Abstract
Microspheres composed of the hydrophilic polymer poly(acrylic acid) (PAA), with and without β-cyclodextrin (β-CD), were prepared by a water-in-oil (w/o) solvent evaporation technique. Microspheres were characterised for particle size, β-CD and residual oil content. The type of matrix formed during microsphere synthesis was investigated by solid state carbon 13C NMR, in vitro release of β-CD and swelling measurements. A high encapsulation efficiency of the β-CD was observed (>90%). The in vitro release of β-CD in water over 24 h was initially rapid (≈70% in 3 h) with no further loss thereafter, suggesting potential covalent binding of the residual β-CD. NMR indicated that in the presence of β-CD, two concomitant chemical processes occur during microsphere synthesis: (i) esterification of the hydroxyl group(s) of the β-CD with the carboxylic acid groups of the PAA; and (ii) the formation of intra-/inter-polymer acid anhydrides.
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