title: Hyper-Crosslinkers Lead to Temperature- and pH-Responsive Polymeric Nanogels with Unusual Volume Change.
abstract: Hydrogels consisting of carboxylic acid groups and N-isopropylacrylamide as pendants on their polymeric network usually exhibit volume expansion upon deprotonation or volume contraction when being heated. Demonstrated here is an anti-intuitive case of a hydrogel containing multiple carboxylic acid groups at each crosslinking point in the polymeric network, which shrinks upon increasing pH from 1 to 7 at 37 °C or expands upon heating from 25 to 37 °C at pH 1. The unexpected volume change originates from the high percentage of the crosslinker in the polymers, as detected by solid-state13C NMR spectroscopy. In addition, the volume changes are thermally reversible. As the first example of the use of functional hyper-crosslinkers to control the pH and thermal responses of nanogels, this work illustrates a new way to design soft materials with unusual behaviors.
authors.affiliation: Department of Chemistry, Brandeis University, 415 South Street, Waltham, MA, 02454, USA.
authors.forename: Ning
authors.initials: N
authors.lastname: Zhou
authors.affiliation: Department of Chemistry, Brandeis University, 415 South Street, Waltham, MA, 02454, USA.
authors.forename: Xiaoyan
authors.identifier: 0000-0001-7571-6482
authors.initials: X
authors.lastname: Cao
authors.affiliation: Department of Chemistry, Brandeis University, 415 South Street, Waltham, MA, 02454, USA.
authors.forename: Xuewen
authors.initials: X
authors.lastname: Du
authors.affiliation: Department of Chemistry, Brandeis University, 415 South Street, Waltham, MA, 02454, USA.
authors.forename: Huaimin
authors.initials: H
authors.lastname: Wang
authors.affiliation: Department of Biomedical Engineering, Tufts University, 419 Boston Ave, Medford, MA, 02155, USA.
authors.forename: Ming
authors.initials: M
authors.lastname: Wang
authors.affiliation: Department of Chemistry, University of Science and Technology of China, 96 Jinzhai Road, Hefei, Anhui, 230026, China.
authors.forename: Shuang
authors.initials: S
authors.lastname: Liu
authors.affiliation: Department of Chemistry, Brandeis University, 415 South Street, Waltham, MA, 02454, USA.
authors.forename: Khang
authors.initials: K
authors.lastname: Nguyen
authors.affiliation: Department of Chemistry, Brandeis University, 415 South Street, Waltham, MA, 02454, USA.
authors.forename: Klaus
authors.identifier: 0000-0002-3188-4828
authors.initials: K
authors.lastname: Schmidt-Rohr
authors.affiliation: Department of Biomedical Engineering, Tufts University, 419 Boston Ave, Medford, MA, 02155, USA.
authors.forename: Qiaobing
authors.initials: Q
authors.lastname: Xu
authors.affiliation: Department of Chemistry, University of Science and Technology of China, 96 Jinzhai Road, Hefei, Anhui, 230026, China.
authors.forename: Gaolin
authors.initials: G
authors.lastname: Liang
authors.affiliation: Department of Chemistry, Brandeis University, 415 South Street, Waltham, MA, 02454, USA.
authors.forename: Bing
authors.identifier: 0000-0002-4639-387X
authors.initials: B
authors.lastname: Xu
keywords: NMR spectroscopy; crosslinkers; electron microscopy; gels; polymers