Polymerization of tert-butyl methacrylate with Ni(acac)2-methylaluminoxane catalyst

The polymerization of tert-butyl methacrylate (tBMA) with nickel(II) acetylacetonate [Ni-(acac)₂] in combination with methylaluminoxane (MAO) was investigated. The binary catalyst is necessary to initiate the polymerization, however, high MAO/Ni mole ratios are not necessary to obtain high catalytic activity. A linear dependence of the molecular weight of the resulting polymers on polymer yield was observed, and the polydispersities of the polymers were relative narrow. The triad tacticity for the polymer obtained was determined to be mm = 3%, mr = 43%, rr = 54%.     

Copolymerization of styrene and butadiene with Co(acac)3‐methylaluminoxane catalyst

The copolymerization of Styrene (St) and butadiene (Bd) with Co(acac)₃‐MAO catalyst was investigated. The copolymers consisting of St and Bd with highly cis‐1,4‐structure could be synthesized with Co‐(acac)₃‐MAO catalyst without formation of homopolymer, although the St contents in the copolymer were not high. The copolymer composition curve for copolymerization of St and Bd with the Co(acac)₃‐MAO is different from that obtained with the Ni(acac)₂‐MAO catalyst. The additive effects of triphenylphosphine (TPP) and trifluoroacetic acid (TFA) on the copolymerization of St and Bd with the Co(acac)₃‐MAO catalyst were also investigated. The copolymer yields increased by adding TPP to the Co‐(acac)₃‐MAO catalyst, although the St contents in the copolymer did not change. In the microstructure of the Bd units in the copolymers, 1,2‐contents increased remarkably. The copolymer yields and the microstructure of the copolymer did not change by addition of TFA.     

Ni(acac)2-DAD/MAO: A new catalytic system for ethylene polymerization

The halide-free combination of Ni(acac)₂ and DAD(diazadiene, ArNCH CHNAr, where Ar = 2,6-C₆H₃(i-Pr)₂) is active for ethylene polymerization in the presence of methylaluminoxane (MAO). The performance of this new catalytic system was evaluated with respect to activity and polymer structure. The degree of branching of the obtained polyethylenes is substantially influenced by the polymerization conditions. The activation mechanism was investigated by ¹H NMR. MAO is proposed to participate in the ligand exchange process.     

Polymerizations of 1-(4-pyridyl)-1,3-butadiene

Polymerization of 1-(4-pyridyl)-1,3-butadiene (PyBu) initiated by 2,2′-azoisobutyronitrile (AIBN) or butyllithium (BuLi) was studied. Radical polymerization gave poly(PyBu) of low molecular weight, soluble in chloroform, tetrahydrofuran, or methanol. PyBu was polymerized by BuLi more rapidly than by AIBN, but the produced polyanion was not living. IR and ¹H NMR spectra of poly(PyBu) indicate the presence of trans-1,4-and trans-3,4-units. The content of trans-1,4-units was found to be 75 mole-% (for radical polymerization) or 90 mole-% (for anionic polymerization). From radical copolymerization with styrene the following reactivity ratios resulted: r₁ (PyBu) = 7,21, r₂ (styrene) = 0,12; Q = 6, 1 and e = ?0,42 (for PyBu). Reaction of PyBu with ethyl bromide in benzene at 30°C produced a polyelectrolyte, as observed in the case of 4-vinylpyridine.     

Polymerization of Butadiene with V(acac)3‐Methylaluminoxane Catalyst

Full Paper: Polymerization of butadiene (Bd) with V(acac)₃‐methylaluminoxane (MAO) catalyst was investigated. The microstructure of the polymer was found to depend strongly on the polymerization conditions. High polymerization temperature and high MAO/V(acac)₃ mole ratios were preferential to produce cis‐1,4 structure. Two kinds of active species were presumed from the GPC measurement of the polymers; one gives a high molecular weight polymer bearing high cis‐1,4 content, another affords a low molecular weight polymer with high trans‐1,4 content. A Solvent effect was observed. A polymer consisting of mainly trans‐1,4 unit was produced in CH₂Cl₂ in contrast to toluene and n‐heptane in which polymers consisting of mainly cis‐1,4 structure were observed. The addition of ethyl benzoate, triethylamine, chloranil, and tetracyanoquinodimethane to the V(acac)₃‐MAO catalyst gave an influence to not only the activity for the polymerization but also the microstructure of the polymer.     

Polymerization of methyl methacrylate with V(acac)3 and VOCl3 in combination with methylaluminoxane

The polymerization of methyl methacrylate (MMA) with V(acac)₃ and VOCl₃ in combination with methylaluminoxane (MAO) was investigated. The obtained polymers have a relatively narrow molecular weight distribution (M?_w/M?_n < 1,5). It was found that the isotactic triad content of the polymers increases with increasing temperature and MAO/V and MAO/MMA mole ratios. The interaction between MMA and MAO has an influence on the tacticity of radically (initiator AIBN) obtained polymers: in presence of MAO the fraction of isotactic triads (mm) is higher. The catalytic activity of MAO-containing catalysts (V(acac)₃/MAO and VOCl₃/MAO) was compared with that of AlEt₃-containing catalysts (V(acac)₃/AlEt₃ and VOCl₃/AlEt₃). It was not much different, but for MAO as cocatalyst the isotacticity of the resulting PMMA's was higher, and the polydispersity lower, than with AlEt₃ as cocatalyst.     

Polymerizations of 1-(9-anthryl)ethyl methacrylate and charge-transfer complex formations with its polymers

1-(9-Anthryl)ethyl methacrylate (9AEMA) was prepared by condensation of 1-(9-anthryl)ethanol with methacryloyl chloride. The rate of AIBN initiated polymerization of 9AEMA in benzene at 60°C was intermediate between the polymerization rates of styrene and methyl methacrylate. 9AEMA/styrene copolymerization studies at 60°C resulted in the copolymerization parameters r_9AEMA = 0,42±0,07 and r_st = 0,37 ± 0,08. Charge transfer complexes are formed between p- chloranil and the 9AEMA homo- and copolymers. The absorption maxima of the CT-complexes shifted to higher wavelengths with increasing 9AEMA content of the copolymers, whereas the equilibrium constant of the CT-complex formation was independent of copolymer composition. Both the complex formation enthalpies and entropies decreased with increasing 9AEMA content of the copolymers.     

Structural studies on 1,4-cis-poly(2-methyl-1,3-pentadiene) synthesized with Nd catalysts

(E)-2-Methyl-1,3-pentadiene was polymerized with the AlEt₂Cl-Nd(OCOC₇H₁₅)₃-Al(iBu)₃ system to a polymer consisting of 98–99% 1,4-cis-structure. The crude polymer was fractionated by successive extractions with boiling diethyl ether, heptane and toluene. Examination of the soluble fractions and of the residue to toluene extraction by NMR, X-ray and DSC techniques indicated that the crude polymer consists of macromolecules differing in stereoregularity. Evidence is reported that the crystalline residue after the toluene extraction has a 1,4-cis-isotactic structure. The existence of two different crystalline phases is shown and the respective cell parameters have been determined. α-Phase: a = 10,74, b = 13,04, c = 7,87 Å (?120°C), space group Pbca, Z = 8, D_c = 1,00 g · cm^?3. β-phase: a = 9,30, b = 7,73, c = 7,90 Å (25°C), space group P2₁2₁2₁Z = 4, D_c = 0,96 g · cm^?3.     

Alternating copolymerization of butadiene and propene with the catalyst VO(ONeo)2 Cl/Al(i-C4H9)3, 1

The influence of basic reaction parameters—the ratio of catalyst components, the composition of the monomer mixture and the temperature—on the progress of the copolymerization, the molecular weight and the molecular weight distribution as well as on the composition of the copolymers obtained is reported. Conversion data for the variation of the mole ratio of comonomers show a maximum for an [Al]/[V] mole ratio of approximately 7, whereas the molecular weight of copolymers is not significantly influenced. An increase in the molecular weight of the copolymers can be obtained by an increase of butadiene content in the monomer mixture. However, there is also an increasing incorporation of butadiene into the copolymer. Raising the temperature from ?60°C to 0°C results in a significant decrease in molecular weight, whereas the composition of the copolymers is not significantly changed.     

Polylactones, 37. Polymerizations of L-lactide initiated with Zn(II) L-lactate and other resorbable Zn salts

Zn(II) L -lactate (ZnLac₂) was prepared either from ZnO and ethyl L -lactate or with slightly higher optical purity from ZnO and L -lactide. Using water-free ZnLac₂ L -lactide was polymerized in bulk at 120°C or 150°C. Higher yields and higher molecular weights were found at 150°C. The highest number average molecular weights (M?_n around 70 000) were obtained at monomer/initiator (M/I) ratios of 4000. Despite the high reaction temperature the isolated poly(L -lactide)s were 100% optically pure. Analogous polymerizations were also conducted with Zn(II) L -mandelate or Zn(II) stearate with inferior results. Poor yields and molecular weights were found, when zinc glycolate salt was used as catalyst. Furthermore, numerous polymerizations were conducted with ZnCl₂, ZnBr₂ or ZnI₂ as initiators. Again poly(L -lactide)s with 100% optical purity were isolated, but most molecular weights were lower and never higher than those obtained with ZnLac₂. Therefore, ZnLac₂ proved to be the most favorable and fully resorbable (biocompatible) initiator of this study. Finally, the combination of ZnLac₂ with a primary alcohol, which plays the role of a coinitiator, allows a broad variation of the molecular weight and the introduction and modification of an ester endgroup. This approach also allows the incorporation of bioactive alcohols such as α-tocopherol, stigmasterol or testosteron in the form of covalently bound ester endgroups.     

Chain and Step Growth Polymerizations of Cyclic Imino Ethers: From Poly(2‐oxazoline)s to Poly(ester amide)s

Cyclic imino ethers (CIEs), such as 2‐oxazolines and 2‐oxazines are a unique class of monomers, which because of their manifold reactivities can be polymerized via multiple techniques. Most prominent, the living cationic ring‐opening polymerization (CROP) of CIEs enables the synthesis of well‐defined tailor‐made poly(CIEs), which have tremendous importance as functional and biocompatible polymers. On the other hand, CIEs are also powerful monomers in polyadditions resulting in the formation of a variety of biodegradable polyamide‐based systems. In this contribution, the enormous potential of CIEs as functional building blocks is discussed, which goes well beyond the CROP. Besides trends in the CROP of CIEs, recent developments in step‐growth polymerizations of CIEs are highlighted, including the spontaneous zwitterionic copolymerization (SZWIP) which provides access to functional alternating N‐acylated poly(amino ester)s (NPAEs) and polyadditions of multifunctional CIEs which give main‐chain poly(ester amide)s (PEAs).

     

Michael Addition Polymerizations of Trifunctional Amines with Divinyl Sulfone

Summary: The mechanisms of the Michael addition polymerization of N‐aminoethyl piperazine (AEPZ) with divinyl sulfone (DVS) were clarified based on the reactivity sequence of three different amines in AEPZ: 2° amine in piperazine ring > 1° amine ≫ 2° amine formed in situ. When the feed molar ratio of DVS to AEPZ was 1:1, the polymerization of AB intermediate formed proceeded, and the linear poly(sulfone amine) containing secondary and tertiary amines in the backbones were produced. The linear structure of the product was confirmed by NMR spectra, and the molecular weights, molecular weight distribution, and properties of poly(sulfone amine)s were characterized by GPC, DSC, and TGA.

Polymerization of linear poly(DVS‐AEPZ).     

Kinetics of homogeneous butadiene polymerization catalyzed by TiI2Cl2/Al(iso-C4H9)3,

Kinetics of homogeneous butadiene polymerization initiated by TiI₂Cl₂/Al(iso-C₄H₉)₃ catalysts were studied at constant monomer concentration. A reaction mechanism involving fast initiation and living chains propagation with reversible deactivation of the active sites was developed. The active sites concentration and number average molecular weight during polymerization were calculated. The molecular weight distribution resulting from the assumed kinetic scheme was also considered. A method was developed to calculate number and weight average molecular weight of polymer at any moment after establishing of the deactivation-reactivation equilibrium. The experimental findings are consistent with the presumed reaction mechanism.     

Polymerization of 4-(ferrocenylethynyl)phenylacetylene with transition metal catalysts

A new conjugated polymer carrying organometallic pendant groups, poly[4-(ferrocenylethynyl)phenylacetylene], has been prepared. [Rh(nbd)(OCH₃)]₂ as a catalyst (nbd = norbornadiene) provides a mixture of an insoluble polymer (yield 71%) free of C≡CH groups and soluble oligomers (yield 22%, MW ca. 1 100). WOCl₄/2Me₄Sn as a catalyst provides almost exclusively a polymer (yield 60%, M_w = 32·10³) containing a small amount of C≡CH groups that is soluble in aromatic and low-polarity solvents. Its solubility, however, decreases upon storage in the solid state, probably due to a subsequent crosslinking. The ¹³C NMR, IR, UV-vis and Raman spectra of the monomer and polymers are reported.     

The copolymerization and 1,4-cycloaddition reactions of polar vinyl monomers with butadiene in the presence of Lewis acids as catalysts

The copolymerizations of acrylonitrile, methacrylonitrile, methyl acrylate, methyl methacrylate, methyl vinyl ketone, acroleine, and acrylic acid with butadiene were carried out in the presence of the Lewis acids ZnCl², BF³, CH₃AlCl₂, C₂H₅AlCl₂, AlCl₃, SnCl₄, and TiCl₄ and also in the absence of catalyst. Relative reactivity orders of the above polar vinyl monomers in the copolymerization and 1,4-cycloaddition reactions with butadiene and also the catalytic activity orders of Lewis acids in these reactions were determined. The composition of the polymers formed and the structure of their butadiene units were also determined. The mechanism of the copolymerization and 1,4-cycloaddition of the polar vinyl monomers with butadiene in the presence of Lewis acids is discussed.     

Copolymerization of propene and butadiene with MgCl2 supported titanium catalytic systems

Upon copolymerization of propene and butadiene, using the recent generation of high mileage stereospecific MgCl₂ supported TiCl₄AIR₃ catalytic systems, it is possible to incorporate a small proportion of butadiene units in polypropene, keeping reasonable, although strongly reduced, activity. The isospecificity of the catalysts for the propene polymerization is not affected, and even may be improved upon butadiene incorporation. The butadiene is incorporated in blocks of trans-1,4 units. The amount of incorporation is dependent on the temperature, on the presence and then on the nature and concentration of a silane compound as an external Lewis base, and also on the nature of the alkylaluminium cocatalyst. The silane causes a small amount of 1,2-butadiene units to be incorporated. The molecular weights of the polymers are strongly decreased but the crystallinity is only slightly affected.     

Polymers of carbonic acid, 6. Polymerization of trimethylene carbonate (1,3-dioxan-2-one) with complexation catalysts

Numerous bulk polymerizations of trimethylene carbonate (1,3-dioxan-2-one, 2 ) were conducted at 90, 120 and 150°C. Tributyltin methoxide, tributyltin acetate, dibutyltin dibromide, tin(II) 2-ethylhexanotate, bismuth(III) 2-ethylhexanoate and zinc stearate were used as initiators. On the basis of GPC measurements with universal calibration, weight-average molecular weights up to approx. 22000 were found. The chemical structure of the resulting polycarbonates was examined by elemental analyses and ¹H NMR spectroscopy. In contrast to similar polymerizations of ethylene carbonate, either groups were never found. However, all polycarbonates contain a CH₂OH end-group. Furthermore, methylcarbonate, acetate, 2-ethylhexanoate or stearate end-groups were found. Cyclic oligomers were not detectable in the gel-permeation chromatograms of reaction mixtures. IR spectra indicate complexation of the carbonyl group by the initiators. The reaction mechanism is discussed.     

Ni(II) activates the Nrf2 signaling pathway in human monocytic cells

Nickel is a component of biomedical alloys that is released during corrosion and causes inflammation in tissues by as yet unknown mechanisms. Recent data show that Ni(II) at concentrations of 10-50 microM amplifies lipopolysaccharide-triggered, NFkappaB-mediated cytokine secretion from monocytes. In the current study, we tested the hypothesis that Ni(II) amplifies cytokine secretion by activating the Nrf2 antioxidant pathway rather than by enhancing activity of the NFkappaB signaling pathway. Human THP1 monocytes were exposed to Ni(II) concentrations of 10-30 microM for 6-72 h, then immunoblots of whole-cell lysates or cytosolic and nuclear proteins were used to detect changes in Nrf2 or NFkappaB signaling. Our results show that Ni(II) increased (by 1-2 fold) whole-cell Nrf2 levels and nuclear translocation of Nrf2, and amplified lipopolysaccharide (LPS)-induction of Nrf2 (by 3-5 fold), but had no detectable effect on the initial activation or nuclear translocation of NFkappaB. Because Nrf2 target gene products are known regulators of NFkappaB nuclear activity, our results suggest that Ni(II) may affect cytokine secretion indirectly via modulation of the Nrf2 pathway.     

Removal of Cr(III), Ni(II) and Cu(II) by poly(gamma-glutamic acid) from Bacillus subtilis NX-2

Poly(gamma-glutamic acid) (gamma-PGA) derived from Bacillus subtilis NX-2 was investigated as a sorbent for heavy metal ions in batch adsorption experiments. The results showed that the heavy metal adsorption capacity of gamma-PGA enhanced with the increase of pH, in the following order: Cr(III) > Cu(II) > Ni(II), within the pH range 3-5. The Langmuir sorption model effectively described the metal sorption of y-PGA through the experiments of isotherm sorption, and it was deduced that the affinity of gamma-PGA for metals was following the sequence: Cr(III) > Cu(II) > Ni(II). Gamma-PGA was also used to trap trace amounts of heavy metals from the electroplating wastewater, which were difficult to be entirely removed by the traditional hydroxide precipitation method. The results showed that Cr(III) and Ni(II) in the electroplating effluent decreased from 3.07 and 9.46 mg/l to 0.15 and 1.01 mg/l, respectively, and the treated solutions reached the effluent standard. Therefore, gamma-PGA is satisfactory as a well biosorbent for the removal of heavy metals. The adsorption mechanism of gamma-PGA binding heavy metals was also studied using HyperChem simulation and FT-IR.