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     

Determination of pressure in the extradendritic liquid area during solidification

Complex-shaped lamellar graphite iron castings are susceptible to casting defects related to the volume change during solidification. The formations of these recurring defects are caused by the flow of the liquid in the intradendritic area, between the austenite dendrite arms, and in the extradendritic area between the austenite grains. The conditions for the liquid flow, in turn, are determined by the solidification behavior. The present study suggests a new measurement method and a novel calculation algorithm to determine the pressure of the extradendritic liquid during solidification. The method involves a spherical sample suspended in a measurement device, where the temperature and the volume changes are measured during solidification. The calculation algorithm is based on the numerical interpretation of the Clausius–Clapeyron equation where the temperature variation, the volume change and the released latent heat are processed to determine the local pressure of the extradendritic liquid area during solidification.

     

Dispersion photopolymerization of styrene

Photopolymerization of styrene was carried out in a dispersed system to obtain 10 μm particles, using d-t-butylperoxide as initiator and poly(vinyl alcohol) as protective colloid. It was shown that particles typical for latex polymerization are also formed and interfere with the dispersion polymerization when excess protective colloid is used.     

A novel UV-sensitive photopolymerization system with microgel matrix

A series of crosslinked microgels with quaternary ammonium ions on the surface was prepared by quaternization with N,N-dimethylbenzylamine in the presence of microgel particles prepared by emulsion copolymerization of styrene (St), chloromethylstyrene (CMS) and divinylbenzene (DVB). Microgels with diameters in the range of 15–100 nm were successfully dispersed in organic solvents such as 2-methoxyethanol and 2-ethoxyethanol without an emulsifier. A photosensitive layer was formed by coating a photosensitive solution on a grained aluminum plate. The solution was comprised of the microgels, the multifunctional monomer and standard ultraviolet (UV) photoinitiators, such as 2,4-diethyl thioxanthone (DETX)/ethyl p-di-ethylaminobenzoate (EPA). This gave a heterogeneous photosensitive layer which produced good polymer patterns after exposure to UV light followed by development in tap water. A typical polymer layer, consisting of the microgels (poly(styrene-co-N,N-dimethylbenzylvinyl-benzylammonium chloride-co-divinylbenzene)), DETX/EPA, and the multifunctional acrylate monomers, exhibited photosensitivity of 0.06 mJ/cm² for UV light. This sensitivity is much higher than the homogeneous photopolymerization system with an analogous composition.     

界面限域效应增强二氧化碳电催化还原

<正>二氧化碳电催化还原,以可再生电能或富余核电等洁净电能为能源,可以在温和的反应条件下将二氧化碳一步转化为一氧化碳、甲酸、碳氢化合物和醇类等高附加值化工原料及化学品,将二氧化碳变废为宝的同时实现了洁净电能的有效存储~1。当前,设计高效电催化剂来降低过电势和提高反应选择性是二氧化碳电催化还原研究中极具挑战性的热点课题。     

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 cationic photopolymerization of alkoxyallene monomers

A series of cationically polymerizable mono-and difunctional alkoxyallene monomers have been prepared via the straight forward base catalyzed isomerization of the corresponding propargyl ethers. Rate studies conducted using real-time infrared spectroscopy showed that these monomers exhibit high reactivity in photoinitiated cationic polymerization. Monomers bearing a single alkoxyallene group undergo rapid polymerization to yield crosslinked polymers indicating that both double bonds react during polymerization. A mechanism has been proposed that explains this observation. © 1995 John Wiley & Sons, Inc.     

Cationic photopolymerization of ambifunctional monomers

Certain metal-catalyzed hydrosilations have been found to occur in a highly regioselective manner which makes them useful for the preparation of unique classes of ambifunctional monomers. These monomers bear two chemically different functional groups within the same molecule. By selection of the appropriate functional groups it is possible to design monomers in which the functional groups react independently, copolymerize, or polymerize by different mechanisms. This article describes some recent results of the synthesis and polymerization of several novel types of ambifunctional monomers.     

Frontal photopolymerization synthesis of multilayer hydrogels with high mechanical strength

Multilayer hydrogels were prepared by frontal photopolymerization of acrylamide and 2-acrylamido-2-methylpropane sulfonic acid using hydrophilic reactive microgels (HRM) as crosslinkers instead of conventional crosslinkers. The hydrophilic microgels (HM) were prepared by inverse emulsion photopolymerization and then were chemical modified by N-methylolacrylamide (NMA) to obtain HRM with CC double bonds. The HM and HRM was characterized by dynamic light scattering measurements, SEM, TEM and FTIR, respectively. It was found that the resulting multilayer hydrogels showed high fracture strength and high tensile elongation along parallel direction. However their fracture strength and tensile elongation along perpendicular direction was very weak. The swollen multilayer hydrogels were about 1.0–2.0 mm in thickness, the maximal equilibrium swelling degree was only 30.45. The multilayer hydrogels were characterized by DSC, TEM and XRD, respectively. The swelling property and mechanical strength of some typical multilayer hydrogels were studied.     

硫代苯甲酸苯酯光解及光引发聚合的研究

硫代苯甲酸-S-苯酯(BPTBN)是一种对烯类单体的聚合具有较高引发效率的引发剂。该类化合物分子的α断裂发生在三重态中间体。用该类化合物引发甲基丙烯酸甲酯(MMA)单体聚合,发现聚合效率依次是对位＞间位≈邻位取代的化合物,这类化合物的光解产物主要有:苯硫酚、二苯基硫醚、苯甲酰基苯甲醛、二苯基二硫醚、二苯基乙二酮等。气-质联用测定这些光解产物的比例,发现它们与BPTBN的取代及取代位置有很大的关系。得到的结果与聚合实验所得结果一致,激光闪光光解实验也证实了该结果。     

Synthesis and photopolymerization of 1-propenyl glycidyl ether

The ambifunctional monomer, 1-propenyl glycidyl ether, was prepared from allyl glycidyl ether, by a ruthenium-catalyzed isomerization reaction in high yield. 1-Propenyl glycidyl ether undergoes facile photoinduced cationic polymerization to yield a crosslinked polymer. The structure of this polymer was studied using ¹H- and, ¹³C-NMR spectroscopies and employing well-characterized related polymers as models. The model polymers were prepared by the cationic polymerization of allyl glycidyl ether with BF₃OEt₂ followed by isomerization of the pendant allyl groups by a ruthenium catalyst. Subsequently, the resulting polyether-bearing pendant 1-propenyl ether groups was subjected to a diaryliodonium salt-photoinitiated polymerization. A comparison of the spectra of the polymers indicated the presence of cyclic acetal units in the polymer backbone. © 1994 John Wiley & Sons, Inc.     

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 and photopolymerization of cholesteric liquid crystalline diacrylates

The synthesis of chiral liquid crystalline diacrylates is described. By mixing one of them with non-chiral liquid crystalline diacrylates. cholesteric phases are obtained of which the wavelength of reflection can be chosen by the composition of the mixture. After isothermal photopolymerization of the mixture a crosslinked network is obtained with thermally stable properties.     

Synthesis and photopolymerization of monomers bearing isopropenylphenoxy groups

The synthesis of a series of monomers containing isopropenylphenoxy groups was carried out. On irradiation with UV light in the presence of onium salt photoacid generators, these monomers undergo a chain extension reaction consisting of a dimerization followed by a Friedel-Crafts ring closure which results in the formation of polymers with indane groups in the backbone. Aryl imide-containing monomers bearing isopropenylphenoxy groups were also shown to undergo facile photoinduced cationic polymerization. The resulting polymers displayed excellent thermal stability. © 1995 John Wiley & Sons, Inc.     

Preparation of antifog and antibacterial coatings by photopolymerization

This paper contains a kind of ultraviolet‐cured antifogging and antibacterial coating. A quaternary ammonium salt (14QAS), which was synthesized in this paper, has been implemented as a monomer. The chemical structure of 14QAS has been confirmed by Fourier transform infrared spectroscopy and nuclear magnetic resonance. The nitrogen atom on the surface of the coatings with 14QAS was observed by X‐ray photoelectron spectroscopy. The Surface wettability of the polymer film was studied by contact angle analysis, which confirmed the hydrophilicity of the coatings with low water contact angle (~25°). The antifog properties were evaluated under different conditions. The antibacterial activity of coatings with 14QAS reached 99.9% against S. aureus and E. coli. Copyright © 2014 John Wiley & Sons, Ltd.     

A calorimetric study of acrylate photopolymerization

The kinetics of the photoinitiated polymerization of lauryl acrylate (LA), 1,6-hexanedioldiacrylate (HDDA) and pentaerythritol tetraacrylate (PET₄A) have been investigated using differential scanning calorimetry (DSC). An autoacceleration phenomenon is observed with the multifunctional acrylates, but not with lauryl acrylate. The empirical dependences of reaction rate on such parameters as incident light intensity, initiator concentration, and temperature have been established and are in general found to vary with monomer conversion. Apparent activation energies for the photopolymerizations have been determined from rate versus temperature data. The multifunctional acrylates show an increasing activation energy with monomer conversion, whereas the apparent activation energy for lauryl acrylate not only decreases with conversion, but becomes negative at conversions greater than about 30%. The ratio k_p/k is calculated from rate versus conversion data under constant illumination and the (independently determined) initiation rate. Analysis of rate versus time data under nonsteady-state conditions (light turned off) yields the ratio k_t/k_p. With these two ratios the rate constants for propagation (k_p) and termination (k_t) may be separated and their respective values calculated. Both k_p and k_t are found to decrease substantially with monomer conversion, indicating a significant change in the rates of both the propagation and termination steps as the polymerization advances. These observations are explained in terms of a radical isolation phenomenon and diffusion control of the propagation step.     

Real-time FTIR-ATR spectroscopy of photopolymerization reactions

Real-time FTIR-ATR spectroscopy was used to study radical photo-polymerization reactions. Investigations on various acrylate systems deal with the effect of temperature on the kinetics of the polymerization reaction and the characterization of the depth profile of the conversion of double bonds. Moreover, first results on the photoinitiator-free photopolymerization of acrylates by exposure to short-wavelength UV radiation will be reported. The potential of the method will also be demonstrated in simulations of various irradiation regimes in technical UV curing processes.     

催化剂的孔道限域效应

限域孔道可以调控催化剂的表面电子分布和几何结构,进而影响催化剂的活性、选择性和稳定性.本文结合理论计算和实验方法,从热力学、动力学、几何效应以及电子转移等角度出发,阐明了不同限域体系中催化剂活性组分和反应分子特性的差异,揭示了限域孔道对反应物种扩散、吸附和反应等过程的影响规律,以期为催化剂的微观结构设计和反应性能调控提供借鉴.     

Cationic photopolymerization with the aid of pyridinium‐type salts

Pyridinium‐type salts containing an N‐ethoxy group belong to the family of onium salts and are photoinitiators appropriate for the polymerization of monomers such as oxiranes and vinyl ethers which are not polymerizable by a free radical mechanism. The initiation is accomplished by direct or indirect (sensitized) photolysis of the onium ion, with the former being restricted to the wavelength range of self absorption, the latter being applicable at wavelengths of visible light. An additionally useful tool, namely free radical‐mediated generation of initiating species enlarges the versatility of pyridinium salts as photoinitiators. In this connection, the oxidation of free radicals by pyridinium‐type ions and the free radical‐induced fragmentation of alkoxy pyridinium ions are addressed in this article. Moreover, an interesting application is noted concerning the synthesis of novel block copolymers with the aid of the onium salt‐based photopolymerization technique.