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A study of the stabilization of vertical alignment for liquid crystals by increasing the side-chain rigidity of polyimides

Authors

  • Long-Fei Yi,

    1. State Key Laboratory of Polymer Materials Engineering, College of Polymer Science and Engineering, Sichuan University, Chengdu 610065, PR China
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  • Sen-Lin Xia,

    1. State Key Laboratory of Polymer Materials Engineering, College of Polymer Science and Engineering, Sichuan University, Chengdu 610065, PR China
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  • Zhen Sun,

    1. State Key Laboratory of Polymer Materials Engineering, College of Polymer Science and Engineering, Sichuan University, Chengdu 610065, PR China
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  • Meng-Si Liu,

    1. State Key Laboratory of Polymer Materials Engineering, College of Polymer Science and Engineering, Sichuan University, Chengdu 610065, PR China
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  • Ying-Han Wang

    Corresponding author
    1. State Key Laboratory of Polymer Materials Engineering, College of Polymer Science and Engineering, Sichuan University, Chengdu 610065, PR China
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Ying-Han Wang, State Key Laboratory of Polymer Materials Engineering, College of Polymer Science and Engineering, Sichuan University, Chengdu 610065, PR China. E-mail: prof_wangpaper@126.com

Abstract

A series of polyimides (PIs) with various side-chain structures were prepared via copolymerization of pyromellitic dianhydride, 3,3′-dimethyl-4,4′-methylenediamine and three functional diamines: 4-(4-octyloxybenzoyloxy)biphenyl-3′,5′-diaminobenzoate (C8-BPDA), 4-octyloxybiphenyl-3′,5′-diaminobenzoate (C8-PDA) and 4-(4-butoxybenzoyloxy)biphenyl-3′,5′-diaminobenzoate (C4-BPDA). PIs derived from C8-BPDA and C4-BPDA exhibited excellent rubbing resistance in comparison with PI from C8-PDA and the pretilt angle could be controlled over 89° after rubbing. Thermogravimetric analysis showed that the thermal degradation of PIs under nitrogen atmosphere occurred above 320 °C, and PI derived from C8-BPDA showed the best thermal stability. Wide-angle X-ray diffraction patterns indicated an amorphous morphology of the PIs, and the PIs also had outstanding solubility in polar aprotic solvents. The resultant PI films were light colored and maintained high transparency in the visible light region. By increasing the rigidity of side-chains, the rubbing resistance and the thermal stability of PIs could be promoted at the same time. © 2012 Society of Chemical Industry

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