Syntheses of L-lactide-PEG multiblock copolymers by means of spirocyclic Ge-PEG initiators

Spirocyclic initiators were prepared by condensation of Ge(OEt)4 and tetra(ethylene glycol), TEG, or PEG-2000 ((M) over barn = 2000 Da). These spirocycles were used as initiators for the ring-expansion polymerization of L-lactide in chlorobenzene at 120 degreesC. The resulting cyclic block co-polymers were reacted in situ with aliphatic dicarboxylic acid dichlorides (ADADs) or with hexamethylene diisocyanate (HMDI) to achieve chain extension. The reaction conditions were optimized via model reactions. The isolated Ge-free multiblock copolymers were characterized by viscosity and by H-1 NMR measurements. In selected cases SEC measurements and MALDI-TOF mass spectroscopy were conducted. The mass spectra revealed small amounts of cyclic oligo- and polylactides, whereas the high molecular weight multiblock copolymers did not "fly".