Methyl methacrylate and p-fluorostyrene were polymerized with Co(acac)3-A1Et3 catalyst system in benzene at 60°. Maximum conversion of polymer was obtained when the catalyst was aged for 15 min. Maximum activity of the catalyst was found at Al/Co ratio of 3. The polymerization was first order with respect to monomer. The orders with respect to catalyst and cocatalyst were found to be 0.5 and 1.5 respectively. The overall activation energies for the polymerizations of methyl methacrylate and p-fluorostyrene were found to be 54.5 and 59.6 kJ/mol respectively. A free-radical mechanism is postulated. 相似文献
The polymerization of methyl methacrylate was carried out with the following Ziegler-Natta type initiating systems: Fe(AcAc)3-AlEt2Br, Fe(AcAc)3-ZnEt2 (acac = acetyl acetonate). Both the catalyst systems are active under homogeneous conditions in benzene at 40°C for methyl methacrylate polymerization. The polymerization kinetics suggests that the average rate of polymerization was first order with respect to [monomer] for both the catalyst systems, and the overall activation energies were found to be 14.0 and 12.8 kcal mol ?1. 相似文献
The mechanism and kinetics of the γ-ray-initiated postpolymerization of octadecyl methacrylate and acrylate in lamellar crystals were investigated by a simple model. This model assumes that the initiation points are distributed as in a checkerboard and that polymerization probability of the monomer molecules decreases conically around each initiation point. The two-dimensional polymerization can be characterized in this cone model by two parameters, a and r; a represents the polymerizability of the monomer for a given condition, and r depends on the number of initiation points per unit area. G values for the initiation reaction of octadecyl methacrylate and acrylate were estimated as 0.8 and 1.6, respectively. The two-dimensional postpolymerization of long-chain compounds proceeds in two stages. The rate of polymerization is very high and zero order with respect to monomer concentration in the first stage. It is lower and obeys first-order kinetics in the second stage. The rate constants of the zero-and first-order polymerizations were kp0 = 1.73 molecule sec-1 and kp1 = 0.93 sec?1, respectively, for octadecyl acrylate at 20°C. 相似文献
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. 相似文献
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. 相似文献
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. 相似文献
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. 相似文献
The kinetics of polymerization of tributyltin methacrylate (TBTM) has been studied in benzene solution in the temperature range 60–75°C in the presence of azobisisobutyronitrile (AIBN). We have obtained the following polymerization rate equation: Rp = Kp [TBTM]1.5 [AIBN]0.5. It shows that the dependence of the polymerization rate on the concentrations of the monomer TBTM and the initiator AIBN are 1.5 and 0.5 order, respectively. The activation energy of polymerization was found to be 18.1 kcal/mol. The activation energy for the degree of polymerization is approximately -12.3 kcal/mol. 相似文献
Summary: ω‐Styryl‐polystyrene macromonomers were synthesized by anionic induced deactivation reactions. Their homopolymerization in the presence of a fluorinated half‐sandwich metallocene catalyst (CpTiF3/MAO) was investigated. In spite of the intrinsic lower reactivity of these macromonomers with respect to the micromolecular monomer, coordination homopolymerization was possible. The influence of several experimental parameters on the polymerization yield and degree could be demonstrated. In most cases, under identical experimental conditions, higher polymerization yields and degrees were observed with respect to the CpTiCl3/MAO catalyst.
The synthesis of p‐polystyryl‐substituted styrene derivatives by the homopolymerization of ω‐styryl‐polystyrene macromonomers in the presence of CpTiF3. 相似文献
The thermal polymerization of methyl methacrylate [MMA] was carried out using ylide (4-picolinium 4-chloro phenacyl methylide) as an initiator. The rate of polymerization (Rp) increases with increasing monomer and initiator concentrations; The exponent value has been computed to be 1 ± 0.02 and 0.5, respectively. The reaction was carried out at four different temperatures and the overall activation energy has been computed to be 16.01 kcal/mol. The polymerization was inhibited in the presence of hydroquinone as a radical scavanger. Kinetic studies indicates that the overall polymerization takes place by a radical mechanism. 相似文献
Methyl methacrylate was polymerized by triethylaluminum—cuprous chloride catalyst. A study of the polymerization kinetics indicated that the overall rate was represented by the equation, Rp = K[AlEt3] [CuCl]½ [M]2. The overall activation energy was 16.5 kcal/mole. From ESR measurement and the results of copolymerization of methyl methacrylate with styrene, it was suggested that the catalytic system has the character of a radical initiator. A polymerization scheme was also proposed. 相似文献
Kinetic studies on methyl methacrylate polymerization were carried out with watersoluble 2,2′-azobisisobutyramidine (ABA). The rate of polymerization was proportional to the square root of the initiator concentration in the solvents chloroform, methanol, and dimethyl sulfoxide (DMSO), which confirms the bimolecular nature of the termination reaction. The monomer exponent was unity in chloroform but in methanol and DMSO the rate of polymerization passed through a maximum when plotted against the monmer concentration. This behavior in methanol has been attributed to be due to the enhanced rate of production of radical with increasing proportion of methanol. The rate of decomposition of the ABA has been observed to be faster in methanol than in chloroform. The situation becomes more complicated with DMSO, which was found to reduce the value of δ = (2kt)1/2/kp in methyl methacrylate polymerization. The rate of polymerization was observed to be highly dependent on the nature of the solvent, the rate increasing with increased electrophilicity of the solvent. The dependence of Rp on the solvent has been explained in the light of the stabilization of the transition state due to increased solvation of the basic amidine group of the initiator with the increased electrophilicity of the solvent. 相似文献
The ylide 4-picolinium, p-chloro phenacylide-initiated thermal polymerization of ethyl methacrylate (EMA) was studied. 4-Picolinium p-chloro phenacylide induces the thermal polymerization of ethyl methacrylate at 65°C. The rate of polymerization (Rp) rose as the initiator concentration increased from 2 × 10?3 to 4 × 10?3M and the initiating exponent was computed as 1.9. The Rp decreased as the concentration of ylide increased from 6 × 10?2 to 1M. The greater initiator concentration also affected the molecular weight inversely. The polymerization was carried out at different temperatures and the overall activation energy was computed as 4.08 Kcal/mol. Polymerization was inhibited in the presence of hydroquinone as a radical scavenger. Kinetic studies and other data show that the overall polymerization takes place in a radical mechanism. The various kinetic parameters, such as the rate and average degree of polymerization, molecular weight, and energy of activation of the present system, were evaluated. 相似文献
The influence of stereoregular poly(methyl methacrylate) (PMMA) as a polymer matrix on the initial rate of radical polymerization of methyl methacrylate (MMA) has been measured between ?11 and +60°C using a dilatometric technique. Under proper conditions an increase in the relative initial rate of template polymerization with respect to a blank polymerization was observed. Viscometric studies showed that the observed effect could be related to the extent of complex formation between the polymer matrix and the growing chain radical. The initial rate was dependent on tacticity and molecular weight of the matrix polymer, solvent type and polymerization temperature. The accelerating effect was most pronounced (a fivefold increase in rate) at the lowest polymerization temperature with the highest molecular weight isotactic PMMA as a matrix in a solvent like dimethylformamide (DMF), which is known to be a good medium for complex formation between isotactic and syndiotactic PMMA. The acceleration of the polymerization below 25°C appeared to be accompanied by a large decrease in the overall energy and entropy of activation. It is suggested that the observed template effects are mainly due to the stereoselection in the propagation step (lower activation entropy Δ Sp?) and the hindrance of segmental diffusion in the termination step (higher activation energy Δ Et?) of complexed growing chain radicals. 相似文献
A systematic study of formation of surface patterns in block copolymer thin layers after their exposure to solvent vapors was performed. The studied effect involves layers of thickness approximately equal to the ordering size of polymers - about 45 nm. Experiments were performed on three styrene - methacrylate derivative block copolymers, synthesized by living anionic polymerization: poly(4-octylstyrene)-block-poly(butyl methacrylate), poly(4-fluorostyrene)-block-poly(butyl methacrylate) and poly(p-octylstyrene)-block-poly(methyl methacrylate). The polymers were exposed to vapors of chloroform, 1,4-dioxane, hexane, acetone and tetrahydrofuran. 相似文献