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Photoisomerizable and Thermoresponsive N ‐isopropylacrylamide–Surfmer Copolymer Hydrogels Prepared upon Electrostatic Self‐Assembly of an Azobenzene Bolaamphiphile
Author(s) -
Friedrich Tatjana,
Mielke Tamara,
Domogalla Monika,
Hentschel Maria,
Kraus Katharina,
Tieke Bernd
Publication year - 2013
Publication title -
macromolecular rapid communications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.348
H-Index - 154
eISSN - 1521-3927
pISSN - 1022-1336
DOI - 10.1002/marc.201200630
Subject(s) - lower critical solution temperature , copolymer , azobenzene , self healing hydrogels , aqueous solution , polymer chemistry , bromide , poly(n isopropylacrylamide) , chemistry , chemical engineering , organic chemistry , polymer , engineering
Abstract Photoreactive and thermoresponsive N ‐isopropylacrylamide (NIPAM)–surfmer copolymer hydrogels containing 4,4′‐di(6‐sulfato‐hexyloxy)azobenzene (DSHA) dianions are described. The functional hydrogels are obtained in a two steps. First a micellar aqueous solution of (11‐(acryloyloxy)undecyl)trimethylammonium bromide (AUTMAB) and NIPAM is exposed to 60 Co‐gamma irradiation, and a thermoresponsive copolymer gel is obtained. Second, DSHA is included by shrinking the gel at 50 °C and subsequent reswelling in an aqueous solution of DSHA disodium salt at 20 °C. Reswelling is accompanied by electrostatic adsorption of DSHA dianions at the positively charged AUTMAB headgroups replacing the bromide ions. Gels containing trans ‐DSHA are transparent yellow at room temperature ( λ max = 370 nm), while gels containing cis ‐rich DSHA are orange ( λ max = 460 and 330 nm). Energy dispersive X‐ray measurements indicate that 41% of the bromide ions are exchanged if trans‐DSHA is used for adsorption, and only 7.5% if cis ‐DSHA is used. The incorporation of DSHA lowers the lower critical solution temperature (LCST) from 34 to 32 °C. Below the LCST, DSHA can be switched from the trans ‐ to the cis ‐rich state and vice versa upon irradiation with UV ( λ = 366 nm) or visible light ( λ ≥ 450 nm). Above the LCST no photoreaction takes place.