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This article reports a chain‐growth coupling polymerization of AB difunctional monomer via copper‐catalyzed azide–alkyne cycloaddition (CuAAC) reaction for synthesis of star polymers. Unlike our previously reported CuAAC polymerization of AB_n(n ≥ 2) monomers that spontaneously demonstrated a chain‐growth mechanism in synthesis of hyperbranched polymer, the homopolymerization of AB monomer showed a common but less desired step‐growth mechanism as the triazole groups aligned in a linear chain could not effectively confine the Cu catalyst in the polymer species. In contrast, the use of polytriazole‐based core molecules that contained multiple azido groups successfully switched the polymerization of AB monomers into chain‐growth mechanism and produced 3‐arm star polymers and multi‐arm hyperstar polymers with linear increase of polymer molecular weight with conversion and narrow molecular weight distribution, for example,M_w/M_n ~ 1.05. When acid‐degradable hyperbranched polymeric core was used, the obtained hyperstar polymers could be easily degraded under acidic environment, producing linear degraded arms with defined polydispersity. © 2019 Wiley Periodicals, Inc. J. Polym. Sci.2020,58, 84–90

Structurally defined hyperbranched polymers (HBPs) bearing multiple azido peripheral groups and alkene dangling groups are constructed using the authors' recently developed chain‐growth copper‐catalyzed azide‐alkyne cycloaddition polymerization (CuAACP) of an alkene‐containing AB₂monomer. Sequential integration of CuAAC and photo‐initiated thiol–ene reactions proves highly efficient and chemo‐selective functionalization of polymers at different placements with quantitative yield of both reactive groups. A variety of HBPs carrying both surface and internal functionalities are then produced, achieving quantitative/ratiometric incorporations of guest molecules in most cases. To demonstrate possible conjugation with bioactive ingredients, well‐defined HBPs decorated with peripheral cysteine moieties are produced as an example, showing pH responsiveness in water.

Copper‐catalyzed azide‐alkyne cycloaddition polymerization (CuAACP) of AB₂monomers demonstrated a chain‐growth mechanism without any external ligand because of the complexation ofin situformed triazole groups with Cu catalysts. In this study, we explored the use of various ligands that affected the polymerization kinetics to tune the polymers’ molecular weights and the degree of branching (DB). Eight ligands were studied, including polyethylene glycol monomethyl ether (PEG₃₅₀,M_n= 350), tris(benzyltriazolylmethyl)amine (TBTA), 2,6‐bis(1‐undecyl‐1H‐benzo[d]imidazol‐2‐yl)pyridine (Py(DBim)₂), 2,2′‐bipyridyl (bpy), 4,4′‐di‐n‐nonyl‐2,2′‐bipyridine (dNbpy),N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA),N,N,N′,N″,N″‐penta(n‐butyl)diethylenetriamine (PBuDETA), andN,N,N′,N″,N″‐pentabenzyldiethylenetriamine (PBnDETA). All ligands except PEG₃₅₀exhibited stronger coordination with Cu(I) than the polytriazole polymer, which freed the Cu catalyst from polymers and resulted in dominant step‐growth polymerization with simultaneous chain‐growth feature. Meanwhile, the use of PEG₃₅₀ligand retained the confined Cu in the polymer, demonstrating a chain‐growth mechanism, but lower polymer molecular weights as compared with the no‐external‐ligand polymerization. Results indicated that aliphatic substituent groups on ligands had little effect on the molecular weights and DB of the polymers, but rigid aromatic substituent groups decreased both values. By varying the ligand species and amounts, hyperbranched polymers with DB value ranging from 0.53 ([TBTA]₀/[Cu]₀= 5) to 0.98 ([PMDETA]₀/[Cu]₀= 2) have been achieved. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem.2018,56, 2238–2244

In the present study, a water‐soluble hyperbranched polymer platform that contained a Förster resonance energy transfer (FRET) array and exhibited varied fluorescence in response to solvent, light, and CN⁻anion stimuli was constructed. The use of chain‐growth copper‐catalyzed azide–alkyne cycloaddition polymerization (CuAACP) enabled accurate control of the ratio and distance of three incorporated fluorophores, coumarin (Cou), nitrobenzoxadiazole (NBD), and photoswitchable spiropyran (SP), that could be reversibly transformed into the red‐emitting merocyanine (MC) state. Within the FRET system, the energy flow from Cou to MC was significantly enhanced by the introduction of NBD as a central fluorophore relay. Moreover, the energy‐transfer efficiency was increased by changing the solvent from tetrahydrofuran to more polar water; this was accompanied by a clear color change and fluorescence behavior. These correlations of polymer composition and solvent polarity to the FRET efficiency were finally applied to the effective detection of CN⁻anion; thus demonstrating a function of this polymer as a CN⁻sensor.

Hyperbranched polymers (HBPs) with decorated donor and acceptor chromophores in different domains were constructed to demonstrate the function of light harvesting in a polymeric nanostructure. Taking advantage of our recently developed chain‐growth copper‐catalyzed azide–alkyne cycloaddition polymerization, two structural parameters in the HBPs, for example, the molar ratio of the acceptor Coumarin 343 in the core to the donor Coumarin 2 on the periphery, and the average distance between these two layers, could be independently varied in a one‐pot synthesis. The results demonstrated an efficient energy transfer from the excited Coumarin 2 to the ground‐state Coumarin 343 in the core, with the efficiency of the energy transfer reaching as high as 98 %. The excited Coumarin 343, after receiving energy from donor Coumarin 2 emitted higher fluorescence intensity than when directly excited, indicating an observed light concentration effect from the periphery dye to the central dye in one polymer structure.

Hyperbranched polymers (HBPs) with decorated donor and acceptor chromophores in different domains were constructed to demonstrate the function of light harvesting in a polymeric nanostructure. Taking advantage of our recently developed chain‐growth copper‐catalyzed azide–alkyne cycloaddition polymerization, two structural parameters in the HBPs, for example, the molar ratio of the acceptor Coumarin 343 in the core to the donor Coumarin 2 on the periphery, and the average distance between these two layers, could be independently varied in a one‐pot synthesis. The results demonstrated an efficient energy transfer from the excited Coumarin 2 to the ground‐state Coumarin 343 in the core, with the efficiency of the energy transfer reaching as high as 98 %. The excited Coumarin 343, after receiving energy from donor Coumarin 2 emitted higher fluorescence intensity than when directly excited, indicating an observed light concentration effect from the periphery dye to the central dye in one polymer structure.