Light and Temperature as Dual Stimuli Lead to Self-Assembly of Hyperbranched Azobenzene-Terminated Poly(N-isopropylacrylamide)

Wenyan Huang; Jing Yang; Yunqing Xia; Xuezi Wang; Xiaoqiang Xue; Hongjun Yang; Guifang Wang; Bibiao Jiang; Fang Li; Sridhar Komarneni

doi:10.3390/polym8050183

Light and Temperature as Dual Stimuli Lead to Self-Assembly of Hyperbranched Azobenzene-Terminated Poly(N-isopropylacrylamide)

Polymers (Basel). 2016 May 7;8(5):183. doi: 10.3390/polym8050183.

Authors

Wenyan Huang¹, Jing Yang², Yunqing Xia³, Xuezi Wang⁴, Xiaoqiang Xue^{5

6}, Hongjun Yang⁷, Guifang Wang^{8

9}, Bibiao Jiang¹⁰, Fang Li¹¹, Sridhar Komarneni¹²

Affiliations

¹ Jiangsu Key Laboratory of Material Surface Science and Technology, School of Material Science and Engineering, Changzhou University, Changzhou 213164, Jiangsu, China. ellahwy@cczu.edu.cn.
² Jiangsu Key Laboratory of Material Surface Science and Technology, School of Material Science and Engineering, Changzhou University, Changzhou 213164, Jiangsu, China. 14101305@smail.cczu.edu.cn.
³ Jiangsu Key Laboratory of Material Surface Science and Technology, School of Material Science and Engineering, Changzhou University, Changzhou 213164, Jiangsu, China. 12441226@smail.cczu.edu.cn.
⁴ Jiangsu Key Laboratory of Material Surface Science and Technology, School of Material Science and Engineering, Changzhou University, Changzhou 213164, Jiangsu, China. 12441208@smail.cczu.edu.cn.
⁵ Jiangsu Key Laboratory of Material Surface Science and Technology, School of Material Science and Engineering, Changzhou University, Changzhou 213164, Jiangsu, China. xxq969@cczu.edu.cn.
⁶ Materials Research Laboratory, Materials Research Institute, The Pennsylvania State University, University Park, PA 16802, USA. xxq969@cczu.edu.cn.
⁷ Jiangsu Key Laboratory of Material Surface Science and Technology, School of Material Science and Engineering, Changzhou University, Changzhou 213164, Jiangsu, China. hjyang0519@cczu.edu.cn.
⁸ Materials Research Laboratory, Materials Research Institute, The Pennsylvania State University, University Park, PA 16802, USA. wangguifang66@163.com.
⁹ School of Resource and Metallurgy, Guangxi University, Nanning 530004, Guangxi, China. wangguifang66@163.com.
¹⁰ Jiangsu Key Laboratory of Material Surface Science and Technology, School of Material Science and Engineering, Changzhou University, Changzhou 213164, Jiangsu, China. jiangbibiao@cczu.edu.cn.
¹¹ Jiangsu Key Laboratory of Material Surface Science and Technology, School of Material Science and Engineering, Changzhou University, Changzhou 213164, Jiangsu, China. 15101314@smail.cczu.edu.cn.
¹² Materials Research Laboratory, Materials Research Institute, The Pennsylvania State University, University Park, PA 16802, USA. sxk7@psu.edu.

Abstract

Hyperbranched poly(N-isopropylacrylamide)s (HBPNIPAMs) end-capped with different azobenzene chromophores (HBPNIPAM-Azo-OC₃H₇, HBPNIPAM-Azo-OCH₃, HBPNIPAM-Azo, and HBPNIPAM-Azo-COOH) were successfully synthesized by atom transfer radical polymerization (ATRP) of N-isopropylacrylamide using different azobenzene-functional initiators. All HBPNIPAMs showed a similar highly branched structure, similar content of azobenzene chromophores, and similar absolute weight/average molecular weight. The different azobenzene structures at the end of the HBPNIPAMs exhibited reversible trans-cis-trans isomerization behavior under alternating UV and Vis irradiation, which lowered the critical solution temperature (LCST) due to different self-assembling behaviors. The spherical aggregates of HBPNIPAM-Azo-OC₃H₇ and HBPNIPAM-Azo-OCH₃ containing hydrophobic para substituents either changed to bigger nanorods or increased in number, leading to a change in LCST of -2.0 and -1.0 °C, respectively, after UV irradiation. However, the unimolecular aggregates of HBPNIPAM-Azo were unchanged, while the unstable multimolecular particles of HBPNIPAM-Azo-COOH end-capped with strongly polar carboxyl groups partly dissociated to form a greater number of unimolecular aggregates and led to an LCST increase of 1.0 °C.

Keywords: azo polymers; hyperbranched; poly(N-isopropylacrylamide)s; self-assembly; stimuli-sensitive.