Unimolecular micelles and reverse micelles based on hyperbranched polyethers - comparative study of AB₂ + A-R and A₂ + B₃ + A-R type strategies

Abstract

Core-shell type hyperbranched polymers that are capable of forming unimolecular micelles and reverse micelles in aqueous and hydrocarbon medium, respectively, were synthesized via two approaches, namely AB₂ + A-R and A₂ + B₃ + A-R type copolymerizations. In case of micelle-forming polymers, an AB₂ monomer carrying a decamethylene spacer was used along with heptaethylene glycol monomethyl ether (HPEG) as the A-R type comonomer. One the other hand, for the preparation of reverse micelle-forming polymers, an AB₂ monomer containing an oligo(oxyethylene) spacer was used along with cetyl alcohol as the A-R type comonomer. The former was readily soluble in water while the latter was soluble in hydrocarbon solvents like hexane. NMR spectral studies confirmed that both the approaches generated highly branched structures wherein about 65-70% of the terminal B groups were capped by the A-R comonomer. Dye-uptake measurements revealed that the polymers prepared via the AB₂ + A-R approach exhibited a significantly larger uptake compared with those prepared via the A₂ + B₃ + A-R approach. This suggests that the AB₂ + A-R approach generates hyperbranched polymers with better defined core-shell topology when compared with polymers prepared via the A₂ + B₃ + A-R approach, which is in accordance with previous studies that suggest that A₂ + B₃ approach yields polymers with significantly lower branching levels and consequently less compact structures.