Controlled Synthesis and Photophysical Properties of Liquid Crystalline Diblock Copolymers with Side⁃Chain Discotic Triphylene and Calamitic Azobenzene Mesogens

doi:10.19894/j.issn.1000-0518.210343

Chinese Journal of Applied Chemistry ›› 2021, Vol. 38 ›› Issue (10): 1340-1352.DOI: 10.19894/j.issn.1000-0518.210343

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Controlled Synthesis and Photophysical Properties of Liquid Crystalline Diblock Copolymers with Side⁃Chain Discotic Triphylene and Calamitic Azobenzene Mesogens

Zhao-Yong ZHANG^1‡, Qian LI^1‡, Da-Lin WANG¹, Jiang-Lin FANG², Dong-Zhong CHEN¹()

¹Key Laboratory of High Performance Polymer Materials and Technology of Ministry of Education，Department of Polymer Science and Engineering，School of Chemistry and Chemical Engineering，Nanjing University，Nanjing 210023，China
²Center of Modern Analysis，Nanjing University，Nanjing 210093，China

Received:2021-07-16 Accepted:2021-08-31 Published:2021-10-01 Online:2021-10-15
Contact: Dong-Zhong CHEN
About author:cdz@nju.edu.cn
Supported by:
National Natural Science Foundation of China(21875098)

Abstract

Abstract:

A series of disk-rod hybrid diblock copolymers based on side-chain discotic triphenylene （TP） and calamitic azobenzene （Azo） mesogens with different length and ratio of the two block segments were well prepared via copper（I）-catalyzed azide-alkyne 1，3-dipolar cycloaddition （CuAAC） click reaction. The reactive precursor blocks were synthesized through atom transfer radical polymerization （ATRP） or reversible addition-fragmentation chain transfer （RAFT） polymerization of Azo methacrylate and TP acrylate monomers using specially designed chain transfer agent and initiator with different functional groups. The structure， molecular mass and liquid crystalline phase behaviors of the thus obtained disk-rod diblock copolymers were characterized by ¹H nuclear magnetic resonance （NMR） spectroscopy， gel permeation chromatography （GPC）， differential scanning calorimetry （DSC） and polarization optical microscopy （POM）. The hybrid diblock copolymer of P（TP₆）₄₀-b-P（Azo）₁₀ with a shorter azobenzene block segment， mainly exhibits the thermal transition temperature and phase behavior of the dominant TP-based discotic liquid crystalline polymer （LCP）. While the copolymers of P（TP₆）₁₀-b-P（Azo）₄₀ and P（TP₆）₄₀-b-P（Azo）₄₀ with a longer azobenzene block segment， reflect more of the phase behavior and photoresponse properties of the Azo-based side-chain LCP. Small-angle /wide-angle X-ray scattering （SAXS/WAXS） analysis confirms that the diblock copolymer films with a longer Azo-based segment are in a layered structure especially after annealing， the Azo mesogens are arranged in a flat lying orientation in parallel with the quartz substrate induced by the planar oriented TP mesogens， which significantly reduce the light absorbance of the UV-Vis spectra， then the light absorbance increases obviously after irradiation with 365 nm ultraviolet and then visible light， where P（TP₆）₄₀-b-P（Azo）₄₀ with the longer TP-based block shows a particularly prominent increment. The study on the unique photophysical properties and specific photoresponse behaviors of such disk-rod hybrid diblock copolymer films can help to deepen the understanding of their interactions and are expected to provide guidance for the design and synthesis of novel photoresponsive materials.

Key words: Disk-rod hybrid diblock copolymers, Controlled radical polymerization, Click reaction, Photoresponse

CLC Number:

O632.5

Zhao-Yong ZHANG, Qian LI, Da-Lin WANG, Jiang-Lin FANG, Dong-Zhong CHEN. Controlled Synthesis and Photophysical Properties of Liquid Crystalline Diblock Copolymers with Side⁃Chain Discotic Triphylene and Calamitic Azobenzene Mesogens[J]. Chinese Journal of Applied Chemistry, 2021, 38(10): 1340-1352.

Figures/Tables 12

Fig.1 Normalized GPC curves of disk-rod hybrid diblock copolymers （A） P（TP6）40-b-P（Azo）10，（B） P（TP6）10-b-P（Azo）40 and （C） P（TP6）40-b-P（Azo）40

Table 1 Molecular characterization results of disk?rod hybrid diblock copolymers with different DP and their corresponding homopolymers via GPC

聚合物代号 Polymer code	设计聚合度 Designed DP	设计相对分子质量 Designed M_W	凝胶渗透色谱GPC
聚合物代号 Polymer code	设计聚合度 Designed DP	设计相对分子质量 Designed M_W	质均相对分子质量 M_w，GPC	数均相对分子质量 M_n，GPC	多分散指数 PDI
P₆?10?N₃	10	9 300	9 500	7 200	1.31
P₆?40?N₃	40	36 300	17 000	12 500	1.36
P（Azo）₁₀?yne	10	5 400	8 300	7 000	1.19
P（Azo）₄₀?yne	40	21 300	35 000	24 400	1.43
P（TP₆）₄₀?b?P（Azo）₁₀	/	41 700	36 300	24 800	1.46
P（TP₆）₁₀?b?P（Azo）₄₀	/	30 600	38 900	26 000	1.49
P（TP₆）₄₀?b?P（Azo）₄₀	/	57 600	41 300	27 500	1.50

Fig.2 DSC curves of disk-rod hybrid diblock copolymers with variant block lengths during the first cooling and second heating scans at a rate of 10 ℃/min under a nitrogen atmosphere

Table 2 Thermal data and phase assignments of the series diblock copolymers of P（TP6）m?b?P（Azo）n

聚合物代号 Polymer code	相转变温度/℃（焓变/（J·g^-1）） Phase transitions/℃（Enthalpy changes/（J·g^-1））
聚合物代号 Polymer code	第1次降温 First cooling	第2次升温 Second heating
P（TP₆）₄₀?b?P（Azo）₁₀	I 52（7.5） Col	Col 26， 47， 58， 66（-7.1） I
P（TP₆）₁₀?b?P（Azo）₄₀	I 135（3.5） N 130（4.0） SmC 110（1.8）	SmC 138（-6.6） I
P（TP₆）₄₀?b?P（Azo）₄₀	I 136（3.5） N 131（4.0） SmC 111（1.8）	SmC 118（-2.0） N 132（-3.2） 137（-3.5） I

Fig.3 POM images of the diblock copolymer P（TP6）40-b-P（Azo）10 under crossed polarizers （A） at room temperature，（B） heating up to isotropic phase and （C） slowly cooling down to room temperature

Fig.4 POM images of the diblock copolymers P（TP6）10-b-P（Azo）40 （A—F） and P（TP6）40-b-P（Azo）40 （G—L） under crossed polarizers upon heating from room temperature to the isotropic phase

Fig.5 UV-Vis absorption spectra of the diblock copolymer films of （A） P（TP6）10-b-P（Azo）40 under irradiation of 365 nm UV light， and （B） recovery under illumination of the visible light；（C） P（TP6）40-b-P（Azo）40 under irradiation of 365 nm UV light， and （D） recovery under illumination of the visible light

Fig.6 UV-Vis absorption spectra of the diblock copolymer film of P（TP6）40-b-P（Azo）40 after annealing （a）， irradiated with 365 nm UV light for different time to cis photostationary state （b—e）， and then illuminated with visible light transforming back to trans state （f）

Fig.7 UV-Vis absorption spectra comparison of the diblock copolymer films of （A） P（TP6）10-b-P（Azo）40 and （B） P（TP6）40-b-P（Azo）40 at different states， as-prepared spin coating film （a）， after annealing （b）， trans steady state （c） and cis photostationary state （d）

Fig.8 Variable temperature SAXS/WAXS curves of （A） P（TP6）10-b-P（Azo）40 and （B） P（TP6）40-b-P（Azo）40， the peaks marked with a star * standing for the background signal from the aluminum foil base

Fig.9 （A） Schematic illustration of the discotic triphenylene induced planar orientation of calamitic azobenzene mesogens in disc-rod diblock copolymer films of P（TP6）40-b-P（Azo）40 and P（TP6）10-b-P（Azo）40 with a longer azobenzene block， and （B） the orientational change after irradiation with 365 nm ultraviolet then visible light

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Controlled Synthesis and Photophysical Properties of Liquid Crystalline Diblock Copolymers with Side⁃Chain Discotic Triphylene and Calamitic Azobenzene Mesogens

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