Thermoresponsive behavior of sodium alginate grafted with poly(N-isopropylacrylamide) in aqueous media.

Thermoresponsive graft copolymers were synthesized. Thermally induced properties were introduced by grafting poly (N-isopropylacrylamide) (PNIPAM) side chains onto a sodium alginate backbone. The resulting graft copolymers cover a broad range in PNIPAM composition and molecular weight. Remarkable thermothickening behavior in water and 0.1 M NaCl is observed by viscometry when the temperature, concentration, weight ratio of PNIPAM side chains to backbone, and PNIPAM molecular weight are higher than certain critical values. This behavior is reversible and could have applications in oil rigs and drug delivery systems.

Microstructure of polyelectrolyte nanoaggregates studied by fluorescence probe method.

The microstructure of water soluble nanoaggregates based on polyelectrolyte complex formed by the cationic comb-type copolymer poly(acrylamide -co-[3- (methacryloyl-amino)propyl] trimethylammonium chloride)-graft- polyacrylamide [P(AM-co-MAPTAC)-g-PAM] and the anionic linear polyelectrolyte sodium polyacrylate (NaPA) was investigated using the fluorescence probe technique. The fluorescence probe were 1-anilinonaphthalene-8-sulfonic acid (ANS), pyrene (Py) and 1,10-bis(1-pyrene) decane (PD). The fluorescence properties in polyelectrolyte complex solutions, which are sensitive to either micropolarity (ANS, Py) or microviscosity (PD), were related to the quantities obtained in different pure or mixed solvents. Micropolarities were quantified utilizing the polarity common index (Reichardt) E(T)(30). ANS and Py showed a variation of the micropolarity with the charge ratio of the two polymers, with the lowest polarity reached at the complex neutralization. The PD probe, by its excimer-to-monomer fluorescence intensities ratio, enabled us to evidence the effect of the composition and the comb-type copolymer grafting density on the microviscosity of the interpolyelectrolytes aggregates. It has been found that the microviscosity increased with the density of the grafting PAM chains.

Characterization of the core-shell nanoparticles formed as soluble hydrogen-bonding interpolymer complexes at low pH.

The formation of soluble hydrogen-bonding interpolymer complexes between poly(acrylic acid) (PAA) and poly(acrylic acid-co-2-acrylamido-2-methyl-1-propane sulfonic acid)-graft-poly(N,N-dimethylacrylamide) (P(AA-co-AMPSA)-g-PDMAM) at pH=2.0 was studied. A viscometric study showed that in semidilute solution a physical gel is formed due to the interconnection of the anionic P(AA-co-AMPSA) backbone of the graft copolymer, in a transient network, by means of the complexes formed between the PDMAM side chains of the graft copolymer and PAA. Dynamic and static light scattering measurements, in conjunction with small-angle neutron scattering measurements, suggest the formation of core-shell colloidal nanoparticles in dilute solution, comprised by an insoluble PAA/PDMAM core surrounded by an anionic P(AA-co-AMPSA) corona. Even if larger clusters are formed in semidilute solution, the size of the insoluble core remains practically stable. Atomic force microscopy performed under ambient conditions reveal that the particles collapse and flatten upon deposition on a substrate, with dimensions close to the ones of the dry hydrophobic core.

Characterization of the soluble nanoparticles formed through Coulombic interaction of bovine serum albumin with anionic graft copolymers at low pH.

A static light scattering (SLS) study of bovine serum albumin (BSA) mixtures with two anionic graft copolymers of poly(sodium acrylate-co-sodium 2-acrylamido-2-methyl-1-propanesulphonate)-graft-poly(N,N-dimethylacrylamide), with a high composition in poly(N,N-dimethylacrylamide) (PDMAM) side chains, revealed the formation of oppositely charged complexes, at pH lower than 4.9, the isoelectric point of BSA. The core-corona nanoparticles formed at pH = 3.00 were characterized. Their molecular weight and radius of gyration were determined by SLS, while their hydrodynamic radius was determined by dynamic light scattering. Small angle neutron scattering measurements were used to determine the radius of the insoluble complexes, comprising the core of the particles. The values obtained indicated that their size and aggregation number of the nanoparticles were smaller when the content of the graft copolymers in neutral PDMAM side chains was higher. Such particles should be interesting drug delivery candidates, if the gastrointestinal tract was to be used.

Water-soluble hydrogen-bonding interpolymer complex formation between poly(ethylene glycol) and poly(acrylic acid) grafted with poly(2-acrylamido-2-methylpropanesulfonic acid).

Comb-type copolymers of poly(acrylic acid) grafted with poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPSA) side chains form with poly(ethylene glycol), at low pH, water-soluble hydrogen-bonding interpolymer complexes. Turbidimetry, viscometry, and dynamic light scattering measurements suggest that compact, negatively charged, colloidal nanoparticles are formed at pH<3.75. The influence of the structure of the graft copolymers and of the ionic strength of the solution on the size of these nanoparticles was investigated. It was found that their hydrodynamic radius decreases by increasing the molecular mass of the PAMPSA side chains of the graft copolymer and increases with increasing the ionic strength of the solution.

Water-soluble complexes through coulombic interactions between bovine serum albumin and anionic polyelectrolytes grafted with hydrophilic nonionic side chains.

The interaction between bovine serum albumin (BSA) and the anionic graft copolymers poly(sodium acrylate-co-sodium 2-acrylamido-2-methyl-1-propanesulfonate)-graft-poly(N,N-dimethylacrylamide) (P(NaA-co-NaAMPS)-g-PDMAMx) was investigated within the acid pH region, 2 < or = pH < or = 7. The weight percentage, x, of the poly(N,N-dimethylacrylamide) (PDMAM) side chains varied from 0 up to 75% (w:w). When BSA and P(NaA-co-NaAMPS)-g-PDMAMx are oppositely charged, i.e., when pH is lower than the isoelectric point of BSA, the two macromolecules associate through Coulombic attractions. When the anionic graft copolymer is rich enough to the nonionic PDMAM side chains, x > or = 50% w:w, the associative phase separation is practically prevented, as revealed by the turbidimetric study of the BSA/P(NaA-co-NaAMPS)-g-PDMAMx mixtures in aqueous solution vs pH. In addition, the viscosity measurements support the formation through a charge neutralization process of a rather compact protein-polyelectrolyte complex stabilized by the hydrophilic PDMAM side chains grafted onto the anionic copolymer backbone.