Huanhuan Liu, Dandan Tang, Rupei Tang, Youliang Zhao*,
“Synthesis
of multifunctional ABC stars with a reduction-labile arm by consecutive ROP,
RAFT and ATRP processes”, Sci. China Chem,
2015, DOI: 10.1007/s11426-015-5436-4.
This study aims at versatile
synthesis of 3-arm ABC-type (A = poly(ε-caprolactone), PCL; B = poly(N-isopropylacrylamide),
PNIPAM; C = poly(tert-butyl acrylate), PtBA, or poly(acrylic
acid), PAA) miktoarm star copolymers with a reducible disulfide linkage. Using
2-((2-((2-hydroxymethyl-2-((2-bromo-2-methyl)propionyloxy)methyl)propionyloxy)ethyl)disulfanyl) ethyl
4-cyano-4-(phenylcarbonothioylthio)pentanoate (HBCP) as a heterotrifunctional
initiator, consecutive ring-opening polymerization (ROP) of ε-caprolactone
(CL), reversible addition-fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide (NIPAM) and atom transfer radical polymerization
(ATRP) of tert-butyl acrylate (tBA) afforded ABC1 star, and followed
by a subsequent hydrolysis to give ABC2 star. 1H NMR and GPC
analyses revealed the desired stars and their precursors had well-controlled
molecular weight and relatively low polydispersity. As confirmed by GPC
analysis, the disulfide linkage in ABC1 star could be efficiently cleaved upon
reductive stimulus, during which the topology was converted from star
terpolymer to mixtures of homopolymer (B) and diblock copolymer (AC1).
In addition to acting as nanocarriers for stimuli-triggered drug delivery
systems, ABC stars with terminal bromide, dithiobenzoate and hydroxyl
functionalities are expected to form other reduction-cleavable multicomponent copolymers
such as (BC-graft-A)m and dendritic graft copolymers
via postpolymerization modification. Our research affords a straightforward
“core-first” method to construct multifunctional star terpolymers with
stimuli-responsive arms and reduction-labile linkage.