Ring-Opening Polymerization of Epoxy End-Terminated Polyethylene Oxide (PEO) as a Route to Cross-Linked Materials with Exceptional Swelling Behavior

Abstract

We report here studies directed toward the synthesis and characterization of cross-linked poly(ethylene oxide) gels for use as drug delivery platforms. These gels were prepared by anionic ring-opening polymerization of diepoxy PEO 400, PEO 3400, and PEO 8000 using t -BuOK as the initiator. The diepoxy PEO 3400 and PEO 8000 derived gels were found to swell to 20× and 30× their initial masses in water, falling in the category of superadsorbants. Evaluation of their behavior as disintegrants using lactose and calcium phosphate, in comparison with commercial disintegrant croscarmellose sodium, showed the diepoxy PEO 3400 gel to be twice as fast in disintegrating a tablet. The diepoxy PEO 3400 and PEO 8000 derived gels were characterized by XRD, DSC, and TGA. and compared with the linear versions of the same materials. XRD powder patterns for all materials are very similar, albeit those for the gels are less intense likely because of packing disorders near cross-links. DSC data indicate that both T m and T c are consistently lower by 5−10 °C in the cross-linked systems. The lower the T m and T c, the greater the degree of swelling. Although the PEO 3400 gels swell less than the PEO 8000 gels, they swell faster as judged by disintegrant studies. One interpretation of these results suggests a potential new mechanism for the design of hydrogels and superadsorbants wherein cross-linking creates higher energy forms than found in the linear polymers. Such higher energy forms would melt and crystallize at lower temperatures. Likewise higher energy forms would solvate and swell more rapidly.