Hyper-Crosslinkers Lead to Temperature- and pH-Responsive Polymeric Nanogels with Unusual Volume Change


Ning Zhou


Ning Zhou, Xiaoyan Cao, Xuewen Du, Huaimin Wang, Ming Wang, Shuang Liu, Khang Nguyen, Klaus Schmidt-Rohr, Qiaobing Xu, Gaolin Liang, and Bing Xu

Author Affiliation: 

N. Zhou, Dr. X. Cao, Dr. X. Du, Dr. H. Wang, K. Nguyen, Prof. K. Schmidt-Rohr and Prof. B. Xu from Department of Chemistry, Brandeis University; Dr. M. Wang, Prof. Q. Xu, from Department of Biomedical Engineering, Tufts University; Dr. S. Liu, Prof. G. Liang, from Department of Chemistry, University of Science and Technology of China.


Hydrogels consisting of carboxylic acid groups and N-isopropylacrylamide as pendants on its polymeric network usually exhibit volume expansion upon deprotonation or volume contraction when being heated. Here we demonstrate an anti-intuitive case of a hydrogel, containing multiple carboxylic acid groups at each crosslinking point in the polymeric network that shrinks upon increasing pH from 1 to 7 at 37C or expands upon heating from 25 to 37C at pH 1. The unexpected volume change originates from the high percentage of the crosslinker in the polymers, as detected by solid-state 13C NMR. 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 the nanogels, this work illustrates a new way to design soft materials with unusual behaviors.