Study of the polymerization of acrylic resins by photocalorimetry

Due to their advantages from an environmental point of view (i.e. reduction of volatile organic compounds (VOC)), photocurable finishes should be extensively used for industrial wood joinery in the near future. However, several problems are reported, particularly the poor durability of the finishing system. In the present work, the curing reaction of acrylic resins containing some improved photoinitiators was studied by means of photocalorimetry under monochromatic irradiation from 366 to 450 nm. The results show that finishes can be cured even under daylight so that they could be directly applied on site in case of restoration.     

Polymerization of photocurable commercial dental methacrylate-based composites

Due to their excellent aesthetics, photopolymers have been extensively used in several dentistry applications. However, several problems are reported, e.g. low mechanical and abrasion resistance, shrinkage during polymerization, etc. Properties of the final restorations are intrinsically related to the polymerization stage, which can be conveniently studied by photocalorimetry. In the present work the polymerization reaction and the filler content of different photocurable commercial dental methacrylate-based composites were studied by means of photocalorimetry and thermogravimetry, respectively. The results show that the values of curing rate, the heat of polymerization and the filler content vary significantly from one composite to another.     

A vitrification and curing study by simultaneous TMDSC-photocalorimetry

The development of photopolymers was helped by the development of photocalorimetry, which is now a basic technique for the study of these materials. This work shows how to obtain vitrification times in single isothermal curing experiments by monitoring the reversing heat capacity along time in modulated temperature DSC–photocuring systems, overcoming the time-consuming problem of standard DSC. The effects of the light intensity and the isothermal curing temperature on the vitrification time of a photocurable system were evaluated. The results obtained at a given curing temperature with different light intensities indicate that the UV-light affects the molecular mobility hindering the vitrification process. The effects of the curing temperature on the vitrification time, the conversion at the vitrification time and the maximum conversion were also evaluated.     

Cure Degree Estimation of Photocurable Coatings by DSC and Differential Photocalorimetry

Radiation-curable coatings have acquired importance, because they are environmentally-friendly (no solvent emission)and require low energy for curing, when compared to other conventional heat-curable products. UV-curable coatings performance depends on the cure quality. Suitable methods were evaluated to estimate the degree of cure applying quantitative techniques, such as differential scanning calorimetry (DSC) and differential photocalorimetry (DPC), in order to determine the residual heat of curing in UV-cured films. The results of the DPC technique showed better sensibility than DSC technique, although the use of suitable pans for the case of clear coats must be considered. This revised version was published online in July 2006 with corrections to the Cover Date.     

Oxygen Inhibition and Coating Thickness Effects on Uv Radiation Curing of Weatherfast Clearcoats Studied by Photo-DSC

Radiation curing is an environmentally-friendly technology. Furthermore, radiation curing is a faster, energy saving and more efficient industrial process than the heat-curable process. One of the most important requirements for the widespread application of UV curable coatings in the coating industry is that they are stable vs. atmospheric degradation. Today's state of the art in oxidative drying and thermosetting coatings is the use of light stabilizers to protect polymers vs. the damage of outdoor exposure. Oxygen has a detrimental effect on the cure response of free radical systems, especially in thin-film coatings. Differential photocalorimetry (photo-DSC) was used to investigate the oxygen effect and the use of light stabilizers on UV curing of photocurable formulations based on acrylate materials. Coating thickness influence was also considered. This revised version was published online in August 2006 with corrections to the Cover Date.     

可紫外光固化的聚乙烯基硅氮烷合成与表征

采用带丙烯酸酯基团的烯丙基溴化合物(4-溴丁烯酸乙酯)和聚乙烯基硅氮烷发生取代反应,实现了丙烯酸酯基团在聚乙烯基硅氮烷主链上的链接.采用质子核磁共振谱(1H-NMR)和二维质子核磁共振谱(2D-1H-1H-NMR)对分子结构进行了表征,采用光学差热分析仪(Photo-DSC)和傅立叶转换红外光谱仪(FT-IR)测试了改性高分子的光敏性能,用热重分析仪(TGA)分析了产物在高纯氮气氛围下的陶瓷收率.结果表明,通过分子改性,交联固化时间从改性前的20min减少到1min之内,功能化的聚乙烯基硅氮烷可以在光刻蚀工艺中作为负性光刻胶使用.     

Regioselective hydrosilations. III. The synthesis and polymerization of ambifunctional silicon-containing epoxy monomers

Silicon-containing epoxide compounds bearing Si ? H groups can be readily prepared in high yields by the regioselective rhodium-catalyzed monohydrosilation of α,ω-dihydrogen functional siloxanes and silanes with vinyl epoxides. The remaining Si ? H groups in these compounds can be further selectively hydrosilated with unsaturated epoxides to give a series of unique ambifunctional monomers containing two different epoxide groups in the same molecule. The photopolymerization of these monomers has been studied using analytical techniques including real time infrared spectroscopy and differential scanning photocalorimetry. On photopolymerization, the new monomers yield interesting networks. © 1993 John Wiley & Sons, Inc.     

Calorimetric study of photopolymerisation of divinyl monomers

Isothermal differential scanning calorimetry (photocalorimetry) enables real‐time measurements of rates of polymerisation as functions of irradiation time to be made. Since it is possible to stop initiation at any point in a reaction (by cutting off the light) and to monitor the dark reaction, this method has been widely used for determinations of the (apparent) rate constants of polymerisation of multifunctional monomers at various degrees of double bond conversion. The work reported here presents the results of photocalorimetric studies of polymerisation kinetics of six related acrylates and methacrylates. Two main topics are discussed: the effects of sulphide and ether groups present in the monomers on network formation, and the determination of polymerisation rate constants according to three termination models (monomolecular, bimolecular and mixed).     

Synthesis and Cationic Polymerization of Open-Chain and Cyclic Enol Ethers

Abstract

Several new open-chain and cyclic enol ether monomers were prepared using simple, straightforward procedures. The reactivities of these monomers were compared using both differential scanning photocalorimetry and Fourier transform real-time infrared spectroscopy. In general, these new monomers were found to possess excellent reactivity in photoinitiated cationic polymerization using a diaryliodonium salt photoinitiator.     

Synthesis,characterization and polymerization characteristics of new dimethacrylates,derived from 3,3,5‐trimethylcyclohexan‐1‐one–phenol adducts,as monomers for dental composites

The object of this study was to synthesize, characterize and evaluate several new dimethacrylate monomers, in order to discover new compositions for possible formulation of improved dental restoratives. Dimethacrylates derived from the 3,3,5‐trimethylcyclohexan‐1‐one–phenol reaction products were prepared and characterized by Fourier transform infrared and nuclear magnetic resonance. Thermal‐ and photopolymerization characteristics of these experimental monomers, in blends with triethyleneglycol dimethacrylate (TEGDMA), were evaluated by differential scanning calorimetry and differential photocalorimetry. An additional dimethacrylate derived from the 3,3,5‐trimethylcyclohexanone–phenol adduct, supplied by Bayer AG, was also evaluated during the study. A control for comparison consisted of a 2,2‐bis[4‐(2‐hydroxy‐3‐methacryloyloxy‐propyl) phenyl]propane (BisGMA) blend with TEGDMA. It was found that the polymerization behavior and properties of the visible light‐cured neat resins were dependent on their chemical structures. The experimental resins exhibited comparable curing characteristics, lower water sorption, higher wet glass transition temperature, and other improved properties, compared with the polymerized BisGMA/TEGDMA control. The more rigid and hydrophobic nature of the experimental resins, accomplished by incorporation of the bulky trimethyl‐substituted cyclohexyl moiety in the novel dimethacrylates, was considered to be the major factor contributing to the improved properties. These new dimethacrylates, for formulating thermosets with lower water sorption and higher glass transition temperature, may offer a path to improving composites for a variety of applications, including such things as dental restoratives and bone cements. Copyright © 1999 John Wiley & Sons, Ltd.     

Closed-loop recycling. A case study of films for greenhouses

The degradation undergone by plastic films used for greenhouse coverage is the main cause of the worsening of the processability, of the mechanical properties and of the durability of secondary materials obtained by their recycling. This means that this secondary material cannot be processed to produce films for the same applications (closed-loop recycling).In this work different strategies are proposed to improve the processability, some mechanical properties and the resistance to photo-oxidation of these secondary materials. In particular, homopolymer blends or multilayer films where the secondary material is used in combination with virgin polymer give the best results.     

The Synthesis,Characterization, and Photoinitiated Cationic Polymerizaton of Difunctional Oxetanes

Abstract

Seven novel difunctional oxetane monomers have been prepared and characterized using standard spectroscopic techniques. The photoinitiated cationic polymerization of these seven monomers was carried out and their reactivity compared to a typical diepoxide monomer. In these studies the reactivities of the various oxetane monomers were evaluated and compared by three different techniques: gel time measurements, differential scanning photocalorimetry, and real time infrared spectroscopy. It was observed that the difunctional oxetanes are generally more reactive than their structurally similar epoxide counterparts in photoinitiated cationic polymerization.     

Study on affecting factors of curing rate in ultraviolet curing adhesives containing modified acrylic ester prepolymers

Abstract

Ultraviolet (UV) curing adhesives have been extensively utilized in fields of health care and electronic components due to low energy consumption and solvent pollution. The most used system is modified acrylic ester system whose merits are low cost, high reliability and tensile strength. However, higher UV curing rate is still pursued especially in field of quick dry adhesives as well as influencing factors of curing rate are very complex. For clarifying affecting factors of curing rate as well as achieving higher curing rate, in this work, several UV curing adhesives with acrylic photosensitive resin prepolymers modified by epoxy and polyurethane were prepared. The impacts of class and content of radical photo-initiators, prepolymers and reactive diluents on UV curing rate were deeply researched. Moreover, the influence of oxygen polymerization inhibition on curing rate was discussed as well. The significantly elevated curing rates were obtained in as-prepared adhesives, in comparison with commercial ones. This work might offer a facile and effective strategy to obtain the promising high-performance modified acrylic ester prepolymer bearing UV curing adhesives with a significantly elevated high curing rate by well controlling these investigated affecting factors.     

Diamidophostes as Precursor for Phosphonitride Glasses

Abstract

Phosphate glasses arc of potential interest because of their low melting points and high thermal expansion coefficient. The chemical durability of these glasses can be improved considerably by substitution of some oxygen ions by nitrogen. This substitution improves the mechanical properties and chemical durability. The substitution of oxygen may be obtained by doping the melt with nitrides or remelting the glass in ammonia.     

Synthesis and Photopolymerization of Multifunctional Propenyl Ether Monomers

Abstract

A novel and facile synthesis of aromatics containing di- and tetrafunctional propenyl ether monomers is reported. These monomers were prepared by the base-catalyzed condensation of allyl glycidyl ether with a variety of bisphenols followed by allylation of the secondary hydroxyl groups and finally isomerization of the allyl groups by a ruthenium catalyst. The cationic photopolymerization of these novel monomers to give crosslinked network polymers was carried out using a diaryliodonium salt photoinitiator. The reactivity of the multifunctional propenyl ether monomers was studied using real-time infrared spectroscopy and by differential scanning photocalorimetry.     

Photopolymerization of (meth)acrylates in the presence of polyheteroarylenes

The free-radical photopolymerization of (meth)acrylates in the presence of a polyheteroarylene dissolved in a monomer has been studied. The kinetics of the radical polymerization of these monomers mediated by polyheteroarylene and the corresponding model compound has been investigated by differential scanning photocalorimetry and IR spectroscopy. Based on the experimental data, it is inferred that copolymers form due to chain transfer and/or chain termination to polyheteroarylene macromolecules. With the use of ESR spectroscopy, new radicals generated upon the addition of model polyheteroarylene compound to the initial solutions are discovered and characterized. The mechanism of the formation of copolymers is advanced.     

Thermal and photochemical ageing of epoxy resin - Influence of curing agents

The thermal and photochemical ageing of epoxy resin was studied using photoacoustic-FTIR spectroscopy. This technique was satisfactory for both unfilled resin and glass fibre filled epoxy composite. The influence of the curing agent (anhydride or amine) was significant for ageing. The durability of anhydride-epoxy system was the best for both thermal and photoageing.     

Investigation on mechanical properties, durability and micro-structural development of steel slag blended cements

To improve the properties of steel slag blended cements, a chemical activator was added into blended cements, the mechanical properties and durability of steel slag blended cements were investigated. The results show that steel slag in blended cement pastes presents low hydraulic activity and makes practically no contribution to strength development. After the addition of chemical activator, the mechanical properties and durability of ternary blended cements are increased significantly. The hydration process and micro-structural development of blended cement was investigated by isothermal calorimeter and scanning electric microscope, respectively. Steel slag started hydration in the first 3?days in the presence of chemical activator, steel slag and granulate blast furnace slag reacted with Ca(OH)₂ to form a dense microstructure as curing proceeded. Therefore, both early and late compressive strengths of steel slag blended cement with 35% cement clinker and 30% steel slag can be comparable with those of Portland cement.     

Propenyl ethers. II. Study of the photoinitiated cationic polymerization of propenyl ether monomers

The results of studies of the photoinitiated cationic polymerization of mono-, di-, and multifunctional propenyl ethers are reported in this article. Real-time infrared spectroscopy and differential scanning photocalorimetry were used to determine the reactivity of the monomers with respect to each other and in relation to other types of cationically polymerizable monomers. Propenyl ethers were observed to be highly reactive monomers in photoinitiated cationic polymerization undergoing very high conversions to polymer at very short irradiation times. Attempts were also made to correlate the structures of these monomers with their reactivity as well as to examine the effects of various experimental parameters on their photopolymerization. © 1993 John Wiley & Sons, Inc.     

Synthesis,characterization, and polymerization of propenyl ether analogues

A series of aromatic monomers bearing cationically polymerizable propenyl groups were prepared and characterized using the readily available starting materials: isoeugenol and o-allyl phenol. Monomers with both propenyl and vinyl ether functional groups were also synthesized by the reaction of these starting materials with chloroethyl vinyl ether. The reactivity of the resulting monomers in photoinitiated cationic polymerization was studied using differential scanning photocalorimetry and photogel point measurements. Their thermal properties were determined using thermogravimetric analysis. © 1994 John Wiley & Sons, Inc.