Effect of spacer length on the thermal properties of side-chain liquid-crystal poly(methacrylate)s
Effect of spacer length on the thermal properties of side-chain liquid-crystal poly(methacrylate)s
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DOI：
10.1039/jm9940401705
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发表时间：
1994
影响因子：
--
通讯作者：
A. Craig;C. Imrie
中科院分区：
文献类型：
--
作者：
A. Craig;C. Imrie
合成了一系列侧链液晶聚合物--聚[ω-(4‘-甲氧基联苯-4-氧基)甲基丙烯酸烷基酯]S，其间隔基团长度为3~12个亚甲基单元。这是基于聚甲基丙烯酸酯的侧链液晶聚合物系列的第一个例子，已经为其制备了多达10个同系物。用差示扫描量热法和偏光显微镜对其热性能进行了表征。所有10个同系物都表现出近晶行为；此外，丁基同系物具有致线虫作用。随着间隔物的长度和奇偶性的变化，清除温度和相关的熵变化表现出明显的奇偶效应，其中奇数成员表现出更高的值。根据改变间隔物的奇偶性时侧链的平均形状的变化，这种行为是合理的。将聚合物的性能与含有相同介晶基团但不同聚合物主链的聚合物进行比较，以考虑柔性对热行为的影响。总体而言，这些比较支持这样一种观点，即增加主干灵活性增强了清算过渡，同时倾向于减少与过渡相关的熵变。这一规则的例外是合理的，无论是在分子量依赖的影响方面，还是在以聚(降冰片烯)为基础的材料的情况下，被认为是由聚合物链的复杂微结构引起的。用低聚(环氧乙烷)链取代烷基间隔减少了聚合物的清除转变。这在低聚(环氧乙烷)间隔物的灵活性和优选构象方面是合理的。
A series of side-chain liquid crystal polymers, the poly[ω-(4′-methoxybiphenyl-4-yloxy)alkyl methacrylate]s, have been synthesized in which the spacer length is varied from 3 to 12 methylene units. This is the first example of a poly(methacrylate)-based side-chain liquid crystal polymer series for which as many as 10 homologues have been prepared. The thermal properties have been characterised using differential scanning calorimetry and polarised light microscopy. All 10 homologues exhibit smectic behaviour; in addition, the butyl homologue is nematogenic. The clearing temperatures and associated entropy changes exhibit a distinct odd–even effect as the length and parity of the spacer is varied with the odd members exhibiting the higher values. This behaviour is rationalised in terms of the change in the average shape of the side chain on varying the parity of the spacer. The properties of the polymers are compared to those containing the same mesogenic group but different polymer backbones in order to consider the effect of flexibility on thermal behaviour. In general, these comparisons support the view that increasing backbone flexibility enhances the clearing transition while tending to decrease the entropy change associated with the transition. Exceptions to this rule are rationalised either in terms of molecular weight dependent effects or in the case of poly(norbornene)-based materials, are thought to arise from the complex microstructure of the polymer chains. Replacing the alkyl spacer by an oligo(ethylene oxide) chain reduces the clearing transition of the polymer. This is rationalised in terms of the flexibility and preferred conformations of an oligo(ethylene oxide) spacer.