A versatile synthesis of poly(lauryl acrylate) using N-(n-octyl)-2-pyridylmethanimine in copper mediated living radical polymerization

A facile synthesis of poly(lauryl acrylate) has been achieved by atom transfer radical polymerization using benzyl-2-bromoisobutyrate, copper (I) bromide, and N-(n-octyl)-2-pyridylmethanimine (OPMI). The latter was of great interest as its synthesis was very easy to carry out and as it allowed the reaction mixture to be homogeneous, which was essential for the control of the reaction. The polymerization was controlled under these conditions and was optimized with the addition of copper (II) bromide as deactivator. We proved that the synthesis of poly(lauryl acrylates) with well defined molecular weights and narrow polydispersities was possible using a ligand which does not require difficult synthesis and purification. We also showed the ability of pyridylmethanimine ligands to control ATRP of an acrylate derivative. Best results were obtained at 130 °C in xylene for [Initiator]₀/[Cu(I)Br]₀/[Cu(II)Br₂]₀/[OPMI]/[lauryl acrylate] equal to 1/1/0.05/2.2/181, respectively (M_n = 19,942, DPI = 1.28).     

Effect of variation of [PMDETA]0/[Cu(I)Br]0 ratio on atom transfer radical polymerization of n‐butyl acrylate

A kinetic study was conducted to examine the effect of varying the ratio of ligand to transition metal in a Cu(I)Br/N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) catalyst system for atom transfer radical polymerization (ATRP) of n‐butyl acrylate (nBA) using methyl 2‐bromopropionate as the initiator. Experimental molecular weights were higher than theoretical when low molecular weight polymers were targeted at low ratios of [PMDETA]₀/[Cu(I)Br]₀ (< 1), indicating inefficient initiation/deactivation. A downward curvature in the plot of M_n versus conversion was observed at high monomer conversion when targeting high molecular weight polymers. This deviation became more significant when an excess of ligand was used, indicating a contribution of chain transfer to ligand. The maximum rate of polymerization was obtained at [PMDETA]₀/[Cu(I)Br]₀ ≈ 0.5 for bulk ATRP of nBA; however for polymerization in the presence of 10 vol% DMF, the maximum appeared at the ratio ≈ 1:1. Addition of acetone or DMF improved solubility of Cu(II) complex, which consequently improved the level of control over the polymerization at low ratios of [PMDETA]₀/[Cu(I)Br]₀, but also reduced the reaction rate. The polymerization rate increased with temperature, but at the expense of increased polydispersities. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3285–3292, 2004     

The Crystal Structures of two Linearly Polymeric Copper(II) Complexes of 2, 2′‐Bipyridine with threefold Glycolato and Oxalato Bridges

The complex [Cu(HGLYO)₂(bipy)] ( I ) and two new copper(II) coordination polymers with the formulas {[Cu(GLYO)_1‐x(ox)_x(bipy)]·2.5H₂O}_n [GLYO = glycolato dianion, ox = oxalato dianion, bipy = 2, 2′‐bipyridine, x = 0.56 (in II ) or 0.71 (in III )] were synthesized using copper(II) glycolate as starting material and were characterized by IR, UV‐Vis and EPR spectrometry, by magnetic measurements ( II and III ), and by single‐crystal X‐ray diffractometry. Both II and III crystallized as one‐dimensional polymers composed of Cu₂O₂‐centred dimers with a Cu‐Cu distance of 3.282(1)Å (mean of II and III ) that are linked by Cu₂(OCO)₂ rings with a Cu‐Cu distance of 5.237(1)Å (mean of II and III ), both dianions acting as (μ‐1, 1, 2, 3) three‐way bridges connecting the two copper atoms of one dimer with one copper atom of a neighbouring dimer. Each copper atom is coordinated tetragonally in a CuN₂O₄ chromophore. In the mononuclear complex I the copper atom has a tetragonally distorted octahedral environment.     

Air‐stable and recoverable catalyst for copper‐catalyzed controlled/living radical polymerization of styrene; In situ generation of Cu(I) species via electron transfer reaction

Copper‐catalyzed controlled/living radical polymerization (LRP) of styrene (St) was conducted using the silica gel‐supported CuCl₂/N,N,N′,N′,N″‐pentamethyldiethylenetriamine (SG‐CuCl₂/PMDETA) complex as catalyst at 110 °C in the presence of a definite amount of air. This novel approach is based on in situ generation and regeneration of Cu(I) via electron transfer reaction between phenols and Cu(II). Sodium phenoxide or p‐methoxyphenol was used as a reducing agent of Cu(II) complexes in LRP. The number–average molecular weight, M_n,GPC, increases linearly with monomer conversion and agrees well with the theoretical values up to 85% conversion The molecular weight distribution, M_w/M_n, decreases as the conversion increases and reaches values below 1.2. The catalyst was recovered in aerobic condition and reused in copper‐catalyzed LRP of St. For the second run, the number–average molecular weights increased with monomer conversion and the polydispersities decreased as the polymerization proceeded and reached to the value <1.3 at 81% conversion. The recycled catalyst retained 90% of its original activity in the subsequent polymerization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 77–87, 2006     

Effect of phenol and derivatives on atom transfer radical polymerization in the presence of air

The various phenolic compounds in conjunction with Cu(II) or Cu(I)‐N,N,N′,N″,N″‐pentamethyl diethylenetriamine (PMDETA) complexes are used to initiate atom transfer radical polymerization (ATRP) of methyl methacrylate, styrene, and methyl acrylate in the presence of a limited amount of air at temperatures in the range of 80–110 °C. Meanwhile, an effort is directed toward the elucidation of the role of phenol and derivatives in ATRP catalyzed by Cu(II)/PMDETA. The catalytic sequence involves the formation of Cu(I) by electron transfer from phenol to Cu(II); Cu(I) so formed can then react in two distinctly different ways: with organic halide to form a propagating radical or with oxygen to form copper salt in its higher oxidation state; and regeneration of Cu(I) by excess phenol. Such regeneration of Cu(I) would be expected to lead to polymerization as a result of the consumption of oxygen and phenol as well. The phenols with electron releasing groups tended to increase the conversion of the polymerization. In this respect, sodium phenoxide, a more effective additive was found, whereas p‐nitro phenol was the least effective. The obtained polymers displayed the common features of a controlled polymerization such as molecular weight control and low polydispersity index value (M_w/M_n < 1.5). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 351–359, 2004     

High‐Pressure Atom Transfer Radical Polymerization of n‐Butyl Acrylate

High‐pressure atom transfer radical polymerization (ATRP) of n‐butyl acrylate (BA) is performed in acetonitrile (MeCN) with Cu^IBr/TPMA [TPMA: tris(2‐pyridylmethyl)‐amine] as the catalyst up to 5 kbar. Increasing either pressure or temperature significantly enhances the rate of polymerization, while retaining control over the polymerization. The polymerizations under high pressure could be efficiently performed with very low levels of Cu catalyst in the absence of any reducing agents. For example, 100 ppm Cu is sufficient to catalyze the polymerization of BA with targeted degree of polymerization (DP_T) = 1000. The conversion reached 79% in 3.0 h at 80 °C providing PBA with M _n = 112 000, M _w/M _n = 1.12. Since the initial Cu^I‐to‐initiator molar ratio is 0.05:1, the molar percentage of terminated chains should remain <5%. For DP_T = 10 000 using only 50 ppm Cu catalyst, a polymer with molecular weight M _n = 612 000 (DP = 4800) was obtained at 67% conversion.

     

CONTROLLED/"LIVING" RADICAL POLYMERIZATION OF STYRENE IN AN AQUEOUS DISPERSION SYSTEM

Atom transfer radical polymerization (ATRP) of styrene catalyzed by cuprous (CuX)/1, 10-phenanthroline (Phen)and CuX/CuX_2/Phen was conducted in an aqueous dispersed system. A stable latex was obtained by using ionic surfactantsodium lauryl sulfonate (SLS) or composite surfactants, such as SLS/polyoxyethylene nonyl phenyl ether (OP-10),SLS/hexadecanol and SLS/OP-10/hexadecanol. Among which SLS and SLS/OP-10/hexadecanol systems established betterdispersed effect during the polymerization. It was found that Phen was a more suitable ligand than N,N,N',N",N"-pentamethyldiethylenetriamine (PMDETA) to maintain an appropriate equilibrium of the activator Cu(I) and the deactivatorCu(II) between the organic phase and the water phase. The effect of several initiators (such as EBiB, CCl_4 and 1-PEBr) andthe temperature on such a kind of ATRP system was also observed. The number-average molar mass (M_n) of polystyrene (PS)increased with the conversion and the molar mass distribution (M_w/M_n) remained narrow. These experimental data show thatthe polymerization could be controlled except for the quick increase of monomer conversion and the number-average molarmass of PS in the initial stage of polymerization. Furthermore, the initiator efficiency was found to be low (～57%) inCuX/Phen catalyzed system. To overcome this problem, Cu(II)X_2 (20 mol%-50 mol% based on CuX) was introduced intothe polymerization system. In this case, higher initiator efficiency (60%-90%), low M_w/M_n of PS (as low as 1.08) wereachieved and the molar masses of the PS fit with the theoretical ones.     

Two‐dimensional square‐grid frameworks formed by self‐associating copper(II) complexes with 1‐(3‐pyridyl)‐ and 1‐(4‐pyridyl)‐substituted butane‐1,3‐diones

In bis­[1‐(3‐pyridyl)butane‐1,3‐dionato]copper(II) (the Cu atom occupies a centre of inversion), [Cu(C₉H₈NO₂)₂], (I), and bis­[1‐(4‐pyridyl)butane‐1,3‐dionato]copper(II) methanol solvate, [Cu(C₉H₈NO₂)₂]·CH₃OH, (II), the O,O′‐chelating diketonate ligands support square‐planar coordination of the metal ions [Cu—O = 1.948 (1)–1.965 (1) Å]. Weaker Cu⋯N inter­actions [2.405 (2)–2.499 (2) Å], at both axial sides, occur between symmetry‐related bis­(1‐pyridylbutane‐1,3‐dion­ato)copper(II) mol­ecules. This causes their self‐organization into two‐dimensional square‐grid frameworks, with uniform [6.48 Å for (I)] or alternating [4.72 and 6.66 Å for (II)] inter­layer separations. Guest methanol mol­ecules in (II) reside between the distal layers and form weak hydrogen bonds to coordinated O atoms [O⋯O = 3.018 (4) Å].     

Influence of the size of aromatic chelate ligands on the one-dimensional structures of copper(II) 4,4′-oxy-bis(benzoate) coordination polymers

Two one-dimensional coordination polymers, [Cu(Oba)(TATP)] _n · nH₂O (I) and [Cu(Oba)(DPPZ)(H₂O)]n · nH₂O (II) (Oba is 4.4′-oxy-bis(benzoate), TATP is 1,4,8,9-tetranitrogen-tris(phene), DPPZ is dipyrido[3,2-a:2′,3′-c]phenazine), have been synthesized under similar conditions and structurally characterized by elemental analysis, IR spectra, and X-ray crystal structure. Compounds I and II are based on topologically identical chains, where the copper centers chelated by the amine ligands are linked by the Oba bridges, as well as the coordination modes of the Oba ligands. However, the angles between the individual links and the environment of the copper centers are substantially different between the two compounds and were found to be primarily influenced by the sizes of the rigid aromatic chelate ligands. The article is published in the original.     

Metal compounds in free-radical processes. III. Polymerization of acrylonitrile initiated by copper (II) nitrate in presence or absence of triphenylphosphine

The bulk polymerization of acrylonitrile (AN) initiated by copper (II) nitrate, Cu(II), in the absence of light has been studied. The rate of the AN polymerization may be expressed in the Cu(II) concentration range from 5 × 10^?4 to 1 × 10^?1 mole 1.^?1 by the equation, R_p = k₅[Cu(II)]^0.68, where k₅ = K_AN[AN]/(1 + K_AN[AN]). From the spectrophotometric measurements the values of 0.70 l./mole and 0.08 l, mole were obtained for the equilibrium constant at 20 and 60°C, respectively, K_AN = [C]/[AN]-[Cu(II)], corresponding to the formation of the complex C from acrylonitrile and copper (II) nitrate. An addition of triphenylphosphine (C₆H₅)₃P into the polymerization system reduces R_p, and no polymerization takes place at all provided [(C₆H₅)₃P]/[Cu-(II)] ≧ 5. The retardation effect of (C₆H₅)₃P on the polymerization of AN initiated by Cu(II) is attributed to a competitive reaction of Cu(II) with (C₆H₅)₃P in which Cu(II) is reduced and the product of this reduction CuNO₃·2(C₆H₅)₃P is inactive with respect to the polymerization of AN.     

Synthesis and spectral studies ofN-2-pyridinylcarbonyl-2-pyridinecarxoximidate copper(II) complexes

Summary Dimeric and polymeric copper(II) complexes containing BPCA (N-2-pyridinylcarbonyl-2-pyridinecarboximidate), having general formulae Cu(BPCA)X·nH₂O (X=Cl, Br, NCS, NCO, N₃, or CN) and Cu₂(BPCA)₂-X·nH₂O [X=oxalate anion (OX), chloranilate anion (CA) or the dianion of 2,5-dihydroxy-1,4-benzoquinone (DHBQ)] have been synthesized by the copper(II)-assisted hydrolysis of 2, 4, 6-tris(2-pyridyl)-1, 3, 5-triazine. Spectroscopic results indicate five-coordinate, approximately square-pyramidal, geometry around the copper(II) ion. Half-field absorption in the M _s=±2 region of the X-band e.p.r. powder spectra has been observed for the dimeric species.     

Decomposition of Copper Formate Clusters: Insight into Elementary Steps of Calcination and Carbon Dioxide Activation

The decomposition of copper formate clusters is investigated in the gas phase by infrared multiple photon dissociation of Cu(II)_n(HCO₂)_2n+1⁻, n≤8. In combination with quantum chemical calculations and reactivity measurements using oxygen, elementary steps of the decomposition of copper formate are characterized, which play a key role during calcination as well as for the function of copper hydride based catalysts. The decomposition of larger clusters (n > 2) takes place exclusively by the sequential loss of neutral copper formate units Cu(II)(HCO₂)₂ or Cu(II)₂(HCO₂)₄, leading to clusters with n=1 or n=2. Only for these small clusters, redox reactions are observed as discussed in detail previously, including the formation of formic acid or loss of hydrogen atoms, leading to a variety of Cu(I) complexes. The stoichiometric monovalent copper formate clusters Cu(I)_m(HCO₂)_m+1⁻, (m=1,2) decompose exclusively by decarboxylation, leading towards copper hydrides in oxidation state +I. Copper oxide centers are obtained via reactions of molecular oxygen with copper hydride centers, species containing carbon dioxide radical anions as ligands or a Cu(0) center. However, stoichiometric copper(I) and copper(II) formate Cu(I)(HCO₂)₂⁻ and Cu(II)(HCO₂)₃⁻, respectively, is unreactive towards oxygen.     

Effect of DMSO used as solvent in copper mediated living radical polymerization

The use of DMSO as solvent for transition metal mediated living radical polymerization was investigated using copper (I) bromide/N‐(n‐propyl)‐2‐pyridyl‐methanimine catalyst system and ethyl‐2‐bromoisobutyrate as initiator. The best conditions for polymerization in DMSO of different methacrylates (MMA, BMA, DMAEMA, HEMA) were determined. In all cases, the measured number‐average molar mass of the product increased linearly with monomer conversion in agreement with the theoretical M_n with low polydispersity products (1.16 < PDI < 1.4) achieved. Solvent was found to play a crucial role in the process. The effect of the polar solvent has been investigated and it was shown that DMSO could coordinate copper (II), increasing the activation process, or copper (I), changing the nature of the copper catalyst by competitive complexation of ligand and DMSO. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6299–6308, 2004     

Syntheses and Structures of Three Copper Coordination Polymers Based on Bis(triazol‐1‐ylmethyl)benzene

Three copper(II) coordination polymers [Cu(mbtz)₂(NCS)₂]_n ( 1 ), [Cu(mbtz)₂Cl₂]_n ( 2 ) and [Cu(mbtz)(btec)_0.5]_n ( 3 ) (mbtz=1,3‐bis(1,2,4‐triazol‐1‐ylmethyl)benzene, btec=1,2,4,5‐benzenetetracarboxylate) were synthesized. In 1 and 2 , two mbtz ligands are wrapped around each other and are held together by Cu(II) atoms to form one‐dimensional double chain. In 3 , each btec ligand connects four Cu(II) atoms through its four carboxylate groups, resulting in a planar two‐dimensional [Cu(btec)_0.5]_n network. The Cu(II) atoms are further coordinated mbtz ligands to fulfil their coordination geometry and construct new [Cu(btec)_0.5(mbtz)]_n network. 2 and 3 further form the three‐dimensional network through the π···π stacking interactions between the mbtz ligands. The thermal stabilities of 1 , 2 and 3 were measured.     

Zur Reaktion der Alkin-Kupfer(I)-Komplexe [CuX(S-Alkin)] (X = Cl,Br, I; S-Alkin = 3,3,6,6-Tetramethyl-1-thia-4-cycloheptin) mit dem Chelat-Liganden N,N,N′,N′-Tetramethylethylendiamin (tmeda)

Organometallic Compounds of Copper. XVII. On the Reaction of the Alkyne-Copper(I) Complexes [CuX(S-Alkyne)] (X = Cl, Br, I; S-Alkyne = 3,3,6,6-Tetramethyl-1-thiacyclohept-4-yne) with the Chelate Ligand N,N,N′,N′-Tetramethylethylendiamine (tmeda) The alkyne copper(I) chloride complex [CuCl(S-Alkyne)]_n ( 2 a ) (S-Alkyne = 3,3,6,6–tetramethyl-1-thiacyclohept-4-yne) adds tetramethylethylene diamine (tmeda) to form the mononuclear compound [CuCl(S-Alkyne)(tmeda)] ( 4 ). The alkyne copper halide complexes [CuBr(S-Alkyne)]_n ( 2 b ) and [CuI(S-Alkyne)]_n ( 2 c ) react with tmeda to yield the complex salts [Cu(S-Alkyne)(tmeda)]⁺ [CuX₂(S-Alkyne)]^– (X = Br ( 5 a ), X = I ( 5 b )). X-ray diffraction studies on all new compounds 4 and 5 reveal distorted tetrahedral coordination of the copper atom in complex 4 and trigonal-planar coordinated copper atoms in the cations and anions of the ionic compounds 5 .     

Mixed pseudohalide complexes of copper(II). Crystal and molecular structure of [Cu(N3)(NCS)(tmen)] n and of [Cu(N3)(NCO)(tmen)]2 (tmen = N,N,N′,N′-tetramethylethylenediamine)

The compounds [Cu(N₃)(NSC)(tmen)]_n (1), [Cu(N₃)(NCO)(tmen)]_n (2) and [Cu(N₃)(NCO)(tmen)]₂ (3) (tmen=N,N,N′,N′-tetramethylethylenediamine) were synthesized and studied by i.r. spectroscopy. Single crystals of compounds (1) and (3) were obtained and characterized by X-ray diffraction. The structure of compound (1) consists of neutral chains of copper(II) ions bridged by a single azido ligand showing the asymmetric end-to-end coordination fashion. Each copper ion is also surrounded by the other three nitrogen atoms; two from one N,N,N′,N′-tetramethylethylenediamine and one from a terminal bonded thiocyanate group. Compound (2) decomposes slowly in acetone and the product formed [Cu(N₃)(NCO)(tmen)]₂ (3) crystallizes in the monoclinic system (P2₁). The structure of (3) consists of dimeric units in which the Cu atoms are penta-coordinated and connected by μ(1,3) bridging azido and cyanate ligands. In both cases the five coordinated atoms give rise to a slightly distorted square-based pyramid coordination geometry at each copper ion. The thermal behavior of [Cu(N₃)(NSC)(tmen)]_n (1) and [Cu(N₃)(NCO)(tmen)]_n (2) were investigated and the final decomposition products were identified by X-ray powder diagrams.     

Mixed‐Ligand Complexes of Copper(II) with α‐Hydroxycarboxylic Acids and 1,10‐Phenanthroline

Eight new two‐ligand complexes of copper(II) with 1,10‐phenanthroline and one of four different α‐hydroxy‐carboxylic acids (glycolic, lactic, mandelic and benzylic) were prepared. The complexes of general formula [Cu(HL)₂(phen)] · nH₂O (HL = monodeprotonated acid) ( 1 – 4 ) were characterized by elemental analysis, IR, electronic and EPR spectroscopy, magnetic measurements and thermo‐gravimetric analysis. The complexes of general formulae [Cu(HL)(phen)₂](HL) · H₂L · nSolv [ 1 a (HL = HGLYO^–, n = 1, Solv = MeCN) and 3 a (HL = HMANO^–, n = 0)] and [Cu(L)(phen)(OH₂)] · nH₂O [ 2 a (L = LACO^2–, n = 4) and 4 a (L = BENO^2–, n = 2)] were characterized by X‐ray diffractometry. In all these latter a pentacoordinated copper atom has a basically square pyramidal coordination polyhedron, the distortion of which towards a trigonal bipyramidal configuration has been evaluated in terms of the parameter τ. In 1 a and 3 a there are three forms of α‐hydroxycarboxylic acid: a monodentate monoanion, a monoanionic counterion, and a neutral molecule lying in the outer coordination sphere; in 2 a and 4 a the α‐hydroxycarboxylic acid is a bidentate dianion coordinating through carboxyl and hydroxyl oxygens.     

Synthesis of star polymer by atom transfer radical polymerization with resorcinol‐core multifunctional initiator: The construction of nanocapsule via hydrolysis and olefin metathesis reaction of the obtained star polymer

Olefin group‐carrying styrene, 1‐but‐3‐enyl‐4‐vinylbenznene (BVB), was polymerized via atom transfer radical polymerization (ATRP) initiated from C‐methylcalix [4]resorcinarene‐based multifunctional initiator (CRA‐bib) at low conversion to produce star polymer [poly(BVB)] with narrow molecular weight distribution (M_w/M_n < 1.35). The copolymerization of styrene (St) with poly(BVB) (M_n = 11,000, M_w/M_n = 1.23) as a macroinitiator afforded star block copolymer [poly(BVB‐b‐St)] with M_n = 35,000 and M_w/M_n = 1.44. The BVB layer of poly(BVB‐b‐St), located between the St shell and the CRA core, was crosslinked by olefin metathesis reaction of olefin groups o the BVB moieties. The removal of the CRA core of the crosslinked poly(BVB‐b‐St) by hydrolysis using KOH as a base gave polymeric hollow sphere [poly(cored crossBVB‐b‐St)] with good solubility in organic solvents. The morphological structure of the poly(cored crossBVB‐b‐St) showed spherical aggregates in THF by scanning electron microscopy (SEM). Furthermore, the nanocapsule structure of poly(cored crossBVB‐b‐St) with hollow spheres was found to be observed by transmission electron microscopy (TEM). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4879–4888, 2008     

“Living”/controlled free radical polymerization of MMA in the presence of cobalt(II) 2‐ethylhexanoate: A switch from RAFT to ATRP mechanism

A metal complex, cobalt(II) 2‐ethylhexanoate (CEH), was added to the system of thermal‐initiated reversible addition‐fragmentation chain transfer (RAFT) polymerization of methyl methacrylate (MMA) with 2‐cyanoprop‐2‐yl 1‐dithionaphthalate (CPDN) as the RAFT agent at 115 °C. The polymerization rate was remarkably enhanced in the presence of CEH in comparison with that in the absence of CEH, and the increase of the CPDN concentration also accelerated the rate of polymerization. The polymerization in the concurrence of CPDN and CEH demonstrated the characters of “living”/controlled free radical polymerization: the number‐average molecular weights (M_n) increasing linearly with monomer conversion, narrow molecular weight distributions (M_w/M_n) and obtained PMMA end‐capped with the CPDN moieties. Meanwhile, CEH can also accelerate the rate of RAFT polymerization of MMA using the PMMA as macro‐RAFT agent instead of CPDN. Similar polymerization profiles were obtained when copper (I) bromide (CuBr)/N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine was used instead of CEH. Extensive experiments in the presence of butyl methacrylate, bis(cyclopentadienyl) cobalt(II) and cumyl dithionaphthalenoate were also conducted; similar results as those of MMA/CPDN/CEH system were obtained. A transition of the polymerization mechanism, from RAFT process without CEH addition to atom transfer radical polymerization in the presence of CEH, was possibly responsible for polymerization profiles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5722–5730, 2007     

Zero‐valent bimetallic iron/copper catalyzed SET‐LRP: A dual activation by zero‐valent iron

In this work, bimetallic zero‐valent metal (Fe(0) powder and Cu(0) powder) was used to mediate the single electron transfer‐living radical polymerization (SET‐LRP) of methyl methacrylate at 25 °C in dimethyl sulfoxide. Different feed ratios of [Fe(0)]₀/[Cu(0)]₀ (0/1.5, 0.5/1, 0.75/0.75, 1/0.5, and 1.3/0.2) were explored. With the increase of Fe(0) feed, the polymerization rate was mildly depressed with a prolonged induction period. While, the control over the molecular weights was improved upon the increase of Fe(0). A best control (initiation efficiency = 91%) was achieved at [Fe(0)]₀/[Cu(0)]₀ = 1/0.5. A further increase of Fe(0) to the feed ratio of [Fe(0)]₀:[Cu(0)]₀ = 1.3: 0.2 led to a uncontrolled polymerization. Explorations of available solvents and ligands for this polymerization confirmed the SET‐LRP mechanism. It was suggested that Fe(0) might act as a dual role in this process: one was the activation agent for Cu(0), which favored a better control over the molecular weights; The other was an alternative catalyst for the activation of R‐X or P_n‐X to generate radicals, which assured a comparable polymerization rate as that of Cu(0). This work provided an alternative and economical catalyst for SET‐LRP, and would eventually reinforce the SET‐LRP technique. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012