氢键构筑的甲壳型液晶高分子的设计合成和自组装

Design,Synthesis,and Self-assembly of Mesogen-Jacketed Liquid Crystalline Polymers Constructed by Hydrogen Bonding

通过引入氢键的方法,以聚(4-乙烯基吡啶)(P4VP)为氢键受体、含羧基的小分子为氢键给体,构筑了一类新结构的超分子甲壳型液晶高分子(MJLCP).利用傅里叶红外光谱(FTIR)、广角X射线散射等表征手段证明了氢键的形成,并系统研究了小分子的化学结构对超分子型MJLCPs液晶相行为的影响.结果表明,由于结构中只含1个(8MP)和3个苯环(4TP、6TP)且烷基尾链较短的氢键给体小分子在与P4VP复合时的“甲壳”效应较弱,P4VP(4TP)_(x)、P4VP(6TP)_(x)和P4VP(8MP)_(x)3类复合物在复合比例_(x)=1.0时仍处于无序状态.而尺寸更大的小分子氢键复合物P4VP(8TP)_(x)、P4VP(10TP)_(x)、P4VP(12MP)_(x)和P4VP(16MP)_(x)则随着复合比例的增加可以出现从无定形态向近晶(Sm)相结构的转变,并且随着烷基尾链长度和小分子刚性的增加,出现液晶相的最低复合比例逐渐减小.对于P4VP(12TP)_(x)这类氢键给体分子刚性较强且具有长烷基尾链的复合物,P4VP链在更高的复合比例下,为了容纳更多的小分子,还发生了从Sm相到六方柱状(Colh)相的结构转变.然而,氢键给体分子过大会阻碍氢键的形成,P4VP(8PP)_(x)在复合比例很低时出现了宏观相分离现象.氢键的引入大大简化了MJLCPs的构筑方法,通过对小分子化学结构和复合比例的控制可以实现对液晶相结构的灵活调控,为具有复杂结构的MJLCPs的分子设计提供了新的思路.

A new type of supramolecular mesogen-jacketed liquid crystalline polymer(MJLCP)was constructed by hydrogen bonding with poly(4-vinyl pyridine)(P4VP)as the hydrogen-bonding acceptor and carboxyl-containing molecules as hydrogen-bonding donors.The formation of hydrogen bonds was proven by Fourier-transform infrared spectroscopy(FTIR)and wide-angle X-ray scattering,and the effect of molecular structures on the phase behaviors of supramolecular MJLCPs was systematically studied.The results showed that because the"jacketing"effect of hydrogen-bonding donor molecules with only one(8MP)and three benzene rings(4TP and 6TP)and relatively short alkyl-chain tails was not strong enough when they were complexed with P4VP,the complexes P4VP(4TP)x,P4VP(6TP)_(x),and P4VP(8MP)_(x) are disordered at a molar complexing ratio x(between the donor and the acceptor)of 1.0.The four types of complexes P4VP(8TP)_(x),P4VP(10TP)_(x),P4VP(12MP)_(x),and P4VP(16MP)_(x) undergo a transition from an disordered structure to the smectic(Sm)phase when the complexing ratio increases,and the minimum ratio for the appearance of liquid crystalline phases gradually decreases when the length of alkyl-chain tails and the rigidity of the hydrogen-bonding donor increase.Because of the high rigidity of the hydrogen-bonding donor and its long alkyl-chain tails,the P4VP(12TP)_(x) undergoes a phase transition from disordered to the Sm phase and then to a hexagonal columnar(Colh)phase with the increase in the complexing ratio.However,if the size of the hydrogen-bonding donor molecule is too large,the formation of hydrogen bonds would be hindered,and macroscopic phase separation occurs in P4VP(8PP)_(x) even when the complexing ratio is very low.The use of hydrogen bonding greatly simplifies the construction of MJLCPs.The liquid crystalline phase can be flexibly regulated by controlling the structure of small molecules and the complexing ratio,which provides a new idea for the structural design of MJLCPs with complex structures.