Stationary-state kinetics in the polymerization of ethyl α-cyanoacrylate by phenazines

Amines 1–5 of a family of phenazines have been examined as initiators for the anionic polymerization of ethyl α-cyanoacrylate in tetrahydrofuran at 20°C. 1 and 2 are inactive; 3 initiates a polymerization of the slow-initiation-no-termination (SINT) type. 4 and 5 induce different kinetic patterns of which that from 5 (Chlofazimine) has been studied in detail. Coloured polymers are produced, whose absorbance gives an (inverse) measure of the chain length. Stationary-state kinetics are established and values of all rate constants evaluated or estimated. The mechanism is interpreted as a zwitterionic polymerization initiated at the secondary NH group, thus making the initial group of the chain a tertiary ammonium ion, whose potentially acidic proton can then act as terminator to the carbanionic propagating ends.     

Studies on the propagation reaction in the free radical polymerization of ethyl α‐hydroxymethacrylate

The free radical propagation kinetics of ethyl α‐hydroxymethacrylate have been investigated using pulsed‐laser polymerization experiments. Experimental conditions were not optimised for successful experiments in bulk monomer, where transfer caused complications in the interpretation of the data. However, in solution and at low temperatures (below 45°C), successful experimental conditions were identified and an extensive data set of propagation rate constants is reported. A remarkable dependence of the propagation rate coefficient, k_p, on the solvent was observed. The variation in k_p is exemplified by the range obtained at 15°C where k_p was found to fall between 580 (THF) and 1 860 (xylene) L/mol/s. The Arrhenius parameters for the propagation reaction were obtained in three solvents (tetrahydrofuran, toluene and ethanol) at three different dilutions. The samples with the highest concentration of EHMA yielded values for the activation energy of 15–16 kJ/mol and pre‐exponential factors 5–10 times lower than those previously reported for ethyl methacrylate. Both Arrhenius parameters were strongly dependent on solvent type and concentration. A hypothesis for these results is tendered – suggesting direct interactions in the transition state between the monomer and the propagating radical. These specific interactions are ameliorated to a greater or lesser extent by the inclusion of different solvents.     

Boundary between acceleration and suppression effects of α-substituent on polymerization and copolymerization of ethyl α-(halomethyl)acrylates

Radical polymerization and copolymerization behaviour of ethyl α-(halomethyl)acrylates was examined. Among them the bromomethylacrylate did not yield a homopolymer nor a copolymer because of fast chain transfer to the monomer. The chloromethylacrylate (ECMA) polymerized slower to form a lower molecular weight polymer than the fluoromethylacrylate (EFMA). In the copolymerizations with styrene and methyl methacrylate, ECMA was less reactive than EFMA owing to the steric effect of the slightly larger chloromethyl group. The reactivity of EFMA in the copolymerization was enhanced by the polar and resonance effects of the α-substituent, prevailing over the steric effect. Characterization of the polymers by NMR spectroscopy and thermogravimetric analysis revealed the existence of steric congestion caused by the halomethyl groups in both polymers.     

Kinetic determination of stereoselectivity in the anionic polymerization of α-ethyl-α-phenyl-β-propiolactone

The kinetics of the anionic polymerization of optically active α-ethyl-α-phenyl-β-propiolactone (optical purity 16,8%) initiated with bis(triphenylphosphine)iminium acetate was investigated and the rate constants for the homo-(k_ph) and crosspropagation (k_pc) (considering R and S enantiomers as comonomers) were determined. The knowledge of the values of k_ph and k_pc, equal to 1,53·10^?4 and 9,0·10^?51· mol^?1·s^?1, respectively (25°C, CH₂Cl₂ solvent), allowed us to calculate the distribution of homosequences in the polymer prepared from racemic monomer. The concentration of homosequences was slightly higher than calculated for the process with random enchainment of enantiomers. Thus, the content of homodyads, homotriads, and homotetrads equals 63, 40, and 25%, whereas for the random process it was 50, 25, and 13%, respectively. This difference is, however, too small to create homoblocks which could be responsible for the observed crystallinity of these polymers.     

Role of bulky α-substituent in free-radical polymerization and copolymerization of methyl α-(alkoxymethyl)acrylates

Methyl α-(alkoxymethyl)acrylates were prepared from methyl α-(bromomethyl)acrylate in 80–90% yield. The monomers homopolymerize fast to yield low-molecular-weight polymers. The monomers bearing a linear alkoxymethyl group except for the ethoxymethyl group are characterized by a relatively low ceiling temperature. The rate constants for propagation k_p and termination k_t of methyl α-(butoxymethyl)acrylate were evaluated to be k_p = 298 dm³ · mol^?1 · s^?1 and k_t = 8 · 10⁶ dm³ · mol^?1 · s^?1 at 60°C, respectively. The α-(alkoxymethyl)acrylates are more reactive than methyl methacrylate toward polystyrene radical, except for the α-(dodecyloxymethyl)acrylate which is slightly less reactive, indicating that an increase in the reactivity by the electron-withdrawing character of the alkoxy group prevails over the steric hindrance against addition of the polymer radical, except for the large dodecyloxymethyl group.     

Polymerization of α-olefins in the presence of δ-TiCl3/Al(CH3)3: Chain propagation rate constants for ethylene and propene

The chain propagation rate constants for the polymerization of ethylene and propene in the presence of δ-TiCl₃/Al(CH₃)₃ at 22 °C are determined by means of a ¹³C NMR analysis of suitable block copolymers. The numerical values of the rate constants are compared with those previously reported.     

Determination of rate constants of initiation and propagation in the cationic polymerization of α-methylstyrene with CF3SO3H and H2SO4

The polymerization of α-methylstyrene with CF₃SO₃H and H₂SO₄ as initiators was studied at 30°C in dichloroethane by the stopped-flow/rapid-scan spectroscopic technique. The propagating cation shows λ_max at 336–340 nm. The initiation process and the early stage of propagation were analyzed kinetically on the basis of the cation formation and monomer consumption by taking into account the equilibrium monomer concentration. The rate of initiation with CF₃SO₃H was found to be proportional to the concentrations of CF₃SO₃H and monomer, but the initiation with H₂SO₄ is not proportional to the H₂SO₄ concentration. The rate constant of initiation was estimated to be (2 ± 1)·10³ 1.mol^?1.s^?1 with CF₃SO₃H, and similar values were found with H₂SO₄. The rate constant of propagation is 3.10⁴ 1.mol^?1.s^?1 with CF₃SO₃H as initiator and 10⁶ ? 10⁷ 1.mol^?1.s^?1 with H₂SO₄ as initiator. These k_p values are close to that obtained previously in the radiation polymerization. Finally, λ_max values of the propagating cation, obtained by the stopped-flow technique, were collected.     

The polymerization,copolymerization and terpolymerization of 1-isopropylidene-3a.4.7.7a-tetrahydroindene by anionic coordinate,radical and anionic catalysts

By means of vanadium based anionic coordinate catalysts 1-isopropylidene-3a.4.7.7a-tetrahydroindene (I) can be terpolymerized with ethylene and propylene and copolymerized with ethylene. IR, NMR, UV spectroscopic data, and mol. wt. distributions are reported for the polymers. The incorporation of I is predominantly by opening of the cyclohexene double bond. The content of I was generally less than 10 mole-%. Attempts to obtain homopolymers of I and copolymers of propylene and I with this type of catalyst were unsuccessfull. No solid polymer could be produced from I by free radical or anionic catalysts. With AIBN only oligomers were obtained which had cyanoisobutyric groups attached to the conjugated double bond system. K or KNH₂ in ammonia solution react with I in equimolar ratios to give waxy products which do not contain NH₂ groups. With K di-hydrogenated derivatives of I are formed. The results have been interpreted in terms of stabilized radicals and anions derived from I which are unable to propagate.     

Synthesis and ring-opening polymerization of α-chloromethyl-α-methyl-β-propiolactone

α-Chloromethyl-α-methyl-β-propiolactone (CMMPL) was synthesized by dehydrohalogenation of α,α-dichloromethyl-β-propionic acid which was obtained by chlorination of α,α-hydroxymethyl-β-propionic acid (DMPA). Due to high strain of the four-numbered ring, CMMPL can be polymerized by ring-opening with or without an initiator. Both electrophiles like trifluoroacetic acid (TFAA) and nucleophiles like triethylamine (TEA) and pyridine, as well as organometallic compounds such as stannous octoate [Sn(Oct)₂)], aluminium triisopropoxide [Al(OⁱPr)₃] and tetrabutyl orthotitanate [Ti(OC₄H₉)₄], were found to be effective initiators. The polymerization can be conducted by either solution or bulk polymerization. P(CMMPL) is insoluble in almost all organic solvents at room temperature. An endothermic peak (ca. 214 ˜ 250°C) attributed to the melting transition of P(CMMPL) was observed in DSC curves. P(CMMPL) tends to have high crystallinity (40% ˜ 60%) as demonstrated by its X-ray diffraction patterns, and the crystallinity was found to vary with the types of initiator used.     

Ring-opening polymerization of ε-caprolactone in the presence of dicarboxylic acids

The ring-opening polymerization of ε-caprolactone (ε-CL) has been investigated in the presence of succinic acid in nitrogen atmosphere at 225°C. Analysis of the resultant polymers suggests that the poly(ε-caprolactone) (PCL) obtained has two terminal carboxylic groups. VPO, ¹H NMR and titration are used to determine the number-average molecular weight of the PCL obtained at ε-CL to acid molar ratios of 4, 8, 12, 14, 16 and 20, respectively. It is found that the molecular weight of the PCL is not related to the ratio of ε-CL to succinic acid except for low ε-CL concentrations. At a molar ratio of 14, the molecular weight of PCL reaches a maximum at a reaction time of 3 h. Beyond 3 h the ester exchange reaction becomes predominant, and the molecular weight approaches the equilibrium value (M?_e) due to the ratio of ε-CL to succinic acid in the feed.     

Determination of the transfer constant of α-thioglycerol in methyl methacrylate free-radical polymerization

Using the Mayo and the Clay-Gilbert method, the transfer rate coefficient of α-thioglycerol (TG) was determined at 50°C for the polymerization of methyl methacrylate (MMA) in a 3 mol · L^?1 tetrahydrofuran solution using different amounts of 2,2′-azoisobutyronitrile (AIBN) as initiator. The transfer rate coefficient was found to be independent of the initiator concentration and higher by a factor of 1.6 when obtained according to the Clay-Gilbert method compared to the Mayo method.     

Equilibria in the anionic polymerization of methyl methacrylate, 1. Chain-length dependence of the rate and equilibrium constants

The rate constants of polymerization and cyclization and the equilibrium constants of polymerization are calculated from kinetic data of the anionic oligomerization of methyl methacrylate initiated by methyl α-lithioisobutyrate in THF at 25°C, and of the “disproportionation” of living oligomers. The numeric method reported earlier was improved. The rate constants of cyclization decrease with chain-length, due to increasing steric hindrance. The rate constants of polymerization depend on the concentration of active centres, due to the formation of associates. Rate and equilibrium constants of polymerization decrease with chain-length. This is discussed in terms of intramolecular coordination of the counterion with ester groups of the chain.     

ESR determination of rate constants for the radical polymerization of methyl phenethyl itaconate

Phenethyl 2-(methoxycarbonylmethyl)acrylate (methyl penethyl itaconate) ( 1 ) was prepared and its polymerization with dimethyl 2,2′-azoisobutyrate ( 2 ) was investigated kinetically in benzene. The polymerization rate (R_p) was found to be expressed by R_p = k·[ 2 ]^0,5·[ 1 ]^1,8 (at 50°C). Further, a higher dependence of R_p (2nd order) on the concentration of 1 was observed at 61°C. The overall activation energy of the polymerization was calculated to be a low value of 50,3 kJ/mol. The initiator efficiency (f) of 2 was determined to be 0,48 to 0,22 at 50°Cand 0,50 to 0,28 at 61°C. f decreases with increasing monomer concentration due to the high viscosity of 1 . The poly( 1 ) radical is stable enough to be observable by ESR at high temperatures (50–60°C). Rate constants of propagation (k_p) and termination (k_t) were estimated using the poly( 1 ) radical concentration determined by ESR. k_p [6,0 to 121/(mol·s) at 50°Cand 7,1 to 15 1/(mol·s) at 61°C] shows a trend to increase with the concentration of 1 . On the other hand, k_t [2,9·10⁴ to 17·10⁴1/(mol·s) at 50°Cand 6,9·10⁴ to 45·10⁴1/(mol. s) at 61°C] decreases with increasing MPI concentration. This behavior is responsible for the high order with respect to monomer concentration. Copolymerization of 1 (M₁) with styrene (M₂) at 50°Cgave the following results: r₁ = 0,36, r₂ = 0,40, Q₁ = 0,82 and e₁ = + 0,59. Using the above results, the rate constants of the cross-propagations were estimated to be k₁₂ = 22 1/(mol·s) and k₂₁ = 308 1/(mol·s) at 50°C.     

Atom transfer radical polymerization (ATRP) of styrene and methyl methacrylate with α,α‐dichlorotoluene as initiator; a kinetic study

The atom transfer radical polymerization (ATRP) of styrene and methyl methacrylate with α,α‐dichlorotoluene ( DCT ) as initiator results in the respective chlorotelechelic polymers. From a kinetic point of view, however, the polymerization of styrene and methyl methacrylate show a different behavior: for the polymerization of styrene DCT is a bifunctional, for the polymerization of methyl methacrylate it is a monofunctional initiator.     

Capacity flow method for determination of propagation and termination rate constants in radical polymerization

The possibility of determination of the propagation and termination rate constants k_p and k_t, resp., as well as their ratios k_p/k_t and k_p/k in homogeneous radical polymerization is shown using the capacity flow method. A theoretical analysis is carried out and relatively simple equations are introduced. The essential point is that the life time of the growing polymer chain is obtained graphically from the residence time of the reactants in the reactor vessel, which is a given quantity. As an experimental example the polymerization of methyl methacrylate initiated by benzoyl peroxide in benzene is investigated in a flow reactor with perfect mixing at 80°C. It is characteristic that the process can be followed by means usually applied for studying slow reactions. The degree of conversion is measured turbidimetrically and gravimetrically, whereas the initiation rate is analysed iodometrically. Thus, through a numerical linear approximation by the method of least squares k_p/k_t = (2,28±0,45)·10^?5, k_p/k = (1,50±0,22). 10^?1 are found from the experimental data, and hence k^p = (9,95±0,83)·10² l mol^?1 s^?1 and k_t = (4,36±0,49)·10⁷ l mol^?1 s^?1 are obtained.