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Polymers 2016, 8(5), 183;

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

Jiangsu Key Laboratory of Material Surface Science and Technology, School of Material Science and Engineering, Changzhou University, Changzhou 213164, Jiangsu, China
Materials Research Laboratory, Materials Research Institute, The Pennsylvania State University, University Park, PA 16802, USA
School of Resource and Metallurgy, Guangxi University, Nanning 530004, Guangxi, China
Authors to whom correspondence should be addressed.
Academic Editors: Nicolay V. Tsarevsky and Alexander Böker
Received: 22 February 2016 / Revised: 11 April 2016 / Accepted: 15 April 2016 / Published: 7 May 2016
(This article belongs to the Special Issue Controlled/Living Radical Polymerization)
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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. View Full-Text
Keywords: poly(N-isopropylacrylamide)s; azo polymers; stimuli-sensitive; self-assembly; hyperbranched poly(N-isopropylacrylamide)s; azo polymers; stimuli-sensitive; self-assembly; hyperbranched

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Huang, W.; Yang, J.; Xia, Y.; Wang, X.; Xue, X.; Yang, H.; Wang, G.; Jiang, B.; Li, F.; Komarneni, S. Light and Temperature as Dual Stimuli Lead to Self-Assembly of Hyperbranched Azobenzene-Terminated Poly(N-isopropylacrylamide). Polymers 2016, 8, 183.

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