Ionic naphthalene thermotropic copolyesters: Effect of ionic content
Ionic naphthalene thermotropic copolyesters: Effect of ionic content
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DOI：
10.1021/ma961703x
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发表时间：
1997-06
期刊：
影响因子：
5.5
通讯作者：
Y. Xue;M. Hara
中科院分区：
文献类型：
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作者：
Y. Xue;M. Hara
以5-磺酸钠形式引入离子型单体，制备了全芳香族（主链液晶）共聚酯型离子型萘系热致聚合物（NTP）。这种间位连接的单体将离子基团以及扭结单元引入聚合物链中。所有离子型NTP均达到成纤分子量。离子NTP的熔体显示出广泛的双折射，并且它们中的大多数在宽的温度范围内表现出双折射中间相织构，而在至少高达380 °C下没有显示出向各向同性相的转变。随着含离子单体含量的增加，离子型NTP的熔融温度（Tm）和结晶温度（Tc）均显著降低，这是由于扭结单元数的增加。在离子含量小于10 mol %时，玻璃化转变温度（Tg）相当恒定，当离子含量达到15 mol %时，Tg值发生跳跃，出现两个不同的Tg值，约为10 mol %。在20摩尔%离子含量下观察到40 °分离。这似乎是由两个相反因素之间的竞争引起的：一个是通过扭结单元降低主链的刚性，这导致较低的Tg，另一个是链之间的分子间离子相互作用，这导致较高的Tg。离子型NTP纤维的断裂表面表明随着离子含量的增加，自发原纤化受到抑制。这表明主链的刚性降低，并且通过聚合物链之间的离子相互作用增加了内聚性。此外，对于高离子含量NTP纤维观察到的平坦断裂表面反映了它们的脆性，这是由于更容易的裂纹扩展。
Ionic naphthalene thermotropic polymers (NTP) based on wholly aromatic (main chain liquid crystalline) copolyesters were prepared, in which ionic monomer was introduced in the form of sodium 5-sulfoisophthalate. This meta-linked monomer introduces ionic groups as well as kinked units into polymer chains. A fiber-forming molecular weight was achieved for all the ionic NTP. The melt of ionic NTP showed extensive birefringence, and the majority of them exhibited nematic mesophase textures over a wide temperature range, without showing a transition to an isotropic phase at least up to 380 °C. The melting temperature (T m ) and the crystallization temperature (T c ) of the ionic NTP are both decreased substantially with an increase in ion-containing monomer content because of an increase of the number ofkinked units. A unique glass transition behavior is also observed: at the ionic content of less than 10 mol %, the glass transition temperature (T g ) is rather constant, the T g value jumps when the ionic content reaches 15 mol %, and two distinct T g 's with ca. a 40 deg separation are observed at 20 mol % ionic content. This seems to arise from the competition between two opposing factors: one is a reduction of the rigidity of backbone chains by kinked units, which leads to lower T g , and another is intermolecular ionic interactions between chains, which lead to higher T g . Fracture surfaces of the ionic NTP fibers indicate suppression of spontaneous fibrillation with an increase of ionic content. This is an indication of decreased rigidity of the backbone chains and increased cohesion through ionic interactions between the polymer chains. Also, flat fracture surfaces observed for the high ionic content NTP fibers reflect their brittleness, arising from easier crack propagation.