Thermoprocessible Hydrogels I: Synthesis and Properties of Polyacrylamides with Perfluoroalkyl Side Chains
Copolymers composed of acrylamide (AM), N,N-dimethylacrylamide (DMAM), N-isopropylacrylamide (NIPAM) and 2-(N-ethyl-perfluorooctanesulfonamido) acrylamide (FOSA) were synthesized by free radical polymerization. The chemical structure of the resulting polymers was characterized with NMR spectroscopy and thermal properties were measured by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). 1H-NMR spectra of the copolymers of NIPAM with FOSA showed that FOSA was incorporated quantitatively. The glass transition temperature (Tg) of the copolymers and the terpolymers decreased with increasing FOSA content. The Tgs, however, were higher than predicted for a random copolymer by the Fox equation, which was attributed to microphase separation of the hydrophobic, fluorinated species. Copolymers of AM and FOSA became discolored above 180°C due to formation of cyclic imide and nitrile moieties through cyclization or dehydration of amide groups. The equilibrium water sorption of the copolymers decreased with increasing FOSA content, but increasing FOSA suppressed the water desorption kinetics. Water sorption and thermal stability were improved by terpolymerization of AM, NIPAM, DMAM and FOSA.