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.
Interaction of poly(N-isopropylacrylamide) (PNIPAM) with sodium dodecyl sulfate (SDS) has been studied
by viscometry, time-resolved fluorescence-quenching (TRFQ), and dialysis measurements. The reduced
viscosity of PNIPAM in SDS aqueous solutions presents an abrupt increase in the low SDS concentration
region, lower than the surfactant critical micelle concentration, whereas TRFQ measurements show the
formation of an increasing number of polymer−surfactant aggregates in the same SDS concentration
region. The aggregation number of these aggregates, determined by combining TRFQ with dialysis data,
remains constant and equal to 7−8 surfactant molecules per polymer-bound surfactant aggregate. Moreover,
the values of the inverse of the intramicellar quenching rate constant, expressing the effective microviscosity
of the aggregates, indicate that these microdomains, formed in the low SDS concentration region, are very
rigid. After saturation of the PNIPAM chain with these aggregates, a further quantity of surfactant is
adsorbed on the polymer, and this is reflected in an increase of their aggregation number. However, the
aggregation number of these polymer−surfactant aggregates remains much lower than that of free surfactant
micelles.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.