Kinetics and mechanism of stereospecific polymerization of methyl methacrylate with VOCl3–AlEt2Cl catalyst system

Methyl methacrylate was polymerized at 40°C with VOCl₃–AlEt₂Cl catalyst system in n-hexane. The rate of polymerization was proportional to catalyst and monomer concentration at Al/V ratio of 2 and overall activation energy of 9.25 kcal/mole support a coordinate anionic mechanism of polymerization. The catalytic activity and stereospecificity of this catalyst system is discussed in comparison with that of VOCl₃–AlEt₃ catalyst system.     

Polymerization of styrene with the VOCL3–AlEt2Br catalyst system

The rate of polymerization with the VOCl₃–AlEt₂Br catalyst system at 30°C. in n-hexane reached a maximum at an Al/V molar ratio of 1.5. At this ratio, the rate of polymerization was first-order with respect to catalyst and second-order with respect to monomer concentrations. The apparent activation energy calculated was 6.4 kcal./mole. Diethylzine was found to act as a chain transfer agent. However, the molecular weights of polymers obtained were low. The possibility of bromide-containing catalyst sites acting in the termination reaction has been investigated. The average valence of vanadium is discussed in relation to molecular weights.     

Cyclopolymerization of isoprene with VCl4–AlEt2Br catalyst system

Isoprene was polymerized at 30°C with VCl₄–AlEt₂Br catalyst system in n-hexane. A linear dependence of rate of polymerization on the monomer and catalyst concentrations was found. The overall activation energy was 8.96 kcal/mole. Infrared spectra of polyisoprene showed the presence of cyclic structure, indicating a cationic mechanism of polymerization.     

Free-radical polymerization of methyl methacrylate and p-fluorostyrene in the presence of the Mn(acac)3–AlEt3 catalyst system

Methyl methacrylate and p-fluorostyrene were polymerized with manganese (III) acetylacetonate–aluminum triethyl catalyst at 60°C in a benzene medium. Maximum activity was found at Al/Mn ratio of 4. Maximum percent conversion of polymer was obtained when the aging time of the catalyst was 10 min. The rate of polymerization was first order with respect to monomer. The rate of polymerization with respect to catalyst and cocatalyst were found to be 0.5 and 1.5, respectively. The overall energy of activation for the polymerization of methyl methacrylate and p-fluorostyrene were found to be 52.6 and 57.0 kJ/mole, respectively. A free-radical mechanism is postulated.     

Stereoblock polymerization of methyl methacrylate with VOCl3?Al(C2H5)3 catalyst system

Kinetics of the polymerization of methyl methacrylate with the VOCl₃? AlEt₃ catalyst system at 40°C in n-hexane have been studied. A linear dependence of rate of polymerization on the monomer and catalyst concentrations as well as an overall activation energy of 5.87 kcal/mole were found. Characterization of the structure of the polymer by NMR spectra revealed the presence of stereoblock units. The mechanism of polymerization is discussed in relation to the kinetic data obtained.     

Role of heterogeneous Cr(AcAc)3–AlEt3 catalyst system in isoprene polymerization

Polymerization of isoprene in presence of a heterogeneous Ziegler-type catalyst system, Cr(AcAc)₃–AlEt₃, has been studied in benzene medium. The rate of polymerization is first-order with respect to catalyst as well as monomer concentration. The rate studies, activation energy, and polymer microstructures are reported in order to follow the probable mechanism of polymerization.     

Kinetics and mechanism of polymerization yielding stereoblock poly(methyl methacrylate) with VCl4-Al(C2H5)3 catalyst system

Methyl methacrylate was polymerized at 40°C with the VCl₄–AlEt₃ catalyst system in n-hexane. The rate of polymerization was proportional to the catalyst and monomer concentration at Al/V ratio of 2, indicating a coordinate anionic mechanism of polymerization. NMR spectra were further used to confirm the mechanism of polymerization and stability of active sites responsible for isotacticity.     

Polymerization of propylene with TiCl3–AlEt2Cl–polymeric electron donor catalyst

Polymeric donors having ether or carbonyl groups were added to the TiCI₃–AlEt₂CI catalyst system as the third component, and the effects on the polymerization of propylene were investigated in comparison with the effect of the electron donors with low molecular weight. The polymeric donors were effective in making the catalyst more active, but the donors of low molecular weight depressed the catalyst activity. In the case of poly(propylene glycol dimethyl ether) (PPG-DME), PPG–DME with a number of propylene oxide units (n) of more than 6.7 was effective in enhancing the catalyst activity. These effects were considered to be due to the different reactivities between TiCI₃ and AlEt₂CI-polymeric donor complexes having various chain lengths.     

Anionic polymerization of methyl methacrylate with Cr(C5H7O2)3–Al(C2H5)3 catalyst system

A homogeneous catalyst system, Cr(C₅H₇O₂)₃–Al(C₂H₅)₃, was used for the polymerization of methyl methacrylate. The yield of polymer increased up to an Al/Cr ratio of 12 and thereafter remained almost constant with increasing Al/Cr. The rate of polymerization increased linearly with increasing catalyst and monomer concentrations at Al/Cr = 12. The molecular weight, however, decreased with increasing catalyst concentration and increased with increasing monomer concentration, indicating anionic polymerization reaction. NMR studies of the polymers indicated the presence of a stereoblock structure, which changed to heteroblock structure in presence of triethylamine and hydroquinone as additives in the catalyst. In the light of these observations, the mechanism of the polymerization is discussed.     

Kinetics of the γ-radiation-induced polymerization of methyl methacrylate in the solid state

Studies have been made of the γ-radiation-induced polymerization of methyl methacrylate in bulk, in the solid state at a temperature of ?65°C. and a radiation intensity of 346,000 rad/hr. The reaction was found to have an extremely long induction period (～50 hr.) when pure monomer was used, and to be first-order with respect to polymer concentration. This first-order dependency was confirmed by a series of irradiations in which 0.6% poly(methyl methacrylate) was dissolved in the monomer before irradiation. These irradiations showed no induction period. Nuclear magnetic resonance spectroscopy indicated a much more heterotactic polymer than that obtained in the liquid state at ?49°C.     

AlEt3–metal soap catalysts for the polymerization of epoxides

Epoxides, propylene oxide in particular, were polymerized by a catalyst system consisting of AlEt₃–metal soap, to high molecular weight polyethers in high conversion. Carboxylic acid salts of Ti, V, Cr, Zr, Mo, Co, and Ni, transition metals of groups IV–VIII in the Periodic Table, were most preferable. Metal salts of stearic, octanoic, lauric and naphthenic acid were examined as catalyst components and proved to be very active for the polymerization of epoxides when used with an organoaluminum compound such as AlEt₃ or AlEt₂Cl. Copolymerization of propylene oxide and allyl glycidyl ether was successfully carried out with an AlEt₃–Zr octoate catalyst.     

Polymerization of vinyl chloride by the Ti(O-n-Bu)4–AlEt3–epichlorohydrin catalyst system

The polymerization of vinyl chloride was carried out by using a catalyst system consisting of Ti(O-n-Bu)₄, AlEt₃, and epichlorohydrin. The polymerization rate and the reduced viscosity of polymer were influenced by the polymerization temperature, AlEt₃/Ti(O-n-Bu)₄ molar ratios, and epichlorohydrin/Ti(O-n-Bu)₄ molar ratios. The reduced viscosity of polymer obtained in the virtual absence of n-heptane as solvent was two to three times as high as that of polymer obtained in the presence of n-heptane. The crystallinity of poly(vinyl chloride) thus obtained was similar to that of poly(vinyl chloride) produced by a radical catalyst. It was concluded that the polymerization of vinyl chloride by the present catalyst system obeys a radical mechanism rather than a coordinated anionic mechanism.     

Ethylaluminum oxide catalysts from Et2AlOLi–Et2AlCl binary system in relation to species of AlEt3–water catalyst

Equimolar reaction of Et₂AlOLi and Et₂AlCl gave Et₂AlOAlEt₂. The catalyst behavior for polymerization of acetaldehyde, propylene oxide, and epichlorohydrin was compared with that of the AlEt₃–H₂O (1:0.5) catalyst system. The thermal disproportionation product of Et₂AlOAlEt₂ derived from Et₂AlOLi–Et₂AlCl had the structure, ? (EtAlO)_n? , and it showed catalyst behavior quite similar to that of the product obtained by the same treatment of AlEt₃–H₂O (1:0.5). These ethylaluminum oxides can be regarded as species predominating in AlEt₃–H₂O (1:0.5) and AlEt₃–H₂O (1:1), respectively. Stereospecific or high molecular weight polymerizations of these species were investigated.     

Polymerization of styrene with VOCl3–aluminum alkyls

The polymerization of styrene with VOCl₃ in combination with AlEt₃ and with Al(i-Bu)₃ in n-hexane at 40°C. has been investigated. The rate of polymerization was found to be second order with respect to monomer in both systems. With respect to catalyst the rate of polymerization was first order for VOCl₃–AlEt₃ and second order for VOCl₃-Al(i-Bu)₃ systems. The activation energies for VOCl₃–AlEt₃ and VOCl₃–Al(i-Bu)₃ systems were 7.37 and 11.25 kcal./mole, respectively. The molecular weight of polystyrene in the AlEt₃ system was considerably higher than that in the Al(i-Bu)₃ system. The valence of vanadium obtained by a potentiometric method showed that the catalyst sites in the AlEt₃ system are different in nature from those in the Al(i-Bu)₃ system. The effect of diethylzinc as a chain-transfer agent in the AlEt₃ system was also studied.     

Effect of a π-donor on the radical bulk polymerization of methyl methacrylate

Bulk polymerizations of methyl methacrylate (MMA) at 60°C initiated with 2,2′-azoisobutyronitrile are influenced by the presence of an organic π-donor such as tetrathiafulvalene (TTF). Upon addition of TTF, the ratio of weight- to number-average molecular weights M̄_w/M̄_n are significantly reduced and the thermal stability of the poly(methyl methacrylate) samples is increased. Kinetic investigations indicate that TTF acts as a retarder on the polymerization mechanism.     

Free-radical polymerization of methyl methacrylate in presence of the Cr(C5H7O2)3–Al(i-C4H9)3 catalyst system

Polymerization of methyl methacrylate has been studied with the chromium acetylacetonate–triisobutyl aluminum catalyst system in benzene medium at 40°C. These studies have been carried out at an Al/Cr ratio of 12 to compare the behavior with the previously studied chromium acetyl acetonate–triethyl aluminum catalyst system. The enhanced yield and gelling of polymer suggests a free-radical mechanism of polymerization. Further, the kinetics of polymerization and the heterotactic structure of polymer as determined by NMR examination have led to confirmation of the freeradical mechanism of polymerization of methyl methacrylate by an excess of triisobutylaluminum in the presence of catalyst complex.     

Atom transfer radical polymerization of methyl methacrylate catalyzed by cobalt catalyst system

A new catalyst system, CoCl₂/tris(2‐(dimethyl amino) ethyl)amine (Me₆ TREN), was used to catalyze the polymerization of methyl methacrylate (MMA) successfully through atom transfer radical polymerization mechanism. The control over the polymerization was not ideal, the molecular weight distribution of the resulting polymer (PMMA) was relatively broad (M_w/M_n = 1.63–1.80). To improve its controllability, a small amount of hybrid deactivator (FeBr₃/Me₆TREN or CuBr₂/Me₆TREN) was added in the cobalt catalyst system. The results showed that the level of control over the polymerization was significantly improved with the hybrid cobalt–iron (or cobalt–copper) catalyst system; the polydispersity index of the resulting polymer was reduced to a low level (M_w/M_n = 1.15–1.46). Furthermore, with the hybrid cobalt–iron catalyst, the dependence of the propagation rate on the temperature and the copolymerization of methacrylate (MA) with PMMA‐Br as macroinitiator were also investigated. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5207–5216, 2005     

Dimethylaniline (DMA)–Cu2+ ion system-induced graft polymerization of methyl methacrylate on viscose

Graft polymerization of methyl methacrylate on viscose fibers induced by the DMA–Cu²⁺ ion system was investigated under different conditions. Variables studied include concentration of DMA, Cu²⁺ ion, and MMA, reaction time, and temperature. There are optimal concentrations of DMA and Cu²⁺; below or above these concentrations lower grafting occured. Within 4 hr reaction time, the grafting reaction showed an initial fast rate followed by a slower one at 80°C. At 70°C, on the other hand, the graft yield increased in proportion to the increase in reaction time. Increasing the monomer concentration did not have a significant effect on the graft yield during the first 45 min of reaction. Beyond this, the effect of monomer concentration was marked.     

γ-radiation-initiated emulsion polymerization of n-butyl acrylate and of methyl methacrylate

We have investigated the γ-radiation-initiated polymerization of n-butyl acrylate (BA) and of methyl methacrylate (MMA) in aqueous emulsions stabilized with sodium lauryl sulfate (SLS). The reaction rate, as measured by a nonabsolute thermocouple technique, varies as the square root of emulsifier concentration for both monomers. In the case of BA, the dose rate exponent of the reaction rate is 0.7 ± 0.3, whereas the corresponding value for MMA is approximately 0.4. The overall activation energy of the BA polymerization is close to zero, whereas for MMA a value of 4.8 ± 2.1 kcal/mole has been found. The poly(butyl acrylate) molecular weight is effectively independent of soap concentration and of dose rate but decreases as the reaction temperature is increased in the range 30–70°C. The general conclusion drawn from this work is that these radiation-induced emulsion polymerizations differ little from conventionally initiated systems insofar as the reaction kinetics are concerned. Poly(butyl acrylate-g-methyl methacrylate) copolymers have been prepared by a direct irradiation method involving a poly(butyl acrylate) prepolymer seed latex. Some physical properties of this material have been examined.