Photoirradiated Atom Transfer Radical Polymerization with an Alkyl Dithiocarbamate at Ambient Temperature

Photoirradiated Atom Transfer Radical Polymerization with an Alkyl Dithiocarbamate at Ambient Temperatur

A Simple and Efficient Synthesis of RAFT Chain Transfer Agents via Atom Transfer Radical Addition−Fragmentation

A simple, versatile, and one-step atom transfer radical addition−fragmentation (ATRAF) technique is reported for the synthesis of chain transfer agents (CTA) containing dithio groups (dithiobenzoate, dithiocarbamate, and xanthate), with various alkyl substituents, in the presence of copper catalyst, alkyl halide, and bis(thiocarbonyl) disulfide. The ATRAF procedure is efficient and selective, leading to almost quantitative conversion of alkyl halide initiators and formation of CTAs in high isolated yield under stoichiometric conditions as well as in the presence of catalytic amounts of copper(I) species. The CTAs synthesized by this process were used for reversible addition−fragmentation chain transfer (RAFT) polymerizations of styrene and methyl methacrylate without any further column purification, producing well-controlled polymers with low polydispersity, thereby demonstrating the effectiveness of ATRAF. Moreover, a simple one-pot, two-step RAFT polymerization was successful, starting from CTA synthesized in situ via ATRAF, followed directly by the addition of a monomer

Concurrent ATRP/RAFT of Styrene and Methyl Methacrylate with Dithioesters Catalyzed by Copper(I) Complexes

Concurrent ATRP/RAFT of Styrene and Methyl Methacrylate with Dithioesters Catalyzed by Copper(I) Complexe

ARGET ATRP of Methyl Acrylate with Inexpensive Ligands and ppm Concentrations of Catalyst

A simple and versatile polymerization technique via activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) of methyl acrylate (MA) with inexpensive commercially available ligands, including diethylenetriamine (DETA), N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDETA), and tris(2-aminoethyl)amine (TREN), is reported. Catalytic amounts of catalyst were utilized achieving ppm levels of CuIIBr2/L in the presence of a zerovalent copper metal (i.e., copper powder or wire) at 25 °C. High molecular weight poly(methyl acrylate) (PMA) could also be obtained with Mn > 1.5 million and Mw/Mn ∼ 1.25. A “map” was generated, illustrating minimal catalyst concentrations (i.e., copper and ligand) required over a range of targeted degrees of polymerization with various ligands. Several conclusions were made: (1) lower catalyst concentrations require higher targeted degrees of polymerization to produce equally controlled polymerizations, (2) higher catalyst concentrations are necessary for lower targeted degrees of polymerization, to ensure every activation−deactivation cycle adds fewer monomer units, (3) catalyst performance decreased from Me6TREN > TREN > PMDETA > DETA, and (4) degrees of polymerization ≥1000 exhibited a catalyst concentration boundary, which required higher CuIIBr2/L catalyst concentrations to produce similarly controlled polymerizations. Successful chain extension of a PMA macroinitiator demonstrated excellent chain-end functionality and living character

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)₂N) were studied with cyclic voltammetry (CV), revealing that increasing the strength of electron donating groups (EDGs) resulted in more stable Cu^II 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)₂N and MeO) and the slowest with electron withdrawing Cl. A 400-fold increase in the polymerization rate was observed with bpy ligands containing <i>p</i>-(Me)₂N compared to H substituents. Linear increases in molecular weight with monomer conversion, and narrow molecular weight distributions were obtained with (Me)₂N-bpy and MeO-bpy ligands. Low catalyst concentrations of 50 to 100 parts-per-million (ppm) were successfully employed with highly active R-bpy ligands (R = MeO and (Me)₂N) and found to be effective in polymerizing MA and MMA, respectively, with narrow molecular weight distributions <1.3

Kinetic Study on Role of Ditelluride in Organotellurium-Mediated Living Radical Polymerization (TERP)

The role of dimethyl ditelluride (MeTe)2 for the organotellurium-mediated living radical polymerizations (TERPs) of styrene (St) and methyl methacrylate (MMA) was kinetically studied. For both St and MMA, there was a rapid reversible activation−deactivation process mediated by (MeTe)2, i.e., P−TeMe + MeTe• ⇄ P• + (MeTe)2:  (MeTe)2 worked as an efficient deactivator of the propagating radical P•, and the radical MeTe• worked as a highly reactive activator of the dormant species P−TeMe. This rapid reversible process accounted for the dramatic improvement of the polydispersity controllability with the addition of even a small amount of (MeTe)2 for these polymerizations

A Systematic Study on Activation Processes in Organotellurium-Mediated Living Radical Polymerizations of Styrene, Methyl Methacrylate, Methyl Acrylate, and Vinyl Acetate

The activation processes for the organotellurium-mediated living radical polymerizations (TERPs) of styrene (St), methyl methacrylate (MMA), methyl acrylate (MA), and vinyl acetate (VAc) were systematically studied. For the St, MMA, and MA homopolymerizations, both thermal dissociation and degenerative chain transfer (DT) were involved in the activation process with the main mechanism being DT at the examined temperatures (40−100 °C). The degenerative (exchange) chain transfer constant Cex increased in the order of MMA Cex was weak and negative for these monomers. The VAc homopolymerization also included DT as the main activation mechanism. For the VAc polymerization, head-to-head monomer addition is significant on propagation, forming a primary alkyl chain-end (−CH2−TeCH3) adduct. The activation of this adduct was too slow to yield low-polydispersity polymers, explaining why the polydispersity control is not satisfactory for VAc at high degrees of polymerization. The Cex for a poly(methyl methacrylate) (PMMA) radical to PMMA−TeCH3 (homopolymerization) and polystyrene−TeCH3 (block copolymerization) adducts were similar, suggesting that the DT in TERP is a (nearly) single-step reaction without forming a kinetically important intermediate

Homopolymerization and Block Copolymerization of <i>N</i>-Vinylpyrrolidone by ATRP and RAFT with Haloxanthate Inifers

Difunctional haloxanthate inifers were used for successive reversible addition−fragmentation transfer (RAFT) polymerization of N-vinylpyrrolidone (NVP) and atom transfer radical polymerization (ATRP) of styrene (St), methyl acrylate (MA), and methyl methacrylate (MMA). Since a quantitative dimerization of NVP in the presence of bromoxanthate inifers occurred, two chloroxanthate inifers, S-[1-methyl-4-(6-chloropropionate)ethyl acetate] O-ethyl dithiocarbonate (CPX) and S-[1-methyl-4-(6-chloroisobutyrate)ethyl acetate] O-ethyl dithiocarbonate (CiBX), were synthesized. These two difunctional chloroxanthate inifers were used to prepare PNVP-b-PSt, PNVP-b-PMMA, and PNVP-b-PMA block copolymers, where each block was synthesized by different polymerization procedures (either RAFT or ATRP). In the RAFT-first approach, well-controlled polymerization of NVP was observed. Well-defined PNVP-b-PSt (Mn,GPC = 15,000 g/mol and Mw/Mn b-PMMA (Mn,GPC = 50,600 g/mol and Mw/Mn b-PMA, resulting in poor control of the MA chain extension. In the ATRP-first approach, a well-controlled polymerization was observed only for the ATRP of MMA with the CiBX initiator (Mn = 13,000 and Mw/Mn CPX initiator. This resulted in poor control and broad molecular weight distribution for the subsequent RAFT chain extension of NVP. Thus, the chloroxanthate inifers provide synthetic access to well-defined PNVP-b-PSt and PNVP-b-PMMA, but not to PNVP-b-PMA block copolymers

Characterization of Low-Mass Model 3-Arm Stars Produced in Reversible Addition−Fragmentation Chain Transfer (RAFT) Process

The reactions of polystyryl (PSt) radical and polystyryl dithiobenzoate (PSt-SCSPh) were modeled by those of 1-phenylethyl (PE) radical and 1-phenylethyl dithiobenzoate (PE-SCSPh). The low-mass homologues, which model the 3-arm star polymers possibly produced by the cross-termination between the PSt radical and the (intermediate) adduct radical of PSt• with PSt-SCSPh, were isolated and characterized by 1H and 13C nuclear magnetic resonance (NMR) spectroscopies, matrix-assisted laser desorption ionization time-of-flight mass spectroscopy (MALDI-TOF-MS), and elemental analysis. The low-mass model 3-arm stars were stable at 100 °C

Determination of ATRP Equilibrium Constants under Polymerization Conditions

Atom transfer radical polymerization (ATRP) equilibrium constants (<i>K</i>_ATRP) were measured during polymerization of methyl acrylate (MA) with Cu^IBr/Cu^IIBr₂ in either dimethyl sulfoxide (DMSO) or acetonitrile (MeCN) in the presence of either tris­(2-pyridylmethyl)­amine (TPMA) or tris­[2-(dimethylamino)­ethyl]­amine (Me₆TREN) as the ligand and with ethyl 2-bromopropionate as the initiator. The ln­(<i>K</i>_ATRP) values changed linearly with the volume fraction of solvents in the reaction medium, allowing extrapolation of the values for <i>K</i>_ATRP to bulk conditions, which were 2 × 10^–9 and 3 × 10^–8 for TPMA and Me₆TREN ligands at 25 °C, respectively. The temperature effect on <i>K</i>_ATRP values was studied in MA/MeCN = 1/1 (v/v) with TPMA as the ligand in the temperature range from 0 to 60 °C. The <i>K</i>_ATRP values increased with temperature providing Δ<i>H</i> = 36 kJ mol^–1 in MeCN