Thermoresponsive Properties of Copolymer Gels Induced by Appropriate Hydrophilic/Hydrophobic Balance of Monomer Combination

Summary The novel thermoresponsive polymer gels were found to be designed by copolymerization of hydrophilic and hydrophobic monomers. Thermoresponsive properties of these novel copolymer gels could be easily regulated by the monomer structures and the feed ratio. First, we copolymerized hydrophilic N,N‐dimethylacrylamide (DMAAm) and hydrophobic N‐n‐butylacrylamide (NBAAm) in various feed ratio, and found that certain compositions (DMAAm : NBAAm = 70 : 30 ∼ 40 : 60) gave the thermoresponsive gels with sharp volume phase transition. It was because of appropriate hydrophilic/hydrophobic balance in the network as same as poly(N‐isopropylacrylamide) gel, in which the balance of hydrophilic amide group and hydrophobic isopropyl group produces thermoresponsive property. Then, we examined the effect of comonomer structures on thermoresponsive behavior of the copolymer gels by utilizing butyl acrylamide isomers (s‐butyl, i‐butyl, and t‐butyl) as hydrophobic component. As a result, all the gels copolymerized by butylacrylamide having isomeric butyl groups with DMAAm were found to show the thermoresponsive properties such as sharp change of the degree of swelling and collapsed temperature, which would be related to the hydration structure of water.