(574h) Morphology and Mesoscale Characterization of Self-Assembled Poly (ethylene glycol)-Poly(MTC-benzyl ester) Triblock Copolymer Hydrogels

Frank, C. W., Stanford University

A novel class of supramolecular hydrogels was produced by synthesizing a triblock polycarbonate material using organocatalytic ring-opening polymerization (ROP) of a poly(ethylene glycol) PEG macroinitiator with a cyclic monomer (MTC-OBn), then subsequently physically cross-linking triblock copolymers by hydrophobic collapse to form hydrogels in water. Controlling the molecular properties of triblock copolymer materials, primarily poly(carbonate) and poly(ethylene glycol) segment lengths, resulted in a viable platform for probing mesoscale material properties using small angle X-ray scattering (SAXS). Furthermore, the macroscale mechanical properties of these supramolecular networks were characterized using oscillatory shear rheology. SAXS spectra show a strong scattering peak, indicating a molecular domain size of 20 - 25 nm. At higher concentrations of the triblock hydrogelator a structural transition from isolated hydrophobic clusters to a lamellar assembly was observed. Modeling of poly(carbonate) and poly(ethylene glycol) backbone size demonstrated that the polymers in this structure behaved as a 2D SAW.  SAXS and rheological characterization indicates that the molecular weight of the polycarbonate segment affects the gel structure on both the mesoscale and macroscale.