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The new branch - the synthesis and properties of linear liquid crystal polymer block

Author: WuJiWen
Tutor: WuPeiZuo
School: Fudan University
Course: Polymer Chemistry and Physics
Keywords: mesogen-jacketed liquid crystalline polymer (MJLCP) block copolymer dendron self-assembly phase structure
CLC: O631.3
Type: Master's thesis
Year: 2011
Downloads: 86
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Abstract


Liquid crystalline block copolymers (LCBCPs) are a fascinating class of polymeric materials consisting of liquid crystalline (LC) polymeric blocks and other polymeric blocks. In recent years, these LCBCP systems are of particular scientific interest since they have fascinating ability to show a hierarchical ordered structure:the morphology due to the microphase separation and the liquid crystalline phase due to the liquid crystallinity of LC blocks. The traditional LCBCPs are composed of distinct linear polymeric blocks. As we known, the molecular architecture has a great influence on the molecular properties. As a result, here we introduced the three-dimensional dendron molecules into the LCBCP system and designed a novel dendritic-linear LCBCP.Firstly, we synthesized the dendritic-linear LCBCPs integrating a Percec type dendrons and the mesogen-jacketed liquid crystalline polymer (MJLCP) poly{2, 5-bis[(4’-methoxyphenyl)oxycarbonyl]styrene} (PMPCS) through the atom transfer radical polymerization with the dendron molecules as macroinitiators. Thermal property investigation of the copolymers revealed that only the glass transition temperature belonging to PMPCS block was observed, indicating that the dendron molecule and the liquid crystalline polymer block were immiscible The subtle interplay between the thermotropic mesomorphic behaviors of PMPCS and the microphase structure in these dendron-LC copolymers was discussed. With increasing the molecular weight of PMPCS block, a morphological evolution from bilayer to interdigitated lamellar structure was proposed based on the small-angle X-ray scattering examination. More importantly, less-ordered columnar nematic phase instead of hexatic columnar nematic phase which should be stabilized in PMPCS block was identified by in-situ wide-angle X-ray diffraction experiments. The degradation of the hierarchical packing of PMPCS chain was attributed to the confinement effect originating from the interdigitated microphase structure.Temperature-variable infrared experiments have been used to trace the LC phase development of PMPCS chains in dendritic-linear LCBCP systems. Two-dimensional correlation spectroscopy (2DIR) and perturbation correlation moving window (PCMW) technique were employed to study the phase transition nature. PCMW show an "S" shaped spectral variation in the temperature range of 140-180℃.2DIR analysis indicated the methoxyl group possessing a largest freedom responded firstly during heating up. As one end of the PMPCS backbone was connected with the dendron molecule, the backbone might be forced to be stretched and would distort during LC phase development. Thus, Compared with the side chain, the backbone of PMPCS has an earlier response. And the response of side chain began from the end groups in the mesogenic units, followed by the movement of the benzene rings of the mesogenic cores.Owing to its peculiarity of molecular architecture, dendritic-linear copolymer acted as a dendron-rod chain in solution. As their shape-persistence, the copolymers could self-assemble into hollow spherical particles in common solvent. This type of self-assembly offers a new convenient route to obtain hollow vesicles in copolymer systems without secondary bond. In the selective good solvent of PMPCS, vesicular structures also could be obtained. And in the selective good solvent of dendrons, compound spherical micelles were formed. The outer surface of spherical micelles is a corona consisting of dendron block and the inner part would be composed of reverse micelles with cores consisting of dendron molecules on the inside and PMPCS blocks in the corona. Additionally, solution-cast films of these dendron-b-PMPCS can form well-defined honey-comb patterns under moisture-rich condition.

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CLC: > Mathematical sciences and chemical > Chemistry > Polymer chemistry ( polymer ) > Polymer physics and physical chemistry of polymers > The chemical nature of polymers
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