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.     

Syndiotactic specific polymerization of styrene: driving energy of the steric control and reaction mechanism

The stereoregularity of polystyrenes prepared in the presence of different syndiotactic specific homogeneous catalysts, at different temperatures and monomer concentrations, has been evaluated by ¹³C NMR. It is confirmed that the statistical model of the stereospecific propagation is first-order Markovian. The stereoregularity of the polymers decreases while increasing the polymerization temperature and is affected by the concentration of the monomer, by the ligands of the transition metal precursor of the catalyst, and is higher in the presence of titanium based catalysts. Polymerization of substituted styrenes is increasingly stereospecific in the order p-chlorostyrene < styrene < p-methylstyrene. The results strongly support the polyinsertion mechanism proposed in a previous paper by some of us.     

Copolymerization of ethylene and styrene with monocyclopentadienyltitanium trichloride/methylalumoxane catalyst

A series of ethylene-styrene copolymerizations was carried out in the presence of cyclopentadienyltitanium trichloride and methylalumoxane at 20°C and at different comonomer feed compositions. By sequential extraction a copolymeric material with a styrene units content up to 36 mol-% can be separated from the homopolymeric products. Some considerations about the relative reactivity of the comonomers and the regioregularity of the styrene insertion are made on the basis of the ¹³C NMR spectra.     

Influence of polymerization conditions on the copolymerization of styrene with ethylene using Me2Si(Me4Cp)(N-tert-butyl)TiCl2/methylaluminoxane Ziegler-Natta catalysts

Styrene was copolymerized with ethylene using Me₂Si(Me₄Cp)(N-tert-butyl)TiCl₂/methylaluminoxane (Me = methyl, Cp = cyclopentadienyl) varying monomer concentration, styrene/ethylene molar ratio and polymerization temperature. Increasing styrene or decreasing ethylene concentration, respectively, in the monomer feed lowered both activity of the catalyst system and molecular weight of the copolymer. Only at low styrene content, a linear correlation of styrene concentration in the monomer feed and styrene incorporation in the copolymer was found. From copolymerizations at various temperatures the activation energy of the insertion step was calculated to be 56 kJ/mol. According to Fineman-Ross plot, the copolymerization parameters are r_E = 23,4 for ethylene and r_S = 0,015 for styrene. Investigation of the thermal properties by means of differential scanning calorimetry and dynamic mechanical analysis revealed pronounced decrease of melting temperature and increase of glass transition temperature with increasing styrene content.     

Cyclopolymerization of 1,7-octadiene with metallocene/methylaluminoxane

Polymerization of 1,7-octadiene was conducted with isospecific rac-dimethylsilylenebis(indenyl)zirconium dichloride ( 1 ), syndiospecific diphenylmethylene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride ( 2 ) and aspecific bis(cyclopentadienyl)zirconium dichloride ( 3 ) metallocene catalysts combined with methylaluminoxane. The microstructure of the poly(1,7-octadiene)s produced was characterized by means of ¹H NMR, ¹³C NMR and DEPT (distortionless enhancement by polarization transfer) spectroscopy. A portion of monomeric units in poly(1,7-octadiene)s is saturated as a result of cycloaddition. The fraction of the saturated units (cyclization selectivity) decreases in the following order: 1 > 3 > 2 . The effect of polymerization temperature was studied, and the cyclization selectivity was found to decrease with lowering the polymerization temperature. The monomer concentration affects the microstructure of poly(1,7-octadiene), and the cyclization selectivity is drastically decreased with increasing monomer concentration.     

Thermally initiated emulsion polymerization of styrene

The thermal polymerization of styrene in emulsion was studied by determination of the number of particles, the rate of polymerization, and the average molecular weight of the polymer formed as a function of the emulsifier concentration. For the number of particles the relation N ～ [E]^1,4 was found, whereas the rate of polymerization showed a dependence of v_br ～ [E]^0,7, only up to an emulsifier content of 0,2 mol. dm^?3, but remained constant at higher concentrations. A transfer of low molecular weight radical species from the organic to the aqueous phase is discussed as a prerequisite of polymerization in the latex particles. The deviations from the Smith-Ewart theory are explained by the low rate of radical formation, which does not provide a constant radical concentration per particle.     

The asymmetric-selection polymerization of styrene oxide

The asymmetric-selection polymerization of styrene oxide was investigated by using diethylzinc/menthol system as catalyst. Monomer consumption was found to follow a second order kinetic, whereas developing of the optical rotation of the remaining monomer followed a first order reaction scheme. This phenomenon is accounted for by the assumption that the polymerization consists of rapid initiation followed by slow stepwise growth. Two moles of monomer participate in the polymerization, one of which is polymerized and the other is responsible for activation of the catalyst. The asymmetric ability of the catalyst is arising from the menthoxyl group but not from propylene oxide complexed to the catalyst.     

Cationic copolymerization of norbornadiene with styrene by AlEtCl2/tert-butyl chloride catalyst system, 1. Effect of norbornadiene/styrene feed ratio

The cationic copolymerization of norbornadiene (NBD) and styrene (St) was carried out with the AlEtCl₂/tert-butyl chloride catalyst system in CH₂Cl₂ at ?50°C, and the effect of NBD/St feed ratio on the solubility, the glass trtansition temperature (T_g) and the molecular weight of the copolymers was investigated. A soluble copolymer was prepared at 40 mol-% (or above) of St in the feed, although the NBD homopolymer comprised an insoluble fraction which might have been formed by a crosslinking reaction between the double bonds in the NBD units of the polymer. The copolymer has a statistically random sequence distribution of the two monomeric units not only in the polymer chain but also over the whole molecular weight range (from 10³ to 10⁶). The T_g of the amorphous copolymer is controlled by the NBD/St composition in the range from 100°C through 290°C. A soluble copolymer with highest T_g (ca. 170°C) could be prepared at a NBD/St feed ratio of 60/40 mol-%.     

Kinetics of living radical polymerization of styrene with macromolecular initiator

Kinetics of living radical polymerization of styrene in emulsion initiated by polypropylene hydroperoxide with triethylenetetramine is proposed on the basis of a two stage mechanism. In the first stage fast initiation and propagation occur on the surface of polypropylene. In the second stage continuous chain propagation without termination proceeds in polymer particles in the emulsion. Dependence of rate and degree of polymerization on reaction time, initiator and activator concentrations predicted by the kinetics are ascertained by experimental results. Each polymer particle in the emulsion is suggested to consist of one polymer molecule with a living chain end. Main requisites for the living nature of this system are probably fast and/or limited decomposition and heterogeneity of the initiator in the emulsion polymerization.     

The effect of temperature on the polymerization of propene with dimethylsilylbis(1-indenyl)zirconium dichloride/methylaluminoxane and dimethylsilylbis(2-methyl-1-indenyl)zirconium dichloride/methylaluminoxane. Modeling of kinetics

Propene polymerizations were performed using the two ansa-zirconocene catalyst systems dimethylsilylbis(1-indenyl)zirconium dichloride/methylaluminoxane and dimethylsilylbis(2-methyl-1-indenyl)zirconium dichloride/methylaluminoxane. The polymerization rate was observed by continuously monitoring the monomer consumption. Reaction rate profiles were obtained in the temperature range from 40°C to 130°C at pressures between 1 and 2.5 bar and catalyst concentrations from 4.6 · 10⁻⁶ M to 4.2 · 10⁻⁵ M. Isotacticity, as measured by NMR, melting point and molecular weight decreases markedly at higher temperatures. Small amounts of 1,3-inserted monomer (<1 mol-%) was observed at polymerization temperatures above 80°C. No 2,1-inserted monomer was detected. A kinetic model was developed that describes the polymerization rate for Me₂Si(Ind)₂ZrCl₂ as the catalyst over the entire observed temperature range, and the polymerization rate for Me₂Si(2-Me-Ind)₂ZrCl₂ in a limited temperature range. The model includes an activation reaction, latent sites that may revert to active sites and a permanent deactivation that is second order with respect to the active sites. The activation energy for the propagation reaction was found to be 37 kJ/mol for Me₂Si(Ind)₂ZrCl₂ and 32 kJ/mol for Me₂Si(2-Me-Ind)₂ZrCl₂/MAO. Several kinetic models are compared and discussed.     

Effects of halogen ligands on 1,3‐butadiene polymerization with cobalt dihalides and methylaluminoxane

We conducted 1,3‐butadiene polymerization at 0 and 18 °C using CoX₂ (X = halogen) combined with MAO to elucidate the role of halogen ligands attached to cobalt. With increasing the polymerization time, the molecular weight distribution curves of the polymers obtained progressively shifted to higher molecular weight regions accompanied by narrowing polydispersity, irrespective of the cobalt halides employed. The polymer yield linearly increased after an exponential induction stage, while the number‐average molecular weight linearly increased vs. polymerization time. Thus, the number of polymer chains calculated from the polymer yield and the number‐average molecular weight increased with polymerization time. After a certain polymerization time, the number of polymer chains was saturated to be about 60% catalyst efficiency in the CoCl₂ and CoBr₂ systems but only about 2% in the CoI₂ system. The number‐average molecular weight increases linearly vs. polymer yield from a small positive intercept. These phenomena were interpreted by a slow initiation system without any termination and chain transfer reaction. The kinetic analysis indicated that the rates of initiation were significantly influenced by the nature of the halides and descended in the following order, CoCl₂ > CoBr₂ > CoI₂ > CoF₂ = 0, whereas the rates of propagation were independent on variation of halogen ligands. ¹H and ¹³C NMR analyses of the polymers indicated that the microstructure of the resulting polymer was high cis‐1,4 irrespective of the halogen ligands.

The number of polymer chains of CoI₂ as a function of polymerization time.     

Photo-sensitized polymerization of styrene under high pressure

The polymerization of styrene, photosensitized by azocyclohexane-1,1′-dinitrile, was studied at 30°C over a pressure range of 1 to ca. 1000 bar. The average lifetimes of the growing polymer chains were determined by the rotating-sector method. By measuring the effect of pressure on the individual reactions of styrene polymerization, the activation volumes for the propagation and the termination were obtained as ?17,9 cm³/mol and 13,1 cm³/mol, respectively. The overall activation volume was also measured as ?17,9 cm³/mol and was nearly equal to that calculated from the individual activation volumes (?17,8 cm³/mol). The propagation rate constant increases exponentially with pressure, whereas the termination rate constant decreases rapidly up to 500 bar and then decreases slowly as the pressure increases further.     

Kinetics of the polymerization of styrene with butoxytitanium trichloride and trialkylaluminium

The kinetics of polymerization of styrene in heptane was investigated using butoxytitanium trichloride and triethylaluminium/triisobutylaluminium as cocatalysts. A steady state polymerization after an initial period of declining rates lasting for 20 – 60 min was observed. Both the catalysts systems polymerize styrene at a slow rate ( ≈ 10^?6 mol · dm^?3 · s^?1). The steady state rates show a maximum at an [A1] : [Ti] ratio of 1,5 and exhibit a first-order rate law with reference to both the monomer and the catalyst. Addition of triethylamine, an electron donor, greatly influences the rates of polymerization when triethylaluminium is used, whereas in the case of triisobutylaluminium, the rates are not greatly influenced by the presence or absence of triethylamine. The effect of the electron donor on the rates of polymerization can be explained by the competitive complexation of the alkylaluminium and the electron donor at the active site. The overall activation energy of polymerization (44 – 46 kJ · mol^?1) is in accord with a coordinated anionic mechanism. An alkylated alkoxytitanium halide species as the chemical entity affecting polymerization is suggested.     

Polymer-supported rare-earth catalysts for polymerization of styrene

A neodymium complex supported on an ethylene-vinyl alcohol copolymer (EVA · Nd) was prepared for the first time and the polymerization of styrene in the presence of a new type of catalyst system composed of this complex was studied. The new catalytic system [EVA · Nd Al(i-Bu)₃ CCl₄] (i-Bu = isobutyl) is characterized by its catalytic activity in comparison with that of conventional rare-earth catalysts. When [Nd] = 10⁻³ mol/L, [Styrene] = 5 mol/L, [Al]/[Nd] = 120 and [CCl₄]/[Nd] = 35, then the conversion to polystyrene (PS) was 55% in 6 h, and the catalytic activity reached 1972 g PS/g Nd which is higher by a factor of 45 than that of conventional rare-earth catalysts. The polymerization reaction shows a short induction period where the rate is first order with respect to the monomer concentration. The activation energy is 27,6 kJ/mol. This polymerization may proceed according to a free-radical or a Ziegler-type coordination mechanism.     

The anionic polymerization of styrene under pressure

The kinetics of the anionic polymerization of styrene were investigated under pressure (1≤p/bar < 1800) with Na⁺ as counter ion in tetrahydropyran (THP) as solvent and with Cs⁺ as counter ion in 1,2-dimethoxyethane (DME) as solvent. The results yielded the activation volume of the contact ion pair ΔV and the sum (ΔV + ΔV_cs) of the activation volume of the solvent separated ion pair ΔV and the volume change upon formation of solvent separated ion pairs from contact ion pairs ΔV_cs. The numerical values are negative. The activation volume of the solvent separated ion pairs could be estimated.     

Initiation of polymerization with substituted ethanes, 14 Free-radical polymerization of methyl methacrylate and styrene with substituted adiponitriles

Tetraarylsuccinonitriles 1 show an atypical “stepwise” initiation mechanism in freeradical polymerization, particularly in the case of methyl methacrylate (MMA) as monomer. In the prior phase of the polymerization reaction very high concentrations of primary radicals lead to the formation of short-chain telechelics with both end groups originating from the initiator. In the further course of polymerization these telechelics are able to from radicals by release of initiator end groups and so to “re-initiate” free-radical polymerization (‘resusciatable’ radical polymerization). In this communication a general synthesis method of MMA telechelics with a formal degree of polymerization of one is presented. These 2,2,5,5-tetraaryl-3-methoxycarbonyl-3-methyladiponitriles 4 dissociate with Arrhenius activation energies in the range of 150 ± 10 kJ/mol. When using these telechelics as initiators in free-radical polymerization of MMA and styrene, respectively, above 80°C no repeated telechelic formation phase is observed and polymer formation starts immediately from the beginning. The polymers obtained have weight-average molecular weights of 200 000 to 950000 (poly(methyl methacrylate)) and 50000 to 400000 (polystyrene), respectively.     

Syndiospecific polymerization of styrene by soluble alkoxytitanium catalysts

The activity of Ti(OEt)₄ (Et: C₂H₅) in combination with methylaluminoxane (MAO) in the syndiospecific polymerization of styrene was investigated concenrning the dependence on temperature, mole ratio of Al/Ti, concentrations of monomer, catalyst and MAO. Reaction products of Ti(OEt)₄ and erythritol and sorbitol, respectively, were also used in the syndiospecific polymerization of styrene revealing that soluble Ti compounds are the active species.     

Kinetics of the polymerization of isoprene with isopropoxyneodymium dichloride/triethylaluminium binary lanthanide catalyst system

The kinetics of the polymerization of isoprene with the heterogeneous rare earth catalyst system isopropoxyneodymium dichloride/triethylaluminium (Nd(OPrⁱ)Cl₂-AlEt₃) was examined in a specially designed dilatometer. The rate of polymerization is expressed as R_p ≈ ?d[M]/dt = k[Nd]^1.40 [M]. The main kinetical parameters such as the concentration of active propagating chain, the efficiency of lanthanide catalyst used (ELCU), the absolute rate constant of propagation as well as the average life time of growing chains, were determined at 30°C, 40°C, 45°C and 50°C.     

The cationic nature of diethylzinc/water system as polymerization catalyst

The nature of the binary system diethylzinc/water as catalyst for the ring opening polymerizations was found to be much influenced by the mole ratio of water to zinc. With mole ratios less than 1, the catalyst system induced the polymerization of tetrahydrofuran, 3.3-bis(chloromethyl)oxetane and styrene with (or without in some cases) suitable cocatalysts; that points at a cationic character of the zinc catalyst. The 1:1 system, on the other hand, failed to polymerize any of these monomers. Discussions are presented on the characters of the two catalyst systems on the basis of these results together with those for D (+)-propylene oxide polymerization.