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

Research output: Contribution to journalArticle

8 Scopus citations

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.

Original languageEnglish (US)
Article number183
JournalPolymers
Volume8
Issue number5
DOIs
StatePublished - 2016

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Polymers and Plastics

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