Gelation of aqueous solutions of diblock copolymers of ethylene oxide and D,L-lactide

The thermally-reversible gelation of aqueous solutions of diblock copolymers of ethylene oxide (E) and D,L-lactide (L), E42L12, E38L16, E39L20, E41L26, E78L14 and E77L26, has been studied using gelation temperature measurements, polarised light microscopy and NMR spectroscopy. The solutions showed a high temperature gel-sol boundary but no low temperature gel-sol boundary. Polarised light microscopy showed that the gel phase was isotropic, and the dependence of sol-gel temperature on concentration suggested that the micelles were prolate ellipsoidal, rather then spherical. NMR spectroscopy showed that below ca. 60 degrees C, the L block in the micelle core became highly restricted. It is tentatively suggested that this is due to the L blocks forming an ordered structure, thus explaining the absence of a low temperature gel-sol boundary.