Exploring Self-Condensing Vinyl Polymerization of Inimers in Microemulsion To Regulate the Structures of Hyperbranched Polymers

Abstract

A synthetic method was successfully developed to produce structurally defined hyperbranched polymers using confined micellar space in microemulsion to regulate atom transfer radical polymerization (ATRP) of inimers. Systematic exploration of experimental variables, including five methacrylate-based inimer species, two ATRP ligands, and varied amounts of inimers and catalysts, produced a series of hyperbranched polymers that encompassed a broad range of molecular weights (Mn = 194–1301 kg/mol), high degrees of branching (DB = 0.26–0.41), and narrow molecular weight distribution (Mw/Mn = 1.1–1.7). The ATRP of inimers in the microemulsion media showed a fast polymerization rate with quantitative conversion of methacrylate groups within 0.5 h. At high conversion, there was essentially one hyperbranched polymer per discrete latex particle, whose dimension (hydrodynamic diameter Dh = 10.95–20.13 nm in water) and uniformity directly determined the molecular weight and polydispersity of the hyperbranched polymer. The DB of hyperbranched polymers was quantitatively determined using inverse gated 13C NMR spectroscopy, and its value was affected by several parameters, all related to the effective amount of copper catalysts in the polymerization loci for dynamic ATRP exchange reactions. The use of inimers and ligands that showed high copper complex solubility and a high feed ratio of copper to inimer could increase the concentration of copper catalyst in the discrete particles and consequently the DB value. Within the investigation, the polymerization of inimer 3 using 4,4′-dinonyl-2,2′-dipyridyl (dNbpy) as ligand produced hyperbranched polymers with the highest DB = 0.41 due to the high solubility of Cu(II)/(dNbpy)2 in inimer 3. When acetal group as a linker was incorporated into the inimer, the produced hyperbranched polymers exhibited complete degradation in acidic environment, indicating potential utility in biomedical applications.