1 research outputs found
Self-Assembly Thermodynamics of pH-Responsive Amino-Acid-Based Polymers with a Nonionic Surfactant
The behavior of pH-responsive polymers
polyÂ(<i>N</i>-methacryloyl-l-valine) (P1), polyÂ(<i>N</i>-methacryloyl-l-phenylalanine) (P2), and polyÂ(<i>N</i>-methacryloylglycyne-l-leucine) (P3) has been
studied in the presence of the nonionic
surfactant Brij98. The pure polymers phase-separate in an acidic medium
with critical pH<sub>tr</sub> values of 3.7, 5.5, and 3.4, respectively.
The addition of the surfactant prevents phase separation and promotes
reorganization of polymer molecules. The nature of the interaction
between polymer and surfactant depends on the amino acid structure
in the side chain of the polymer. This effect was investigated by
dynamic light scattering, isothermal titration calorimetry, electrophoretic
measurements, small-angle neutron scattering, and infrared spectroscopy.
Thermodynamic analysis revealed an endothermic association reaction
in P1/Brij98 mixture, whereas a strong exothermic effect was observed
for P2/Brij98 and P3/Brij98. Application of regular solution theory
for the analysis of experimental enthalpograms indicated dominant
hydrophobic interactions between P1 and Brij98 and specific interactions
for the P2/Brij98 system. Electrophoretic and dynamic light scattering
measurements support the applicability of the theory to these cases.
The specific interactions can be ascribed to hydrogen bonds formed
between the carboxylic groups of the polymer and the oligoÂ(ethylene
oxide) head groups of the surfactant. Thus, differences in polymer–surfactant
interactions between P1 and P2 polymers result in different structures
of polymer–surfactant complexes. Specifically, small-angle
neutron scattering revealed pearl-necklace complexes and “core–shell”
structures for P1/Brij98 and P2/Brij98 systems, respectively. These
results may help in the design of new pH-responsive site-specific
micellar drug delivery systems or pH-responsive membrane-disrupting
agents