N-allyl-bis(diphenylphosphino)amide nickel dibromide as a catalyst of the polymerization of methyl methacrylate

The polymerization of methyl methacrylate initiated by a catalytic system based on the complex CH₂=CHCH₂N(PPh₂)₂NiBr₂ containing a bidentate phosphine ligand in the coordination sphere of nickel is studied. The activities of this system and of the catalytic system based on NiBr₂(PPh₃)₂ with a monodentate ligand at the nickel atom in the synthesis of PMMA are compared. A scheme of polymerization catalyzed by the CH₂=CHCH₂N(PPh₂)₂)NiBr₂ system is advanced.     

Anionic polymerization of methyl methacrylate with Cr(C5H7O2)3–Al(C2H5)3 catalyst system

A homogeneous catalyst system, Cr(C₅H₇O₂)₃–Al(C₂H₅)₃, was used for the polymerization of methyl methacrylate. The yield of polymer increased up to an Al/Cr ratio of 12 and thereafter remained almost constant with increasing Al/Cr. The rate of polymerization increased linearly with increasing catalyst and monomer concentrations at Al/Cr = 12. The molecular weight, however, decreased with increasing catalyst concentration and increased with increasing monomer concentration, indicating anionic polymerization reaction. NMR studies of the polymers indicated the presence of a stereoblock structure, which changed to heteroblock structure in presence of triethylamine and hydroquinone as additives in the catalyst. In the light of these observations, the mechanism of the polymerization is discussed.     

Polynuclear and 1-D derivatives of 1,3-bis(dimethylamino)-2-propanolato ligand. Structure and magnetic characterization

Several new Cu(II) derivatives of the 1,3-bis(dimethylamino)-2-propanolato (bdmap) ligand with formula [Cu(2)(bdmap)(acac)(NH(3))(3)(MeOH)](ClO(4))(2), [Cu(2)(bdmap)(NO(2))(3)(H(2)O)](4) and [Cu(2)(bdmap)(OH)(ox)(0.5)(H(2)O)(2)](n)(ClO(4))(n)xnH(2)O were synthesized and characterized both structurally and magnetically. Dinuclear compound crystallizes in the monoclinic system, space group P2(1)/c, octanuclear compound crystallizes in the triclinic space group P1 and the 1-D alternating system crystallizes in the monoclinic system, space group P2/n. Magnetic analysis indicates strong antiferromagnetic coupling for all derivatives, mainly due to the interaction through the alkoxo O-atom of the bdmap ligand. The effect on the magnetic behaviour of the additional bridging ligands is analysed.     

Bis(3,6-di-tert-butylcatecholato)tin(IV) ditetrahydrofuranate in radical polymerization of methyl methacrylate

The effect of bis(3,6-di-tert-butylcatecholato)tin(IV) ditetrahydrofuranate (1) on the kinetic parameters of methyl methacrylate polymerization and on the molecular weight characteristics of polymers prepared was studied. According to EPR data, complex 1 can accept and eliminate the growing macroradicals in monomer media. This allows the lifetimes of the growing polymer chains to be controlled. The optimal temperature range for accomplishing controlled synthesis of polymer in the presence of complex 1 was determined. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1314–1319, July, 2007.     

Free-radical polymerization of methyl methacrylate in presence of the Cr(C5H7O2)3–Al(i-C4H9)3 catalyst system

Polymerization of methyl methacrylate has been studied with the chromium acetylacetonate–triisobutyl aluminum catalyst system in benzene medium at 40°C. These studies have been carried out at an Al/Cr ratio of 12 to compare the behavior with the previously studied chromium acetyl acetonate–triethyl aluminum catalyst system. The enhanced yield and gelling of polymer suggests a free-radical mechanism of polymerization. Further, the kinetics of polymerization and the heterotactic structure of polymer as determined by NMR examination have led to confirmation of the freeradical mechanism of polymerization of methyl methacrylate by an excess of triisobutylaluminum in the presence of catalyst complex.     

Atom‐transfer radical polymerization of methyl methacrylate (MMA) using CuSCN as the catalyst

The effect of CuSCN as a catalyst in atom‐transfer radical polymerization (ATRP) was investigated. CuSCN can successfully be used for the ATRP of MMA. Substituted bipyridines as well as imines can be used to stabilize the copper complex in solution. CuSCN induces faster polymerization compared to CuBr and CuCl when tosylchloride is used as the initiator. However, the polydispersity is larger than that obtained in the cases of CuCl and CuBr.     

Preparation of a nitrate-coordinated copper(II) complex of 2-(pyrazol-3-yl)-6-(pyrazolate)pyridine as an efficient catalyst for methyl methacrylate polymerization

Treatment of [CuCl(2)(bppyH(2))] (1, bppyH(2) = 2,6-di(1H-pyrazol-3-yl)pyridine) with 2 equiv. of AgNO(3) in DMF gave rise to a binuclear Cu(II) complex [Cu(2)(bppyH)(2)(NO(3))(2)] (bppyH = 2-(pyrazol-3-yl)-6-(pyrazolate)pyridine) (2). Complex 2 was characterized by elemental analysis, IR and single crystal X-ray diffraction. Complex 2 has a dimeric structure in which the two Cu(ii) centers are bridged by a couple of the in situ-generated bppyH(-) anions. Each Cu(II) center is further coordinated by one O atom of a NO(3)(-) anion and three N atoms of one bppyH(-) anion. Complex 2 exhibited a higher catalytic activity in the polymerization of methyl methacrylate (MMA) than the precursor complex 1. Even though the ratio of catalyst to MMA was raised up to 1 : 1500, the PDI for 2 (reaction time was fixed at 4 h) is 1.63 and the conversion is up to 72%. The effects of solvent, reaction temperature and the ratio of MMA to catalyst were also investigated.     

Synthesis, characterization and catalytic activity of the complex titanium bis(dimethylmalonate)-bis(diethylamido) in the polymerization of propylene

In this account we present the synthesis, characterization and catalytic activity in the polymerization of propylene of a bis(dimethyl malonate) titanium bis(diethylamine) complex (1). The complex exhibits in solution a dynamical isomerization following an internal Bailar twist. The activation of complex 1 was obtained by its reaction with methylalumoxane (MAO). The activated complex in solution shows a different dynamic process involving an equilibrium between a monodentate η¹ and bidentate η² binding of the dimethylmalonate ligand to the metal center. This equilibrium is responsible for the formation of, at least, two active species for the polymerization reaction bearing major symmetry differences. The monodentate coordination (opened form) of the ligand was found to be the major form of the active species of the complex when activated with MAO, most probably due to a strong interaction of the oxygen atoms in the ligand with the strong Lewis acid co-catalyst. The active species in the polymerization were studied by NMR and ESR spectroscopies. The resulting polypropylene showed elastomeric properties with low tacticites.     

Free-radical polymerization of methyl methacrylate and p-fluorostyrene in the presence of the Mn(acac)3–AlEt3 catalyst system

Methyl methacrylate and p-fluorostyrene were polymerized with manganese (III) acetylacetonate–aluminum triethyl catalyst at 60°C in a benzene medium. Maximum activity was found at Al/Mn ratio of 4. Maximum percent conversion of polymer was obtained when the aging time of the catalyst was 10 min. The rate of polymerization was first order with respect to monomer. The rate of polymerization with respect to catalyst and cocatalyst were found to be 0.5 and 1.5, respectively. The overall energy of activation for the polymerization of methyl methacrylate and p-fluorostyrene were found to be 52.6 and 57.0 kJ/mole, respectively. A free-radical mechanism is postulated.     

Novel catalyst system of MCl2/FeCl3·6H2O/PPh3 (M = Ni,Co, or Mn) for the atom transfer radical polymerization of methyl methacrylate

MCl₂ (M = Ni, Co, Sn, or Mn) and PPh₃ together acted as a catalyst for the radical polymerization of methyl methacrylate (MMA) in the presence of ethyl 2‐bromoisobutyrate as an initiator. The four systems all led to conventional radical polymerizations, which yielded polymers with a weight‐average molecular weight/number‐average molecular weight (M_w/M_n) ratio greater than 2.0 and became well controlled when a certain amount of FeCl₃·6H₂O was added. The polymerizations of MMA catalyzed by these four FeCl₃‐modified catalyst systems provided well‐defined polymers with low polydispersities (M_w/M_n < 1.28). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2625–2631, 2005