A new multi-stimuli-responsive homopolymer of poly[N-[2-(diethylamino)ethyl]acrylamide] (PDEAEAM), which combines the thermoresponsive and pH/CO2-responsive moieties of the diethylamino and acrylamide groups, was proposed and synthesized by RAFT polymerization. Well-defined PDEAEAM was synthesized by solution RAFT polymerization as indicated by the linear increase in the polymer molecular weight with the monomer conversion and the narrow molecular weight distribution. The appending diethylamino group in the polymer backbone was found to be crucial to determine the thermoresponse of PDEAEAM in water. The parameters including the polymerization degree, the polymer concentration, the deuterated solvent, the terminal attached on the polymer backbone, the additives of salt and urea, and pH and bubbling CO2 affecting the thermoresponse of PDEAEAM in aqueous solution at the lower critical solution temperature (LCST) were investigated. The temperature-variable 1H NMR analysis suggests that the dehydration of PDEAEAM at temperature above LCST is ascribed to the weakened hydrogen bonding between the CONHCH2 and/or (CH2N(CH2CH3)2) moieties with the solvent of water. The proposed multi-stimuli-responsive homopolymer of PDEAEAM has two advantages of (1) the convenient and controllable RAFT synthesis and (2) the pH/CO2 tunable LCST at ∼36 °C being very close to body temperature.
A homopolymer strategy was developed to synthesize temperature and pH/CO 2 stimulus-responsive homopolymers. A new class of acrylamide monomers bearing oligo(ethylene glycol) unit and N,N -diethylaminoethyl group were designed and prepared through Aza-Michael addition reaction followed by amidation with acryloyl chloride using amino group as a linkage to connect oligo(ethylene glycol), N,N -diethylaminoethyl, and polymerizable double bond groups together. Subsequently, the corresponding homopolymers containing oligo(ethylene glycol) unit and N,N -diethylaminoethyl group in each repeated unit were prepared via RAFT polymerization with controlled molecular weights and relatively narrow molecular weight distributions . The lower critical solution temperature (LCST) of homopolymer was examined to be influenced by molecular weight, salt concentration, and pH value of aqueous solution. The LCSTs of homopolymers could be tuned in a wide temperature window by changing pH value of aqueous solution and it increased with the decrease of pH value. Particularly, CO 2 gas as a unique pH stimulus can also reversibly adjust the solubility of homopolymer without the addition of acids or bases.
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