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51.
In this preliminary report we present the mesomorphic properties and electro-optic investigations of three new 'banana-shaped' mesogens. The materials are structurally similar to Niori's the original bent-core materials but possess alkylthio substituents in place of alkoxy substituents. Microscopic investigations revealed an unusual 'spiral-domain texture', similar to that observed in the 'B7' phase of related materials. Further investigations support our earlier observations that the materials display antiferroelectric switching in this phase, in two of the new materials studied. The nature of this phase, in comparison with the 'switchable' (B2) and 'chiral-domain' (B4) phases of the original materials, is discussed. 相似文献
52.
Mira Abdallah Diego Magaldi Akram Hijazi Bernadette Graff Frdric Dumur Jean‐Pierre Fouassier Thanh‐Tun Bui Fabrice Goubard Jacques Laleve 《Journal of polymer science. Part A, Polymer chemistry》2019,57(20):2081-2092
In this article, new compounds based on the carbazole scaffold (DMs = DM1 and DM2, constituted by a carbazole unit connected on positions 3 and 6 to a two 4,4′‐dimethoxydiphenylamine groups and differing by the substituent present on the nitrogen heteroatom of the carbazole core) were synthesized and proposed as high‐performance visible light photoinitiators/photosensitizers for both the free‐radical polymerization of methacrylates and the cationic polymerization of epoxides upon visible light exposure using LED@405 nm. Remarkably, DM2 leads to higher final conversions than DM1. In order to study the photophysical and photochemical properties of the carbazole derivatives, different parameters were taken into account such as the light absorption, the steady‐state photolysis, and the fluorescence spectroscopy. Using different techniques such as fluorescence quenching, redox behavior, and cyclic voltammetry, we are able to discuss the photosensitization/photoinitiation reactions providing a full coherent picture of the involved chemical mechanisms. The photosensitization of the carbazole derivatives occurred predominantly via singlet excited states at the rate of the diffusion limit. Upon exposure to laser diode at 405 nm, DMs show high performance in initiating systems for 3D resins. Remarkably, DM2 can also be used in photocomposite synthesis using light‐emitting diode conveyor. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2081–2092 相似文献
53.
Flash DSC crystallization study for blown film grade bimodal HDPE resins. I. Isothermal kinetics and its application of the blown film modeling
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Cecilia D. Treviño‐Quintanilla Ramanan Krishnamoorti Jaime Bonilla‐Ríos 《Journal of Polymer Science.Polymer Physics》2016,54(23):2425-2431
Isothermal ultra‐cooling crystallization tests were conducted on three blown film grade bimodal HDPE resins using an ultrafast scanning calorimeter, the Flash DSC. Isothermal tests were performed to study the regime transition, the thermal nucleation and the spherulitical growth using the Hoffman‐Lauritzen theory in a range between 90 °C and 116 °C. Temperature profile estimations using such data were in good agreement with actual blown film process data. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2425–2431 相似文献
54.
Mohamed Baqar Tarek Agag Hatsuo Ishida Syed Qutubuddin 《Journal of polymer science. Part A, Polymer chemistry》2012,50(11):2275-2285
A new class of high‐performance resins of combined molecular structure of both traditional phenolics and benzoxazines has been developed. The monomers termed as methylol‐functional benzoxazines were synthesized through Mannich condensation reaction of methylol‐functional phenols and aromatic amines, including methylenedianiline (4,4′‐diaminodiphenylmethane) and oxydianiline (4,4′‐diaminodiphenyl ether), in the presence of paraformaldehyde. For comparison, other series of benzoxazine monomers were prepared from phenol, corresponding aromatic amines, and paraformaldehyde. The as‐synthesized monomers are characterized by their high purity as judged from 1H NMR and Fourier transform infrared spectra. Differential scanning calorimetric thermograms of the novel monomers show two exothermic peaks associated with condensation reaction of methylol groups and ring‐opening polymerization of benzoxazines. The position of methylol group relative to benzoxazine structure plays a significant role in accelerating polymerization. Viscoelastic and thermogravimetric analyses of the crosslinked polymers reveal high Tg (274–343 °C) and excellent thermal stability when compared with the traditional polybenzoxazines. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
55.
《Journal of polymer science. Part A, Polymer chemistry》2018,56(9):977-985
Polymeric networks are produced by step‐growth polyaddition and co‐polyaddition reactions of 1‐ethylimidazoline in combination with various diisocyanates. Five aromatic, two aliphatic diisocyanates and a polyurethane prepolymer are used as particular reactant in N,N‐dimethylformamide as solvent at room temperature. Obviously, 1‐ethylimidazoline can serve as trifunctional monomer, which enables a crosslinking reaction with diisocyanates. Molecular structure elements of the polymeric networks were studied by solid state 13C‐NMR spectroscopy revealing that detailed molecular structure formations are determined whether aromatic or aliphatic diisocyanates are used. Quantum chemical calculations were used as supporting method to elucidate the complex reaction cascades. Hence, it can be shown that beside 3:1 stoichiometric structures 2:1 based structures are formed as well. These structures are observed as kinetically controlled products only when aromatic diisocyanate monomers are used. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 977–985 相似文献
56.
57.
Sylvain Cousinet Ali Ghadban Imène Allaoua Frédéric Lortie Daniel Portinha Eric Drockenmuller Jean‐Pierre Pascault 《Journal of polymer science. Part A, Polymer chemistry》2014,52(23):3356-3364
Vinyl levulinate (VL) is used as a biobased reactive diluent in styrene (St)‐free unsaturated polyester resins (UPR). The reactivity ratios for the radical copolymerization of VL with diethyl fumarate (DEF) are determined by the Jaacks method (rVL = 0.01 and rDEF = 0.81 at 60 °C in DMSO‐d6). The properties of UPRs having a stoichiometric ratio between unsaturated groups from the UPR and either St or VL are compared. Defect‐free, slightly yellow, transparent, and rigid thermosets are obtained after a mild curing cycle. Due to unfavorable reactivity ratios about 5.5 wt % of unpolymerized VL remains inside the network and acts as plasticizer. Consequently, compared with St‐based ones, VL‐based UPRs exhibit lower α relaxation (Tα = 180 and 100 °C, respectively), lower elastic moduli at the rubbery plateau (G′ = 108 and 107 Pa) and lower mechanical properties as measured by three points bending tests. Strain at break (εf = 1.8 ± 0.2%) and Charpy impact strength (~2.7 ± 0.3 kJ m?2) are comparable independently of the RD chemical nature. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3356–3364 相似文献
58.
59.
Adel M. Elsharkawy Harvey W. Yarranton Tahar A. Al‐sahhaf Mohamed A. Fahim 《Journal of Dispersion Science and Technology》2013,34(2):224-229
Asphaltenes and resins separated from emulsion samples collected from Burgan oil field were used with heptane‐toluene mixtures as model oil to study the effect of oil aromaticity, resin content, and pH of the aqueous phase on the stability of water in model emulsions. It was confirmed that, as long as the asphaltenes are completely solubilized, increasing aromaticity leads to less stable emulsions. A consistent correlation between emulsion stability and relative resin mass content (R/(R+A)) was observed for all three of the field samples. There was a sharp decrease in stability when the R/(R+A) value exceeded 0.75. Emulsion stability was enhanced at high pH and possibly at very low pH (<2). 相似文献
60.
Ahmed M. Donia Asem A. Atia Hassnaa M. Abd El-Latif 《Journal of Dispersion Science and Technology》2014,35(3):380-389
Cellulose was modified via chlorination using phosphorous oxychloride followed by functionalization with amine and thiol moieties. The obtained modified cellulose samples were investigated by means of FTIR, TGA, TEM, and nitrogen-adsorption surface area (BET). The BET measurements showed a remarkable increase in the surface area of Cell-N-S (477.7 m2/g) and Cell-N (706 m2/g). The resins gave an uptake capacities of 38 and 7.2mmol/g for Cell-N-S and Cell-N, respectively toward Hg(II) from its solutions. These values are considered much better compared with other reported resins. Regeneration of the resins was achieved effectively using acidified thiourea. 相似文献