Janus long-chain hyperbranched copolymers of PSt and POEGMA from a self-assembly mediated click reaction

Abstract

A self-assembly mediated synthesis was successfully adopted in the preparation of Janus long-chain hyperbranched copolymers composed of polystyrene (PSt) and poly[oligo(ethylene glycol) methacrylate] (POEGMA) half-dendrons. Firstly, seesaw macromonomers with one alkynyl group at the chain center and one azido group at each chain end, [alkynyl-(PSt-N₃)₂ and alkynyl-(POEGMA-N₃)₂], were prepared through atom transfer radical polymerization and used to produce their own long-chain hyperbranched homopolymers (lhb-PSt and lhb-POEGMA) through a click reaction, followed by the conversion of azido end-groups into amino end-groups. Meanwhile, one hetero four-arm copolymer of μ-PSt₂-POEGMA₂ with four azido end-groups was obtained by the sequential click reaction of alkynyl-(PSt-Br)₂ and alkynyl-(POEGMA-Br)₂ with α,ω-diazido tetra(ethylene glycol) and the conversion of bromo groups into azido groups. Finally, with the help of self-assembly in different selective solvents, lhb-POEGMA and lhb-PSt were linked alternately onto μ-PSt₂-POEGMA₂ through click chemistry, resulting in a Janus long-chain hyperbranched copolymer [μ-(lhb-POEGMA)(lhb-PSt)]. The different analytical techniques confirmed the successful preparation of μ-(lhb-POEGMA)(lhb-PSt) and its different precursors. The self-assembly behavior of different amphiphilic copolymers was investigated by TEM, DLS and DSC. The variation of the contact angle of μ-(lhb-POEGMA)(lhb-PSt) with the casting solvent was correlated with its self-assembly behavior in selective solvents.