共查询到20条相似文献,搜索用时 31 毫秒
1.
Maurizio Ferrante Morena Petrini Paolo Trentini Giuseppe Spoto 《Journal of Thermal Analysis and Calorimetry》2012,107(2):757-761
The aim of this study is to evaluate light-curing composites polymerization quality (monomer/polymer) carried out at different
times and distances of irradiation through the thermal analysis (TG-DTA). Samples have been polymerized at 20, 40 and 60 s
(0-2-4-6-8 mm) through a constant polymerization and subsequently analysed by TG-DTA. The TG/DTA analysis shows that different
light-curing times and different distance of irradiation affect the quality of polymerization; it is necessary to increase
the curing time when the irradiation distance is longer than 2 mm. 相似文献
2.
Maurizio Ferrante Paolo Dottore Morena Petrini Paolo Trentini Giuseppe Spoto 《Journal of Thermal Analysis and Calorimetry》2012,109(2):939-944
The aim of this study has been to evaluate light-curing composites polymerization quality carried out by halogen and new-diode lamps through the thermal analysis (TG?CDTA). Samples have been polymerized at 3?C20?C40?C60?s by halogen lamp and 1?C3?C6?C9?s by new-diode lamp. The TG/DTA analysis shows that different light-curing times affect the degree of conversion of the composite, since by increasing the curing time the quantity of the monomer that has not reacted (residual) decreases. The new-diode lamp, according to the manufacturer, can cure composite restorations in few seconds; but at the conditions used in this study, the samples cured by the halogen lamp at the standard times of exposure, compared to the samples cured in few seconds by the new-diode lamp, show a lower mass loss. 相似文献
3.
Varghese Mathew Lizymol Xavier C. K. Mahadevan K. E. Abraham 《Journal of Thermal Analysis and Calorimetry》2011,105(1):123-127
Thermal decomposition of manganese malonate dihydrate single crystals grown by gel method has been studied using the TG-DTA
and DSC techniques. The presence of water molecules and the dehydration stages are discussed. Dielectric constant, dielectric
loss, and AC conductivity have been estimated as a function of temperature in the range of 40–120 °C for four different frequencies.
Thermal studies reveal that the material is thermally stable up to123 °C. The dielectric measurements indicate that the dielectric
parameters increase with the increase in temperature. Also, the dielectric constant and dielectric loss factor values decrease
whereas the electrical conductivities increase with the increase in frequency of the AC applied. 相似文献
4.
A radical polymerization reaction of acrolein is reported in this article. The free radical initiator which can effectively promote the free radical polymerization of acrolein is screened out. The optimal conditions of the reaction are investigated and the yield could be up to 93.67%, in which the ratio of initiator to monomer is 1:50, monomer concentration is 7.5 mol L?1, reaction temperature is 50 °C, and the reaction time is 6 h. The structure characterizations of the obtained polymers are performed using hydrogen nuclear magnetic resonance spectroscopy, fouriertransform infrared spectroscopy, and matrix‐assisted laser desorption ionization time of fligh mass spectroscopy. The results show that the structure of the polymer contains fragments generated by decomposition of the initiator, aldehyde groups, and vinyl groups. The reaction mechanism of acrolein polymerization in the presence of free radical initiator is proposed. Thus, a novel method for the preparation of polyacrolein via radical polymerization is provided in this article. 相似文献
5.
采用乳液聚合法将甲基丙烯酸甲酯(MMA)接枝到氯丁胶乳上,红外光谱和核磁共振氢谱证实了接枝产物的生成。 研究了反应温度、乳化剂浓度、引发剂浓度和单体浓度对表观聚合速率的影响。 结果表明,当反应温度为50 ℃,引发剂叔丁基过氧化氢 四乙烯五胺(t-BHP/TEPA)用量为氯丁胶乳干重的0.5%,单体/聚合物质量比m(M)∶m(P)=3∶5,乳化剂十二烷基连苯醚二磺酸钠(DSB)用量为单体总质量1%时,单体转化率和接枝效率分别为99.1%和54.9%。 聚合反应动力学关系式为:Rp=Kc(E)0.15c(I)0.30c(MMA)1.41,式中,K为常数,在40~55 ℃范围内,聚合反应的表观活化能Ea=60.2 kJ/mol。 接枝聚合基本符合自由基反应机理。 相似文献
6.
Jacques Laleve Mohamad‐Ali Tehfe Frdric Dumur Didier Gigmes Bernadette Graff Fabrice Morlet‐Savary Jean‐Pierre Fouassier 《Macromolecular rapid communications》2013,34(3):239-245
Two new photoinitiators with unprecedented light absorption properties are proposed on the basis of a suitable truxene skeleton where several UV photoinitiators PI units such as benzophenone and thioxanthone are introduced at the periphery and whose molecular orbitals MO can be coupled with those of the PI units: a red‐shifted absorption and a strong increase of the molecular extinction coefficients (by a ≈ 20–1000 fold factor) are found. These compounds are highly efficient light‐harvesting photoinitiators. The scope and practicality of these photoinitiators of polymerization can be dramatically expanded, that is, both radical and cationic polymerization processes are accessible upon very soft irradiation conditions (halogen lamp, LED…︁) thanks to the unique light absorption properties of the new proposed structures. 相似文献
7.
M Vivas 《European Polymer Journal》2003,39(1):43-47
In the present work the polymerization of ε-caprolactone (ε-CL) using Ph2Zn as initiator is reported. The effects of reaction temperature, molar ratio of monomer/initiator and reaction time on the yield and the molecular weight are investigated. The temperature is varied between 20 and 120 °C and the molar ratio of monomer to initiator between 200 and 800 mol/mol. The results indicate that the Ph2Zn induces the polymerization of ε-CL to high conversion and produces polymer with high molecular weight at temperatures around 40-60 °C. 相似文献
8.
The copolymers of methyl methacrylate (MMA) (or styrene (ST))/stearyl methacrylate (SMA) obtained from miniemulsion polymerization
were prepared and characterized. All the miniemulsions showed satisfactory colloidal stability upon aging due to the effectively
retarded Ostwald ripening by the reactive costabilizer SMA. In subsequent miniemulsion copolymerizations, monomer droplet
nucleation predominated in the particle formation process, but homogeneous nucleation could not be ruled out even at such
high levels of SMA (20–50 wt.%). The contact angle first increased rapidly and then leveled off when the SMA content increased
from 20 to 50 wt.% for both the copolymers of MMA/SMA and ST/SMA. At constant level of SMA, the copolymer of MMA/SMA with
a less hydrophobic composition showed a larger contact angle compared to the ST/SMA counterpart. The contact angle (103 ± 1°)
of the copolymer MMA/SMA (50/50 w/w) was comparable to that (104°) of PSMA. A schematic model was proposed to explain the experimental results. 相似文献
9.
Koji Takagi Kanami Okamura 《Journal of polymer science. Part A, Polymer chemistry》2019,57(24):2436-2441
The cationic polymerization of n‐hexyloxyallene was investigated by using halogen‐bonding organocatalysts ( Cat A – Cat D ). Although the neutral catalyst Cat C showed a poor polymerization activity, iodine‐carrying bidentate cationic catalyst Cat A brought about the smooth polymerization giving rise to a polymer with Mn of 2710 under [ Cat A ]:[IBVE‐HCl]:[monomer] = 10:10:500 in mM concentrations. Judging from the color change of polymerization system and electrospray ionization mass spectra of recovered catalyst, the decomposition of organocatalyst was suggested. When α‐bromodiphenylmethane was used as an initiator, the relatively controlled polymerization proceeded at the low monomer conversion likely due to the weak halogen‐bonding interaction of Cat A with the bromide anion. On the other hand, bromine‐carrying bidentate catalyst Cat D gave low‐molecular‐weight polymers (Mn < 1550) to be less suitable for polymerization. From the 1H‐NMR spectrum, it was found that the 1,2‐polymerization unit and 2,3‐polymerization unit are included in 75:25. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2436–2441 相似文献
10.
Various classes of dental composites have evolved over the years for various clinical applications, differing mainly in the relative proportions of their individual components (BisGMA, TEGDMA, UDMA, fillers, etc.). Four classes of composites have been investigated here via DSC and TG (after curing with blue light from a halogen light-curing unit): a ‘microhybrid’, a ‘nanocomposite’, a ‘flowable’ and a ‘fluoride-releasing’ variety. The aims were to compare various thermal properties amongst the four classes and also to compare the quality of polymerization of halogen light cure. We concluded that the DSC scans of all the polymers showed no exotherms, signifying the absence of any residual reactivity. However, the scans showed onset of endothermic regions before glass transition temperature (GTT), which may signify structural rearrangements within the polymers. The overall enthalpy ranged from ?1.4 to ?50 J g?1, with significant differences between the ‘fluoride-releasing’ variety and the rest. The ‘fluoride-releasing’ variety showed the largest endotherm, signifying greater mass loss than the rest. The GTT (129 °C) did not differ significantly amongst the composite types. These same parameters, on a second DSC run of the same samples, followed a pattern similar to the first run, albeit to a lesser degree in magnitude. Hence, no benefit was gained by heating after the initial ‘light’ cure. The initial and total mass losses were higher for ‘fluoride-releasing’ (19 and 46%) and ‘flowable’ (12 and 38%) types compared to ‘microhybrid’ (3 and 24%) and ‘nanocomposite’ (4 and 20%). In a clinical scenario, the ‘fluoride-releasing’ composite may adequately photopolymerize, given its use in thin layers. The microhybrid and nanocomposites might also polymerize well in thinner layers without the need for a secondary heat treatment. The ‘flowable’ variety on the other hand, is not recommended to be subjected to a secondary heat treatment, due to its inferior thermal stability. 相似文献
11.
J. L. Mateo M. Calvo P. Bosch 《Journal of polymer science. Part A, Polymer chemistry》2001,39(12):2049-2057
The kinetics and mechanism of the photoinitiated polymerization of tetrafunctional and difunctional methacrylic monomers [1,6‐hexanediol dimethacrylate (HDDMA) and 2‐ethylhexyl methacrylate (EHMA)] in a polystyrene (PS) matrix were studied. The aggregation state, vitreous or rubbery, of the monomer/matrix system and the intermolecular strength of attraction in the monomer/matrix and growing macroradical/matrix systems are the principal factors influencing the kinetics and mechanism. For the PS/HDDMA system, where a relatively high intermolecular force of attraction between monomer and matrix and between growing macroradical and matrix occurs, a reaction‐diffusion mechanism takes place at low monomer concentrations (<30–40%) from the beginning of the polymerization. For the PS/EHMA system, which presents low intermolecular attraction between monomer and matrix and between growing macroradical and matrix, the reaction‐diffusion termination is not clear, and a combination of reaction‐diffusion and diffusion‐controlled mechanisms explains better the polymerization for monomer concentrations below 30–40%. For both systems, for which a change from a vitreous state to a rubbery state occurs when the monomer concentration changes from 10 to 20%, the intrinsic reactivity and kp/kt1/2 ratio (where kp is the propagation kinetic constant and kt is the termination kinetic constant) increase as a result of a greater mobility of the monomer in the matrix (a greater kp value). The PS matrix participates in the polymerization process through the formation of benzylic radical, which is bonded to some extent by radical–radical coupling with the growing methacrylic radica, producing grafting on the PS matrix. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2049–2057, 2001 相似文献
12.
《Radiation Physics and Chemistry》2007,76(5):852-856
Radiation polymerization of butyl acrylate was performed in a microemulsion stabilized with a mixture of sodium of 12-acryloxy-9-octadecenoic acid and sodium dodecyl sulfate in a weight ratio of 2 at room temperature. BA content in microemulsion can be successfully improved up to 40 wt% with low surfactant concentration (lower than 10 wt%). The resulted stable, translucent microlatex contain particles with average diameter from 28.1 to 38.1 nm with different monomer content. Particle size depends on the dose rate and surfactant concentration. Effects of monomer content and dose rate on the maximum polymerization rate are discussed. 相似文献
13.
Naphthalic anhydride derivatives: Structural effects on their initiating abilities in radical and/or cationic photopolymerizations under visible light
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Pu Xiao Frédéric Dumur Jing Zhang Bernadette Graff Fabrice Morlet‐Savary Jean Pierre Fouassier Didier Gigmes Jacques Lalevée 《Journal of polymer science. Part A, Polymer chemistry》2015,53(24):2860-2866
Only one naphthalic anhydride derivative has been reported as light sensitive photoinitiator, this prompted us to further explore the possibility to prepare a new family of photoinitiators based on this scaffold. Therefore, eight naphthalic Naphthalic anhydride derivatives (ANH1‐ANH8) have been prepared and combined with an iodonium salt (and optionally N‐vinylcarbazole) or an amine (and optionally 2,4,6‐tris(trichloromethyl)‐1,3,5‐triazine) to initiate the cationic polymerization of epoxides and the free radical polymerization of acrylates under different irradiation sources, that is, very soft halogen lamp (~ 12 mW cm?2), laser diode at 405 nm (~1.5 mW cm?2) or blue LED centered at 455 nm (80 mW cm?2). The ANH6 based photoinitiating systems are particularly efficient for the cationic and the radical photopolymerizations, and even better than that of the well‐known camphorquinone based systems. The photochemical mechanisms associated with the chemical structure/photopolymerization efficiency relationships are studied by steady state photolysis, fluorescence, cyclic voltammetry, laser flash photolysis, and electron spin resonance spin‐trapping techniques. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2860–2866 相似文献
14.
J. L. Mateo M. Calvo P. Bosch 《Journal of polymer science. Part A, Polymer chemistry》2001,39(14):2444-2453
The kinetics and mechanism of the photoinitiated polymerization of tetrafunctional and difunctional methacrylic monomers [1,6‐hexanediol dimethacylate (HDDMA) and 2‐ethylhexyl methacrylate (EHMA)] in a polybutadiene matrix (PB) have been studied. The maximum double‐bond conversion, the maximum polymerization rate, the intrinsic reactivity, and the kinetic constants for propagation and termination have been calculated. Unlike the behavior followed by the SBS‐HDDMA and PS‐HDDMA systems, where a reaction‐diffusion mechanism occurs from the start of the polymerization at low monomer concentrations (<30–40%), in the PB‐HDDMA system the reaction diffusion controls the termination process only after approximately 10% conversion is reached, as for the bulk polymerization of polyfunctional methacrylic monomers. Before reaching 10% conversion the behavior observed can be better explained by a combination of segmental diffusion‐controlled (autoaccelerated) and reaction‐diffusion mechanisms. This is probably a consequence of the lower force of attraction between the monomer and the matrix and between the growing macroradical and the matrix than those corresponding to the other systems mentioned. For the PB‐EHMA system, the termination mechanism is principally diffusion‐controlled from the beginning of the polymerization for monomer concentrations below 30–40%, and for higher monomer concentrations, a standard termination mechanism takes place (kt ≈ 106) at low double‐bond conversions, which is diffusion‐controlled for high conversions (>40%). For PB‐HDDMA and PB‐EHMA systems, crosslinked polymerized products are obtained as a result of the participation of the double bonds of the matrix in the polymerization process. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2444–2453, 2001 相似文献
15.
UV光引发的丙烯酰胺反相乳液聚合 总被引:7,自引:0,他引:7
报道了不透明丙烯酰胺反相乳液体系的UV光引发聚合新方法 .使用普通中压汞灯并辅以适当搅拌 ,UV光引发丙烯酰胺 水 煤油 Span80 +OP 10反相乳液聚合可在 2 0min左右完成 ,所得聚合物分子量达千万 ;聚合过程中不存在恒速期 ,扫描电镜未观察到聚合前后乳胶粒径有数量级的变化 ,表明聚合反应以单体液滴成核为主 .此外 ,考察了光引发剂类型及浓度、单体浓度、乳化剂用量、反应温度等对聚合反应的影响 ,结果表明不同光引发剂的引发活性为Irgacure 2 95 9>(ITX +EDAB) >BDK ,引发剂浓度增加 ,反应速度先增加而后降低 ,存在一最大值 ;单体浓度增加 ,反应速度加快 ,聚合物分子量提高 ;乳化剂用量增加 ,反应速度加快而分子量变化不明显 ;聚合表观活化能为 13 34kJ mol. 相似文献
16.
Diogo P. Moraes Juliana S. F. Pereira Liange O. Diehl Márcia F. Mesko Valderi L. Dressler José Neri G. Paniz Guenter Knapp Érico M. M. Flores 《Analytical and bioanalytical chemistry》2010,397(2):563-570
In this work, three sample preparation methods were evaluated for further halogen determination in elastomers containing high
concentrations of carbon black. Samples of nitrile-butadiene rubber, styrene-butadiene rubber, and ethylene-propylene-diene
monomer elastomers were decomposed using oxygen flask combustion and microwave-induced combustion (MIC) for further Br and
Cl determination by ion chromatography (IC), inductively coupled plasma optical emission spectrometry (ICP OES), and inductively
coupled plasma mass spectrometry (ICP-MS). Extraction assisted by microwave radiation in closed vessels was also evaluated
using water or alkaline solution. Digestion by MIC was carried out using 50 mmol l−1 (NH4)2CO3 as the absorbing solution. The effect of the reflux step was also evaluated. Accuracy was evaluated using certified reference
materials with polymeric matrix composition and by comparison of results using neutron activation analysis. Agreement for
Br and Cl was better than 95% by MIC using 5 min of reflux, and no statistical difference was found using IC, ICP OES, and
ICP-MS for determination of both analytes. For MIC, the relative standard deviation (RSD) was lower than 5%. Using extraction
in closed vessels, a high amount of residues was observed, and recoveries were lower than 45% for both analytes. For oxygen
flask combustion, the agreement was similar using MIC but RSD was higher (20%). The residual carbon content, an important
parameter used to evaluate the digestion efficiency, was always below 1% for MIC. Using MIC, it was possible to digest elastomers
with high efficiency, resulting in a single solution suitable for halogen determination by different techniques. 相似文献
17.
Patel Sanjay V. Hobson Stephen T. Cemalovic Sabina Mlsna Todd E. 《Journal of Sol-Gel Science and Technology》2010,53(3):673-679
The responses of alkylamine functionalized organic bridged polysilsesquioxanes on chemicapacitive sensors to carbon dioxide
(CO2) are described operating at temperatures ranging from 15 to 50°C. These hybrid organic–inorganic network materials were synthesized
by the sol–gel polymerization of a mixture of a matrix monomer and functional monomer at various ratios followed by aging
and ink-jet deposition of the sol on each capacitive sensor. During exposure of the sensor to known concentrations of analyte,
the material’s capacitance was measured. From these changes in capacitance, detection limits ranging from 40 to 100 ppm were
calculated. Furthermore, a correlation was observed with increasing length of the alkyl chain in the amine monomer correlating
with an increase in CO2 sensitivity and a decrease in water sensitivity. These materials offer a new method for CO2 detection for building control systems or other low-power applications using low operating temperatures. 相似文献
18.
Ulrica Edlund Ann‐Christine Albertsson 《Journal of polymer science. Part A, Polymer chemistry》2011,49(19):4139-4145
Chloro (Cl)‐ and bromo (Br)‐functionalized macroinitiators were successfully prepared from the softwood hemicellulose O‐acetylated galactoglucomannan (AcGGM) and then explored and evaluated with respect to their ability and efficiency of initiating single electron transfer‐living radical polymerization (SET‐LRP). Both halogenated species effectively initiate SET‐LRP of an acrylate and a methacrylate monomer, respectively, yielding brushlike AcGGM graft copolymers, where the molecular weights are accurately controlled via the monomer:macroinitiator ratio and polymerization time over a broad range: from oligomeric to ultrahigh. The nature of the halogen does not influence the kinetics of polymerization strongly, however, for acrylate graft polymerization, AcGGM‐Cl gives a somewhat higher rate constant of propagation, while methacrylate grafting proceeds slightly faster when the initiating species is AcGGM‐Br. For both monomers, the macroinitiator efficiency is superior in the case of AcGGM‐Br. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
19.
New flame-retardant nano/micro particles of sizes ranging between 0.06 ± 0.01 and 1.70 ± 0.23 μm were formed by dispersion polymerization of the pentabromobenzyl acrylate monomer (PBBA) in methyl ethyl ketone as a continuous phase. The effect of various polymerization parameters, e.g., monomer concentration, initiator type and concentration, stabilizer concentration and crosslinker monomer concentration, on the size, size distribution and polymerization yield of the produced poly(pentabromobenzyl acrylate) particles has been elucidated. Poly(pentabromobenzyl acrylate)/polystyrene (PPBBA/PS) nano/micro blends of the contents of different PPBBA particles were prepared by mixing the PPBBA particles with a PS solution in methylene chloride, followed by evaporation of the methylene chloride from the mixture. The thermal stability of these blends was also studied. 相似文献
20.
K. J. Ivin 《Angewandte Chemie (International ed. in English)》1973,12(6):487-494
The polymerizability of compounds such as 1,l-disubstituted ethylenes, aldehydes, ketones, isocyanates, and five- and six-membered ring compounds is determined largely by thermodynamic considerations. The transition from non-polymerizability to polymerizability, correspondlng to a change in the sign of ΔG, is often quite sharp. Factors which generally make the free energy of polymerization more negative, and which therefore favor polymerization, are low temperature, high pressure, and high monomer concentration. Additional driving force is sometimes available if the monomer is in the supercooled (glassy) state rather than the crystalline state, or if the polymer crystallizes on formation. Alkyl substituents have an unfavorable effect on polymerizability; halogen substituents have a favorable effect. Many monomers which do not homopolymerize for thermodynamic reasons will copolymerize with a second monomer to the extent of forming copolymers containing 50 or even 66 mol per cent of the first monomer. 相似文献