Effect of addition of organoaluminum and organoboron compounds in the stereospecific polymerization of acrylonitrile using dialkylmagnesium as catalyst

An attempt was made to clarify the effect of addition of organoaluminum and organoboron compounds in the stereospecific polymerization of acrylonitrile (AN) initiated by dialkylmagnesium (R₂Mg) above 100°C. The triad isotacticity (i.e. the content of mm (m: meso)) as well as the viscosity-average molecular weight (M?_v) of polyacrylonitrile (PAN) increased when trialkylaluminum (R₃Al) and trialkylboron (R₃B) were used as additives. Diisobutylaluminum hydride [(i-C₄H₉)₂AlH] was found to be the best additive. in the stereospecific polymerization of AN, giving PAN with higher (mm) content (0.63), higher M?_v value (5.2 × 10⁴), and a yield approximately double that obtained using (n-C₆H₁₃)₂Mg alone. When the (n-C₆H₁₃)₂Mg/(i-C₄H₉)₂AlH system was used, the yield, (mm), and M?_v of PAN increased with polymerization temperature (T_p); maximum values of yield, (mm), and M?_v were obtained at c. 130°C. The optimum amount of additives was approximately equimolar to R₂Mg as initiator. The ¹³C chemical shift of α-carbon in R₂Mg at 90°C shifted by mixing with R₃Al and R₃B, respectively, indicating the existence of interaction between R₂Mg and the additives. The main role of the additives is considered to be suppression of the self-association of R₂Mg by strong interaction with R₂Mg.     

Studies of a Supported Titanium Catalyst System Using Magnesium Dichloride–Alcohol Adduct

Magnesium dichloride reacts with aliphatic alcohols [ROH; R = n-C₂H₅, n-C₃H₇, i-C₃H₇, n-C₄H₉, i-C₄H₉, t-C₄H₉, n-C₅H₁₁, n-C₆H₁₃, C₆H₁₂(C₂H₅)] to form well-defined solid adducts. Compositional analysis of adducts indicates that the stoichiometric ratio of magnesium dichloride to alcohol depends on length of alkyl group and nature of isomeric alcohol. Magnesium dichloride-2-ethyl-l-hexanol adduct was treated with diphenyldichlorosilane in the presence of dibutylphthalate to obtain active magnesium dichloride support. The titanation process of active magnesium dichloride gives supported magnesium–titanium catalyst (Mg–Ti). The catalyst was characterized by compositional analysis and specific surface area measurements. Performance of the catalyst for polymerization of propene was evaluated with triethylaluminum (TEAL) and phenyltriethoxysilane (PES) as cocatalyst. The yield and isotacticity of the polymer is governed by polymerization parameters such as Si/A1 ratio and polymerization time.     

Ethylene polymerization using an asymmetric dinuclear titanocene catalyst carrying a novel 3-oxa-pentamethylene bridge

The asymmetric 3-oxa-pentamethylene bridged dinuclear titanocenium complex (CpTiCl₂)₂ (η⁵-C₉H₆(CH₂CH₂ OCH₂CH₂)-η⁵-C₅H₃ CH₃) (1) has been prepared, characterized by ¹H NMR spectroscopy and elemental analysis, and after activation with MAO tested as a homogenous catalyst for the polymerization of ethylene. The results show that the catalytic activity of 1 as well as the molecular weight of the produced polyethylene are higher than those using the alkylidene bridged asymmetric dinuclear metallocenes (CpTiCl₂)₂ (η⁵-C₉H₆(CH₂) _n-η⁵-C₅H₄), n = 3 (4), 4 (5). The molecular weight distribution of polyethylene produced with 1/MAO reaches 11.00 and the HT-GPC curve shows a bimodal distribution. The melting point of the polyethylene obtained by 1/MAO is higher than 135 °C and the ¹³C NMR spectrum of PE shows only one strong signal at 30 ppm for the methylene units indicating a highly linear and crystalline polymer.     

Incorporation of methacryloisobutyl POSS in bio-based copolymers by nitroxide mediated polymerization in organic solution and miniemulsion

In this study, nitroxide mediated polymerization of methacryloisobutyl POSS (POSSMA) and bio-sourced monomers: isobornyl methacrylate (IBOMA) and C13 methacrylate (C13MA, an alkyl methacrylate with an average chain length of 13 units) was conducted in solution (toluene) and miniemulsion. BlocBuilder-MA (with 10 mol% acrylonitrile [AN] controlling co-monomer, for the solvent-based system) and Dispolreg 007 (for the miniemulsion) were used as the alkoxyamine for initiation and controlling the polymerization. POSSMA/IBOMA/C13MA effective terpolymerization (having 10 mol% AN controlling co-monomer) with monomer conversion (X) <72% in toluene resulted in resins with M_n up to 21.3 kg mol⁻¹ and Ð < 1.67. Next, terpolymerizations were conducted in dispersed aqueous media to completely remove the organic solvent, resulting in polymers with M_n up to 46.7 kg mol⁻¹ and Ð < 1.65. The successful chain extension of poly(IBOMA/AN) with a mixture of POSSMA/C13MA/AN (M_n = 74.1 kg mol⁻¹ and Ð = 1.55) showed high chain-end fidelity, exemplified by a clear, monomodal shift in the GPC chromatogram from the macroinitiator. Finally, it was shown that the addition of 20 mol% POSSMA improved the decomposition temperature of bio-based polymers of IBOMA/C13MA by 15%.     

Temperature effect on ethylene polymerization with a catalyst prepared by mixing Mg(C2H5)(n-C4H9), Al(C2H5)1.5Cl1.5 and iron(II)bis (imino)pyridyl complex

Summary Ethylene polymerization was conducted with a catalyst prepared by mixing 2,6-bis{1-[2,6-(diisopropylphenyl)imino]ethyl}pyridine iron dichloride, Mg(C₂H₅)(n-C₄H₉) and Al(C₂H₅)_1.5Cl_1.5 in the presence of common alkylaluminium as cocatalyst. Both the activity and the molecular weight of polymers produced were markedly dependent upon the polymerization temperature. The end-group analysis of polymers showed that the molecular weight of polymers produced at higher temperature was reduced by chain transfer with Al(C₂H₅)₃ in addition to β-hydrogen elimination.     

A Novel Branched–Hyperbranched Block Polyolefin Produced via Chain Shuttling Polymerization from Ethylene Alone

A novel branched-hyperbranched polyethylene was synthesized via chain walking and chain shuttling polymerization by one step. In polymerization, {2,6- ⁱ Pr₂-C₆H₃N?C(CH₃)-(CH₃)C?N- ⁱ Pr₂-C₆H₂}NiBr₂(CatA) and {2,6-Me₂-C₆H₃N?C(CH₃)-(CH₃)C?N-Me₂-C₆H₂}NiBr₂(CatB) was adopted to yield branched and hyperbranched segments via chain walking polymerization at one ethylene atm and 20°C, respectively. Then the chain transfer agent(ZnEt₂) facilitated chain transfer between two active metal centers to accomplish chain shuttling polymerization of ethylene. This strategy stands out from “living”/controlled polymerization and coupling block polymers techniques for just using ethylene as monomer, carrying out under moderate polymerization and obtaining the resultant polymer with novel microstructure.     

Synthesis of stereoblock poly(methyl methacrylate) via transformation of isotactic-specific living polymer anion to syndiotactic-specific anion

Polymerization of methyl methacrylate (MMA) by isotactic poly(methyl methacrylate) (PMMA) living anion, prepared with t-C₄H₉MgBr in toluene at ?60°C, was carried out at ?78°C in the presence of trialkylaluminiums (R₃Al; R = CH₃, C₂H₅, and n-C₄H₉) to obtain a stereoblock PMMA, isotactic PMMA-block-syndiotactic PMMA. Among the R₃Als, (CH₃)₃Al gave most effectively the steroblock PMMA with narrow molecular weight distribution. The fraction of rr triad in the syndiotactic PMMA block increased with increase in the ratio of Al/Mg and reached about 76% at a ratio of Al/Mg ≥ 6. The method was also used to prepare stereoblock copolymer comprising isotactic PMMA block and syndiotactic block of butyl methacrylate. Stereocomplex formation and solution viscosity of the stereoblock PMMA were also studied.     

Polymerization of lactides and lactones. III. Ring-opening polymerization of DL-lactide by the (η3-C3H5)2Sm(μ2-Cl)2(μ3-Cl)2Mg(tmed)(μ2-Cl)Mg(tmed) complex

Ring-opening polymerization of DL -lactide (LA) has been initiated with the (η³-C₃H₅)₂Sm(μ₂-Cl)₂(μ₃-Cl)₂Mg(tmed)(η₂-Cl)Mg(tmed) complex both in bulk and solution. The effects of reaction conditions, such as reaction time, reaction temperature, and monomer/initiator molar ratio on the polymerization has been discussed. The results showed that (η³-C₃H₅)₂Sm(μ₂-Cl)₂(μ₃-Cl)₂Mg(tmed)(μ₂-Cl)Mg(tmed) was more effective for the polymerization of LA, and high molecular weight of polylactide was obtained by this initiator. The solvent affected the polymerization significantly. The polymerization mechanism was in agreement with the coordination mechanism. The polymer was characterized by FTIR, ¹H-NMR, and DSC. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2857–2862, 1999     

New crystalline complex chlorides containing transition metal chlorides or oxychlorides as components of coordination catalysts

Novel complex chlorides have been obtained by reacting TiCl₄, VOCl₃, MoOCl₄, WOCl₄, or AlCl₃, with Be, Mg, Ca, or Sr chlorides in the presence of electron donors such as POCl₃ (L) or C₆H₅POCl₂, (L′). The resulting products, obtained with good yield, show defined stoichimetry, ionic character, and crystalline structure, and may be considered reference systems for high-yield catalysts in the low-pressure polymerization of ethylene (HDPE). Complexes (TiCl₆)MgL₆, (TiCl₅L′)₂ MgL′₆, and (Ti₂Cl₁₀)MgL₆ associated with (i-C₄H₉)₃Al were found very active in HDPE synthesis, but completely unable to polymerize propylene. This result and other evidence suggest that part of the catalytic activity of these systems is displayed by soluble species. The role played by the Mg ion in high-yield catalysts is displayed by soluble species. The role played by the Mg ion in high-yield catalysts is discussed in the light of the peculiar behavior shown by the complex chlorides containing this earth-alkali metal.     

Variation with chain length in acute toxicity of alkylhydroxamic acids to salmon (Salmo salar) fry

The acute toxicity of saturatedn-alkylhydroxamic acids to salmon (Salmo salar) fry was determined. Within the seriesn-C₆H₁₃CONHOH ton-C₁₀H₂₁CONHOH, acute toxicity (indicated by death) increased with chain length. Shorter and longer chain compounds were not toxic under similar conditions. Factors governing the variation in toxicity with chain length and possible mechanisms of action are discussed. Presented in part at the AOCS Meeting, Atlantic City, October 1971.     

Butadiene polymerization in the presence of VOCl3–dialkylmagnesium catalytic system

The butadiene polymerization in toluene at 25°C on VOCl₃? (n‐C₄H₉)Mg(iso‐C₈H₁₇) catalytic system was investigated. The kinetic parameters of polymerization and molecular characteristics of polybutadiene were determined. It was shown that substitution of traditional organoaluminum cocatalysts in trans‐regulating vanadium systems does not have an effect on its stereospecificity, but significantly influences on the active centers reaction ability. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 596–600, 2003     

Studies of the stereospecific polymerization mechanism of propylene by a modified Ziegler-Natta catalyst based on 125 MHz 13C n.m.r. spectra

The mechanism of stereospecific polymerization of propylene (catalysed by a modified Ziegler-Natta system, TiCl₄/MgCl₂/C₆H₅COOC₂H₅/Al(C₂H₅)₃), has been analysed using the values of triad and pentad tacticity determined using 125 MHz ¹³C n.m.r. spectroscopy. The well-known single active-site models, such as the Bernoullian, first- and second-Markovian, and enantiomorphic models, were found to be inadequate to describe the observed tacticity. A two-sites model, in which at one site the stereospecific polymerization proceeds in obedience to the Bernoullian model and at the other proceeds under the control of enantiomorphic-site model, is proposed. It was found that the pentad tacticities of both soluble and insoluble (in boiling heptane) fractions of polypropylene agreed well with the two-sites model.     

Silica-grafted polyisobutylene and butyl rubber

Summary Silica surfaces have been modified by reaction with ClSi(CH₃)₂CH₂-CH₂-C₆H₄CH₂Cl (I) and the solids were used in conjunction with Et₂AlCl to initiate the surface-graft polymerization of isobutylene. Experimental conditions have been defined to obtain respectable grafting rates, grafting ratios and grafting efficiencies.     

Effect of Low-Temperature Solution Polymerization Conditions of Acrylonitrile on the Molecular Characteristics of Polyacrylonitrile

Abstract

Acrylonitrile (AN) was solution-polymerized in dimethyl sulfoxide (DMSO) and tertiary butyl alcohol (TBA) at 30,40 and 50°C using a low temperature initiator, 2,2′-azobis(2,4-dimethylvaleronitrile) (ADMVN), and effects of polymerization conditions were investigated in terms of molecular structures of polyacrylonitrile (PAN). Low polymerization temperature by adopting ADMVN proved to be successful in obtaining PAN of high molecular weight with smaller temperature rise during polymerization. Through a polymerization of AN in DMSO at 30°C, PAN having weight-average molecular weight (M _w ) of 931,000 was obtained, whose polydispersity index of 1.89. For the same polymerization conditions, DMSO was slightly superior to TBA in increasing molecular weight of PAN. In addition, DMSO was superior to TBA in diminishing molecular structural defects such as enaminonitrile structure in PAN polymerized, indicating that differences in polymerization and termination rates due to a different polymerization mechanisms using two polymerization solvents. The M _w , linearity, molecular structural regularity, and whiteness were higher with PAN polymerized at lower temperatures.     

Reduction of n-C5H11N3 Catalyzed by [Mo2Fe6S8(OMe)3(SC6H4-p-n-C8H17)6]3– in an Aqueous Micellar Solution

Reduction of n-C₅H₁₁N₃ by Na₂S₂O₄ was performed in the presence of (n-Bu₄N)₃ [Mo₂Fe₆S₈(OMe)₃(SC₆H4-p-n-C₈H₁₇)₆] ((n-Bu₄N)₃ [Mo-Fe]) as a catalyst in aqueous Triton X-100 micellar solutions. The rate of the reduction is enhanced efficiently by the addition of methyl viologen (MV²⁺). The methyl viologen radical cation (MV⁺) produced by the reaction of MV²⁺ with Na₂S₂O₄ undergoes a disproportionation reaction to afford MV²⁺ and MV° in the micellar solution. The resultant MV° formed in the micelle transfers two electrons to [Mo-Fe]³⁻ effectively to give [Mo-Fe]⁵⁻, which reduces n-C₅H₁₁N₃ with two electrons to produce n-C₅H₁₁NH₂ and N₂.     

Ethylene polymerization by alkylidene‐bridged asymmetric dinuclear titanocene/MAO systems

Two asymmetric alkylidene‐bridged dinuclear titanocenium complexes (CpTiCl₂)₂(η⁵‐η⁵‐C₉H₆(CH₂)_nC₅H₄), 1 (n = 3) and 2 (n = 4) have been prepared by treating two equivalents of CpTiCl₃ with the corresponding dilithium salts of the ligands C₉H₇(CH₂)_nC₅H₅ (n = 3, 4). Additionally, Ti(η⁵:η⁵‐n‐BuC₅H₄C₅H₅)Cl₂ (3) and Ti(η⁵:η⁵‐n‐BuC₉H₆C₅H₅)Cl₂ (4) were synthesized as corresponding mononuclear complexes. All complexes were characterized by ¹H, ¹³C NMR, and IR spectroscopy. Homogenous ethylene polymerization catalyzation using those complexes has been conducted in the presence of methylaluminoxane (MAO). The influences of reaction parameters, such as [MAO]/[Cat] molar ratio, catalyst concentration, ethylene pressure, temperature, and time have been studied in detail. The results showed that the catalytic activities of both dinuclear titanocenes were higher than those of the corresponding mononuclear titanocenes. Although the two dinuclear complexes were different in only one [CH₂] unit, the catalytic activity of 2 was about 50% higher than that of 1; however, the molecular weight of polyethylene (PE) obtained by 2 was lower than that obtained from 1. The molecular weight distribution of PE produced by these dinuclear complexes reached 6.9 and 7.3, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3317–3323, 2006     

Ethylene polymerization by 3‐oxa‐pentamethylene bridged asymmetric dinuclear titanocene/MAO system

An asymmetric 3‐oxa‐pentamethylene bridged dinuclear titanocenium complex (CpTiCl₂)₂(η⁵‐η⁵‐C₉H₆(CH₂CH₂OCH₂CH₂)C₅H₄) ( 1 ) has been prepared by treating two equivalents of CpTiCl₃ with the corresponding dilithium salts of the ligand C₉H₇(CH₂CH₂OCH₂ CH₂)C₅H₅. The complex 1 was characterized by ¹H‐, ¹³C‐NMR, and elemental analysis. Homogenous ethylene polymerization catalyzed using complex 1 has been conducted in the presence of methylaluminoxane (MAO). The influences ofreaction parameters, such as [MAO]/[Cat] molar ratio, catalyst concentration, ethylene pressure, temperature, and time have been studied in detail. The results show that the catalytic activity and the molecular weight (MW) of polyethylene produced by 1 /MAO decrease gradually with increasing the catalyst concentration or polymerization temperature. The most important feature of this catalytic system is the molecular weight distribution (MWD) of polyethylene reaching 12.4, which is higher than using common mononuclear metallocenes, as well as asymmetric dinuclear titanocene complexes like [(CpTiCl₂)₂(η⁵‐η⁵‐C₉H₆(CH₂)_nC₅H₄)] (n = 3, MWD = 7.31; n = 4, MWD = 6.91). The melting point of polyethylene is higher than 135°C, indicating highly linear and highly crystalline polymers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Gas permeation properties of poly(2,5-dialkyl-p-phenyleneethynylene) membranes

Dipropynylbenzenes with alkyl groups (CH₃C ≡ CRC₆H₂RC≡CCH₃, R=n-C₆H₁₃, n-C₈H₁₇, n-C₁₀H₂₁, 1a–c, respectively) were polymerized with Mo(CO)₆ to afford solvent-soluble poly(2,5-dialkyl-p-phenyleneethynylene)s (2a–c). The polymers (2a–c) had high molecular weight over 3×10⁴, and gave free-standing membranes by solution casting method. According to thermogravimetric analysis (TGA), these poly(p-phenyleneethynylene)s showed high thermal stability (T₀ ≥380 °C). The densities of membranes of poly(2,5-dialkyl-p-phenyleneethynylene)s (2a–c) were 0.936–0.965, and their fractional free volume (FFV) were relatively large (ca. 0.14–0.15). The oxygen permeability coefficients (PO₂) of membranes of 2a–c were 4.88, 7.06, and 16.6 barrers, respectively.     

Synthesis of pyrrole-bridged constrained geometry complexes and their application for olefin polymerization

In this article, four constrained geometry complexes 4a [(η⁵-C₅H₄)CH₂(α-C₄H₃N)]Ti(NMe₂)₂, 7a [(η⁵-C₉H₆)CH₂(α-C₄H₃N)]Ti(NMe₂)₂, 4b [(η⁵-C₅H₄)CH₂(α-C₄H₃N)]Zr(NEt₂)₂, 7b [(η⁵-C₉H₆)CH₂(α-C₄H₃N)]Zr(NEt₂)₂ with pyrrole-bridged fragment were synthesized and characterized by ¹H NMR, ¹³C NMR, MASS, and EA. When combined with MAO, complex 4b given the highest activity, the activity of copolymerizing ethylene and 1-hexene reached 2.48 × 10⁶ g polymer/mol·M·h. The effects of temperature, pressure, and ratio of Al/Metal on the polymerization reaction and properties of polymers had been investigated. The polymers with these complexes were characterized by ¹³C NMR and DSC, and the results shown that polymer with 4a had the highest α-olefin incorporation, the incorporation of 1-hexene reached up to 9.81 mol%, and the 1-octene was 8.84 mol%. Actually, there was no [HH] or [OO] sequence in the copolymer, according to the formula of reactivity ratio, rE • rH = 0, all these results suggested that the copolymerization mode is alternating copolymerization. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48620.