The synthesis of thermoresponsive graft copolymers based on a carboxymethylcellulose
(CMC) backbone is reported. Thermal responsive properties are introduced by grafting the CMC sample
with amino-terminated poly(N-isopropylacrylamide) (PNIPAM) side chains of a relatively low molecular
weight. Turbidity measurements in dilute copolymer solutions showed that, due to the hydrophilic CMC
backbone, macroscopic phase separation by increasing temperature above the lower critical solution
temperature (LCST) of PNIPAM is not allowed for pH ≥ 3. Pyrene fluorescence probing studies in aqueous
solutions revealed the formation of hydrophobic microdomains above the LCST of PNIPAM. In semidilute
solution these microdomains interconnect the polymer chains, leading to the thermally induced formation
of a physical network. The macroscopic result is the observation in semidilute solutions of a pronounced
thermally induced viscosity enhancement. This thermothickening phenomenon is almost irrespective of
pH, and it remains very important even at pH values as low as 3.
SUMM A F~We present potentiometric and viscometric results on the interpolymer complexation between polyacrylamide (PAAM) and poly(N-isopropylacrylamide) (PNIPAAM) with poly(acry1ic acid) (PAA) in dilute aqueous solution. A potentiometric procedure for the determination of the complex stoichiometry in monomeric units has been proposed. The temperature dependence of the strength of the complexes formed has been investigated. From the results obtained it has been concluded that hydrogen bonding is the main factor stabilizing the PAAMRAA complex, strengthened by decreasing the temperature while the much stronger PNIPAAMPAA complex, strengthened by increasing the temperature, is stabilized by hydrophobic interaction.
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