Graft-type poly(N-isopropylacrylamide-co-acrylic acid) microgels exhibiting rapid thermo- and pH-responsive properties

A novel graft-type poly(N-isopropylacrylamide-co-acrylic acid) (poly(NIPAM-co-AAc)) microgel with linear grafted poly(NIPAM-co-AAc) side chains was prepared by incorporating the dual stimuli-responsive chains into conventional copolymerized poly(NIPAM-co-AAc) backbones as side chains through a grafted modification of molecular structure. The grafted chains with unfettered ends can unfold and shrink freely in response to environmental stimuli. Due to the mobile nature and the tractive force of the grafted poly(NIPAM-co-AAc) side chains, the prepared microgels were verified to have a synchronously rapid thermo- and pH-response property. When the environmental temperature was increased suddenly from 25 °C to about 63 °C, the graft-type microgels in ultrapure water deswelled 95% by volume at best within 40 s but the normal-type microgels deswelled only 17% by volume within the same period. The analogous trends were observed in either alkaline or acid buffered solution. The graft-type microgels may thus be very promising for use in many applications in which rapid responses to dual environmental stimuli are required.