Synthesis and aqueous solution properties of novel thermoresponsive graft copolymers based on a carboxymethylcellulose backbone

The synthesis of thermoresponsive graft copolymers based on a carboxymethyl cellulose (CMC) backbone is reported. Thermal responsive properties are int roduced by grafting the CMC sample with amino-terminated poly(N-isopropylac rylamide) (PNIPAM) side chains of a relatively low molecular weight. Turbid ity measurements in dilute copolymer solutions showed that, due to the hydr ophilic CMC backbone, macroscopic phase separation by increasing temperatur e above the lower critical solution temperature (LCST) of PNIPAM is not all owed for pH greater than or equal to 3. Pyrene fluorescence probing studies in aqueous solutions revealed the formation of hydrophobic microdomains ab ove the LCST of PNIPAM. In semidilute solution these microdomains interconn ect the polymer chains, leading to the thermally induced formation of a phy sical network. The macroscopic result is the observation in semidilute solu tions of a pronounced thermally induced viscosity enhancement. This thermot hickening phenomenon is almost irrespective of pH, and it remains very impo rtant even at pH values as low as 3.