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以差示扫描量热法对热致液晶聚酯酰亚胺的结晶过程和液晶化过程的非等温相转变动力学行为进行了初步研究,根据Jeziorny方法处理数据得到了表征聚合物非等温相转变动力参数Zc,Gc并对其进行了讨论,结果表明,在所研究的条件下聚合物的相转变过程基本上符事Jeziorny结论,但两种相转变的成核与生长方式是不同的。 相似文献
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在经典的热力学理论基础上,探讨了磁场对聚合物本体结晶过程的成核与生长的影响,建立了相关结晶动力学理论方程.初步认为,磁场产生的"磁结晶效应"可能是由于晶相与非晶相之间磁化率差异导致了两相之间磁化能的差异,也可能由于聚合物体系在结晶前会形成一种有序相,减小了体系的熵值,进而改变了结晶过程中的体系自由能,影响其成核与晶体生长,乃至整个结晶动力学方程.利用Matlab软件结合PLLA的各结晶参数值,绘制了结晶自由能与各成核临界参数之间的函数图像.结果表明,在低过冷度下,较小的自由能扰动可能导致较大的晶核临界参数变化. 相似文献
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将N-异丙基丙烯酰胺(NIPAm)与具有温敏性的大分子单体进行共聚,制得了主链与支链在水溶液中具有不同相转变温度的温敏支化聚合物。经过双重相转变过程后,通过扫描电子显微镜(SEM)可以观察到聚合物链形成的具有较大比表面积的"葡萄串"结构,光散射实验中聚合物粒径大小随着温度升高发生两次突变进一步解释了双重相转变过程中聚合物微观形态的变化。在温敏支化聚合物溶液样品的差示扫描量热法(DSC)曲线中可以观察到35℃与21℃出现两组相对独立的吸热峰,从热力学的角度描述了双重相转变行为。通过使用二维红外相关光谱技术分析了温敏支化聚合物各基团对温度扰动的响应顺序,其结果说明仅存在于支链中的丙烯酸丁酯(BA)结构单元要先于NIPAm结构单元发生变化,对双重相转变行为的机理有了更进一步的说明。"葡萄串"结构的形成有效地提高了温敏聚合物的疏水比表面积,有望应用于生化分离领域。 相似文献
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用粗粒化的分子动力学(MD)模拟方法从分子层次研究了受限于粗糙壁内的聚合物熔体的动力学性质. 结果表明, 对于链长较短的受限聚合物熔体体系, 随着膜厚的增加, 体系内部高分子链的松弛时间逐渐减少; 然而对于链长较长的受限体系, 聚合物链的松弛时间随着膜厚的增加先减少后增加. 推测这种由于链长的变化所引起的动力学性质的差异源自受限熔体内聚合物链聚集状态的改变, 并且通过考察交叠参数对这种改变进行了分析. 结果表明, 在膜厚增加的过程中, 决定受限状态高分子长链松弛机理的因素逐渐从受限效应转变成为链间的缠结效应. 相似文献
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含非线性光学侧基的共聚酯的合成及相行为研究 总被引:2,自引:0,他引:2
通过熔融缩聚法合成了一类侧链含有非线性光学基元的共聚酯,用FTIR,NMR和元素分析等对单体和聚合物进行了表征,并用DSC,WAXD和偏光显微镜等对聚合物的相转变行为进行了研究,发现规整侧链的引入仍然结晶聚合物,对其结晶相的成因进行了初步分析。 相似文献
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伴随液晶相转变而产生的转变焓、转变熵可提供有关各相的结构、状态及有序度等信息.本文从动力学、热力学角度分析了液晶聚合物从各向同性熔体冷却时系统的热熵变化,建立了液晶聚合物升降温过程中的热熵图,提出了定量判断液晶聚合物从各向同性熔体冷却后所处状态的新方法. 相似文献
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The morphological features of a side-chain liquid crystalline polymer during the mesophasetransitions were investigated by using the DSC technique. The polymer used was polyacrylate with mesogensof three benzene rings attached to the main chain through a flexible spacer. A special two-phase texture wasobserved in the transition temperature range. Similar to main-chain liquid crystalline polymers the transitionprocess of the side-chain liquid crystalline polymer was composed of an initiation of the new phase at localplaces of the old phase matrix and a growth process of the new phase domains. 相似文献
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A new side chain liquid crystalline polymers have been synthesized and characterized in which [geraniol-co-MMA] polymer are
used as a backbone linked via polymethylene spacer to phenyl benzoate mesogenic group. The polymer exhibits enantiotropic
liquid crystallinity with nematic phase and does not exhibit side chain crystallization .A clear difference between the nature
of the mesophase is evidenced between [Geraniol-co-MMA] main chain and methacrylate polymers .The LC polymer exhibit glass
transition at 40 °C. In a comparative analysis, we discuss the relevance of polymer backbone in the synthesis of side chain
liquid crystalline polymers. 相似文献
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A series of cross-linked liquid crystalline polymers are prepared by graft copolymerization, and their liquid crystalline properties are characterized by DSC and POM. The results show that low levels of cross-linking do not obviously affect the phase behavior of the network polymers; in contrast, high levels of cross-linking may have more drastic influences, and liquid crystalline phases may lose, and more marked variation in phase transition will occur in materials with more direct coupling through a shorter or stiffer coupling chain between mesogenic side units and polymer backbone. At the same time, the coupling between the polymer chain and sidegroups results in stress-induced orientation in LCEs. 相似文献
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利用Higashi芳香聚酯直接缩聚法的原理,采用分步投料的方法,以N,N′-1,6-亚己基-双苯偏三酸酰亚胺二酸(IA6)、6-羟基-乙-萘甲酸(HNA)和4,4′-二羟基二苯酮(DHBP)为单体原料,合成了一系列聚酯酰亚胺共聚物.用核磁共振(NMR)、差热分析(DSC)、偏光显微镜(PLM)、广角X射线衍射(WAXD)、热重分析(TGA)等手段对所合成的聚酯酰亚胺的液晶行为、结构以及热性能进行了表征.研究结果表明,当HNA投料量占单体总投料量高于33mol%时,所得聚合物均呈明显的向列型热致液晶特性.但是,此类液晶聚合物仅在升温过程中出现液晶的相转变,而在降温过程中并未观察到液晶的相转变行为.由DSC结果分析可知,此类聚合物具有较高的玻璃化转变温度(Tg)和较低的熔融温度(Tm),有望成为一类既具有较低加工温度又有较高使用温度的液晶聚合物材料. 相似文献
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The synthesis and property of a new series of "mesogen-jacketed liquid crystal polymers" are reported. These polymers have aromatic amide structures as the mesogenic groups and are represented by poly-2,5-bis(4-methoxy- benzamido)styrene. The preliminary study on properties shows that the polymers have very high glass transition temperatures as well as very low critical concentrations for the formation of the lyotropic liquid crystal phase. The results indicate a high degree of chain rigidity. However, the liquid crystalline order of molecular organization in bulk samples disappears upon heating to the glass transition temperature as revealed by polarizing microscopy and by X-ray diffractometer. Therefore, the liquid crystalline order of these polymers forms only through solution but not through heating. This behavior is different from that of the previously studied poly-2,5-bis[(4-methoxybenzoyl)oxy]styrene and its homologs. The latter polymers are liquid crystals both lyotropically and thermotropically. © 1997 John Wiley & Sons, Ltd. 相似文献
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Mihaela Prajinaru Natalia Hurduc Silvia Alazaroaie Otilia Catanescu Nicolae Hurduc 《Central European Journal of Chemistry》2003,1(4):387-401
The paper presents a study of the thermal properties of some aromatic polyethers obtained by phase trasfer catalysis technique.
The polymes were synthesized starting from 1,8-dichloro-octane and various bisphenols: 4,4′-dihydroxyazobenzene, 4,4′-dihydroxydiphenyl,
bisphenol A and 2,7-dihydroxynaphthalene. Molecular simulations were performed in order to obtain supplementary information
concerning the chain conformation and inter-chain interactions. The presence of azobenzenic moieties induces high phase transition
values, situated near the thermal stability limit. Therefore, the thermogravimetrical study of these polymers is very important
for establishing the temperature limits for DSC and optical microscopy studies. All the polymers present a good thermal stability
situated above the isotropization values. In these circumstances no special precautions are necessary for the characterization
methods of the liquid crystalline behavior. The kinetic characteristics suggest a similar degradation mechanism by successive
reactions. The inter-chain interactions do not influence the thermostability of the samples if the polar surface of the polymer
is situated below a certain value. 相似文献
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A new series of liquid crystalline main chain copolyesters were prepared, having ferrocene in the mesogenic segment and a methyl phosphate group along with a methylene spacer. The even numbered methylene groups were varied from two to ten. Liquid crystalline behaviour was investigated on a hot stage optical polarized microscope. Thermal properties of the polymers were analysed by TGA and DSC, revealing that the polymers yield high char products, probably caused by the formation of phosphorus and iron oxides. The glass transition (Tg) temperatures of the polymers were found to be fairly low, the result of the incorporation of bulky phosphorus and ferrocene moieties in the chain. The phase behaviour was analysed and correlated with the structure of the polymers. The liquid crystalline textures of the polymers became more transparent with increasing spacer length. Energy minimized structures for the polymer repeating units reveal that both the ferrocene and phosphorus moieties produce more molecular entanglement, thus reducing the Tg and Tm of the polymers. 相似文献
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Chang‐An Yang Guo Wang Helou Xie Qing Wang Hailiang Zhang Erqiang Chen Qifeng Zhou 《Journal of polymer science. Part A, Polymer chemistry》2010,48(5):1149-1159
The first‐ and second‐generation dendronized polymers containing azobenzene mesogen were designed and successfully synthesized via free radical polymerization. The chemical structures of the monomers were confirmed by elemental analysis, 1H NMR, and 13C NMR. The molecular characterizations of the polymers were performed with 1H NMR and gel permeation chromatography. The phase structures and transition behaviors were studied using differential scanning calorimetry, polarized light microscopy, and small‐angle X‐ray scatter experiments. The experiment results revealed that the first‐generation dendronized polymer exhibited liquid crystalline behavior of the conventional side‐chain liquid crystalline polymer with azobenzene mesogen, that is, the polymer exhibited smectic phase structure at lower temperature and nematic phase structure at higher temperature. However, the second‐generation dendronized polymers exhibited more versatile intriguing liquid crystalline structures, namely smectic phase structure at lower temperature and columnar nematic phase structure at higher temperature, and moreover, the phase structure still remained before the decomposition temperature. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1149–1159, 2010 相似文献