Simulation of conversion profiles and temperature distributions within dimethacrylate thick material during photopolymerization

Photoinitiated polymerization of multifunctional monomers is an usual method to prepare highly crosslinked networks which have a wide variety of applications. This method leads to high reaction rates and the resulting exothermic effect of this reaction can be the cause of defects in the final material. The heterogeneities alter greatly the physical properties of ultimate products, particularly the optical ones, what causes problems in the design of thick and optically perfect materials. The knowledge of the conversion profile and the temperature distribution within the material during the photopolymerization is useful for the process optimization. Unfortunately, these parameters cannot be measured during the process. Thus, we decided to simulate them. Firstly, the necessary parameters (like conversion and reaction rate) were measured on thin material in isothermal conditions by photocalorimetry. Secondly, these kinetic data were used in a computational calculation to obtain the conversion profile and the temperature distribution within dimethacrylate thick material. The calculated temperature and conversion-time curves are in good agreement with the experimental curves determined under the same conditions.     

Photopolymerization kinetics of an epoxy based resin for stereolithography

Curing reactions of photoactivated epoxy resins are assuming an increasing relevance in many industrial processes, such as coatings, printing, adhesives. Besides these processes, stereolithography makes use of photoactivated resins in a laser induced polymerization for 3D building. The kinetic behaviour of photocuring is a key point for a full comprehension of the cure conditions occurring in the small zone irradiated by the laser beam. Furthermore, the kinetic analysis is very important in order to determine the cure time needed for part building in a stereolithographic equipment. The mechanisms involved in a cationic photopolymerization are complex when compared with radical photopolymerization. In this paper the photoinitiated polymerization of a commercially available epoxy based resin for stereolitography has been studied by means of differential scanning calorimetry (DSC). The polymerization rate and the amount of unreacted monomer are determined directly from the conversion vs. time curves during DSC isothermal scans. Kinetic characterization of epoxy photopolymerization has been carried out as a function of the temperature and experimental results have been compared with an original mathematical model. This revised version was published online in July 2006 with corrections to the Cover Date.     

Solid state photopolymerization of acrylic acid at low temperature

Near‐infrared spectroscopy was used to investigate the kinetic characteristics of acrylic acid photopolymerized at ?70°C and room temperature, respectively. The obtained results showed that at ?70°C the double bond conversion increased with increase in the initiator's concentration. Addition of soft chain component polyethylene glycol 400 (PEG400) could lead to high conversion in the solid state, and then high final double bond conversion after post‐curing. The introduction of water at low temperature also contributed largely to the enhancement in the initial and final double bond conversion in solid state. SEM photographs showed that more pores came up in the cured films with the increase in the water content in the reaction system. The change in the photoinitiator concentration, amount of PEG400, and content of water had significant effect on samples cured at lower temperature than at room temperature under the same conditions. Different kinds of photoinitiators showed different contributions to the initial and final double bond conversion on photopolymerization of acrylic acid at low temperature. Significant post‐curing phenomena for photopolymerization of acrylic acid at low temperature could be observed as well. Copyright © 2009 John Wiley & Sons, Ltd.     

Influence of temperature and UV intensity on photo-polymerization reaction studied by photo-DSC

Photo-DSC was used to investigate the cure kinetics of a photo-initiated resin. The exothermal photo-polymerization reactions were performed in isothermal mode. The irradiation of photo-initiated resin was studied under different conditions of temperature, UV lamp intensity, and reaction atmosphere (nitrogen and air). The results obtained by photo-DSC allowed us to determine kinetic data of the photo-polymerized reactions: the global activation energy and reaction enthalpy, and the conversion as a function of time and temperature. Modulated temperature DSC measurements were carried out to verify whether vitrification occurs during polymerization. The conversion at the top and bottom of irradiated samples was obtained by FT-IR spectroscopy before and after photo-polymerization. A non-homogenous photo-polymerization into the material was observed, probably because of the light absorptions effects within the uppermost layers.     

Photo - DSC and real time - FT-IR kinetic study of a UV curable epoxy resin containing o-Boehmites

Nanocomposite coatings based on a cycloaliphatic epoxy resin (3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylate - CE) with two different o-Boehmites (content ranging from 5 to 10 wt.%) were prepared by cationic photopolymerization. Two different in situ monitoring techniques, photocalorimetry (p-DSC) and real time FT-IR spectroscopy (RT-IR) were used in order to investigate the kinetics of the photopolymerization process. A theoretical approach for establishing the equivalence of the irradiation conditions in the two experimental set-ups was developed in order to compare the obtained results.A substantial correspondence of the two techniques was found for the qualitative trend of the final conversion of the epoxy groups of the filled formulations relatively to the pure CE resin. Conversely, the final conversion of the epoxy groups and the reaction rate were found to be quite different. Higher kinetic profiles were obtained in RT-IR experiments, in which were also observed lower final conversions of the epoxy groups relatively to the p-DSC measurements. The presence of the nanofillers resulted in a decrease in the reactivity of the epoxy system, which was attributed to the light absorbance of Boehmites due to scattering from the clusters in the micron-size range.All the nanocomposites exhibited a high level of transparency and high T_g values, which were found to decrease slightly with increasing the nanofiller content.     

Monitoring photopolymerization reactions through thermal imaging: A unique tool for the real‐time follow‐up of thick samples, 3D printing,and composites

The ever increasing applications of photopolymers from historical thin (<50 µm) coatings to very deep samples (>1 cm) require the development of robust 4D monitoring strategies able to assess photopolymerization efficiencies (first dimension) as a function of time (second dimension) and position (third and fourth dimensions). Therefore, here, we demonstrated that thermal imaging is a valuable photopolymerization monitoring device showing: (a) very high response times (<1 s); (b) high repeatability of the measurement; (c) strong adaptability of the setup to various conditions (e.g., onto irregular surfaces or inside a real time Fourier transformed infrared spectrometer (RT‐FTIR)); (d) extremely deep photopolymerization follow‐ups (and subsequent rationalization) with good resolution in time and in space (real‐time thermal imaging microscopy experiments); (e) adaptability to applied materials. This monitoring strategy was found particularly robust when taking into account all the heat generating phenomena (i.e., direct heating from the lamp vs. temperature raised due to monomer conversion). As a result, we propose thermal imaging as the next reference monitoring system for the new ranges of thick and/or filled samples (e.g., 3D objects, composites) and/or applied photopolymerizations (e.g., 3D printing) more and more present in the literature. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 889–899     

Photopolymerization of bis-aromatic and alicyclic based solid urethane acrylate macromonomer in the presence of large excess of reactive diluent

A solid urethane acrylate macromonomer with bis-aromatic as well as alicyclic moieties was synthesized and the kinetics of photopolymerization reactions were studied in the presence of varying concentration of photoinitiator and large excess of reactive diluent using photo DSC. The studies show that the rate of maximum polymerization was found to increase with increase in concentration of photoinitiator while a decrease was observed by an increase in temperature. The final conversion showed a decrease at highest isothermal condition due to vitrification. Estimation of kinetic parameters including applicability of autocatalytic and modified autocatalytic models were investigated by nonlinear regression. It was observed that the modified models gave a better fit with the experimental data and kinetic parameters showed a decrease with increase in temperature and an increase with increase in concentration of photoinitiator.     

High‐throughput kinetic analysis of acrylate and thiol‐ene photopolymerization using temperature and exposure time gradients

In this work, a high‐throughput technique for evaluating photopolymers is developed to enable simultaneous measurement of the effects of temperature in combination with exposure time. Temperature and exposure time gradients were produced in orthogonal directions on a single sample, and subsequently sampled using Fourier transform infrared (FTIR) spectroscopy. The technique developed here allows for photopolymerization kinetics to be analyzed rapidly over a large range of industrially relevant temperatures, giving insight into the role temperature and the polymer's glass transition temperature have in dictating the photopolymerization kinetics. In the 70/30 wt % hexyl acrylate and hexanediol diacrylate system, conversion in samples below the glass transition temperature (T_G) was 66 ± 2% after 12 s, significantly lower than the 93 ± 4% conversion at 12 s for samples polymerized at temperatures above the T_G. In addition, a thiol‐ene system was analyzed to study the effect of temperature on the ene homopolymerization in allyl ether monomers, which leads to incomplete thiol conversion in stoichiometrically balanced systems. At a 60% thiol conversion, the allyl ether‐ene conversion at all temperatures is 65 ± 3% irrespective of initial formulation temperature, indicative of the homopolymerization behavior being nearly independent of temperature. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1502–1509, 2008     

Multicyclic study on the carbonation of CaO using different limestones

Different samples of limestones, with small differences in their stoichiometry, have been studied comparatively. The carbonation reaction has been studied for a large area of isothermal temperatures. The conditions for the multicyclic experiments of calcination/carbonation were: isothermal temperature 670°C, heating time 60 min and carrier gas CO₂. The final carbonation conversion depends mainly on the isothermal temperature of the carbonation reaction and the heating time. The final temperature of the calcination reaction depends on the percentage of CaO that it has not been conversed to CaCO₃ in the repeated carbonation experiments. The quantity of CaO that has not been carbonated, in the same sample, affects the values of the coefficients of the kinetic model that fit the calcination reaction. In the multicyclic experiments the carbonation conversion for two of the four studied samples, was high enough in comparison to other samples of calcite. At sample A the reduction of the carbonation conversion during the first five cycles is less than it is at other samples from the literature. Under the above experimental conditions — isothermal temperature and heating time — specific samples consisted mainly of calcite can absorb larger quantities of CO₂ than samples consisted mainly of dolomite.     

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     

The simulation of the thermal behavior of energetic materials based on DSC and HFC signals

Two small calibre and four medium calibre types of propellants were investigated non-isothermally (0.25–4K min⁻¹) by differential scanning calorimetry (DSC) in the range of RT-260°C and isothermally (60–100°C) by heat flow calorimetry (HFC). The data obtained from both techniques were used for the calculation and comparison of the kinetic parameters of the decomposition process. The application of HFC allowed to determine the kinetic parameters of the very early stage of the reaction (reaction progress α below 0.02) what, in turn, made possible the precise prediction of the reaction progress under temperature mode corresponding to real atmospheric changes according to STANAG 2895. In addition, the kinetic parameters obtained from DSC data enabled determination of self-accelerating decomposition temperature (SADT) and comparison of the predicted ignition temperature during slow cook-off with the experimental results. The study contains also the results of the calculation of the time to maximum rate (TMR_ad) of the propellants under adiabatic conditions.     

THE PHOTOPOLYMERIZATION KINETICS OF PHOTOSENSITIZED ACRYLAMIDE SYSTEM INDUCED BY He-Ne LASER

The kinetics of the photopolymerization of sensitized acrylamide (AM) system induced by He-Ne laser has been investigated. Using methylene blue (MB)-triethanolamine (TEOA) as the photosensitive system, the photopolymerization followed a nonsteady-state kinetic scheme in the initial period of polymerization (the monomer conversion C%<2%) and then followed a steady-state kinetic scheme (5% >C%>2%). Accirding to the steady-state hypothesis, the mechanism of photopolymerization was proposed. The deduced kinetic equation of the photopolymerization of AM is in good coincidence with the experimental results.     

Photopolymerization kinetics of a thiol–enol composition determined via recording/playback of a transmission holographic diffraction grating

The kinetics of thiol–enol photopolymerization of a hybrid composition based on a tetraacrylate monomer and a thiol-siloxane oligomer was studied with the use of a holographic recording of elementary transmission phase gratings. The degrees of conversion of double bonds in the tetraacrylate monomer after the polymerization in air and in an inert atmosphere of SF₆ were measured via IR spectroscopy. It is shown that the use of the thiol-siloxane oligomer efficiently suppresses oxygen inhibition of the photopolymerization. When the photoinitiator concentration is increased to more than 10^–2 mol/L, the photopolymerization rate levels off. An increase in the thiol-siloxane oligomer concentration leads to an extremal dependence of the photopolymerization rate on the oligomer concentration; the maximum rate is reached at an oligomer concentration of about 0.07 mol/L. The kinetic scheme of photopolymerization in the hybrid photopolymer composition was analyzed, and an analytical expression for the photopolymerization rate was obtained. The correlation between the kinetic constants of the thiol–enol photopolymerization was evaluated on the basis of the obtained parameters of the kinetic model.     

Characterization and Studies on Grafting of Methyl Methacrylate onto PAN Fibers

The graft copolymerization of methyl methacrylate (MMA) onto commercial acrylic fibers (PAN) has been studied using Azobis(isobutyro)nitrile (AIBN) as an initiator. MMA grafting initiated by radicals formed from thermal decomposition of AIBN. In this study, the effects of monomer and initiator concentration, time and temperature reaction on the grafting yield have been investigated.

The optimum conditions for this grafting reaction were obtained with an MMA concentration of 0.7 M, an AIBN concentration of 0.0073 M, a reaction temperature of T=85°C and with a 60 min reaction time.

The fiber structure has been investigated by different experimental techniques of characterization such as Fourier transform infrared spectroscopy (FT‐IR), calorimetric analysis (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), water absorption and the physical and mechanical properties has also been investigated in this study. The thermal analysis data showed that by increasing grafting yield, little changes have occurred in fibers samples up to 13.5% of grafting yield and the thermal transitions of grafted fibers have approximately the same behavior compared with the raw fibers sample. Grafting also slightly affected the fiber morphology. The experimental data of mechanical properties clearly show that by increasing grafting yield, max extension will decrease but this change up to 13.5% grafting yield is barely noticeable. Grafting of poly MMA improved water absorption.     

Photopatternable hybrid sol–gel films: A liquid Si NMR investigation of the inorganic network formation

Methacryloxypropyltrimethoxysilane precursor has been involved in the realization of optical elements in crack free thick films (ranging from 15 to 100 μm), through spatially controlled photopolymerization. First, alkoxysilane functions were partially hydrolyzed and condensed. Then, using a photoinitiator, free radical photopolymerization was proceeded by irradiating the sample under UV or visible light. Since an organic network is formed in the matrix of the primarily formed inorganic network, understanding the formation of the silicate backbone was of first importance to ensure the creation of crack free thick films through efficient polymerization.

Liquid ²⁹Si NMR spectroscopy was used to investigate the inorganic network formation. Material preparation required evaporation of the volatile solvents released by the sol–gel process and limitation of the condensation degree. Both conditions were achieved by a drying process at room temperature. The structure and the composition of the dried sols were investigated and compared to non-dried sols. NMR peak fitting pointed out to the presence of a large variety of cyclic and linear oligomers in the sol. The structure of the dried sol appeared to depend both on the aging time and on the storage temperature. All these results have to be taken into account when the condensation degree has to be limited for specific optical applications.     

Alkyl chain length effects on copolymerization kinetics of a monoacrylate with hexanediol diacrylate

Copolymerizations of hexanediol diacrylate with three monoacrylates were analyzed using high-throughput conversion analysis to elucidate the effects of varying alkyl pendant groups at different compositions. Each analyzed copolymerization system contained hexanediol diacrylate (HDDA), and copolymerizations with 30-60 wt % monoacrylate reached nearly complete conversion after 30 s of exposure time. For higher amounts of monoacrylate, the photopolymerization kinetics of the hexyl acrylate (HA) copolymerization were significantly slower than the copolymerization with either ethylhexyl acrylate (EHA) or dodecyl acrylate (DDA). With 20 wt % HDDA, conversion at 30 s with a comonomer of HA was 62+/-3%, as compared to 76+/-3% and 84+/-3% when copolymerized with EHA and DDA, respectively. Model kinetic parameters were estimated for all four monomer systems, with HDDA monomer parameters found to be within the same error when estimated from any of the copolymerizations. With kinetic parameters for each monomer, comparison maps showing the difference in conversion between two copolymerizations were generated. These comparison maps allow for an assessment of two comonomer systems to determine the optimal photopolymerization conditions. Slower photopolymerization kinetics for HA occur at nearly all compositions containing monoacrylate, with the largest reduction occurring between 20 and 40 wt % monoacrylate.     

丁腈羟增韧环氧树脂固化反应

丁腈羟增韧环氧树脂固化反应李绍英＊＊韩孝族＊刘振海张庆余（中国科学院长春应用化学研究所长春１３００２２）关键词丁腈羟，增韧环氧树脂，固化反应动力学，ＤＳＣ１９９６－０５－０４收稿，１９９６－０９－１７修回＊＊现在河北轻化工学院化工设计研究所工作环氧树...     

新型红外光引发剂的激光光聚合研究

目前对紫外区敏感的光聚合体系的研究已经比较成熟 ,并且在工业生产中得到了实际应用 .对可见光区的光聚合体系的研究也已引起了不少研究者的关注 .而有关近红外 /红外区敏感的光聚合体系的报道还很少 .已经商业化的红外半导体激光器具有体积小、价格便宜、操作简便、性能稳定等特点 ,配合计算机布线技术 ,可大大提高生产效率 ,这些优点使得与之匹配的对红外区域敏感的光聚合体系具有广阔的应用前景[1 ] ,尤其是在计算机直接制版 (Ｃｏｍｐｕｔｅｒ ｔｏ ｐｌａｔｅｓ,ＣＴＰｓ)领域[2 ] .Ｃｈａｔｔｅｒｊｅ等曾经研究了用阳离子菁染料与不…     

基于UV-LED茂铁盐体系对脂环族环氧单体的阳离子光聚合动力学研究

本文利用实时傅里叶变换红外光谱(real-time FTIR)研究了脂环族环氧单体(CE)在405 nm UV-LED光源下的光聚合动力学。以η6-异丙苯茂铁六氟磷酸盐(I-261)作为阳离子光引发剂,2-异丙基硫杂蒽酮(ITX)、姜黄素(CC)和1-[4-(苯基偶氮)苯基偶氮]-2-萘酚(SudanⅢ)作为光敏剂,探究该茂铁盐体系对CE单体环氧基团转化率及聚合速率的影响。结果表明,尽管所有光敏剂都能有效地引发光聚合,但是ITX和CC体系在405 nm光源的辐照下表现出更高的聚合效率。在8.0%(质量分数)I-261和0.5%ITX条件下,CE的单体转化率从74.4%提高至89%以上,最大聚合速率提高了1.9倍。在8.0%(质量分数)I-261和1.0%CC条件下,CE的单体转化率从74.4%提高至88%以上,最大聚合速率提高了1.7倍。     

Depth characterization by confocal raman microscopy of oxygen inhibition in free radical photopolymerization of acrylates: Contribution of the thiol chemistry

The oxygen inhibition of acrylate photopolymerization using visible light was depth characterized by confocal Raman microscopy. The sample thickness was found to influence the depth conversion profile. With increasing sample thickness, the conversion at the surface was increased and the oxygen‐affected layer (OAL) decreased, up to a limit where the profiles became independent of the thickness. The addition of a thiol in the acrylate mixture reduced the OAL and the conversion in this region increased. This effect was noticeable even at low concentration of thiol. Real‐time infrared spectroscopy (RT‐FTIR) experiments pointed out that for low thiol content, this beneficial effect is not only attributable to the thiol–ene process—oxygen insensitive—but also to the homopolymerization of acrylates which is enhanced. Homopolymerization and thiyl radical addition were found to have the same impact on the overall mechanism. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013