Functional poly(ethylene oxide) multiarm star polymers:: Core-first synthesis using hyperbranched polyglycerol initiators

Hyperbranched polyglycerol as well as polyglycerol modified with short apolar oligo(propylene oxide) segments (DPn = 23-52; M-w/M-n = 1.2-1.4) was deprotonated with diphenylmethylpotassium and used as polyfunctional initiators for the anionic polymerization of ethylene oxide to prepare poly(ethylene oxide) (PEO) multiarm star polymers; In the case of unmodified polyglycerol, after metalation, aggregation occurred, preventing efficient initiation and propagation. Using the apolarly modified polyglycerols with terminal oligo(propylene oxide) segments, hydroxyfunctional PEO multiarm star polymers with M-n values in the range 34 000-95 000 g/mol, arm numbers in the range 26-55, and narrow polydispersity (M-w/M-n < 1.5) were obtained in a core-first strategy. H-1 and C-13 NMR measurements evidenced complete conversion of all end groups of the propylene oxide-capped end groups of the initiator. Reinitiation of the multiarm PEO stars by deprotonation was possible and afforded star polymers with considerably larger molecular weights (M-n = 180 000 g/mol) and identical functionality. The thermal properties of the stars (DSC) were found to depend strongly on the arm length. The novel multiarm star architectures prepared consist of polyether structures only and are thus of interest for biomedical applications, e.g., in hydrogels.