含二茂铁的双取代哒嗪的合成和介晶性

合成了8个未见报道的中心桥连基为哒嗪环、酯基、CHN基,含有二茂铁、三个苯环、不同末端链长度的双取代哒嗪化合物,并通过示差扫描量热仪(DSC)对其介晶性进行了表征.研究表明,末端链长度对相变温度和清亮点温度均有影响,但对相变温度范围影响较小.     

含胆甾基的双取代哒嗪的合成和介晶性

合成了8个未见报道的中心桥连基为哒嗪环、酯基、CH＝N基,含有胆甾基、二个苯环、不同末端链长度的双取代哒嗪化合物,并通过示差扫描量热法(DSC)对其介晶性进行了表征.研究表明,末端链长度对相变温度和清亮点温度均有影响,但对相变温度范围影响较小.     

双取代哒嗪有机液晶的合成、结构及刚性实对介晶性的影响

合成了16个中心桥连基为哒嗪环、酯基或CH=N基,含有苯环、不同刚性实长度和不同末端链长的哒嗪化合物,并通过DSC对其介晶进行了表征。研究表明,末端链长度对相变温度和清亮点温度均有影响,但对相变温度范围影响较小,而刚性实长度对其影响却较大。     

含西佛碱的3,6-双取代哒嗪的合成和介晶性

合成了8个中心桥连基为哒嗪环、酯基、CH=N基,含有胆甾基、三个苯环、不同未端链长度的双取代哒嗪化合物,并通过示差扫描量热法（DSC）对其介晶性进行了表征。研究表明,末端链长度对相变温度和清亮点温度均有影响,但对相变温度范围影响小。     

单取代二茂铁有机液晶的合成、结构及刚性实对介晶性影响

合成了17个未见报道的中心桥连基为酯基、C==N基,分别含有3-4个苯环,不同刚性实长度以及不同末端链长度的二茂铁化合物,并通过DSC和偏光显微镜对其介晶性进行了表征.研究表明,末端长度对相变温度和清亮温度均有影响,但对相变温度范围影响较小,而刚性实长度对其影响却很大.当刚性实达到一定长度时,末端为H原子也具有介晶性---这是第一个无柔性末端链的金属有机液晶化合物.     

3-甲氧基-6-(4-烷氧苯基)哒嗪的合成及介晶性研究

在三苯基膦钯的催化下，由3－氯－3－甲氧基哒嗪与对烷氧苯基硼酸偶联合成了7种具有液晶性的中心桥连基为哒嗪环，不同烷氧基长度的含有苯环的哒嗪衍生物，并通过DSC和偏光显微镜对其介晶性进行了表征。研究表明，末端链长度对相变温度和清亮点温度均有影响，但对相变温度的影响较小。     

3-烷氧基-6-（4-甲氧羰基苯基）哒嗪的合成及介晶性研究

3，6-二氯哒嗪和醇在相转移催化剂(C_4H_9)_4NBr和浓碱作用下，合成3-氯- 6-烷氧基哒嗪，在三苯基膦钯的催化下，用3-氯-6-烷氧基哒嗪与对甲氧羰基苯基 硼酸偶联，并以较好产率合成了八种中心桥连基为哒嗪环，含有苯环、酯基、不同 长度烷氧基的哒嗪衍生物，并通过差示扫描量热法（DSC）对其介晶性进行了表征 ，同时发现其中七种都具有介晶性。研究表明，末端链长度对相变温度和清亮点温 度均有影响。     

疏水改性无规共聚物水凝胶体积相变研究

以偶氮二异丁腈(AIBN)为引发剂,合成了一系列疏水改性的甲基丙烯酸β-羟乙酯(HEMA)无规共聚物水凝胶,研究了离子强度、pH、温度等条件对凝胶体积相变的影响。结果表明,疏水基末端端基的疏水程度决定凝胶体积相变的速率,随着疏水性单体甲基丙烯酸酯烷基链的增长,凝胶的疏水性增强,凝胶的相转变pH向低pH处迁移;温度高于LCST时,分子间的氢键作用减弱,疏水基团间的相互作用加强,凝胶发生体积相变。     

长链烷酸接枝羟丙基纤维素相变材料的制备及其性能

采用酯化的方法将具有相变特征的长链脂肪酸接枝到羟丙基纤维素主链上, 得到了一系列性能稳定, 温度范围适宜的高分子固-固相变材料, 并利用傅里叶红外光谱(FT-IR)、核磁共振(NMR)、差示扫描量热仪(DSC)、热失重分析仪(TGA)和X射线散射等技术手段对其化学结构及相变行为进行了研究。 结果表明, 该材料呈现出可逆的固-固相转变特性, 相变温度范围可通过改变脂肪酸的长度调节。 利用棕榈酸、硬脂酸和花生酸获得的相变材料焓值达到60 J/g, 所获得的材料在250 ℃以内不发生热分解。 通过将两种长链脂肪酸混合同时接枝到羟丙基纤维素主链上, 所得产物的吸/放热温度随着混合脂肪酸组分含量的变化而变化, 同时X射线散射的结果也证明羟丙基纤维素混合酯的分子间距是位于其两种单一酯之间的。这一结果为制备一定温度范围内任意相变温度的高分子固-固相变材料提供了简便的方法。     

无柔性间隔基侧链型液晶高分子复合定形相变材料的制备与性能研究

设计合成了一系列具有不同烷氧基尾链长度的单体4′-烷氧基-4-联苯酚甲基丙烯酸酯Mbi Cm(m=1,2,4,6,8,10,12,14,16,18),通过自由基聚合方法合成了相应的具有不同烷氧基尾链长度的无柔性间隔基侧链型液晶高分子PMbi Cm,将所得的侧链型液晶高分子和相变材料石蜡按一定质量比混合,通过"加热-冷却法"成功制备了定形相变材料.通过凝胶测试发现当尾链长度为m=12,14,16,18时,高分子对固体石蜡具有良好的凝胶定形效果,且随着烷氧基尾链的增长,聚合物和石蜡的相容性增加,最低凝胶浓度降低,得到定形相变材料的凝胶解缔温度也相应下降.通过示差扫描量热法(DSC)、热重分析法(TG)、流变(Rheology)等测试考察了定形相变材料的相变储能性能、热稳定性和流变性能,实验结果表明该定形相变材料具有相变焓值高、热稳定性好、凝胶强度高等优点.通过红外光谱(FTIR)、偏光显微镜(POM)和扫描电镜(SEM)等测试发现PMbi Cm通过非共价键作用力自聚集形成三维凝胶网络结构,对石蜡起固定支撑作用.     

Active fiber length distribution and its application to determine the critical fiber length

A new test and evaluation method has been developed to determine the critical fiber length characteristic of short fiber reinforced composites. From the so-called active ‘barbe’ (beard) length distribution calculated from the length distribution of the fibers in the composite and from the length distribution of the fibers protruding from the fracture surface, measurable characteristics have been derived, from which the critical fiber length can be determined. In order to demonstrate the applicability of the method, some measurements and calculations have been performed for injection molded glass fiber reinforced poly(ethylene-terephthalate) samples and the critical length determined has been compared with that obtained from droplet pull-out tests. It has been concluded that the new method provides an easily evaluated result, which is closer to reality than those obtained by other methods.     

Liquid crystalline properties and dependence of transition temperatures on the length of the flexible alkylene spacer of symmetric dimers composed of bent-core units

Three new series of symmetric dimers composed of bent-core molecules connected by a flexible alkylene spacer have been synthesized and their mesomorphic properties studied. The effect of varying the length of the terminal chains for fixed odd and even spacers, as well as varying the spacer length for a fixed terminal chain length, on the mesomorphic properties has been investigated. Remarkably, all the dimers investigated show the same type of mesophase, which has been characterized as a Col_obP_F phase, on the basis of X-ray diffraction and electro-optical measurements. It is found that for a fixed spacer length, the thermal range of the mesophase increases with increase in the number of methylene units in the terminal chain. On the other hand, interestingly an odd-even effect is observed when the length of the flexible spacer is varied; dimers having an odd number of methylene units possess higher clearing points.     

Bond lengthening and through-bond interactions in p,p'-dibenzene and related molecules

The structure of p,p'-dibenzene (PDB) has been investigated by full geometry optimizations using the empirical force field (EFF) and MINDO/3 methods. While other structural parameters are in good agreement, the central bond length calculated by MINDO/3 (1.595 Å), as confirmed by an ab initio (STO-3G basis set) optimization (1.596 Å), is in striking contrast to the corresponding length calculated by EFF (1.543 Å). A detailed analysis of the electronic structure of PDB based on a quantitative perturbational molecular orbital treatment reveals that through-bond coupling of the four π systems is responsible for an elongation of the σ bond which mediates this interaction. Further studies using the EFF and MINDO/3 approaches demonstrate that extended C-C single bonds can arise even in structures with fewer than four π systems. The effect of substituents on the central bond length in PDB has been briefly investigated. (MINDO/3). A variety of other structures have been identified in which bond lengthening may result from through-bond coupling.     

Synthesis and phase behaviour of a homologous series of polymethacrylate-based side-chain liquid crystal polymers

The homologous series of side chain liquid crystal polymers, the poly[ω-(4-methoxyazobenzene-4′-oxy)alkyl methacrylate]s, has been prepared in which the length of the flexible alkyl spacer has been varied from 3 to 11 methylene units. All the polymers exhibit liquid crystalline behaviour. The propyl and butyl members show exclusively nematic behaviour. The pentyl, hexyl, octyl and decyl members show a nematic and a smectic A phase while the heptyl, nonyl and undecyl homologues exhibit only a smectic A phase. The smectic A phase has been studied using X-ray diffraction and assigned as a smectic A₁ phase in which the side chains are fully overlapped and the backbones are confined to lie between the smectic layers. For the nonyl member an incommensurate smectic phase is observed. The dependence of the transition temperatures on the length of the flexible spacer is understood in terms of the average shapes of the side chains.     

Structural studies of ultrahigh-modulus polyethylene using nitric acid etching and gel permeation chromatography. II. Influence of polymer molecular weight,draw temperature,and annealing

The technique of nitric acid etching followed by gel permeation chromatography has been used to determine the crystal length distribution in ultrahigh-modulus polyethylenes. The crystal length distribution has been studied as a function of draw ratio, polymer molecular weight, processing conditions, and annealing. The results confirm that although there is a considerable broadening of the crystal length distribution on drawing, the majority of crystals have lengths less that 500 Å. There are detailed changes in the length distribution due to changes in draw temperature, molecular weight, and annealing which are not always reflected in corresponding changes in the long period determined from small-angle x-ray scattering. Possible reasons for these discrepancies are discussed.