An H-shaped polymer bonding β-cyclodextrin at branch points: Synthesis and influences of attached β-cyclodextrins on physical properties

We report on the synthesis of an H-shaped polymer bonding β-cyclodextrin (β-CD) at branch points and influences of attached β-CD on physical properties. First, a poly(ethylene glycol)(PEG)-based functional macroinitiator bearing two azidos and four chlorines at chain-ends (PEG-2N₃(-4Cl)) was prepared via terminal modification reactions. Then, PEG-2N₃(-4Cl) was applied to initiate the atom transfer radical polymerization of N-isopropylacrylamide, leading to the synthesis of an H-shaped block polymer with PEG as the central chain and poly(N- isopropylacrylamide) (PNIPAM) as side-arms (PEG-2N₃(-4PNIPAM)). Azido groups were at the branch points of the polymer. Finally, the click reaction between PEG-2N₃(-4PNIPAM) and alkynyl monosubstituted β-cyclodextrin (β-CD) afforded another H-shaped polymer with two β-CDs bonding at the polymer branch points (PEG-2CD(-4PNIPAM)). The glass transition temperature (T_g) and lower critical solution temperature (LCST) of the H-shaped polymer increased after the attachment of β-CD. The self-assembly and thermal responsive behaviors, as well as the encapsulation behaviors of PEG-2CD(-4PNIPAM) were also altered. When temperature was below the LCSTs, PEG-2N₃(-2PNIPAM) dissolved in water molecularly, whereas PEG-2CD(-4PNIPAM) could self-assemble into nano-sized micelles. After the LCST transitions, PEG-2N₃(-4PNIPAM) aggregated into micron-sized unstable particles, whereas PEG-2CD(-4PNIPAM) transformed into PNIPAM-cored nanomicelles. Besides, PEG-2CD(-4PNIPAM) can encapsulate doxorubicin below its LCST due to the formation of micelles.