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Zhen-hua Yuan De-yan Shen Ren-yuan Qian Polymer Physics Laboratory Center for Molecular Science Institute of Chemistry Chinese Academy of Sciences Beijing China 《高分子科学》2001,(4):399-405
Viscoelastic behavior of the non-Hooke deformation of amorphous PET film before yield was investigated in thetemperature region 74--80.5℃ around the glass transition temperature. The film specimen was drawn to yield point followedby unloading to zero stress, then the residual deformation was held constant, while the subsequent evolution of the stress wasrecorded. An induction period was found in the course of stress evolution fol1owed by a stress step-increase. The inductionperiod decreases with increasing drawing temperature with an activation energy of 1.10 MJ/mol·K, which is attributed tothe time needed for the relaxation of rubbery deformation through cooperative internal rotations. At temperatures lower than74℃, there is no stress increase or the induction period becomes too long to be observed. Thus the nature of anelasticity inthe non-Hooke region before yielding is attributed to stress induced rubbery deformation. The experimental results areinterpreted in terms of Perez' rheological model of a series connected Hooke spring and a Voigt element consisting of aparallel connected elastic spring and a dashpot. 相似文献
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A flexible approach to ethyl (3R,4S)-N-Boc-4-amino-3-hydroxy-5-phenylpentanoate (N-Boc-AHPPA-OEt), the γ-amino-β-hydroxy acid moiety of hapalosin is described. The synthetic method features a ring-opening ethanolysis of an activated N-Boc-lactam, which is obtained via a diastereoselective reductive-alkylation of (R)-malimide derivative. The flexibility of the method resides in the introduction of the alkyl side chain by Grignard reagent addition. 相似文献
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The present paper discusses some characteristics of the molecular volumes of phosphates, arsenates and vanadates. In the salts, the volumes of per acid radical ((?)) quantitatively depend on the radii, charges, numbers of cations and anions. The functional relations between the (?) values of phosphates, arsenates, vanadates and the factors mentioned above are obtained. The molecular volumes of these salts are equal to the sum of the topological volumes of cations and anions. The authors have got a series of universally united topological volume values of cations and anions. It confirms that the topological molecular volume of the crystal water (H_2O) in the hydrates of the salts approximates to a constant, 244 (?)~3 with σ_(n-1)= 2.1. The topological volume of the hydroxide ion (OH~-) approximates to a constant too. The average value is 16.89 (?)~3 with σ_(n-1)=1.68. 相似文献
127.
WANG Yan-Xia YE Song ② 《结构化学》2006,25(6):681-688
1 INTRODUCTION 2-Methylfuran belongs to the basic heteroaromatic compounds relevant to many fields of modern che- mistry, ranging from the study of natural products and biologically active substances to the develop- ment of building blocks for organic synthesis and conducting polymers[1]. Since the photochemistry ofR-furan was gradually recognized in 1960s[2~7], lots of interest has been aroused. Herein we only study one branch of photoche- mistry of R-furan: the isomerization of 2-methy… 相似文献
128.
Crosslinking is one of the effective routes for improving the orientation stability of poledpolymer films. The derivative of polyvinyl alcohol containing 4-nitro-4'-alkoxystilbene andphoto-crosslinkable cinnamyl groups as side chains has been synthesized. The in-situ simul-taneous photo-crosslinking poling of synthesized polymer films has been performed. Thesecond order nonlinear optical coefficient d_(33) of poled film is 11 pm/V. The SHG mea-surements show that the break-over temperature of SHG signal is raised obviously afterirradiation, its orientation stability is doubled as compared with that of non-crosslinkingsamples. 相似文献
129.
通过在聚氨酯泡沫模板中沉积多壁碳纳米管,用炭的预制体酚醛树酯将碳纳米管粘接固定在一起,经过高温碳化过程制备了碳纳米管-炭复合泡沫材料。红外光谱结果表明利用浓硫酸和浓硝酸的混合溶液处理可以使复合泡沫表面活化形成羧基和羟基,从而使复合泡沫具备较强的分子吸附能力。扫描电镜和氮吸附实验表明这种复合泡沫同时具备大孔和介孔,大孔能够满足流体自由流动的通畅性,介孔可以满足中分子的吸附需要。对标定物维生素B12的吸附实验证明这种复合泡沫对中分子量的生化分子具有有效的吸附能力。这种宏观尺寸的泡沫材料与传统的颗粒状活性炭相比具有简化工艺,提高吸附效率的应用潜力。 相似文献
130.