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Dmitriy Alhazov Arkadiusz Gradys Pawel Sajkiewicz Arkadii Arinstein Eyal Zussman 《European Polymer Journal》2013
Analysis of the thermo-mechanical behavior of electrospun thermoplastic polyurethane (TPU) block co-polymer nanofibers (glass transition temperature ∼−50 °C) is presented. Upon heating, nanofibers began to massively contract, at ∼70 °C, whereas TPU cast films started to expand. Radial wide-angle X-ray scattering (WAXS) profiles of the nanofibers and the films showed no diffraction peaks related to crystals, whereas their amorphous halo had an asymmetric shape, which can be approximated by two components, associated with hard and soft segments. During heating, noticeable changes in the contribution of these components were only observed in nanofibers. These changes, which were accompanied with an endothermic DSC peak, coinciding with the start of the nanofibers contraction, can be attributed to relaxation of an oriented stretched amorphous phase created during electrospinning. Such structure relaxation becomes possible when a portion of the hard segment clusters, forming an effective physical network, is destroyed upon heating. 相似文献
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用动态光散射和透射电镜研究了嵌段共聚物聚苯乙烯-聚甲基丙烯酸甲酯(PS-b-PMMA)和其对应的均聚物聚甲基丙烯酸甲酯(PMMA)在选择性溶剂四氢呋喃/环己烷(THF/CYH)中的自组装行为.选择性溶剂对PS嵌段是良溶剂,对PMMA嵌段和均聚物PMMA是非良溶剂,实验结果表明,在适当的分子量及组成条件下,PS-PMMA/PMMA在选择性溶剂中形成了单分散的纳米胶束,均聚物PMMA与PMMA嵌段一同形成了胶束的核,通过控制均聚物PMMA的量可以在较大的范围内调整胶束的尺寸. 相似文献
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In order to investigate the potential of cyclodextrins for the preparation of block-like substituted polysaccharides, we submitted mixtures of heptakis[2,3,6-tri-O-methyl]-β-cyclodextrin (Me21-β-CD, 1) and heptakis[2,3,6-tri-O-methyl-d
3]-β-cyclodextrin ((Me-d
3)21-β-CD, 2) to cationic ring-opening polymerisation (CROP). Reactions were performed with BF3·OEt2, methyl triflate (MeOTf), and Et3OSbCl6. Products were compared with respect to their degree of polymerisation (DP) and the average block length (BL). Highest DP was observed with BF3·OEt2, while Et3OSbCl6 was the most active initiator. Average block length decreased from 14 in the early stage of product formation to about 2 due to competing chain transfer reaction. 1H NMR spectroscopy, GLC, GLC–MS, ESI-MS and MALDI-TOF-MS were applied for detailed investigations of side reactions. During incubation with BF3·OEt2, a stereroisomeric β-CD with one β-glucosidic linkage (Me21-β-CD6α1β, 3a (Me-d
3)21-β-CD6α 1β, 3b) is formed as an intermediate, while linear Me21- and (Me-d
3)21-maltoheptaose (4a/b) was detected in the early stage of the reaction promoted by MeOTf. In the case of Et3OSbCl6, both intermediates (3a/b, 4a/b) can be observed during the lag phase of polymerisation, but to a very low degree. End group analysis by GLC reveals that some alkyl exchange occurs at position 3 and 6 in the presence of Et3OSbCl6, and that polymerisation is also initiated by protons. Copolymerisation of heptakis[2,3,6-tri-O-benzyl]-β-cyclodextrin (Bn21-β-CD, 5) and Me21-β-CD (1) and subsequent debenzylation yielded a polymer of only 1,4-glcp-Me3- and 1,4-glcp-residues. Reactivity of Bn21-β-CD was significantly lower than of Me21-β-CD, resulting in higher average block length of 1,4-glcp-Me3-units. 相似文献
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Raquel Fernández Iñaki Zalakain José Angel Ramos Loli Martin Iñaki Mondragon 《European Polymer Journal》2011,(5):1176-1185
The main goal of this work was the synthesis of new azo-functionalized block copolymers (BCP) from epoxidized poly(styrene-b-butadiene-b-styrene) modified with azobenzene groups by one-step facile reaction between the epoxy groups and an azo-amine. The epoxy/amine reaction was verified by Fourier transform infrared spectroscopy. Additionally, we studied the effect of covalent attachment of the azobenzene moieties by analyzing the morphology and the optical anisotropic response of the resulting azo-containing BCP, with respect to solution mixing of the azobenzene as a guest in the BCP host without chemical bonding. Self-assembly of all modified BCP resulted in phase-separated morphologies on the nanometer scale. Nonetheless, segregation of azobenzene aggregates onto the BCP surface was observed in guest–host systems. In relation to the optical anisotropic behaviour of the resulting materials, two distinct optical responses were observed depending on the existence or not of covalent attachment of the azo-chromophores to the BCP. 相似文献
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