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New organodilithium initiators were prepared in a hydrocarbon solvent in the absence of any polar additive. Although these initiators are insoluble when they are synthesized, they may be easily purified and reacted with dienes to give perfectly telechelic polydienes having unimodal distributions and low dispersity. A good agreement between experimental and theoretical molecular weights was observed. The polymer microstructures were similar to those of polymers initiated by butyllithium in the same solvent. Triblock thermoplastic elastomers were also prepared, the characteristics of which are given. The mechanical properties of a S.B.S. sample support also the claim of a good initiating ability and difunctionality of these initiators. 相似文献
23.
MgO/Ni系梯度功能材料的设计与制备 总被引:11,自引:0,他引:11
对MgO/Ni系梯度功能材料(FGM),分别用实验和微观力学模型测定和计算了用于热应力缓和设计的各物性参数。讨论了两种结果之间存在差异的原因。用有限元方法模拟了制备过程中FGM的热应力,得到MgO/Ni系FGM的综合设计准则。按设计结果进一步调整粉末工艺性质,成功地烧制出MgO/Ni系FGM。 相似文献
24.
25.
R.N. Sheppard 《Polymer》1984,25(3):369-374
Solution-chlorinated polyethylene prepared by a modified method has been characterized using 13C nuclear magnetic resonance (n.m.r.) and differential thermal analysis (d.t.a.). The results show that the residual paraffin segments, melting point and crystallinity decrease rapidly with increasing chlorine content. The prepared polymer seems to have a homogeneous chlorine distribution. 相似文献
26.
Highly oriented poly(p-phenylene benzobisthiazole) films were stressed in a miniature hydraulic tensile tester interfaced to a fast scanning Fourier transform infra-red spectrometer. The changes in relative intensity, polarization, frequency and shape of infrared bands have been useful in the elucidation of microstructures. With the short time resolution achievable, vibrational bandshape and frequency have been shown to change at different rates when an external stress was applied. 相似文献
27.
A review of analytical modeling of particulate reinforcement is made as a prelude to the problem of microstructural inhomogeneity in nanocomposite materials. Noting the inevitability of dispersion nonuniformity, and variations in agglomerate morphology and filler‐matrix interaction, the need to question the application of such models to novel materials arises. Employing the mechanical properties of alumina/epoxy nanocomposites, with known dispersion characteristics, an evaluation of the predictive capability of various models for Young's modulus, strength, and failure strain is made. Comparison between models is accompanied by a discussion of the parameters used in the fitting of macroscopic behavior to microstructural features. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 869–879, 2005 相似文献
28.
锆莫来石材料的反应烧结机制和显微结构特征 总被引:5,自引:0,他引:5
研究了用锆英石和工业氧化铝合成锆莫来石材料的反应烧结过程和显微结构。结果表明,添加适量MgCl2·6H2O可以促进反应烧结进程。锆英石大颗粒完全分解以后形成ZrO2聚集体,结构中出现封闭气孔可能与ZrO2聚集体有密切关系。加入MgCl2·6H2O后锆莫来石材料显微结构的主要特征:ZrO2有聚集体和均匀分布两种赋存形式;封闭气孔一般与ZrO2聚集体相邻。 相似文献
29.
A method for evaluating the dipole moments of copolymers in relation to the distribution of polar unit sequences is proposed. Experimental data on the synthesis and dipole moments of styrene-p-chlorostyrene and styrene-p-methoxystyrene copolymers were used to calculate the effective dipole moment of a polar unit in a copolymer. For this purpose, we assumed the following effective moment values for the corresponding polar unit sequences along the copolymer chains: when both of the nearest neighbours are polar, μPP, when one of the nearest neighbours is polar and the other is non-polar, μPS, and when both of the nearest neighbours are non-polar, μSS. The relative magnitudes of μSS, μPS and μPP calculated for both copolymers reflect the influence of dipole-dipole interactions on the effective dipole moment of a polar unit in a copolymer molecule. 相似文献
30.
The length and number of side chain branches have a profound influence on the microstructure and physical properties of polyethylene (PE). For a series of linear PE copolymers: environmental stress cracking resistance (ESCR), melting points, creep resistance and modulus, and equilibrium spherulite size were all found to increase with increasing branch length (methyl to hexyl) at a given density and molecular weight. It is proposed that (at a fixed molecular weight) branch length and branch concentration determine spherulite size and, consequently, spherulitic boundary areas, in which the dry crazing/voiding occurs during the incubation period of environmental stress cracking (ESC). At a fixed density, decreased spherulite size contributes to greater spherulite boundary slip and increased creep at low (less than 2 MPa) stresses. 相似文献