Transformation of a monotropic liquid crystalline polymer to an enantiotropic one by increasing molecular weight of the polymer
Transformation of a monotropic liquid crystalline polymer to an enantiotropic one by increasing molecular weight of the polymer
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通过增加聚合物的分子量将单向液晶聚合物转变为对映异构体
DOI：
10.1021/ma00155a042
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发表时间：
1986
期刊：
影响因子：
5.5
通讯作者：
Yaei Liu
中科院分区：
文献类型：
--
作者：
Qifeng Zhou;Xiaoqing Duan;Yaei Liu
液晶化合物有一个有趣的现象：有些是单性的，而大多数是对映性的。如果一种化合物在加热到其熔点(或在某些情况下，在玻璃化转变温度以上)和从其透明温度(即各向同性温度)以上冷却时都表现出稳定的液晶状态，则它是对映异性体。另一方面，如果它只在冷却时显示液晶状态，那么它是单色的。人们认为，这种单向性通常是由于晶体的有序性足够大，足以在介相热稳定性范围1以上保持真正的固体，因此，通过充分降低固体的熔点，可以揭示单性化合物潜在的对映行为。对于许多低分子体系，已经使用了各种杂质来实现这一目标。2 Lenz团队最近的一份报告讨论了通过在聚合物链中加入少量共聚单体将表面上的非液晶聚合物转化为向列相的工作。3虽然共聚可以降低熔点，从而有利于液晶态的形成，但共聚单体的加入也可以显著改变聚合物体系。无论添加的共聚物量多么少，聚合物的行为都是共聚的，而不是均聚的。也有聚合化合物的单色体系。Blumstein和他的同事首次观察到通过增加分子量从单色液晶化合物向对映体液晶化合物的转变。4合成了向列型聚酯聚(2，2‘-二甲基-4，4’-二氧基偶氮苯-十二烷基基)的模型化合物，发现分子量和分子量分布对转变温度和中间相稳定性有很大影响。它们的模型化合物9-DDA-9和9-DDA-9-DDA-9是单向性的，显示对映体向列相的最低分子量约为2800。最近，我们以L、10-二((氯甲酰基)苯甲酰氧基)正庚烷和2-甲酰基-1，4-二苯酚为原料，通过缩聚反应合成了一种低相对分子质量的单向型液晶聚酯。在这篇通讯中，我们报道了通过增加聚合物的相对分子质量将这种单性聚合物转化为对映性聚合物的过程。实验区。以1，10-二(氯甲酰基)苯甲酰氧基)癸烷和2-甲酰基-L，4-二苯酚为原料，通过溶液缩聚反应合成了该聚合物。
There is an interesting phenomenon associated with liquid crystalline compounds: some are monotropic whereas most are enantiotropic. A compound is enantio-tropic if it shows a stable liquid crystalline state both on heating to above its melting point (or, in certain instances, glass transition temperature) and on cooling from above its clearing temperature (ie, isotropization temperature). It is monotropic, on the other hand, ifit shows a liquid crystalline state only on cooling. It is believed that the monotropism is usually due to the extent of the crystalline order being great enough to preserve the true solid above the range of mesophase thermal stability, 1 and it is, therefore, possible to reveal the potential enantiotropic behavior of a monotropic compound by sufficiently de-pressing themelting point of the solid. For many low molecular weight systems various impurities have been used to achieve this objective. 2 A recent report from Lenz’s group discussed thework of transforming an apparently non-liquid crystalline polymer to nematic by incorporating a small amount of a comonomer into the polymer chains. 3 Although copolymerization can depress a melting point and thus favor theformation of a liquid crystalline state, a polymeric systemalso can be changed significantly by the incorporation of comonomers. No matter how little the amount of added comonomer, the polymer behaves as a copolymer and not as a homopolymer. There are also monotropic systems of polymeric compounds. The transformation of a monotropic liquid crystalline com-pound to an enantiotropic one by increasing molecular weight was first observed by Blumstein andcoworkers. 4 They synthesized model compounds of the nematic poly-ester poly (2, 2'-dimethyl-4, 4'-dioxyazoxybenzene-dodecanedioyl) and found that molecular weight and molecular weight distribution have a drastic influence on transition temperatures and mesophase stability. Their model compounds 9-DDA-9 and 9-DDA-9-DDA-9 are monotropic, and the lowest molecular weight to display an enantiotropic nematic phase is approximately 2800. Recently, we synthesized a monotropic liquid crystalline polyester of low molecular mass by polycondensation of l, 10-bis ((chloroformyl) benzoyloxy) decane and 2-formyl-1, 4-dihydroxybenzene. 5 In this communication we report the conversion of this monotropic polymer to an enantio-tropic one by increasing polymer molecular weight. Experimental Section. The polymer was synthesized by the solution polycondensation of the monomers 1, 10-bis-((chloroformyl) benzoyloxy) decane and 2-formyl-l, 4-di-hydroxybenzene: