Controlling the melting transition of semi-crystalline self-assembled block copolymer aggregates: controlling release rates of ibuprofen

Bicontinuous nanospheres and multi-lamellar micelles were self-assembled from poly[ethylene oxide]block-( poly[octadecyl methacrylate]-random-poly[docosyl methacrylate]), (PEO-b-[PODMA-co-PDSMA]) where PEO is the hydrophilic block (25 wt%) and PODMA/PDSMA is the semi-crystalline hydrophobic block (75 wt%) that gives a thermoresponsive component to the self-assembled aggregates. By varying the relative molar proportion of DSMA to ODMA (from 0 : 1 to 1 : 0) in the synthesis of the copolymers by atom transfer radical polymerisation, the melting transition Tm of the hydrophobic block could be varied from 21.5 to 41.1 degrees C in the solid state. When self-assembled in aqueous dispersions the Tm range was 23.4 to 41.3 degrees C, closely matching that of the solid samples. Preliminary analysis of the rate of release of ibuprofen from three of the block copolymer aggregates demonstrated that the rate of release was correlated with the degree of crystallinity of the hydrophobic block and that increasing temperature causes melting and a significantly enhanced release rate.