Stimuli‐Responsive Polymers Based on N‐Isopropylacrylamide and N‐Methacryloyl‐L‐Leucine

Linear and cross‐linked polymers capable of responding to both temperature and pH changes were synthesized by radical copolymerization of N‐isopropylacrylamide (NIPAAm) and N‐methacryloyl‐L ‐leucine (MALEU) in different NIPAAm/MALEU molar ratios. The solution behavior of linear polymers was investigated in 0.1 M NaCl and in citrate buffers pH 4.0, 4.5, 5.0 and 6.0. A sharp increase in the cloud point temperature (T_CP) was observed to occur around pH 4–5. Hydrogels were synthesized employing N,N ′‐methylenebisacrylamide as cross‐linking agent. The influence of composition and degree of cross‐linking on water absorption was investigated in 0.1 M NaCl and in citrate buffers pH 4.0 and 5.0. A reversible phase transition within a wide range of temperatures, depending on the composition and the pH, in accordance with the behavior of linear polymers, was observed.