Unimolecular micelles and reverse micelles based on hyperbranched polyethers - comparative study of AB<SUB>2</SUB> + A-R and A<SUB>2</SUB> + B<SUB>3</SUB> + A-R type strategies

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