Synthesis of multifunctional ABC stars with a reduction-labile arm by consecutive ROP, RAFT and ATRP processes

This study aims at versatile synthesis of 3-arm ABC-type(A=poly(?-caprolactone), PCL; B=poly(N-isopropylacrylamide), PNIPAM; C=poly(tert-butyl acrylate), Pt BA, 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 ?-caprolactone(CL), reversible addition-fragmentation chain transfer(RAFT) polymerization of N-isopropylacrylamide(NIPAM) and atom transfer radical polymerization(ATRP) of tert-butyl acrylate(t BA) afforded ABC1 star, and followed by a subsequent hydrolysis to give ABC2 star. 1H nuclear magnetic resonance(1H NMR) and gel permeation chromatography(GPC) analyses revealed the desired stars and their precursors had well-controlled molecular weight and relatively low polydispersity(PDI?1.12). 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.

Facile synthesis of silicapolymer hybrids via simultaneous RAFT process and hydroxyl-alkoxysilane coupling reaction

This study aimed at the synthesis of silica particles grafted with better-defined homopolymers and block copolymers by tandem approach.Z-functionalized Sbenzyl S’-(3-trimethoxysilyl)propyltrithiocarbonate(BTPT)was used as a couplable RAFT agent to synthesize the target inorganic-organic hybrids.Simultaneous coupling reaction and RAFT process using silica particles and BTPT as raw materials efficiently afforded homopolymers grafted silica,and RAFTsynthesized macro chain transfer agents withω-terminal trimethoxysilane moiety were utilized to mediate graft reaction to prepare silica particles grafted with di-,tri-and tetrablock copolymers comprised of polymer segments such as polystyrene,polyacrylamides and polyacrylates.When the grafted chains had molecular weights ranging between 3920 and 24800 g/mol,the molar grafting ratios,which were dependent on reaction conditions and types and compositions of grafted chains,were estimated to be in the range of 15.2–101μmol/g,and grafted polymers usually had polydispersity indices lower than 1.3,revealing that the grafting process was almost controllable.To the best of our knowledge,this versatile tandem approach is one of the most facile techniques to prepare silica particles grafted with polymeric chains with controlled molecular weight,low polydispersity and precise composition due to its minimal reaction steps,mild conditions,straightforward synthesis and satisfactory controllability.