摘要
一些具有伸展构象的侧链液晶高分子,如甲壳型液晶高分子或树枝化高分子,可以经由分子链的平行排列而呈现柱状液晶相.一般认为,该类柱状相的基本结构单元是单根高分子链所形成的超分子柱.而以几根链组装形成的超分子柱,即"多链超分子柱",也可作为侧链液晶高分子柱状相的基本结构单元,但多年以来这一现象并未引起人们的重视.近期,我们以hemiphasmid型侧链液晶高分子为研究对象,阐明了"多链超分子柱"是侧链液晶高分子柱状相微相分离的一种重要形式.本文从hemiphasmid型侧链液晶高分子的柱状相结构分析、化学结构对"多链超分子柱"的影响、"多链超分子柱"模型的理论分析与预测、"多链超分子柱"的"柱内缠结"以及hemiphasmid型侧链液晶聚降冰片烯的功能性等若干方面,对基于"多链超分子柱"的侧链液晶高分子柱状相进行了介绍.我们认为,深入研究"多链超分子柱"性质,将拓展侧链液晶高分子的应用领域,加深对高分子物理基本问题的认识.
Side-chain liquid crystalline polymer(SCLCP) can form columnar liquid crystalline(LC) phases, in addition to the conventional nematic and smectic phase. For the SCLCP containing the discotic mesogenic group attached to the main-chain through a flexible spacer, the columnar phase relies on the assembly of the discotic mesogens. On the other hand, the SCLCP with extended conformation, such as mesogen-jacketed LC polymers and dendronized polymers, can exhibit the columnar phase based on the parallel packing of the cylindrical chains.In this case, "single chain column " is considered to be the building block of the columnar phase in general.Recently, our work on hemiphasmid SCLCP demonstrates that the "multi-chain column" is also important for the columnar phases of SCLCP. Hemiphasmid SCLCP possesses the hemiphasmid side-chain composed of a rod-like mesogen linked with a half-disk end group. It can readily self-organize into columnar phases with a pretty lager lattice parameter(e.g., 5 – 10 nm). It is found that the number of repeating units(Zrep) packed in a column stratum with a thickness of ~ 0.4 nm is surprisingly large. As an example, for the hexagonal columnar phase with the a parameter of ~ 6 nm, the value of Zrep is ~ 10. Squeezing a chain segment with 10 repeating units into the 0.4 nmthick column stratum is physically unreasonable. The "unusual Zrep" indicates the existence of "multi-chain column" that consists of a bundle of chains(e.g., 4 – 5 chains) laterally associated together. We synthesized a series of hemiphasmid SCLCPs with different chemical structures. Various main-chains have been employed,including polystyrene, poly(methacrylate), polyacetylene, and polynorbornene. The hemiphasmid moieties can invoke different rod-like mesogens, and can be attached to the main-chain directly or via a flexible spacer. For all the samples obtained, we have verified that the "multi-chain column" is applicable. The formation of "multi-chain column " can be understood from the nano-segregation among the main-chain, the rod-like mesogen and the flexible tails. Theoretical analysis indicates that the "multi-chain column " is a structure of thermodynamic equilibrium. The number of chains in the column is dependent on the volume fraction of the rigid component of the SCLCP. We propose that the chains in the column can interlock and intertwine, resulting in the intra-column entanglement. This hypothesis is supported by the study of hemiphasmid side-chain polynorbornene, which illustrates that the intra-column entanglement can endow the polymer with properties of thermoplastic elastomer.Moreover, the polymer can further exhibit excellent multi-shape memory effect at high strain. We anticipate that the further study of the "multi-chain column", which has been overlooked for years, will deepen our understanding of some fundamental issues of the structure and dynamics of polymers, and will also help to explore the new properties and applications of SCLCPs.
引文
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