Thermally induced hydrogel formation in aqueous solutions of poly(N-isopropylacrylamide) and fluorocarbon-modified poly(oxyethylene)s

A number of perfluorooctyl-modified poly(oxyethylene)s (FQPEOs) of molar masses of approximately 2000 and 4000 were synthesised using a two-step procedure: (a) preparation of PEO precursors bearing tertiary amino groups (NPEOs) and (b) their quaternisation with perfluorooctyl iodide to obtain one-ended (FQEn), telechelic (FQEnFQ) or PEO modified with a C8F17-group in the mid of the polyether chain (EnFQEn). FQ is abbreviation of the C8F17-group attached to a PEO chain (En) through a quaternary ammonium group. The aqueous solution properties of FQPEOs were studied by viscosity measurements at 25 °C. The cationic charge affects the association ability of the FQ group and the one-ended FQEn behaves like PEO modified with a C6F13-group through urethane linkage. Temperature induced interactions in aqueous mixtures of FQPEOs with poly(N-isopropylacrylamide) (PNIPAM) were studied by turbidity and rheological measurements. In the semi-dilute regime, the aqueous polymer mixtures exhibit a large viscosity enhancement upon heating as soon as the temperature reaches 35 °C. In the range from 35 to 40 °C the mixtures of PNIPAM with FQEn and E50FQE50 form gels with viscoelastic response. The solution of PNIPAM mixed with the telechelic FQE100FQ reveals shear-thickening at 35 and 40 °C.