Symmetric reduction‐responsive amphiphilic comblike copolymers mid‐disulfide‐functionalized comblike copolymers with alternating copolymer comprised of styrenic unit and N‐(2‐hydroxyethyl) maleimide (HEMI) unit (poly(St‐alt‐HEMI)) backbones and alternating PEG and PCL side chains (S‐CP(PEG‐alt‐PCL)) with poly(St‐alt‐HEMI) backbones and alternating poly(ε‐caprolactone) (PCL) and poly(ethylene glycol) (PEG) side chains were synthesized and used as nanocarriers for in vitro release of doxorubicin. The target copolymers with predetermined molecular weight and narrow molecular weight distribution (Mw/Mn = 1.15–1.20) were synthesized by reversible addition‐fragmentation chain transfer (RAFT) copolymerization of vinylbenzyl‐terminated PEG and N‐(2‐hydroxyethyl) maleimide mediated by a disulfide‐functionalized RAFT agent S‐CPDB, and followed by ring‐opening polymerization of ε‐caprolactone. When compared with linear block copolymer comprised of poly(ethylene glycol) (PEG) and poly(ϵ‐caprolactone) (PCL) segments (PEG‐b‐PCL) copolymers, comblike copolymers with similar PCL contents usually exhibited decreased crystallization temperature, melting temperature, and degree of crystallinity, indicating the significant influence of copolymer architecture on physicochemical properties. Dynamic light scattering measurements revealed that comblike copolymers were liable to self‐assemble into aggregates involving vesicles and micelles with average diameter in the range of 56–226 nm and particle size distribution ranging between 0.07 and 0.20. In contrast to linear copolymer aggregates, comblike copolymer aggregates with similar compositions were of improved storage stability and enhanced drug‐loading efficiency. In vitro drug release confirmed the disulfide‐linked comblike copolymer aggregates could rapidly release the encapsulated drug when triggered by 10 mM DL‐dithiothreitol. These reduction‐sensitive, biocompatible, and biodegradable aggregates have a potential as controlled delivery vehicles. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Menschutkin reaction and controlled polymerization were combined to construct three types of star polymers with a branched core. Branched PVD was synthesized by reversible addition–fragmentation chain transfer (RAFT) copolymerization and used as a core reagent to synthesize multiarm and miktoarm stars with poly(ε-caprolactone) (PCL), polystyrene, poly(methyl methacrylate), poly(tert-butyl acrylate), and poly(N-isopropylacrylamide) segments. Effects of reaction time, feed ratio, and arm length on coupling reaction between PVD and bromide-functionalized polymer were investigated, and a variety of A m -type stars (m ≈ 7.0–35.1) were obtained. Meanwhile, A m B n stars (m ≈ 9.0, n ≈ 6.1–11.3) were achieved by successive Menschutkin reactions, and A m C o stars (m ≈ 8.8–9.0, o ≈ 5.0) were generated by tandem quaternization and RAFT processes. Molecular weights of various stars usually agreed well with the theoretical values, and their polydispersity indices were in the range of 1.06–1.24. The arm number, chain length, and chemical composition of star polymers could be roughly adjusted by control over reaction conditions and utilization of alternative methods, revealing the generality and versatility of these approaches. These ion-bearing stars were liable to exhibit solubility different from normal covalently bonded polymers, and the chain relaxation and melting behaviors of polymer segments were strongly dependent on the macromolecular architecture.

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An original strategy is presented to synthesize homopolymers and diblock copolymers grafted graphene oxide by simultaneous coupling reaction and RAFT process. Zfunctionalized S-methoxycarbonylphenylmethyl S′-3-(trimethoxysilyl)propyltrithiocarbonate (MPTT) and R-functionalized S-4-(trimethoxysilyl)benzyl S′-propyltrithiocarbonate (TBPT) were used as couplable RAFT agents to prepare the target nanocomposites. Under similar conditions, MPTTmediated grafting reaction was liable to afford grafted chains with shorter chain length, narrower molecular weight distribution and lower grafting density than TBPT-based reaction owing to increased shielding effect and different grafting process. The grafted polymers had nearly controlled molecular weight and polydispersity ranging between 1.11 and 1.38, and the apparent molar grafting ratio was estimated to be 73.6−220 μmol/g as the molecular weights of grafted polymers were in the range of 3980−12500 g/mol. The improved solubility and dispersibility of GO−polymer composites in various solvents comprising hexane and water confirmed their amphiphilicity. The grafting process offers an opportunity to alter GO morphologies, and surface morphologies involving nanosheets, nanoparticles, and nanorods were observed as the composites were dispersed in different solvents with the aid of sonication treatment. This tandem approach is promising for surface modification of solid substrates with hydroxyl surface due to its mild conditions, straightforward synthesis and good controllability.