Thermoresponsive Homopolymer Tunable by pH and CO.

A new acrylamide monomer bearing isopropylamide and ,-diethylamino ethyl groups in the side chain, i.e., -(2-(diethylamino)ethyl)--(3-(isopropylamino)-3-oxopropyl)acrylamide (DEAE-NIPAM-AM), was synthesized through Aza-Michael addition reaction followed by amidation with acryloyl chloride. The homopolymers, poly(-(2-(diethylamino)ethyl)--(3-(isopropylamino)-3-oxopropyl)acrylamide)s [poly(DEAE-NIPAM-AM)], with controlled molecular weights and relatively narrow molecular weight distributions were then prepared via RAFT polymerization. The lower critical solution temperature (LCST) of the homopolymer was examined to be influenced by molecular weight, salt concentration, and pH value of aqueous solution. The LCST of the homopolymer could be tuned in a wide temperature window by changing the pH value of aqueous solution, and it increased with the decrease of pH value. Particularly, CO gas as a unique pH stimulus can also reversibly adjust the solubility of homopolymer without the addition of acids or bases.