A method for cyclic and tadpole‐shaped polymers

Reversible addition–fragmentation chain transfer polymerization (RAFT) was used to produce well‐defined telechelic poly( N ‐isopropylacrylamide) (PNIPAM) with dibromomaleimide and dithiobenzoate groups at each end of the polymer chain by virtue of the functional RAFT agent 3,4‐dibromo‐1‐(4‐cyano‐4‐(phenylcarbonothioylthio)pentanoic)‐2,5‐dihydro‐1 H ‐pyrrole‐2,5‐dione. Cyclic PNIPAM was then obtained using an in situ intramolecular bromomaleimide–thiol substitution reaction after NaBH 4 reduction of the dithiobenzoate end group to release a thiol group. In this ring‐closure process, another bromo substituent on the maleimide group survived, being a single reactive site for post‐functionalizing the cyclic PNIPAM by a second bromomaleimide–thiol substitution reaction. After being reacted with 2‐aminoethanethiol, the resultant amino‐functionalized cyclic PNIPAM was further demonstrated as a building block to construct a tadpole‐shaped block copolymer by coupling with linear succinimidyl ester end‐functionalized poly(ethylene oxide) based on active ester click chemistry. © 2015 Society of Chemical Industry