The dynamics of complexation graft copolymers: Structural analysis, NMR spectroscopy, and their implications for biomedical applications

Anthony Michael Lowman, Purdue University

Abstract

In this work, copolymers of poly(methacrylic acid) grafted with polyethylene glycol) were prepared. These polymers exhibited large changes in their swelling behavior due to changes in the external pH. The pH-dependent swelling behavior was due to the formation/dissociation of interpolymer complexes due to hydrogen bonding between protonated pendant acid groups and the ether groups of the poly(ethylene glycol). The effects of complexation on the hydrogel structure was studied through the use of swelling studies and mechanical analysis. The degree to which the network swelled was affected by the degree of complexation in the gel. The degree of complexation in the networks was dependent on the copolymer composition and the pH of the environmental fluid. The rates of swelling and collapse of the networks were strongly affected by the degree of complexation in the gel. Additionally, the molecular level degree of complexation was experimentally determined using tensile testing and complexation theory. The presence of the molecular level complexes was detected using NMR nuclear Overhauser enhancement spectroscopy. For polymer gels of PMAA and PEG swollen in acidic media, an NOE was detected from the PMAA protons to the PEG carbons. The appearance of enhancement in the spectra was indicative of carbon-proton distances of less than 5 Å due to interpolymer complexation. For the same gels swollen in basic solutions and methanol, no NOE was detected as the complexes did not form under these conditions. Additionally, drug release studies were performed to examine the possibility of the use of complexation gels in controlled release applications. In acidic media, the diffusion of drugs in the gels was significantly hindered due to complexation. The diffusion coefficient for vitamin B12 in the gels varied by greater than an order of magnitude for gels in the complexed and uncomplexed state. Finally, the ability of these gels to function as oral carriers for insulin for the treatment of diabetes was examined. Oral formulations of the polymers containing insulin were effective in reducing the blood glucose levels back to near normal levels for up to eight hours following administration of a single capsule.

Degree

Ph.D.

Advisors

Peppas, Purdue University.

Subject Area

Chemical engineering|Polymers|Biomedical research

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