One-Pot Controlled Synthesis of Homopolymers and Diblock Copolymers Grafted Graphene Oxide Using Couplable RAFT Agents

An original strategy is presented to synthesize homopolymers and diblock copolymers grafted graphene oxide by simultaneous coupling reaction and RAFT process. Z-functionalized <i>S</i>-methoxycarbonylphenylmethyl <i>S′</i>-3-(trimethoxysilyl)­propyltrithiocarbonate (MPTT) and R-functionalized <i>S</i>-4-(trimethoxysilyl)­benzyl <i>S′</i>-propyltrithiocarbonate (TBPT) were used as couplable RAFT agents to prepare the target nanocomposites. Under similar conditions, MPTT-mediated 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

Versatile Synthesis of Multiarm and Miktoarm Star Polymers with a Branched Core by Combination of Menschutkin Reaction and Controlled Polymerization

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(<i>tert</i>-butyl acrylate), and poly­(<i>N</i>-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_<i>m</i>-type stars (<i>m</i> ≈ 7.0–35.1) were obtained. Meanwhile, A_<i>m</i>B_<i>n</i> stars (<i>m</i> ≈ 9.0, <i>n</i> ≈ 6.1–11.3) were achieved by successive Menschutkin reactions, and A_<i>m</i>C_<i>o</i> stars (<i>m</i> ≈ 8.8–9.0, <i>o</i> ≈ 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

Precise Synthesis of ABCDE Star Quintopolymers by Combination of Controlled Polymerization and Azide–Alkyne Cycloaddition Reaction

A facile approach based on integrated utilization of ring-opening polymerization (ROP), reversible addition–fragmentation chain transfer (RAFT) process, and azide–alkyne cycloaddition reaction was efficiently used to construct amphiphilic 5-arm ABCDE star quintopolymers. The miktoarm stars are composed of poly­(ethylene glycol) (A), poly­(ε-caprolactone) (B), polystyrene (C), poly­(l-lactide) (D), poly­(<i><i>N,N</i></i>-dimethylaminoethyl methacrylate) (E₁), poly­(methyl methacrylate) (E₂), and poly­(methyl acrylate) (E₃). Alkyne-in-chain-functionalized BC and DE diblock copolymers were synthesized by successive ROP and RAFT process. Selective [3 + 2] click reaction between two-azide-end-functionalized PEG and BC copolymer gave azide-core-functionalized ABC star terpolymer, and a subsequent click reaction with DE copolymer afforded well-defined ABCDE stars with well-controlled molecular weight, low polydispersity, and precise composition, as evidenced from ¹H NMR, GPC, and GPC-MALLS analyses. DSC analyses revealed part of polymer segments in ABCDE stars were compatible. This general methodology has some advantages such as straightforward synthesis, mild reaction conditions, versatile polymerizable monomers, and high yields, which is promising for the construction of numerous functional star copolymers with multiple compositions and precise microstructures