Supercritical carbon dioxide (CO2) assisted preparation of hydrogen-bonded interpolymer complexes

Abstract

The use of supercritical CO2 as medium in polymer processing eliminates many of disadvantages associated with other means of processing, i.e. high temperatures or toxic solvents. The “soft” processing conditions make CO2 specifically suitable as medium in the preparation of polymeric drug delivery systems. A unique drug delivery system is based on interpolymer complexation, formed by the association of two polymers via, for instance, hydrogen bonding. Very limited information is available on hydrogen bonding behaviour between polymers in CO2, or how operating conditions and polymer properties affect such interactions. Drug-loaded polymer complexes prepared in CO2 have also not yet been investigated. First, the degree of homogeneity and H-bond interaction in blends of poly(ethylene glycol) (PEG) and poly(vinylpyrrolidone) (PVP) prepared in CO2, ethanol and as physical mixtures were studied. Homogeneity of samples prepared in CO2 were greater than physically mixed samples, but less than ethanol cast samples. This was attributed to differences in mass-transport properties under the various preparation conditions. The level of PEG-PVP H- bond interaction was higher for ethanol cast blends compared to blends prepared in CO2. This was attributed to: reduced PEG-PVP H-bond interaction in CO2 medium and rapidly reduced PEG and PVP chain mobility upon CO2 venting, delaying rearrangement for optimum interaction.