Mixed Block Copolymer Solutions: Self-Assembly and Interactions

This thesis incorporates studies on the aqueous systems of two types of thermoresponsive amphiphilic block copolymers; a series of nonionic triblock copolymers comprising blocks of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) denoted as PEO-PPO-PEO block copolymers, and a series of ionic diblock copolymers consisting of one charged block and one block of poly(N-isopropylacrylamide) (PNIPAAM). Various techniques, such as dynamic and static light scattering (DLS and SLS), small angle X-ray and neutron scattering (SAXS and SANS), high sensitivity differential scanning calorimetry (HSDSC), turbidimetry, electrophoretic mobility measurements, and two-dimensional proton NMR nuclear Overhauser effect spectroscopy (2D 1H NMR NOESY), were applied to study these block copolymer systems.In the first part of the thesis, the influence of a bile salt, sodium glycodeoxycholate (NaGDC), on the self-assembly of the three PEO-PPO-PEO block copolymers, P123, F127 and P65, was studied. Apart from the fundamental physio-chemical point of view, the overall aim of this study was to investigate if these types of block copolymers are potential candidates to be used as bile acid sequestrants in the treatment of bile acid diarrhea and hypercholesterolemia diseases. It was found that the NaGDC does influence the self-assembly of these block copolymers in a similar way, but not as effectively as the classical ionic surfactants. At low bile salt concentrations and above the CMT of the pure aqueous solutions of these polymers, charged PEO-PPO-PEO micelle-NaGDC complexes are formed. The SAXS results indicated that the NaGDC molecules are located mostly in the corona of the block copolymer micelles, close to the core-corona interface. However, at higher bile salt concentrations, during their disintegration, these complexes are generally in coexistence with small NaGDC-rich complexes. The latter complexes resemble the NaGDC micelles in terms of size and structure. Among the three studied block copolymers, P65 micelles are the easiest to disintegrate by NaGDC. The F127 and P123 micelles show almost the same stability when interacting with NaGDC.The second part in this thesis primarily describes the investigation of the effects of temperature, salt, PNIPAAM block length, and polymer concentration on the association behavior of a series of the three diblock copolymers, poly(N-isopropylacrylamide)-b-poly((3-acrylamidopropyl) trimethylammonium chloride) (PNIPAAMn-b-PAMPTMA(+)20), where n=24, 48, and 65. It was shown that the cloud point (CP) of the polymer solutions decreases upon an increase in PNIPAAM block length, and polymer and salt concentrations. At temperatures below CP of the polymer solutions, unimers and micellar/intermicellar clusters coexist. However, at temperatures above the CP, the dominant particles in the solutions are the large aggregates, which generally retain stable sizes in the presence of salt and upon increasing the temperature.Finally the aqueous mixed solutions of PNIPAAM26-b-PAMPTMA(+)15 and poly(N-isopropylacrylamide)-b-poly(sodium 2-acrylamido-2-methyl-1-propanesulfonate) (PNIPAAM27-b-PAMPS(−)15) with an equimolar charge condition were studied. Mixed micelles were observed at total concentrations ranging from 0.2 to 0.5 wt % in all studied temperatures (10– 30 oC). The mixed micelles have a cylindrical structure, and are formed via an attractive electrostatic interaction between the oppositely charged PAMPTMA(+) and PAMPS(−) blocks. However, in addition to the charged blocks interaction, there is evidence of interaction between the PNIPAAM and the charged blocks, as demonstrated by 2D 1H NMR NOESY experiments.