Dextran carbamates - materials for microencapsulation

Hydrophobic dextran-N-alkyl carbamates were synthesised as wall materials for microparticles with core/shell structure, using the hydrophilic indicator phenolphthalein as core material. The performance of the carbamates was possible by adding alkylisocyanates to the hydroxy-groups of the dextrans. The synthesises were carried out by using homogeneous reaction conditions with dimethyl sulfoxide (DMSO) as solvent. Two different average molecular weights of the dextrans (9900 and 505,000 g/mol), a theoretical degree of substitution (DS) of the carbamates, DS=2 and different alkyl chains with 7, 11 and 18 carbon atoms were chosen as structural features of the dextran carbamates. Both intrinsic viscosities and the solubility of the dextran derivatives in selected organic solvents were investigated. Additionally, the average molecular weights were analysed by gel permeation chromatography. The preparation of microparticles with core/shell structures was performed by a solvent evaporation technique. The release of phenolphthalein was analysed by suspending the particles in alkaline solution. The dependence of the described structural features on the releasing properties of the manufactured microparticles was discussed.