Polymerization of vinyl ethers by 3d-transition metal oxides

Studies on the relative efficiencies of 3d-transition metal oxides as catalysts for the polymerization of vinyl ethers revealed that V₂O₅ is the most efficient catalyst. Some kinetic studies with the system isobutyl vinyl ether/V₂O₅/benzene were carried out at ambient temperature. It was found that the rate is second order in isobutyl vinyl ether (IBVE) concentration (0,25 to 2,0mol.1^?1) and the inhibition of the polymerization by pyridine suggests a cationic mechanism. R_p increases by the use of benzaldehyde along with V₂O₅, whereas water (3.10^?3mol.1^?1) seems to have no effect on R_p. Over the temperature range of 15 to 60°C, R_p as well as [η] attain a maximum value at about 32°C. [η] is unaffected by varying the amounts of oxides, whereas it increases with increasing IBVE concentration. No stereoregularity in the product polymer was observed by using V₂O₅ alone or in combination with modifiers such as benzaldehyde or carbon disulfide. The kinetics are interpreted in terms of the Hinshelwood-Langmuire mechanism assuming a single point adsorption.     

Polymerization of N-vinylcarbazole by (3d)-transition metal oxides

The bulk polymerization of N-Vinylcarbazole (NVC) is carried out using some 3 d-metal oxides as catalysts and the following order of reactivity is suggested for the various metal oxides studied: the oxides of copper and cobalt being ineffective. Some kinetic studies are carried out with the NVC/MnO₂ system. Endorsed by the observed retardation of the rate in the presence of water and thiophene a cationic mechanism is suggested for the polymerization. The incapability of the oxides of Cu and Co to act as good catalysts is tentatively explained by supposing that they act as oxidizing rather than π-complexing polymerization catalysts. Stirring does not show any influence on the rate of polymerization.     

Polymerization of aromatic aldehydes, 11. Polymerization of 3-(o-formylphenyl)propionaldehyde and o-phenylenediacetaldehyde

Polymerization of 3-(o-formylphenyl)propionaldehyde ( 4 ) and o-phenylenediacetaldehyde ( 5 ) were performed with several ionic catalysts. The cationic polymerization of 4 yielded polyacetals which contained a seven-membered cyclic unit ( 7 ) in mole fractions of 0,3–0,5. The uncyclized unit ( 6 ) contained the pendant aromatic aldehyde. Apparently, the aromatic aldehyde group reacted during the course of the intramolecular cyclization. Polymerizations of 5 with BF₃·O(C₂H₅)₂, lithium tert-butoxide, or Al(C₂H₅)₃-TiCl₄ as catalysts, similarly gave polyacetals containing a seven-membered cyclic unit ( 10 ) in mole fractions of 0,5–0,8. The extent of cyclization decreased with increase in temperature in the cationic polymerization, resulting in a difference of ?7,5 kJ mol^?1 (?1,8 kcal mol^?1) between the activation energy of intramolecular cyclization and that of intermolecular propagation. The polymerization with Al(C₂H₅)₃ as catalyst gave a polyester via propagation involving a hydride shift.     

Polymerization of tetrahydrofuran: By the system triethylaluminum/water. I. General kinetic studies

Kinetic studies have been carried out on the polymerization of tetrahydrofuran with the ternary catalyst system Al(C₂H₅)₃H₂O-epichlorohydrin at 0°C. It has been found that this is a stepwise addition polymerization, i.e., the propagating species is formed mostly in an induction period and during the subsequent second stage of polymerization the propagating species of an almost constant concentration continues to grow without being interrupted by chain transfer or termination. Based upon the above polymerization mechanism, the concentration of propagating species, [P^*], was determined from the amount and the molecular weight of polymer. [P^*] in the second stage was found to be proportional to the amounts of Al(C₂H₅)₃ and of epichlorohydrin.     

Polymerization of methyl methacrylate with non-bridged zirconocene catalysts

Four non-bridged dimethylzirconocene complexes, i.e., bis(η⁵-cyclopentadienyl)dimethylzirconium ( 1 ), (η⁵-cyclopentadienyl) (η⁵-fluorenyl)dimethylzirconium ( 2 ), bis(η⁵-indenyl)dimethylzirconium ( 3 ) and (η⁵-cyclopentadienyl)(η⁵-pentamethylcyclopentadienyl)dimethylzirconium ( 4 ) were synthesized and used as a catalyst for the methyl methacrylate polymerization combined with triphenylmethyl tetrakis(pentafluorophenyl)borate in the presence of ZnEt₂ or Al(i-Bu)₃. The catalyst activity strongly depends on the zirconocene compound and decreases in the order 2 > 1 > 3 ≫ 4 . The polymerization proceeds in a living manner when 1 and 2 are used combined with ZnEt₂. On the other hand, stereoregularities of the resulting polymers are independent of the zirconocene compound, and syndiotactic-rich polymers are formed by a chain-end controlled mechanism.     

Vinyl polymerization 270. Polymerization of methyl methacrylate initiated by azibenzil

The polymerization of methyl methacrylate initiated by azibenzil (AB) was studied kinetically. The initial rate of polymerization (R_p) was found to be expressed by the equation R_p = k[AB]^0.47[MMA]^0.97. The polymerization proceeded through a radical mechanism. The overall activation energy for the polymerization was estimated as 16.1 kcal/mole. Furthermore, the rate of decomposition of AB was measured in benzene and the following rate equation was obtained: k_d[sec^?1] = 5.75·10¹⁰ exp(-21.9 kcal/RT). From these results the initiation mechanism was discussed.     

Propene polymerization with a magnesium chloride-supported ziegler catalyst, 1. Principal kinetics

The main kinetic behavior of the slurry polymerization of propene with a MgCl₂-supported TiCl₄/C₆H₅COOC₂H₅ catalyst, activated by Al(C₂H₅)₃, was studied, Examination of the dependence of the polymerization rate on temperature and concentrations of Al(C₂H₅)₃ and of propene resulted in a Langmuir-Hinshelwood rate law with the number of polymerization centers dependent on time. The Polymerization rate as function of the polymerization temperature shows a maximum, which is compatible with the rate law. The analysis of the phenomenon of an optimum temperature gave 15 KJ. mol^?1 and 36 KJ. Mol ^?1 for the activation energy of the rate determining step and the adsorption energy of Al(C₂H₅)₃, respectively. Examination of the rapid decay of the polymerization rate showed that the main part of the decay is represented by a second order decay independent of the amount of polymer produced, which can be understood by a second order decay of surface sites by Al(C₂H₅)₃. The number of active centers of the catalyst in gas phase polymerization was estimated applying the inhibition method with carbon monoxide. The results show a constant value for the propagation rate constant, K_p, during the second order rate decay. The observed polymerization kinetics strongly suggest the existence of two kinds of polymerization centers (isotactic and atactic).     

A kinetic study of the photoinitiated polymerization of isobutylene in the presence of vanadium tetrachloride

A kinetic study of the polymerization of isobutylene with VCl₄ induced with monochromatic light, wave length 436 nm, has revealed that the light-induced polymerization is spontaneously quenched after the light source has been switched off; this process depends on the duration of preceding irradiation. The polymerization rate increases with increasing concentration of catalyst and monomer and with the intensity of light. The polymerization rate with respect to the catalyst and monomer concentration at constant light intensity can be expressed by an experimentally found relationship: The polymerization rate increase with decreasing temperature (in polychromatic visible light) and its activation energy for temperatures ranging from ?20 to ?78°C is E = ?19,2±0,8 KJ/mol. The molecular weight of the polymer increases with increasing monomer concentration and with decreasing polymerization temperature. The “activation energy” of the degree of polymerization is E_DP = ?20,9±0,8 kJ/mol. The molecular weight of the polymer is independent of the catalyst concentration and of light intensity. It slightly decreases from the very beginning depending on conversion. The induction period decreases with increasing catalyst and monomer concentration at constant light intensity. The kinetic study has shown that the propagation in the polymerization of isobutylene proceeding via cation-radical intermediates is cationic.     

A Novel Bifunctional Addition‐Fragmentation Agent for Photoinitiated Cationic Polymerization

A novel addition‐fragmentation agent (AFA), namely, 2‐benzyl‐2‐(N,N‐dimethyl‐2‐ethoxycarbonyl‐1‐propenyl) ammonium hexafluoroantimonate‐1‐(4‐morpholinophenyl)‐butane‐1‐one, for photoinitiated cationic polymerization was synthesized and characterized. With this compound, it is possible to initiate the cationic polymerization of cyclohexene oxide (CHO), butyl vinyl ether (BVE) and N‐vinylcarbazole (NVC) photochemically at λ = 380 nm. The mechanism involves the formation of radicals from the alkylphenone moiety and the addition of these radicals to the allylic site and fragmentation of the AFA.     

Characteristics and Mechanism of Styrene Cationic Polymerization in Aqueous Media Initiated by Cumyl Alcohol/B(C6F5)3

Styrene cationic polymerizations initiated by cumyl alcohol (CumOH)/B(C₆F₅)₃ are systematically studied in aqueous suspension and emulsion. Theoretical calculations and experimental research suggest that CumOH/B(C₆F₅)₃ has higher initiating activity than H₂O/B(C₆F₅)₃. During emulsion polymerization of styrene, molecular weight and polymerization rate decrease with the addition of surfactants. These polymerization processes share the same features. Specifically, all elemental reactions (initiation, propagation, and termination) in aqueous media occur at the droplet interface. End structure analysis indicates that chain transfer reactions to water and a‐proton elimination and chain transfer reactions to monomer occur. The possible mechanism for the styrene cationic polymerization in aqueous media is demonstrated.     

Polymerization of propylene to syndiotactic polymer. III. Behaviour of the catalyst system VCl4-Al(C2H5)2Cl in the presence of lewis bases

Polymerizations of propylene to syndiotactic polymer have been carried out in the presence of the catalyst system VCl₄-Al(C₂H₅)₂Cl-anisole. The data obtained have been related to those previously reported concerning the catalyst system, VCl₄-Al(C₂H₅)₂Cl. It was thus possible to propose a mechanism of formation of the catalytic complexes and to put forward or confirm some hypotheses on their constitution. A polymerization mechanism is also proposed that can justify both the type of stereoregularity of the polymer and the variation of steric regularity on varying the polymerization conditions.     

Polyethers for biomedical applications. Polymerization of propylene oxide by organozinc/organotin catalysts

The polymerization of propylene oxide to obtain a high-molecular-weight polymer with an atactic structure required for the application as artificial blood vessels was investigated using combinations of organozinc and organotin compounds as catalyst. The composition of the most active catalyst, resulting from the reaction of diphenyltin sulfide with bis(3-dimethyl-aminopropyl)zinc, was found to be R(C₆H₅)₂Sn(SZn)₂R with R = (CH₂)₃N(CH₃)₂. Using this catalyst, an anionic coordination polymerization was observed with neither stereoselectivity nor living type or cationic features. At low catalyst concentration (0,03 mol-% Zn) a high-molecular-weight poly(propylene oxide) (PPOX) was obtained in 80–90% yield (M _w = 500000; 40% isotactic). Lowering of the catalyst concentration and increasing the polymerization temperature changed the kinetics and the stereochemistry of the polymerization leading to polymers of lower molecular weight and to a decrease in the isotactic PPOX fraction to 20%, probably due to an association of the catalytic species.     

Polymerization of tetrahydrofuran by the AlEt3-H2O-promoter system. II. Behavior of promoter in initiation

The initiation mechanism of the tetrahydrofuran polymerization catalyzed by the AlEt₃–H₂O(2:1)-epichlorohydrin system was studied. The products formed by treatment of the polymerization system at an early stage with sodium methoxide was examined by v.p.c. analysis. It has been shown that the cationic ring-cleavage of epichlorohydrin i.e., the formation of a cyclic trialkyloxonium ion, constitutes the initiation reaction. This finding is consistent with the assumption of the mechanism for the initiating behavior of reactive oxacyclic compounds according to the proposal “promoter”.     

Stereospecific Polymerization of Methylthiirane in Homogeneous Phase, 6. 13C NMR Study of the Stereocontrol Mechanism: An Access to the Size of Stereoblocks

The polymerization of methylthiirane initiated by bis(isopropyl‐(S)‐cysteinato)cadmium is stereospecific and enantioasymmetric and occurs through a catalyst site control. Until now, the mechanism of polymerization could not be verified by NMR because the too low resolution of the spectra showed only a diad effect. ¹³C NMR at 125.76 MHz shows triad effects that permit the examination of the polymerization mechanism. Experimental triad contents do not fit either with the values calculated from the expected catalyst site control (Bernoullian statistics) or from a growing chain‐end control (Markov 1^st order statistics). This can be explained by the interconversion between active sites occurring in this homogeneous system. These interconversions lead to the formation of stereoblocks the length of which have been estimated by comparing experimental NMR results with those calculated from catalyst site control. We found about 38 interconversions for the studied polymer corresponding to DP_n of stereoblocks of around 12–14.     

Polymerization of styrene with the VOCl3/Li(iC5H11) catalyst system

The polymerization of styrene with the VOCl₃/Li(iC₅H₁₁) catalyst system has been studied. Rates of polymerization fall sharply with increase in Li/V ratio; the molecular weights, however, show a maximum at Li/V = 1. Polymerization is first order with respect to catlyst as well as monomer concentrations. Activation energy was found to be 5.67 kcal/mole. Zinc diethyl acts as chain transfer agent. There was no effect of trans-stilbene on molecular weights as well as on rate of polymerization. Valence of vanadium at Li/V molar ratio 1 is 4.12 and it decreases with increase in ratio.     

Ethylene Polymerization with Supported Vanadium‐Magnesium Catalyst: Number of Active Centers and Propagation Rate Constant

The data on the number of active centers in the ethylene polymerization with highly active supported vanadium‐magnesium catalyst (130 kg‐PE/g‐V·h·bar) were obtained by using ¹⁴CO as a radioactive inhibitor. The number of active centers was found to attain 0.06 mol/mol‐V and the propagation rate constant equaled 2.2·10⁴ L/mol·s (80°C). The effect of reversible deactivation of the catalyst in ethylene polymerization in the presence of hydrogen was studied. It was found that a part of the active centers containing vanadium‐polymer bonds transforms to a temporary inactive (dormant) state during the polymerization in presence of hydrogen that may explain the catalyst deactivation. As hydrogen is removed from the reaction medium, these centers transform to the active state again.     

Photosensitized cationic polymerization using allyl sulfonium salt

The cationic polymerization of cyclic ethers such as cyclohexane oxide (CHO) and vinyl monomers such as butyl vinyl ether (BVE) and N-vinylcarbazole (NVC) is initiated upon irradiation at λ 380 nm in CH₂Cl₂ solution containing an allylic sulfonium salt, namely, 2-ethoxycarbonyl-2-propenylthiophenium hexafluoroantimonate ( 1 ) (EMT⁺SbF₆^?), and one of the following compounds: benzophenone, anthracene, thioxanthone, perylene or phenothiazine. Electron transfer and hydrogen abstraction mechanisms were proposed for the initiation step. Stable cation radicals of phenothiazine were also prepared, and the cationic polymerization of butyl vinyl ether was initiated by these cation radicals.     

Cationic Bottlebrush Polymers from Quaternary Ammonium Macromonomers by Grafting‐Through Ring‐Opening Metathesis Polymerization

Cationic bottlebrush homopolymers are polymerized using a grafting‐through approach by ring‐opening metathesis polymerization (ROMP) to afford well‐defined polymers. Quaternary ammonium macromonomers (MMs) are prepared by quaternizing tertiary amine MMs synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization. The quaternary ammonium MMs undergo ROMP to target molecular weights (M_n = 30 000–100 000 g mol^?1) and a low dispersity (? = 1.10–1.30). Halide‐ligand exchange between the third generation Grubbs catalyst (G3) and halide counter ions (bromide and iodide ions) of MMs changes the catalyst activity throughout ROMP, causing it to deviate from pseudo‐first order kinetic behavior; however, the polymerization still follows controlled behavior without significant catalyst termination. Increasing steric bulk of the MMs decreases the polymerization rate as well. Amphiphilic block copolymers are synthesized by sequential polymerization of quaternary ammonium MMs and polystyrene (PS) MMs. Using a PS macroinitiator affords block copolymers with lower ? values as compared to the less active cationic macroinitiator.     

Concurrent Initiation by Air in the Atom Transfer Radical Polymerization of Methyl Methacrylate

The effect of air in atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was studied. Air initiated polymerization was clearly noticed by the appearance of a low molecular weight peak in the synthesis of high molecular weight poly(isobutylene)‐graft‐poly(methyl methacrylate) (M _n = 5.0 × 10⁵ g/mol). The concentration of chains initiated by oxygen (air) was ≈8 × 10^?4 mol/L, determined using the Gladstone‐Dale relationship. The tentatively proposed mechanism for air initiated polymerization was supported by kinetic studies. Similar to typical ATRP systems, the rate of air initiated polymerization increased with temperature, [MMA], amount of air, and activity of the catalyst complex. Polymers with lower polydispersities (M _w/M _n = 1.13) were obtained in the presence of Cu(II) as compared to Cu(I) catalyst complex system.

Kinetic plots for the air initiated bulk polymerization of MMA at (?) 20 °C, (?) 50 °C, and (?) 90 °C.     

Polymerization of 2-vinyl-1,3-dioxolane

When 2-vinyl-1,3-dioxolane was treated at low temperature (?78 or ?130°C.) with cationic catalysts, oily or semi-solid polymer was produced. The result of alkaline hydrolysis showed that the polymeric product contained ester units whose amount was about 2 to 15 mole-% of the total units. The remaining part of the polymer consisted of units containing the dioxolane ring. In the alkaline alcoholysis of the polymer with ethanol ethyl δ-hydroxyvalerate was formed. These findings indicate that in the low temperature cationic polymerization of 2-vinyl-1,3-dioxolane the ester unit, ? O(CH₂)₄CO? , is formed in addition to the unit of vinyl polymerization. A mechanism for the formation of the ester unit has been proposed, in which the process of hydride-shift is followed by ring-opening of the resulting carbonium ion species of dioxolane.