materials. A polymerizable PI 4‐methylbenzophenone acrylate (MBPAc) was synthesized by a facile procedure and characterized by ¹H NMR, ¹³C NMR, and MS analyses. A systematic study of the photopolymerization kinetics of MBPAc was explored by the Real‐Time Fourier Transform Infrared Spectrometer. The results show that the final conversion and photopolymerization rate of acrylate monomers are closely related to the factors of their chemical structure, viscosity, functionality and light intensity, which means MBPAc is an efficient PI. Ultraviolet‐visible Spectrophotometer and vitro cytotoxicity measurement results indicate that the noncytotoxic MBPAc shows significantly lower migration than its analogue. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 313–320     

A new visible light sensitive photoinitiator system for the cationic polymerization of epoxides

This communication reports the development of an efficient three‐component visible light sensitive photoinitiator system for the cationic ring‐opening photopolymerization of epoxide monomers and epoxide functional oligomers. The photoinitiator system consists of camphorquinone in combination with a benzyl alcohol to generate free radicals by the absorption of visible light. Subsequently, the radicals participate in the free radical chain induced decomposition of a diaryliodonium salt. The resulting strong Brønsted acid derived from this process catalyzes the cationic ring‐opening polymerization of a variety of epoxide substrates. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 866–875, 2009     

Photopolymerization kinetics of tributylmethylammonium‐based (meth)acrylate ionic liquids and the effect of water

Polymerizable ionic liquids were synthesized from the neutralization reaction between tributylmethylammonium hydroxide and methacrylic or acrylic acid, and their photopolymerization kinetics have been determined. The acrylate monomer polymerization rate exhibited a profound dependence on the water content as follows: the monomer viscosity was a strong function of the water content, increasing substantially as the water content increased from less than 5 to 30%. For the tributylmethylammonium acrylate with less than 5% water, the viscosity was 2000 times greater than that of butyl acrylate. The high viscosity is proposed to reduce both the propagation and termination steps. Both monomers exhibited an increase in rate with temperature. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3766–3773, 2008     

INVESTIGATION OF THE USE OF POLY(3,4-EPOXY-1-BUTENE) IN FREE RADICAL PHOTOPOLYMERIZATIONS

ABSTRACT

The use of poly(3,4-epoxy-1-butene) (polyEPB) in photoinduced free radical polymerizations has been investigated. It was observed that the inclusion of polyEPB into these photopolymerizations has several beneficial effects. In combination with aromatic ketones, polyEPB functions as a hydrogen donor to form a highly effective photoinitiator for the polymerization of acrylate monomers. At the same time, polyEPB undergoes facile autoxidation that serves to mitigate inhibition effects due to oxygen during free radical photopolymerizations. PolyEPB is an effective chain transfer agent that tends to increase both the rate and conversion in photoinduced crosslinking polymerizations in which multifunctional monomers are employed. Lastly, polyEPB is a interesting matrix-modifying agent that becomes incorporated into the resin matrix during photopolymerization due to photoinduced grafting reactions.     

Design and synthesis of highly photopolymerizable styrenyl compounds in solid‐state photoinitiated polymerization

We designed a new type of styrenyl compound applicable to conventional photopolymerization systems, aiming at the production of polymers with improved mechanical properties, resistance to chemicals, and elevated glass‐transition temperatures (T_g's). A series of styrenyl monomers bearing 2,5‐dithio‐1,3,4‐thiadiazole groups were prepared, and their reactivity was studied in solid‐state photopolymerization initiated by 2‐(4′‐methoxystyryl)‐4,6‐bis(trichloromethyl)‐1,3,5‐triazine. These monomers exhibited much higher polymerization rates than usual, and the final conversion nearly reached completion, despite the relatively high T_g of the solid‐state photopolymerization system. Even at temperatures below T_g, the polymerization proceeded without a ceiling phenomenon. These features were explained by intermolecular interactions between the monomers that induced monomer alignments effective for solid‐state polymerization, large excess free volumes arising from rotation around the methylthio groups, and intramatrix radical migration leading to encounters with the remaining monomers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3227–3242, 2003     

丙烯酸酯/液晶复合体系的光聚合动力学

采用光差示扫描量热分析,研究了以2, 4, 6-三甲基苯甲酰基-二苯基氧化膦(TPO)为光引发剂、丙烯酸异辛酯(EHA)和三羟甲基丙烷三甲基丙烯酸酯(TMPTA)为单体、液晶为P0616A的丙烯酸酯/液晶复合体系在-40~80℃的光聚合动力学。研究表明：丙烯酸酯/液晶复合体系光聚合的自动加速现象非常显著,聚合反应速率和表观动力学常数在聚合过程中均存在最大值。随着反应温度的提高,体系的最终转化率、最大聚合反应速率(Rpmax)均明显提高,当反应温度高于20℃后,其增长均趋于平缓。随着体系中液晶含量的增加,体系的Rpmax呈下降趋势,体系的聚合反应转化率随时间的增长速率较慢,但是最终转化率差别不大,均接近80%。随着UV光强的增高,体系的Rpmax和最终转化率均明显提高, 体系的阈值光强约为4 mw/cm2。而随着体系平均官能度的增加,体系的Rpmax和最终转化率则呈下降的趋势。     

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