Determination of ATRP Equilibrium Constants under Polymerization Conditions.

Atom transfer radical polymerization (ATRP) equilibrium constants () were measured during polymerization of methyl acrylate (MA) with CuBr/CuBr in either dimethyl sulfoxide (DMSO) or acetonitrile (MeCN) in the presence of either tris(2-pyridylmethyl)amine (TPMA) or tris[2-(dimethylamino)ethyl]amine (MeTREN) as the ligand and with ethyl 2-bromopropionate as the initiator. The ln() values changed linearly with the volume fraction of solvents in the reaction medium, allowing extrapolation of the values for to bulk conditions, which were 2 × 10 and 3 × 10 for TPMA and MeTREN ligands at 25 °C, respectively. The temperature effect on values was studied in MA/MeCN = 1/1 (v/v) with TPMA as the ligand in the temperature range from 0 to 60 °C.

Highly Active Bipyridine-Based Ligands for Atom Transfer Radical Polymerization.

A series of 2,2'-bipyridines with 4,4'-substituents (R-bpy) were investigated for atom transfer radical polymerization (ATRP) of methyl acrylate (MA) and methyl methacrylate (MMA). Ligand substituents with a large range of Hammett parameters (R = Cl, H, Me, dinonyl (dN), MeO, and (Me)N) were studied with cyclic voltammetry (CV), revealing that increasing the strength of electron donating groups (EDGs) resulted in more stable Cu complexes and larger ATRP equilibrium constants. Normal ATRP experiments confirmed the obtained CV data by showing the fastest rates of polymerization with R-bpy ligands containing EDGs ((Me)N and MeO) and the slowest with electron withdrawing Cl.

Synthesis of Amphiphilic Poly(-vinylpyrrolidone)--poly(vinyl acetate) Molecular Bottlebrushes.

Well-defined molecular bottlebrushes with poly(-vinylpyrrolidone) and poly(-vinylpyrrolidone)--poly(vinyl acetate) (PNVP--PVOAc) side chains were prepared via a combination of atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer (RAFT). A macro chain transfer agent poly(2-((2-ethylxanthatepropanoyl)oxy)ethyl methacrylate) (PXPEM) was prepared by attaching xanthate chain transfer agents onto each monomeric unit of poly(2-hydroxyethyl methacrylate). Subsequently, a RAFT polymerization procedure was used to synthesize molecular bottlebrushes with PNVP side chains with controlled molecular weight and low polydispersity by grafting from the PXPEM backbone.

Critical evaluation of the microwave effect on radical (co)polymerizations.

Critical evaluations of the microwave effect on initiation, propagation, and termination during conventional radical polymerizations (RPs) of methyl methacrylate (MMA) and random copolymerization of styrene (St) with (meth)acrylates are examined by comparing microwave heating (MWH) and conventional heating (CH). Poly(methyl methacrylate) with similar $ \overline M_{\rm n} $, $ \overline M_{\rm w} $/$ \overline M_{\rm n} $, and conversion are obtained under precisely controlled temperature, indicating very small changes of propagation rate constant. Rate enhancement in the absence of precise temperature control is mostly due to the higher reaction temperature of the reaction mixture than the apparent value indicated on display.

Photo-cross-linkable thermoresponsive star polymers designed for control of cell-surface interactions.

Star polymers with thermoresponsive arms, consisting of 2-(2-methoxyethoxy)ethyl methacrylate (MEO₂MA) and oligo(ethylene glycol) methacrylate with ~4 ethylene oxide units (OEOMA₃₀₀, M(n) = 300), were synthesized via atom transfer radical polymerization (ATRP). 25% of the arms contained benzophenone chain-end functionality at the star periphery. A mixture of linear poly(MEO₂MA-co-OEOMA₃₀₀)-Br macroinitiators without and with benzophenone end-group macroinitiators were (MI and Bzp-MI, respectively) cross-linked with ethylene glycol dimethacrylate to form star polymers.

Synthesis of poly(vinyl acetate) block copolymers by successive RAFT and ATRP with a bromoxanthate iniferter.

Poly(vinyl acetate)-b-polystyrene, poly(vinyl acetate)-b-poly(methyl acrylate) and poly(vinyl acetate)-b-poly(methyl methacrylate) block copolymers with low polydispersity (M(w)/M(n) < 1.25) were prepared by successive reversible addition-fragmentation chain transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP) employing a bromoxanthate iniferter (initiator-transfer agent-terminator).

Understanding atom transfer radical polymerization: effect of ligand and initiator structures on the equilibrium constants.

Equilibrium constants in Cu-based atom transfer radical polymerization (ATRP) were determined for a wide range of ligands and initiators in acetonitrile at 22 degrees C. The ATRP equilibrium constants obtained vary over 7 orders of magnitude and strongly depend on the ligand and initiator structures. The activities of the Cu(I)/ligand complexes are highest for tetradentate ligands, lower for tridentate ligands, and lowest for bidentate ligands.

Highly versatile organostibine mediators for living radical polymerization.

A new versatile method for conducting living radical polymerization has been developed in which organostibines induce consecutive group-transfer radical reactions with alkenes. The method has been successfully applied, for the first time, to the controlled polymerization of both conjugated and unconjugated vinyl monomers, and the desired polymers with predetermined molecular weight and low polydispersity index were obtained in excellent yields. This characteristic feature of this method is exemplified in the first synthesis of block copolymers composed of conjugated and unconjugated monomers, which would be of great importance as functional smart organic nanomaterials.

Mechanism-based invention of high-speed living radical polymerization using organotellurium compounds and azo-initiators.

Kinetic analysis reveals the existence of two competing pathways in the organotellurium-mediated living radical polymerization (TERP) at elevated temperature. The rate-determining step, namely, the thermal dissociation process, could be bypassed by the addition of conventional radical initiators, and the polymerization proceeded at low temperature by the degenerative transfer-mediated polymerization. The polymerization conditions are applicable to a variety of vinyl monomers, and the desired polymers form in a highly controlled manner.