Photopolymerization kinetics of 2-phenylethyl (meth)acrylates studied by photo DSC

The present work deals with the photopolymerization of 2-phenylethyl (meth)acrylates and estimation of their kinetic parameters. Formulations were made by independently homogenizing the monomers with photoinitiators of two different classes. Two different compositions of photoinitiators were used to study the effect of concentration of photoinitiator on cure kinetics. These compositions obtained were tested for photo curing performance using differential photocalorimetry (DPC) or photo DSC under polychromatic radiation. The heat flow against time was recorded for all formulations under isothermal conditions and the rates of polymerization as well as the percentage conversions were estimated. It was observed that due to a longer timescale for reaction diffusion, the methacrylate formulations showed a higher conversion than acrylate formulations. Other parameters such as induction time, maximum rate and conversion attained as well as the time to attain peak maximum were noted. The photopolymerization and kinetic estimations of the formulations including evaluation of kinetic models are discussed.     

Photopolymerization of N,N‐dimethylaminoethylmethacrylate studied by photocalorimetry

Photopolymerization of dimethylaminoethylmethacrylate (DMAEMA) is studied in bulk and in solutions in the presence of different photoinitiators using differential photocalorimetry (DPC). The rate of DMAEMA photopolymerization is slow compared to that of alkylmethacrylates. Bimodal DPC curves of DMAEMA photopolymerization in bulk are obtained. The type I photoinitiators (IRGACURE® 651 and IRGACURE® 1700), which produce free radicals by homolytic fragmentation of photoexcited molecules, are more effective in promoting photopolymerization of DMAEMA. The type II photoinitiators (benzophenone and IRGACURE® 500), which initiate DMAEMA photopolymerization through an H‐abstraction mechanism involving an amino group from the monomer (polymer), are less efficient and favor the formation of partly crosslinked products. The effects of the photoinitiator concentration, temperature, and solvent on the kinetic data are evaluated and discussed. A scheme of photopolymerization of DMAEMA, including the formation of intermediate DMAEMA based macromonomers, is proposed. The main point of the suggested scheme is a high chain transfer to the DMAEMA monomer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 579–588, 2002     

Kinetic studies of a UV-curable powder coating using photo-DSC, real-time FTIR and rheology

The curing kinetics of UV-curable powder coatings based on commercial unsaturated polyesters were monitored using photo-DSC, Real-Time FTIR-ATR and a modified rheometer equipped with a UV source. The effect of physical and chemical factors on curing such as type of photoinitiator, photoinitiator concentration, temperature and atmosphere of curing were evaluated. Coatings containing amounts of photoinitiator from 0.5 to 10 wt% were cured at different temperatures in less than 10 s reaching conversions approximately of 60%. The increase of the temperature of curing reduces the final conversion and also the rate of polymerization due to the chain transfer process and depolymerization that dominates the photopolymerization at high temperatures. The reactivity of the photoinitiators was similar for all the studied photoinitiators apart from benzophenone that was found to be the slowest initiator.     

Photopolymerization of powder suspensions for shaping ceramics

The photopolymerization of suspensions of ceramic powders in monomer solutions is the fundamental step for forming techniques where a liquid suspension is solidified with UV light. The photopolymerization behavior is determined by the properties of the monomer and photoinitiator and by the transport of photons in the suspension. Photon transport in suspensions involves scattering from the particle and absorption by photoinitiators and inert dyes. The photopolymerization behavior is related to the formulation of the suspensions. Proper formulations are discussed for several applications. Techniques for characterization include cure depth measurements, photocalorimetry, and photorheology.     

Photoinitiated cationic polymerization of urethane vinyl ether crystalline monomers

Photoinitiated cationic polymerization of crystalline monomers based on urethane vinyl ether has been investigated by means of differential photocalorimetry (DPC). The crystalline monomers in the melt state polymerized rapidly by exposure to UV light in the presence of a cationic photoinitiator such as an iodonium salt, sulfonium salt or iron arene salt. The kinetics of the cationic photopolymerization process were studied by following k_p[M⁺] as a function of conversion. High conversions, of around 90 %, were obtained for most of the systems investigated. The efficiency of the cationic photoinitiators in initiating the polymerization of the vinyl ether monomers was in the order: iodonium salt > iron arene salt > sulfonium salt. Monomers modified with different saturated alcohols had different activities in photopolymerization, although they all carry the same functional group, i.e. vinyl ether. Copyright © 2005 Society of Chemical Industry     

Kinetics of the nonstationary photopolymerization of diacrylates

The kinetics of non‐stationary photopolymerization (post‐polymeryzation) of some diacrylates at the wide range of initial conversions was investigated. All kinetic curves has two regions: quick and short, slow and long. Experimental results were compared with the kinetic model of the photoinitial three‐dimensional photopolymerization. It was determined that kinetic model allows us to describe the process of the post‐polymerization in the whole range of conversions. The rate constants of the linear break of the primary and secondary chains in the interphase layer were estimated. The increasing rate constants in the interphase are the similar for investigated diacrylates and do not depend on the glicol chain. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1892–1895, 2002     

Photopolymerization of thermoplastic polyurethane/acrylate blends

The kinetics of photopolymerization of thermoplastic polyurethane/acrylate blends have been studied using Real Time Fourier Transform Infrared Spectroscopy (RT-FTIR). The polymerization rate curves were autocatalytic in nature at the initial stage of reaction; then a retardation of the reaction conversion occurred gradually as the polymer matrix became vitrified and the reaction became diffusion controlled. A kinetic rate equation with a diffusion control factor term has been employed to characterize the diffusion-controlled reaction behavior. As the reaction conversion reaches the transition point, at which the maximum value of k_p/k _t ^0.5 in the rate expression is obtained, the reaction becomes to be controlled by diffusion due to the restricted mobility of acrylate macromonomers, resulting in the rapid drop of the polymerization rate even keeping the same reactivity of all the double bonds of acrylate macromonomers. Interpenetrating polymer networks (IPNs) of thermoplastic polyurethane/acrylate systems were formed in the limit of TPU content in the formulations. As the content of thermoplastic polyurethane increased, the polymerization rate increased in the early stage of cure reaction. Blends containing polyurethane up to 30 phr have single glass transition temperature, which indicates that they are miscible in blends and no phase separation has been observed.     

Effect of photosensitive groups on the photoefficiency of polymeric photoinitiators

The purpose of this paper is to determine the effect of photosensitive groups contained in the main chain of polymeric photoinitiator on photopolymerization. Through polycondensation of toluene-2,4-diisocyanate (TDI), different diamines and N-phenyldiethanolamine (PDEA), three novel polymeric photoinitiators containing in-chain benzophenone (BP) and coinitiator amine were synthesized in comparison with the corresponding side-chain ones. FT-IR, ¹H NMR and GPC analyses confirm the structures of all polymers. UV-Vis spectra showed that the maximal absorption and the molar extinction coefficient of polymeric photoinitiator can be greatly improved by the electron donating groups and the imino nitrogen that directly link to BP structure. The photopolymerization of trimethylolpropane triacrylate (TMPTA) and PU prepolymer, initiated by these polymeric photoinitiators, was studied by photo-DSC. The results indicate that the location of photosensitive group has an important effect on the photoefficiency of polymeric photoinitiators. The efficiency order of polymeric photoinitiators comprising in-chain BP is different from that of the side-chain ones: PUIBA-s and PUIBA-n are the most efficient for TMPTA and PU prepolymer, respectively.     

Revisiting aromatic thiols effects on radical photopolymerization

Influence of thiols on kinetics of acrylate radical photopolymerization in the presence and absence of photoinitiators was studied. The kinetics was monitored by infrared absorption and photo-differential scanning calorimetry. It was found that aromatic thiols at concentrations, <0.5% (∼0.05 M), can accelerate radical photopolymerization. Initiation of radical photopolymerization by some aromatic thiols in the absence of conventional photoinitiators was observed. As well as expected inhibition of photopolymerization at higher concentration of aromatic thiols due to chain transfer was detected. A ground state charge-transfer complex formation between thiols and benzoin based photoinitiators was detected.Mechanism of thiols participation in photopolymerization involving reduction of oxygen inhibition and dissociation of charge-transfer complexes is discussed.     

Visible light sensitive photoinitiating systems: Recent progress in cationic and radical photopolymerization reactions under soft conditions

Although there have been many reports on photoinitiating systems adapted to visible lights for radical photopolymerization, the challenge for the design and development of photoinitiating systems for cationic photopolymerization or concomitant radical/cationic photopolymerization (for interpenetrating polymer network IPN synthesis) with visible lights still remains open. Particularly, the recent development of cheap and easily accessible LEDs operating upon soft visible light irradiations has opened new fields for polymer synthesis. Since 2011, many novel photoinitiating systems based on organic and organometallic compounds with excellent visible light absorption have emerged and exhibited outstanding photoinitiating abilities especially for cationic photopolymerization. In this review, recent progress (mainly from 2011 to early 2014) in applications of photoinitiators and sensitive photoinitiating systems under visible lights are reported. In addition, their relative efficiencies in the photopolymerization of different monomers are exemplified and discussed.     

High throughput kinetic analysis of photopolymer conversion using composition and exposure time gradients

In this work, monomer composition and exposure time gradients were produced, allowing for rapid, parallel measurements of conversion as a function of composition and exposure time using Fourier transform infrared (FT-IR) spectroscopy. A more comprehensive understanding of how composition affects photopolymerization kinetics is needed due to the complexity of current industrial formulations. In nearly all cases, these applications use multiple monomers, fillers, initiators, and other components to achieve the required properties. The developed technique allows for photopolymerization kinetics to be analyzed rapidly over a large range of compositions, giving a unique insight into the role composition contributes to polymerization kinetics and ultimate conversion within complex formulations. This work analyzed three varied two-component systems, each showing different effects from composition on polymerization kinetics due to formulation changes in functionality, viscosity, and reactivity.     

二苯基碘(钅翁)氟硼酸盐引发AGE阳离子光聚合与光交联的研究

用合成的二苯基碘(钅翁)氟硼酸盐作为光敏引发剂,研究了含乙烯基和环氧基两种不同官能基的烯丙基缩水甘油醚(AGE)的阳离子光聚合和聚合前后微观结构的变化,讨论了其阳离子光聚合的特征和机理,测定了光聚合引起光交联的凝胶转化率曲线.     

二苯基碘鎓氟硼酸盐引发AGE阳离子光聚合与光交联的研究

用合成的二苯基碘钅翁氟硼酸盐作为光敏引发剂 ,研究了含乙烯基和环氧基两种不同官能基的烯丙基缩水甘油醚 ( AGE)的阳离子光聚合和聚合前后微观结构的变化 ,讨论了其阳离子光聚合的特征和机理 ,测定了光聚合引起光交联的凝胶转化率曲线     

In situ study of photopolymerization by fourier transform infrared spectroscopy

The Fourier transform infrared (FTIR) in situ method was developed for the investigation of photopolymerization. Ultraviolet (UV) cure of a mixture of a cycloaliphatic epoxide, a 2-ethylhexyl acrylate, and photoinitiators, which forms simultaneous interpenetrating polymer network (IPN), was monitored while the sample was irradiated with UV light. Triphenylsulfonium salt and benzoin ether were used as photoinitiators. For the sake of comparison, similar experiments were performed for the epoxide with the triphenylsulfonium salt photoinitiator and the acrylate with the benzoin ether photoinitiator. The epoxy photopolymerization was monitored using an epoxy CH stretching band at 3005 cm^?1 and a ring vibration band at 790 cm^?1. The acrylic photopolymerization was monitored using a C?C stretching band at 1637 cm^?1. The epoxy conversion was less than 60% when the acrylic polymerization was completed in the IPN.     

Kinetic studies of UV-waterborne nanocomposite formulations with nanoalumina and nanosilica

UV-waterborne coatings are gaining in popularity because of their environment friendly advantages. Most of the mechanical properties of such coatings are lower in comparison with high solids content UV coatings. For these reasons a nanocomposite-based approach was followed and seems promising in order to promote the use of UV-waterborne coatings in the wood products industry. The kinetic study of coatings gives interesting information regarding the curing process and photodifferential scanning calorimetry (photo-DSC) has proved its efficiency. The aim of this work was to study the photopolymerization kinetics by photo-DSC of a typical UV-waterborne coating formulation containing different amounts of nanoparticles. Formulations were mainly based on a polyurethane–acrylate (PUA) resin and a photoinitiator. Nanoalumina and functionalized nanosilica were added to the formulation at three concentrations: 1, 3 and 5 wt%. UV-waterborne formulations were dried during 10 min at 80 °C before curing under a UV source (47 mW/cm²). DSC-exothermic curves demonstrated that photopolymerization was less efficient when nanoparticles were introduced but the UV-curing of coatings based on functionalized nanosilica were better than those containing nanoalumina. Finally the kinetic profile of UV-waterborne coating formulations were characterized using an autocatalytic model and kinetic parameters k, m and n were determined.     

Novel chemical-bonded polymerizable sulfur-containing photoinitiators comprising the structure of planar N-phenylmaleimide and benzophenone for photopolymerization

As a continuation of the research on chemical-bonded photoinitiators comprising the structure of planar N-phenylmaleimide (NPMI) and benzophenone (BP), three novel polymerizable sulfur-containing photoinitiator MTPBP, CMTPBP and BMTPBP were synthesized by introducing NPMI group into benzophenone (BP). BP was selected as the reference to evaluate their photoefficiency. These novel photoinitiators possess greatly red-shifted UV maximal absorption, and their fluorescence emission varies. Three representative types of different functionality monomers, methyl methacrylate (MMA), 1,6-hexanediol diacrylate (HDDA) and trimethylolpropane triacrylate (TMPTA), initiated by the three novel photoinitiators were studied through dilatometer and photo-DSC using unsaturated tertiary amine N,N-dimethylaminoethyl methacrylate (DMAEMA) as the coinitiator. The results show surprising high efficiency of these chemical-bonded photoinitiators towards different monomers in contrast to BP, and they can initiate photopolymerization without the coinitiator because of the photolysis at C-S bond. The results also verify that the higher viscosity of monomers and the larger molecular size of the photoinitiators may restrict the bimolecular H-abstraction reaction.     

采用唯象理论研究光聚合动力学

文章探讨紫外光固化的自加速现象,并用唯象理论从数学上作出阐述、考察了单体种类,光引发剂种类对动力学参数的影响,并对不同条件下该模型的参数进行了计算。结果表明,该数学模型能很好地量化在不同条件下光聚合反应的变化。     

Kinetic investigations on the UV‐induced photopolymerization of nanocomposites by FTIR spectroscopy

The kinetics of the photopolymerization for nanocomposites containing nanosilica with 2,2‐dimethoxy‐1,2‐diphenylethan‐1‐one or benzophenone/n‐methyl diethanolamine (BP/MDEA)as photoinitiators were studied by FTIR spectroscopy. It was found that nanocomposites containing nanosilica had higher conversion in comparison with pristine EA. The presence of MPS and ethanol accelerated the photopolymerization of nanocomposites, while the presence of water decelerated it. The photopolymerization of nanocomposites was more sensitive to oxygen than that of pristine EA. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99:1429–1436, 2006     

Efficient visible photoinitiator with high‐spectrum stability in an acid medium for free‐radical and free‐radical‐promoted cationic photopolymerization based on erythrosine B derivatives

Three dye‐linked photoinitiators with excellent spectral stability in an acid medium were synthesized by the covalent bonding of a coinitiator (tertiary amine) and a benzoyl group or two coinitiators to the phenolic and carboxyl group position of erythrosine B. The combination of the iodonium salt and free tertiary amino used to initiate the free‐radical/cationic visible photopolymerization was investigated to acquire the relationship between the structure and performance. The photoinitiating ability of the derivative with the phenolic position bearing a coinitiator was poorer than of the derivative with the carboxyl group bearing one because of the strong back electron transfer of the former. For the derivative with a linked coinitiator on the carboxyl position, the proximity effect between the sensitizer and the coinitiator moiety resulted in an excellent photoinitiating ability for radical/cationic polymerization; this suggested its potential for application. Although radical/cationic photopolymerization could be initiated by the derivative/coinitiator/iodonium salt, the different component ratios between them had different effects on these two polymerizations; this provided useful information for the design of effective photoinitiators for different polymerizations. On the basis of the fluorescence quenching and photopolymerization results, a corresponding synergistic mechanism was proposed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43035.     

聚氨酯型高分子硫杂蒽酮光引发剂的制备及性能研究

通过三种二异氰酸酯、2-（2,3-二羟基）丙氧基硫杂蒽酮（HPTX）及N-甲基二乙醇胺(MDEA)进行逐步聚合反应,将硫杂蒽酮结构及共引发剂胺结构引入到同一高分子链上,得到侧链含有硫杂蒽酮,主链含有共引发剂胺的聚氨酯型高分子光引发剂。傅立叶红外变换光谱和核磁共振氢谱证实了高分子光引发剂的结构。紫外光谱证实了高分子链的结构对硫杂蒽酮单元的最大紫外吸收几乎没有影响。用光致差示量热计（photo-DSC）研究聚氨酯型高分子光引发剂引发聚氨酯丙烯酸酯树脂（PUA）的光聚合反应,发现PU-IMTX是本文合成的引发剂中引发PUA光聚合最有效的光引发剂。