Diblock copolymers composed of a thermo-responsive poly(2-isopropyl-2-oxazoline) (PIPOZ) block (Mn = 7,000 g/mol) linked to a poly(3-acrylamidopropyl)-trimethylammonium chloride) (PAMPTMA) block (Mn = 3,500 or 8,200 g/mol) readily dissolve in salt-free water at room temperature. The solvent quality of water with respect to the PIPOZ block changes from good to poor when the solution temperature exceeds a specific temperature (36 oC to 63 oC, depending on the PIPOZ block length). At this temperature, the PIPOZ blocks dehydrate and associate. As a consequence of the relative length of the two blocks, the diblock copolymers form vesicles. Evidence from light scattering indicates that the vesicle formation involves either spheres or worm-like micelles precursors, depending on the heating rate. The kinetic control of the pathway towards vesicles may be attributed to the existence of several metastable states in the system, by analogy with studies of the isothermal self-assembly of diblock copolymers in selective solvents. The temperature-driven change in solvent condition also affects the interactions between PIPOZ blocks tethered to silica substrates via electrostatic attraction of the cationic block to silica. The effects of polymer concentration, pH, and temperature on the diblock adsorption on silica were investigated using quartz crystal microbalance with dissipation monitoring and ellipsometry. The interactions between adsorbed layers were assessed by AFM. As the solvent condition worsens, an attraction develops between adsorbed PIPOZ layers, an observation that is in good agreement with predictions of the mean-field theory.

Temperature-dependent assembly of thermosensitive cationic diblock copolymers in water and on interfaces

254th National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.