Bimetallic catalysis for styrene homopolymerization and ethylene-styrene copolymerization. Exceptional comonomer selectivity and insertion regiochemistry

This communication reports the styrene homopolymerization behavior and ethylene-styrene copolymerization behavior of the covalently linked bimetallic constrained geometry catalyst (mu-CH2CH2-3,3'){(eta5-indenyl)[1-Me2Si(tBuN)](TiMe2)}2 (Ti2), which is the first single-site catalyst that effects not only styrene homopolymerization with high activity, but also efficient ethylene-styrene copolymerization over a broad styrene composition range (0-76% at 20 degrees C, 1.0 atm ethylene pressure). In styrene homopolymerization, a 50x increase in polymerization activity is achieved with Ti2 vs the mononuclear analogue, Ti1, using an identical trityl borate cocatalyst and polymerization conditions. In ethylene + styrene copolymerization, Ti2 enchains approximately 20% more styrene than Ti1 under identical reaction conditions. 13C NMR spectroscopy indicates that greater than two consecutive styrene units are enchained in the copolymer backbone produced by Ti2 + Ph3C+B(C6F5)4-. End group analysis of the styrene homopolymer produced by Ti2 + Ph3C+B(C6F5)4- suggests that 1,2-regiochemistry is installed in approximately 50% of the initiation steps. This unusual microstructure is believed to be related to the bimetallic catalyst structure.     

Emulsion copolymerization of styrene with a nonionic styrenic polymerizable surfactant

Among the variety of possible structures for polymerizable surfactants, it seems clear that the most interesting should be those with the reactive group located in the hydrophobic part of the molecule. We report here a study based on such a surfactant. Its general formula is A set of surfactants has been produced with m varying from 23 to 48 and n = 6 or 12. The compounds have been characterised by ¹H-NMR (nuclear magnetic resonance), size exclusion chromatography, surface tension measurements and turbidimetry. These surfactants have been copolymerized with styrene in emulsion polymerization. The coagulum is rather important, except if m is large enough. Although the incorporation of the surfactant in the latex is rather high. Most of the anchored surfactant remains at the surface and is not too buried inside. The particle size decreases with both the amount of surfactant and the length of its hydrophilic part. The use of these polymerizable surfactants leads to an excellent stability of the latex against the addition of electrolytes, and also against freeze-thawing constraints.     

Enantiomerically pure phosphaalkene-oxazolines (PhAk-Ox): synthesis, scope and copolymerization with styrene

The design of a synthetic route to a class of enantiomerically pure phosphaalkene-oxazolines (PhAk-Ox) is presented. The condensation of a lithium silylphosphide and a ketone (the phospha-Peterson reaction) was used as the P=C bond-forming step. Attempted condensation of PhC(=O)Ox (Ox = CNOCH(iPr)CH(2)) and MesP(SiMe(3))Li gave the unusual heterocycle (MesP)(2)C(Ph)=CN-(S)-CH(iPr)CH(2)O (3). However, PhAk-Ox (S,E)-MesP=C(Ph)CMe(2)Ox (1?a) was successfully prepared by treating MesP(SiMe(3))Li with PhC(=O)CMe(2)Ox (52?%). To demonstrate the modularity and tunability of the phospha-Peterson synthesis several other phosphaalkene-oxazolines were prepared in an analogous manner to 1?a: TripP=C(Ph)CMe(2)Ox (1?b; Trip = 2,4,6-triisopropylphenyl), 2-iPrC(6)H(4)P=C(Ph)CMe(2)Ox (1?c), 2-tBuC(6)H(4)P=C(Ph)CMe(2)Ox (1?d), MesP=C(4-MeOC(6)H(4))CMe(2)Ox (1?e), MesP=C(Ph)C(CH(2))(4)Ox (1?f), and MesP=C(3,5-(CF(3))(2)C(6)H(3))C(CH(2))(4)Ox (1?g). To evaluate the PhAk-Ox compounds as prospective precursors to chiral phosphine polymers, monomer 1?a and styrene were subjected to radical-initiated copolymerization conditions to afford [{MesPC(Ph)(CMe(2)Ox)}(x){CH(2)CHPh}(y)](n) (9?a: x = 0.13n, y = 0.87n; GPC: M(w) = 7400?g mol(-1) , PDI = 1.15).     

Di(4-isopropenylphenoxy)alkanes as cross-linking comonomers in three-dimensional copolymerization with styrene

Di(4-isopropenylphenoxy)alkanes were synthesized by condensation of 4-isopropenylphenol with symmetrical dihaloalkanes in the presence of KI promoter. Three-dimensional polymeric structures were prepared by compolymerization of these monomers with styrene.     

Free-radical homopolymerization and copolymerization of vinylferrocene

The benzene solution homopolymerization of vinylferrocene, initiated by azobisisobutyronitrile, gave a series of benzene-soluble homopolymers. Thus, free-radical copolymerization studies were performed with styrene, methyl acrylate, methyl methacrylate, acrylonitrile, vinyl acetate, and isoprene in benzene. With the exception of vinyl acetate and isoprene, which did not give copolymers with vinylferrocene under these conditions, smooth production of copolymers occurred. The relative reactivity ratios, r₁ and r₂, were obtained for vinylferrocene–styrene copolymerizations by using the curve-fitting method for the differential form of the copolymer equation, by the Fineman-Ross technique, and by computer fitting of the integrated form of the copolymer equations applied to higher conversion copolymerizations. In styrene (M₂) copolymerizations, the curve-fitting and Fineman-Ross methods both gave r₁ = 0.08, r₂ = 2.50, while the integration method gave r₁ = 0.097, r₂ = 2.91. Application of the integration method to methyl acrylate and methyl methacrylate (M₂) gave values of r₁ = 0.82, r₂ = 0.63; r₁ = 0.52, r₂ = 1.22, respectively. The curve-fitting method gave r₁ = 0.15, r₂ = 0.16 for acrylonitrile (M₂) copolymerizations. From styrene copolymerizations, vinylferrocene exhibited values of Q = 0.145 and e = 0.47.     

Graft copolymerization of itaconic acid-methacrylamide comonomers onto poly(ethylene terephthalate) fibers

The graft copolymerization of itaconic acid-methacrylamide (IA-MAAm) comonomers was carried out using benzoyl peroxide as initiator onto poly(ethylene terephthalate) (PET) fibers in an aqueous medium. The grafted fibers were characterized by FTIR, TGA, DSC and SEM analysis. Effect of various parameters on graft yield such as feed composition, feed and initiator concentration, reaction time and temperature were investigated. The graft yield in the presence of MAAm increased because of the synergistic effect of MAAm comonomer. While, the graft yield alone with the IA onto PET fiber was 2.2%, the use of MAAm as a comonomer increased the amount of IA introduced to the PET fiber up to 13.7%. The reactivity ratios for both monomers were determined by using a Fineman-Ross plot. The grafting rate and saturation graft yield was increased upon increasing the temperature between 65 °C and 85 °C. When the temperature increased further than 85 °C, the saturation graft yield decreased. The graft yield has shown an increase up to an initiator concentration of 1.0 × 10⁻² M and slightly decreased. The grafting increased the dyeability with acidic and basic dyes, and moisture absorption capacity but decreased the thermal stability of the fibers.     

In situ ethylene homopolymerization and copolymerization catalyzed by zirconocene catalysts entrapped inside functionalized montmorillonite

Ethylene homopolymerizations and copolymerizations were catalyzed by zirconocene catalysts entrapped inside functionalized montmorillonites that had been rendered organophilic via the ion exchange of the interlamellar cations of layered montmorillonite with hydrochlorides of L ‐amino acids (AAH⁺Cl^?) or their methyl esters (MeAAH⁺Cl^?), with or without the further addition of hexadecyltrimethylammonium bromide (C₁₆H₃₃N⁺Me₃Br^?; R₄N⁺Br^?). In contrast to the homogeneous Cp₂ZrCl₂/methylaluminoxane catalyst for ethylene homopolymerizations and copolymerizations with 1‐octene, the intercalated Cp₂ZrCl₂ activated by methylaluminoxane for ethylene homopolymerizations and copolymerizations with 1‐octene proved to be more effective in the synthesis of polyethylenes with controlled molecular weights, chemical compositions and structures, and properties, including the bulk density. The effects of the properties of the organic guests on the preparation and catalytic performance of the intercalated zirconocene catalysts were studied. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2187–2196, 2003     

Branching kinetics in copolymerization of styrene with a chain-transfer monomer

In an earlier work it was shown that a random long-chain branching structure can be incorporated in polystyrene by copolymerizing styrene with a small amount of monomer that contains a chain transfer group. The use of vinylbenzylthiol as the chain transfer monomer produced a polystyrene with low number-average molecular weight and a degree of branching lower than expected. In this study polymerization kinetics were used to compute the theoretical molecular weight and degree of branching. The results show that if the chain-transfer constant of the chain transfer monomer is as high as that for vinylbenzylthiol the expected molecular weight and degree of branching will indeed be as low as those found experimentally. The theory also predicts that if the chain transfer constant is near one a highly branched bushy structure will result.     

Radical-Initiated homopolymerization and copolymerization of methylthiomethyl methacrylate

Methylthiomethyl methacrylate (MtMA) was synthesized and homopolymerized in solution. The poly(MtMA) is readily soluble in benzene, acetone, tetrahydrofuran, and methylene chloride at room temperature. The values of K and a in the Mark–Houwink equation, [η] = KM^a, were found to be K = 2.88 × 10^–5 and a = 0.75 when M = M_w. The glass transition temperature of poly(MtMA) was observed to be 72°C by thermomechanical analysis. Intramolecular anhydride formation occurred when poly(MtMA) was heated to 250–300°C. The kinetics of MtMA homopolymerization was investigated in benzene, using azobisisobutyronitrile as initiator. The rate of polymerization R_p was expressed by R_p = k[AIBN]^0.5[MtMA]^1.05 and the overall activation energy was calculated to be 75.7 kJ/mol. The relative reactivity ratios of MtMA in styrene copolymerizations (r₁ = 0.33, r₂ = 0.55) were obtained. Applying the Q-e scheme led to Q = 1.07 and e = 0.51 for MtMA.     

Emulsifier-free emulsion copolymerization of styrene and butyl acrylate. II. Kinetic studies in the presence of ionogenic comonomers

Batch emulsifier-free copolymerizations of styrene (S) and butyl acrylate (BuA) have been performed for a S/BuA weight ratio = 50/50 in the presence of two types of functional comonomers [methacrylic acid (MAA) at different pHs] or potassium sulfopropylmethacrylate (SPM) and two initiators [potassium persulfate or 4–4′azobiscyanopentanoic acid (AZO)]. The use of AZO/MAA system results in the formation of polymer particles with only surface carboxylic end groups. The particle size of the final latexes can be adjusted with the MAA concentration, provided the polymerization is carried out at pH > 6.5. However, the higher the MAA concentration, the sooner the polymerization levels off in conversion. With the K₂S₂O₈/SPM system, particles bearing only sulfate and sulfonate groups are produced and the polymerization is complete. In that case, the particle size of the final latexes is smaller than with the previous system and 30% of the SPM is fixed on the particle surface, instead of 10% with MAA. Using SPM, a too high functional monomer concentration results in the latex destabilization caused by the formation of a large amount of polyelectrolytes. Kinetic studies indicate that most of the functional monomer is incorporated onto the particle surface during the last 30% conversion of the polymerization. A tentative explanation of such a behavior is discussed, based on the existence of two polymerization loci in the latex system.     

Mathematical modeling of styrene and butyl acrylate homopolymerization via the reversible addition-fragmentation mechanism

A mathematical model is suggested for the kinetics of the controlled free-radical polymerization of two monomers—styrene and butyl acrylate—via the reversible addition-fragmentation chain transfer (RAFT) mechanism (with 2,2′-azobisisobutyronitrile as the initiator and dibenzyl trithiocarbonate as the RAFT agent). A comparison of experimental molecular weight characteristics of polystyrene and poly(butyl acrylate) with those calculated using the model indicates that the model is valid. The effects of the process control parameters (temperature and the initial concentrations of the initiator, monomer, and RAFT agent) have been elucidated by a computational experiment.     

Stereoregular and Bernoullian copolymerization of styrene and ethylene by bridged metallocene catalysts

A stereoregular and Bernoullian copolymer of styrene and ethylene was produced by the catalyst system of rac-[isopropylidenebis(1-indenyl)]zirconium dichloride and MAO. This catalyst system yields a high molecular weight copolymer with good activity at 50°C. The copolymer consists of Et-Et, St-Et, and head to tail St-St sequences and has a highly isotactic Et-St alternating sequence. This copolymer shows a melting point (80 – 110°C), due to the isotactic alternating sequence.     

Free‐radical copolymerization of styrene with butyl acrylate. II. Elemental kinetic copolymerization step predictions from homopolymerization data

The free‐radical copolymerization of styrene and butyl acrylate has been carried out in benzene at 50 °C. The lumped k _p/k parameter (where k _p and k _t are the average copolymerization propagation and termination rate constants, respectively) has been determined. Applying the implicit penultimate unit model for the overall copolymerization propagation rate coefficient and the terminal unit effect for the overall copolymerization termination rate coefficient and using the homopolymerization kinetic coefficients, we have found good qualitative agreement between the experimental and theoretical k _p/k values. The variation of the copolymerization rate in solution with respect to the values previously found in bulk has been ascribed to a chain length effect on the copolymerization termination rate coefficient. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 130–136, 2004     

Influence of intrachain interactions on the kinetics of styrene polymerization and copolymerization

In the free-radical polymerization of styrene, it has been observed that the onset of an acceleration of the polymerization due to increased solution viscosity can be quantitatively measured as occurring at a critical point. The product of the degree of polymerization of the polymer in solution at the critical point times its volume fraction can be represented by a temperature-dependent constant (P?_n, V_c, = K ). The value of the constant passes through a maximum between 60 and 90°C. The value of the constant is somewhat lower than that for the phenomenon called chain entanglement. It is postulated that the temperature-dependent behavior of K is due to a previously reported solution phase transition which is believed to be caused by interaction between phenylgroups on the polystyrene chain. Observations on the ultraviolet absorbance of styrene copolymers and calculations on the absolute rate of copolymerization of styrene with methyl methacrylate are presented to support the postulated intrachain interactions.     

Photoinitiated homopolymerization and copolymerization of furfuryl methacrylate and N-vinylpyrrolidone

The study of the homo- and copolymerization of furfuryl methacrylate ( F ) and vinylpyrrolidone ( P ) in bulk, initiated by the photoactivation of AIBN at low temperatures (0 and 40°C), is described. The kinetic diagrams for the homopolymerization of F and P were obtained following the evolution of the heat of reaction by DSC, and revealed the autoacceleration and the vitrification effects on the polymerization rate. The influence of oxygen in the photoinitiated polymerization was analyzed by determining the steady-state concentration of oxygen from the kinetic data obtained for polymerizations performed out in the presence and absence of oxygen. The results obtained indicate that P is more sensitive than F to the presence of oxygen in free radical polymerization. The photoinitiated copolymerization process is little affected by the concentration of monomers, giving similar R_p and θ_m values for both systems. However, at low polymerization temperature 0°C non-crosslinked copolymers are obtained, whereas at a temperature of 40°C, the copolymers prepared at conversion higher than 20 mol % become crosslinked as a result of the active participation of the furfuryl ring in the polymerization process at this temperature. © 1996 John Wiley & Sons, Inc.     

Substituent effects in ethene/styrene copolymerization: Dormant state destabilization?

Homogeneous metallocene and CGC catalyzed copolymerizations of ethene (E) and various substituted styrenes are examined. It is found that those with p‐tert‐butylstyrene (TBS) occur with dramatically higher degrees of incorporation and overall productivity than those observed under the same conditions with styrene. It is argued that that the σ‐donating effect of the tert‐butyl substituent is responsible for this performance, effecting a destabilization of an otherwise dormant benzylic species following 2,1‐insertion of the styrene. It was found possible to produce what is essentially TBS‐alt‐E (44% TBS with no sequential TBS units) using a standard constrained geometry catalyst at impressively high productivity [1.5 × 10⁶ g/(mol_Ti.bar_E.h)] and unusually low concentration of TBS (0.7 M). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3111–3117, 2009     

Selective dimerization,oligomerization, homopolymerization and copolymerization of olefins with complex organometallic catalysts

Review embarrasses the problems of low molecular weight olefins (ethylene and propylene) selective oligomerization to butene-1, hexene-1, octene-1, 4-methylpentene-1; selective polymerization of olefins to obtain polymers with a given molecular mass, molecular mass distribution, branching (for the polyethylene), chain structure [atactic, iso-, syndio-, gemiisotactic, stereoblock type and containing terminal vinyl and vinylidene bonds (for polypropylene)]; “live” homo-and copolymerization of olefins, and alternating copolymerization of olefins in the presence of complex organometallic catalysts.