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931.
Jae Woo Chung Se‐Bum Son Sang‐Wook Chun Tae Jin Kang Seung‐Yeop Kwak 《Journal of Polymer Science.Polymer Physics》2008,46(11):989-999
Exfoliated poly(ethylene terephthalate) (PET)‐layered silicate nanocomposites (PetLSNs) excluding (PetLSNeom) and including (PetLSNiom) organic modifiers were obtained by solution methods with and without solvent‐nonsolvent system, respectively. From wide angle X‐ray diffraction and high resolution transmission electron microscopy, both PetLSNs were found to have exfoliated structure attributed to sufficient dispersion of silicate in prepared solvents, regardless of sample preparation method. However, organic modifier in PetLSNeom was confirmed to be well removed by elemental analysis, whereas organic modifier was still remained in PetLSNiom. Thus, the effect of the presence and absence of organic modifiers in PetLSNs on the nonisothermal crystallization behavior was investigated by differential scanning calorimetry (DSC) on the basis of a modified Avrami analysis and polarized optical microscopy (POM). From DSC results, it was found that both PetLSNs had higher degrees of crystallinity and shorter crystallization half‐times than neat PET, because of the dispersed silicate layers acted as nucleating agents in both PetLSNs. However, PetLSNiom exhibited a lower degree of crystallinity and longer half‐time of crystallization than PetLSNeom. Difference of crystallization behavior between PetLSNeom and PetLSNiom was ascribed to organic modifier in PetLSNiom, which may act as crystallization inhibitors. POM measurements also revealed the results which were in good agreement with crystallization behavior observed from DSC measurement. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 989–999, 2008 相似文献
932.
Charles Kung Jeff Hixon Sung Choe Kevin Marks Stefan Gross Erin Murphy Byron DeLaBarre Giovanni Cianchetta Shalini Sethumadhavan Xiling Wang Shunqi Yan Yi Gao Cheng Fang Wentao Wei Fan Jiang Shaohui Wang Kevin Qian Jeff Saunders Ed Driggers Hin Koon Woo Lenny Dang 《Chemistry & biology》2012,19(9):1187-1198
933.
934.
Jin‐Woo Choi Byoung‐Ki Cho 《Journal of polymer science. Part A, Polymer chemistry》2011,49(11):2468-2473
We studied the conducting and mesomorphic behavior of a dendritic‐linear copolymer on adding hydrophilic additives and lithium salts. For the preparation of the pristine block copolymer ( A ), a click reaction of a hydrophobic Y‐shaped dendron block and a hydrophilic linear poly(ethylene oxide) coil with Mn = 750 g mol?1 was performed. For ionic block copolymer samples ( 1–3 ), a hydrophilic compound ( B ) bearing two tri(ethylene oxide) chains was used as the additive. In all ionic samples, the lithium concentration per ethylene oxide was chosen to be 0.05. As characterized by polarized optical microscopy and small angle X‐ray scattering techniques, copolymer A showed a hexagonal columnar mesophase. On addition of lithium‐doped additives, ionic samples 1 and 2 with the additive weight fractions (fw) of 10 and 20%, columnar and bicontinuous structures coexisted in the liquid crystalline phase. On the other hand, ionic sample 3 with fw = 30% displayed only a bicontinuous cubic mesophase. Based on the impedance results, with increasing the amount of additives, the conductivity value increased from 3.80 × 10?6 to 2.34 × 10?5 S cm?1 at 35 °C. The conductivity growth could be explained by the interplay of the plasticization effect of the mobile additive and the morphological transformation from 1D to 3D of the ion‐conducting cylindrical cores. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
935.
Eun Seon Kim Tai Young Park Kyoung Hwan Choi Woo Jin Choi Dong Hack Suh 《Journal of polymer science. Part A, Polymer chemistry》2021,59(18):2094-2106
The ability to tune the physical properties of polymeric materials through the different compositions in copolymer networks is suitable for the strategy of materials accompanied by combined high mechanical strength and stretchability simultaneously. Here, we developed a practical and straightforward strategy of a copolymer network structure via controlling the compositions of the acrylic-based urethane copolymers of diurethane acrylate (DUA) and diurethane cyclic acrylate (DUCA) with hydrogen-bonds through photo-polymerization. The copolymer networks led to the development of a physically cross-linked structure between the amide groups of DUA and/or DUCA and the hydroxyl groups of pentaerythritol ethoxylate (PEEL) by hydrogen-bonds. Based on the rheological analysis, the composition of the copolymer networks had a significant effect on the control of physical properties and development of cross-linked structure and thus led to the tunable comprehensive properties including high elastic modulus, high chain mobility and high recovery performance with a higher proportion of DUCA in the copolymer networks. Consequently, the tunable copolymer networks based on the developed physically cross-linked structure can improve the elastic properties, recovery performance, and healing ability simultaneously, providing significant progress in the fields of coating and adhesive. 相似文献
936.
937.
Dr. Irene Erdelmeier Dr. Gerd Bülow Dr. Chang-Wan Woo Dr. Jürgen Decker Prof. Dr. Gerhard Raabe Prof. Dr. Hans-Joachim Gais 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(35):8371-8386
In this article, the cross-coupling reaction (CCR) of exocyclic, axially chiral, and acyclic alkenyl (N-methyl)sulfoximines with alkyl- and arylzincs is described. The CCR generally requires dual Ni catalysis and MgBr2 promotion, which is effective in diethyl ether but not in THF. NMR spectroscopy revealed a complexation of alkenyl sulfoximines by MgBr2 in diethyl ether, which suggests an acceleration of the oxidative addition through nucleofugal activation. The CCR of alkenyl sulfoximines generally proceeds in the presence of Ni(dppp)Cl2 as a precatalyst and MgBr2 with alkyl- and arylzincs with a high degree of stereoretention at the C and the S atom. CCR of axially chiral alkenyl sulfoximines with Ni(PPh3)2Cl2 as a precatalyst and ZnPh2 does not require salt promotion and is stereoretentive. The reaction with Zn(CH2SiMe3)2, however, demands salt promotion and is not stereoretentive. CCR of axially chiral α-methylated alkenyl sulfoximines afforded persubstituted axially chiral alkenes with high selectivity. Alkenyl (N-triflyl)sulfoximines engage in a stereoretentive CCR with Grignard reagents and Ni(PPh3)2Cl2. Ni-Catalyzed and MgBr2-promoted CCR of E-configured acyclic alkenyl sulfoximines and aminosulfoxonium salts with ZnPh2 and Zn(CH2SiMe3)2 is stereoretentive with Ni(dppp)Cl2 and Ni(PPh3)2Cl2. CCRs of acyclic alkenyl sulfoximines and alkenyl aminosulfoxonium salts, carrying a methyl group at the α position, take a different course and give alkenyl sulfinamides under stereoretention at the S and C atom. CCR of acyclic, exocyclic, and axially chiral alkenyl sulfoximines has been successfully applied to the stereoselective synthesis of homoallylic alcohols, exocyclic alkenes, and axially chiral alkenes, respectively. 相似文献
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940.