Atom Transfer Radical Coupling Research Articles

Synthesis of Hydroxy-Telechelic Poly(methyl acrylate) and Polystyrene by Atom Transfer Radical Coupling

Hydroxy-terminated poly(methyl acrylate) (HO-PMABr) and polystyrene (HO-PStBr) were synthesized by atom transfer radical polymerization (ATRP) using a HO-functionalized initiator. These HO-functional polymers were further employed in an atom transfer radical coupling (ATRC) reaction in the presence of a zerovalent metal forming hydroxy-telechelic poly(methyl acrylate) (HO-PMA-OH) and polystyrene (HO-PSt-OH). In ATRC process macroradicals, generated in situ by an atom transfer radical equilibrium, take part in bimolecular termination reactions in the presence of a reducing agent, such as nanosize copper. The coupling of hydroxy-terminated PSt was fast; after 3 h more than 95% of polymeric chains being reacted. Under similar ATRC conditions, the coupling of poly(methyl acrylate) was slow since the ATRP equilibrium constant, and consequently radical concentration, is much smaller than those of polystyrene. This difficulty was overcome by introducing small amounts of St in the ATRC of polyacrylate. The acrylate radicalsgenerated during the activation step in the presence of cuprous halide complexreact with styrene producing styrene-terminated acrylate macroradicals that combine in a similar manner and at rates similar to polystyrene chains. Equimolar amounts of St vs polyacrylate chain end provided hydroxy-telechelic polymers with high coupling efficiency after a short reaction time. NMR analyses performed on the coupling product of hydroxy-terminated poly(methyl acrylate) showed the incorporation of catalytic amounts of St during ATRC.

Polystyrene with Designed Molecular Weight Distribution by Atom Transfer Radical Coupling

Copper-mediated atom transfer radical coupling (ATRC) was studied for monobrominated and dibrominated polystyrenes as well as their mixtures. In the ATRC process macroradicals, generated in situ by an atom transfer radical equilibrium, participate in coupling reactions in the presence of a reducing agent, such as nanosize copper, zerovalent iron, tin octanoate (SnOct2), and ascorbic acid. 1H NMR analyses performed on the coupling product of monobrominated polystyrene (PStBr) showed the disappearance of the signal attributed to the methine proton located in the α-position to the bromine. ATRC is influenced by the nature of ligand as well as the amounts of ligand and zerovalent metal used in the process. The molecular weight of the coupling product is a function of the extent of coupling, which is defined by the proportion of polymeric chains participated in the reaction. Thus, molecular weights of the ATRC products of monobrominated polystyrene were approximately twice higher than those of PStBr precursors, while the polydispersities were low. The coupling of α,ω-dibrominated homologues gave high molecular weight products with higher polydispersities.

Synthesis and Characterization of α,ω‐Telechelic Polymers by Atom Transfer Radical Polymerization and Coupling Processes

AbstractInitiators for atom transfer radical polymerization (ATRP) bearing different functional groups (aldehyde, aromatic hydroxyl, dimethyl amino) were synthesized and characterized. Monotelechelics with low molecular weight were obtained by ATRP of styrene using these initiators in the presence of the CuBr/bpy catalytic complex. α,ω‐Telechelic polymers with double molecular weights with respect to the starting materials were prepared by coupling of monotelechelics under atom transfer radical generation conditions, in the absence of monomer, using CuBr as catalyst, tris[2‐(dimethylamino)ethyl]amine (Me6TREN) as a ligand, under Cu0 mediated reductive conditions and with toluene as solvent. Terminal Br atoms present in monotelechelic polystyrenes (PS) as a consequence of the ATRP mechanism also offer other routes for preparing telechelic polymers. Aldehyde functionalized polymer was etherified with hydroquinone furnishing telechelic PS with a molecular weight that was two times higher. All polymers were characterized by spectral methods (NMR, IR spectroscopy) as well as by GPC.Synthesis of initiators for atom transfer radical polymerization bearing different functional groups, for example, aldehyde, aromatic hydroxyl, dimethyl amino.magnified imageSynthesis of initiators for atom transfer radical polymerization bearing different functional groups, for example, aldehyde, aromatic hydroxyl, dimethyl amino.