Combination Of Atom Transfer Radical Research Articles

Syntheses and specific interactions of poly(hydroxyethyl methacrylate- b-vinyl pyrrolidone) diblock copolymers and comparisons with their corresponding miscible blend systems

Combination of atom transfer radical and conventional free radical polymerizations has been successfully used to prepare poly(hydroxyethyl methacrylate- b-vinyl pyrrolidone) (PHEMA- b-PVP) copolymers with controlled molecular weight and low polydispersity (<1.4). The thermal behavior and specific interaction of PHEMA- b-PVP diblock copolymers and their corresponding PHEMA/PVP blends were characterized. The result shows that glass transition temperatures of diblock copolymers analysed by differential scanning calorimetry (DSC) are higher than those of the blends. Infrared and solid-state NMR spectroscopic analyses show that hydrogen-bonding interaction of hydroxyl–carbonyl groups of diblock copolymers was also greater than that of the blends. Measurement of the proton spin–lattice relaxation time in the rotating frame, ( T 1 ρ H ) , reveals that all diblock copolymers and blends possess one composition-dependent T 1 ρ H , indicating that both diblock copolymers and blends are homogeneous, which is consistent with the DSC analysis.

Well-Defined (Co)polymers with 5-Vinyltetrazole Units via Combination of Atom Transfer Radical (Co)polymerization of Acrylonitrile and “Click Chemistry”-Type Postpolymerization Modification

Well-defined homo- and copolymers of acrylonitrile were prepared by atom transfer radical polymerization, which were further modified using a “click chemistry” reaction with sodium azide and zinc chloride to yield polymeric materials with 5-vinyltetrazole units. Using optimized reaction conditions ([NaN3]:[ZnCl2]:[RCN] = 4:1:1 in DMF at 120 °C for 48−50 h), essentially complete transformation of the nitrile groups was achieved, as judged from IR and 13C NMR spectra. The produced tetrazole-containing polymers had markedly better solubility or swellability in protic solvents (methanol or aqueous base solutions) compared to the precursors. Random copolymers of acrylonitrile and styrene were also grown from polystyrene and silica particles with immobilized initiator groups and were similarly modified to the corresponding tetrazole-containing polymers. All materials were characterized by means of thermogravimetry, which showed that the polymeric tetrazoles started to decompose with evolution of significant amounts of gas at 120−190 °C, i.e., at lower (by 60−130 °C) temperature than the starting nitrile-based materials.

Synthesis of block copolymers by combination of atom transfer radical and promoted cationic polymerization mechanisms

Block copolymers of p-methoxystyrene (MOS) and styrene (St) with cyclohexene oxide (CHO) were prepared by sequential atom transfer radical polymerization and promoted cationic polymerization. In the first step, bromine terminated polyMOS and polySt were obtained by ATRP of the corresponding monomers at 115°C for 5 h by using (1-bromoethyl) benzene (1-(PE)-Br), as an initiator, CuBr as a catalyst and 4-4′-di-(5-nonyl)-2,2′-bipyridine (dNbipy) as a complexing ligand. Polymeric radicals formed by the same radical generation process of ATRP were successively oxidized to the corresponding carbocations to initiate the polymerization of cyclohexene oxide. Block copolymer formation was evidenced by 1H-NMR and gel permeation chromatography (GPC) measurements.