| dc.description.abstract | Micellization behavior and sol-gel transition of the new biocompatible, temperature and pH responsive penta-block terpolymers, PDEAEMAx-b-PNIPAAMy-b-PEGz-b-PNIPAAMy-b-PDEAEMAx synthesized by Atom Transfer Radical Polymerization (ATRP) were investigated in aqueous solutions. The three examined polymers differed in PDEAEMA block length, which was the pH-responsive block and PEG block length as the permanent hydrophilic part of the polymer. The temperature responsive block, i.e., PNIPAAM block length kept constant in the three systems. Micellization in the dilute regime (0.5% w/w) was investigated by fluorescence spectroscopy, turbidimetry, densitometry, ζ-potential, 1H NMR, Dynamic Light Scattering (DLS), Static Light Scattering (SLS), Small Angle Neutron Scattering (SANS) and steady shear viscosity measurements. A core-shell spherical model was proposed for the micelles. Critical Micelle Concentration (CMC) at a higher pH, detected to have a lower value. Cloud point (CP) and transition point in Density measurements were consistent in the three polymers and at a higher pH, the transitions were observed at lower temperatures. ζ-potential measurements propounded the PDEAEMA block to be situated toward the surface of the micelles at pH below the pKa of the penta-block terpolymers ( 6 < pKa < 7.4) . Steady shear measurements showed an increasing trend of the viscosity by heating up the solutions. At pHs above the pKa of the penta-block terpolymers and temperatures above the Lower Critical Solution Temperature (LCST), the solutions displayed a shear-thinning behavior. The longer PDEAEMA block along with a longer PEG block offered well-shaped and monodispersed micelles in the aqueous solutions. The shorter PEG block resulted in a higher level of hydrophobicity in the polymer, while the shorter PDEAEMA block along with a longer PEG block made the penta block terpolymer more hydrophilic. The micellar characteristics were different in heavy water (D2O) than in phosphate buffer solution (PBS). In DLS, bimodal correlation functions were recognized in PBS solutions, while polymers in D2O solutions mostly showed single mode correlation functions. At a higher concentration (20% w/w) a sol-gel transition was observed for the three penta-block terpolymers. At a higher pH for the solutions of higher level of hydrophobicity, the gel point was observed at a lower temperature. The dual-responsive properties of the described system, along with the possibility to tailor the blocks length suggest potential application values in drug-controlled delivery, both in the micellar form in dilute regime, and in the gel form for localized and sustained delivery. | eng |