pH-sensitive superabsorbent polymers: a potential candidate material for self-healing concrete

Superabsorbent polymers (SAPs) have already found their way in many applications. These ‘smart’ polymers undergo major characteristic changes by small environmental variations. In the present work, copolymer networks composed of acrylic acid, acrylamide and N,N′-methylenebisacrylamide have been synthesized using free radical precipitation polymerization. The polymers obtained have been characterized for their chemical structure, moisture (de)sorption and swelling behaviour using, respectively, attenuated total reflectance-infrared spectroscopy, high-resolution magic-angle spinning NMR spectroscopy, dynamic vapour sorption and swelling studies. The results indicated a remarkable moisture uptake capacity at high relative humidities of more than 90 % the original polymer weight with a negligible hysteresis. The latter implies that the SAPs developed are very promising water reservoir candidates, which become useful in concrete-related applications. Furthermore, the swelling data revealed that polymers with a low cross-linking density result in materials with superabsorbent properties. In addition, these SAPs show a pH-dependent swelling behaviour up to 450 times their original weight at pH 12.