Temperature-responsive properties of poly(acrylic acid-co-acrylamide)-graft-oligo(ethylene glycol) hydrogels

A series of temperature- and pH-responsive hydrogels were prepared from acr ylic acid (AAc), acrylamide (AAm), oligo(ethylene glycol)monoacrylate (OEGM A), and oligo(ethylene glycol)diacrylate by varying the AAc:AAm molar ratio and the OEGMA content. Phase-transition temperatures and swelling ratios o f the obtained poly(AAc-co-AAm)-graft-OEG gels were measured as a function of temperature and pH. At pH < 5, the obvious transition temperatures rangi ng from 5 to 35<degrees>C were obtained as the AAc : AAm molar ratio was va ried. The highest transition temperature was obtained at the AAc : AAm rati os of 5 : 5 and 6 : 4, and the sharp transition curves were observed at the AAc : AAm ratios from 5 : 5 to 8 : 2. The transition temperature further i ncreased with increasing OEGMA content. It was suggested that OEG graft cha ins with a large mobility played an important role for the formation of hyd rogen bonding in the hydrogels. The gels prepared here showed obvious repro ducibility of the phase transition in response to temperature changes, whic h suggests the feasibility of their practical applications. (C) 2001 John W iley & Sons, Inc.