Ligand effect in the synthesis of hyperbranched polymers via copper‐catalyzed azide‐alkyne cycloaddition polymerization (CuAACP)

Abstract

Copper‐catalyzed azide‐alkyne cycloaddition polymerization (CuAACP) of AB2 monomers demonstrated a chain‐growth mechanism without any external ligand because of the complexation of in situ formed 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, Mn = 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), and N,N,N′,N″,N″‐pentabenzyldiethylenetriamine (PBnDETA). All ligands except PEG350 exhibited 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 PEG350 ligand 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

Chain‐growth polymerization of azide–alkyne difunctional monomer: Synthesis of star polymer with linear polytriazole arms from a core

“…The peak at δ = 8.37 ppm decreased and ultimately disappeared and shifted to a new peak at δ = 8.27 ppm, which was between the previous peaks of 8.17 and 8.37 ppm. By calculating the change of chemical shift, 32 it was estimated that f pAB = (8.37-8.27)/(8.37-8.17) = 50% of Cu I was complexed with Bn-pAB-N 3 polymer in the TBTA-Cu I -pAB-100 sample. This result also confirms that about half of the Cu I catalyst was still bound to the B 3 core by the end of polymerization of AB monomers at feed ratio of [AB] 0 :[B 3 ] 0 = 100.…”

Synthesis and Characterization of New Phosphorus Containing Sulfonated Polytriazoles for Proton Exchange Membrane Application

“…The CuAAC synthetic route has ascended as a leading model of “click chemistry” family, a term invented in 2001 by sharpless to define a set of “near‐perfect” bond forming reactions appropriate for quick assembly of molecules with favored functional groups . As a result, the CuAAC click reactions have been a steady practice in polymer chemistry in the current times for synthesizing graft copolymers, block copolymers, hyperbranch copolymers, polymer composites, linear polymers, and metallogels …”

Click chemistry strategies for the accelerated synthesis of functional macromolecules

“…Stronger coordination ligands could free the Cu catalyst from triazole branching point and turned the polymerization mechanism back to step-growth dominant. 451 Hyperbranched polytriazoles with advanced multilayer structures were also developed from functional AB 2 -F monomer (A, B, and F corresponded to alkyne, azide, and a post polymerization functionalization handle) and B 3 core through combination of highly efficient tandem functionalization reactions, including ultrafast TAD-diene reaction, alkoxyamine-ketone reaction, and thiol-epoxy reaction, all conducted under mild conditions (Figure 11). The multifunctional hyperbranched backbone was first constructed through CuAACP to provide a large number of attachment points, followed by stepwise modifications, for example, in the order of thiol-epoxy, oxime formation, esterification, and potentially thiol-ene as shown in Figure 11(B).…”