Polymerization of vinyl monomers initiated by KO2–charge transfer agent systems. II

Vinyl monomers having electron acceptor groups such as nitroethylene, acrylonitrile, and acrolein were polymerized by KO₂–charge transfer agent initiator systems in dimethylsulfoxide (DMSO) at 25°C. The new initiator systems were found to be stable for almost 1 month under nitrogen atmosphere. The initial rate of polymerization was so fast that both conversion and molecular weight of the polymers obtained were high. Especially their molecular weight distribution was observed to be very narrow by means of gel permeation chromatography (GPC). The anion radicals generated by one electron transfer from potassium superoxide (KO₂) to charge transfer agents such as naphthalene, benzoquinone, azobenzene, etc., were suitable as initiator for the anionic polymerization of electron acceptor monomers. Study on block copolymerization of nitroethylene with acrylonitrile or acrolein was also attempted.     

Metal chelates in vinyl polymerization: Kinetics and mechanism of acrylonitrile polymerization initiated by Cu(II) imine complexes

The free radical polymerization of acrylonitrile (AN) initiated by Cu(II) 4-anilino 2-one [Cu(II) ANIPO] Cu(II), 4-p-toluedeno 3-pentene 2-one [Cu(II) TPO], and Cu(II) 4-p-nitroanilino 3-pentene 2-one [Cu(II) NAPO] was studied in benzene at 50 and 60°C and in carbon tetrachloride (CCl₄), dimethyl sulfoxide (DMSO), and methanol (MeOH) at 60°C. Although the polymerization proceeded in a heterogeneous phase, it followed the kinetics of a homogeneous process. The monomer exponents were ≥2 at two different temperatures and in different solvents. The square-root dependence of R_p on initiator concentration and higher monomer exponents accounted for a 1:2 complex formation between the chelate and monomer. The complex formation was shown by ultraviolet (UV) study. The activation energies, kinetics, and chain transfer constants were also evaluated.     

Chain-transfer constant of fluoroalcohols

Chain transfer constants of some fluoroalcohols [HCF₂(CF₂)_n?1CH₂OH, n = 2, 4, 6] in the catalyzed polymerization of vinyl acetate, styrene, acrylonitrile, and methyl methacrylate at 60°C have been evaluated by a method based on degree of polymerization. Since fluoroalcohols are normally nonsolvents for polymers, a homogeneous reaction phase is maintained by carrying out the polymerization in benzene (except in case of acrylonitrile, where no solvent was used). The transfer constants vary, depending on the reactivity as well as the polarity of the radicals, in the following order: vinyl acetate > styrene > methyl methacrylate > acrylonitrile. Of the three fluoroalcohols studied, the transfer constants increase with the increasing value of n. The results have been interpreted in terms of polar structure contribution in the transition state of the transfer reactions.     

Polymerization of diethylene glycol bis(allyl carbonate) by means of di-sec-butyl peroxydicarbonate

The initial stages of the free radical polymerization of diethylene glycol bis(allyl carbonate) at temperatures of 35–65°C have been studied. The polymer is unsaturated and cyclization to give a 16-membered ring occurs only to a small extent. The kinetic order with respect to the initiator, di-sec-butyl peroxydicarbonate, has an average value of 0.79; the order increases slightly with peroxydicarbonate concentration over the range 0.018–0.22M. The molecular weight of the polymer isolated after 3% polymerization is close to 19,000. It shows no significant dependence on initiator concentration or on temperature. The dominant feature of the bulk polymerization, as in free radical polymerization of the other allyl and diallyl monomers, is degradative chain transfer in which the growing polymer radical abstracts a hydrogen atom from a monomer unit to give a relatively unreactive allylic radical. The dependence of rate on initiator concentration is rationalized if some of these allylic radicals are able to reinitiate polymerization. The transfer constant to monomer is 0.014 at 50°C, assuming that the main termination step involves mutual termination of allylic radicals. Carbon tetrachloride is an active transfer agent with a transfer constant of 0.20 ± 0.04 at 50°C. Toluene, which is less active, has a transfer constant of 0.0064 at 50°C and also retards the polymerization. Some kinetic studies have been made with other initiators, including di-2-methyl-pentanoyl peroxide which initiates polymerization at temperatures as low as 13°C.     

Polymerization of vinyl monomers with salts of bronsted acids

The polymerization of vinyl monomers (N-phenylmaleimide, acrylamide, acrylonitrile, methyl vinyl ketone, methyl methacrylate, vinyl chloride, and styrene) with sodium salts of Brønsted acids (sodium cyanide, sodium nitrite, sodium hydroxide, etc.) were investigated at 0°C in dimethylformamide. N-Phenylmaleimide, acrylonitrile, and methyl vinyl ketone were found to undergo polymerization with sodium cyanide, however the other monomers were not polymerized with this salt. In the polymerizations of acrylonitrile and N-phenylmaleimide with sodium cyanide, the rates of the polymerizations were found to be proportinal to the initiator concentration and to the square of the monomer concentration. The activation energy of acrylonitrile polymerization was 3.7 kcal/mole, and that of N-phenylmaleimide ws 3.0 kcal/mole. The results of the copolymerization of acrylonitrile with methyl methacrylate at 0°C in dimethyl-formamide with sodium cyanide confirm that these polymerizations proceeded by an anionic mechanism initiated by the Michael addition reaction of the monomers with the salts. In these polymerizations, the monomer reactivity increased with increase in the e values. The initiation ability of sodium salts increased with increasing pK_a of the conjugate acids and with decreasing electronegativity of metal ion in the series of lithium, sodium, and potassium cyanide. The polymerizations took place only in aprotic polar solvents, and did not occur in weak polar solvents and in protonic solvents.     

Controlled radical copolymerization of β‐pinene and acrylonitrile

The feasibility of the radical copolymerization of β‐pinene and acrylonitrile was clarified for the first time. The monomer reactivity ratios evaluated by the Fineman–Ross method were r_β‐pinene = 0 and r_{acrylonitrile} = 0.66 in dichloroethane at 60 °C with AIBN, which indicated that the copolymerization was a simple alternating copolymerization. The addition of the Lewis acid Et₂AlCl increased the copolymerization rate and enhanced the incorporation of β‐pinene. The first example for the synthesis of an almost perfectly alternating copolymer of β‐pinene and acrylonitrile was achieved in the presence of Et₂AlCl. Furthermore, the possible controlled copolymerization of β‐pinene and acrylonitrile was then attempted via the reversible addition–fragmentation transfer (RAFT) technique. At a low β‐pinene/acrylonitrile feed ratio of 10/90 or 25/75, the copolymerization with 2‐cyanopropyl‐2‐yl dithiobenzoate as the transfer agent displayed the typical features of living polymerization. However, the living character could be observed only within certain monomer conversions. At higher monomer conversions, the copolymerizations deviated from the living behavior, probably because of the competitive degradative chain transfer of β‐pinene. The β‐pinene/acrylonitrile copolymers with a high alternation degree and controlled molecular weight were also obtained by the combination of the RAFT agent cumyl dithiobenzoate and Lewis acid Et₂AlCl. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2376–2387, 2006     

Photopolymerization of acrylonitrile in the presence of substituted triphenyl phosphites

It was found that acrylonitrile was polymerized at 30°C by ultraviolet irradiation in the presence of triphenyl phosphite and its derivatives, namely m-CH₃, p-C₂H₅, and p-CH₃ substituted triphenyl phosphites under conditions where acrylonitrile alone did not polymerize and phosphites did not undergo photolysis. The rate of polymerization in the presence of triphenyl phosphite and tri-p-tolyl phosphite was found to be proportional to the monomer concentration, the phosphite concentration, and the light intensity. From these results, it was thought that a donor–acceptor complex formed between phosphite and acrylonitrile which absorbed light and initiated the radical polymerization. In the photopolymerization of acrylonitrile with substituted triphenyl phosphites, the rate of polymerization increased with an increase in electron-donating ability of substituent. From the plot obtained by use of Hammett's equation (log R_p/R_p0 = ρσ), the ρ value was found to be ?1.0.     

Polymerization of acrylonitrile: Kinetics of the reaction initiated by the Fe2+/BrO3− redox system

The aqueous polymerization of acrylonitrile initiated by the bromate—ferrous redox system in aqueous sulfuric acid was studied under nitrogen atmosphere. The rate of polymerization increased with increasing concentration of ferrous in the range of 0.25-1 × 10^?2M. The percentage of conversion increased with increasing concentration of the catalyst, but beyond 2.5 × 10^?3M there was a decreasing trend in the rate of polymerization. The rate varied linearly with [monomer]. The initial rate of polymerization as well as the maximum conversion increased within the range of 1–2.5 × 10^?3M KBrO₃, but beyond 2.5 × 10^?3M the rate of polymerization decreased. The initial rate and limiting conversion increased with increasing polymerization temperature in the range 30–40°C; beyond 40°C they decreased. The effect of certain neutral salts, water-miscible solvents, complexing agents, and copper sulfate concentration on the rate of polymerization was investigated.     

Vinyl Polymerization Initiated by Ceric Ion–Ethyl Cellosolve Redox System in Aqueous Nitric Acid

Abstract

Polymerizations of methyl methacrylate (MMA) and acrylonitrile (AN) were carried out in aqueous nitric acid at 30°C with the redox initiator system ammonium ceric nitrate-ethyl cellosolve (EC). A short induction period was observed as well as the attainment of a limiting conversion for polymerization reactions. The consumption of ceric ion was first order with respect to Ce(IV) concentration in the concentration range (0.2–0.4) × 10^?2 M, and the points at higher and lower concentrations show deviations from a linear fit. The plots of the inverse of pseudo-first-order rate constant for ceric ion consumption, (k ¹)^?1 vs [EC]^?1, gave straight lines for both the monomer systems with nonzero intercepts supporting complex formation between Ce(IV) and EC. The rate of polymerization increases regularly with [Ce(IV)] up to 0.003 M, yielding an order of 0.41, then falls to 0.0055 M and again shows a rise at 0.00645 M for MMA polymerization. For AN polymerization, R _p shows a steep rise with [Ce(IV)] up to 0.001 M, and beyond this concentration R _p shows a regular increase with [Ce(IV)], yielding an order of 0.48. In the presence of constant [NO^? ₃], MMA and AN polymerizations yield orders of 0.36 and 0.58 for [Ce(IV)] variation, respectively. The rates of polymerization increased with an increase in EC and monomer concentrations: only at a higher concentration of EC (0.5 M) was a steep fall in R _p observed for both monomer systems. The orders with respect to EC and monomer for MMA polymerization were 0.19 and 1.6, respectively. The orders with respect to EC and monomer for AN polymerization were 0.2 and 1.5, respectively. A kinetic scheme involving oxidation of EC by Ce(IV) via complex formation, whose decomposition gives rise to a primary radical, initiation, propagation, and termination of the polymeric radicals by biomolecular interaction is proposed. An oxidative termination of primary radicals by Ce(IV) is also included.     

Effect of amines on the ceric ion-initiated polymerization of vinyl monomers. II. Polymerization of acrylonitrile by ceric ion in presence of various substituted amines

The effect of various substituted amines on the polymerization of acrylonitrile initiated by ceric ammonium sulfate has been studied in aqueous solution at 30°C. It was found that the secondary and tertiary amines considerably increased the rate of polymerization, whereas the primary amines seemed to have no effect at all. From the kinetic studies it was found that the overall polymerization rate R_p is independent of ceric ion concentration and can be expressed by the equation: R_p = k₁ [amine] [monomer] + k₂[monomer]², where k₁ and k₂ are constants (involving different rate constants). The accelerating effect of the amines was attributed to a redox reaction between the ceric ion and the amine involving a single electron transfer, the relative activity of the different amines being thus dependent on the relative electron-donating tendency of the substituents present in the amine. The mechanism of the polymerization is discussed on the basis of these results, and various kinetic constants are evaluated.     

Novel solvent effects in the photopolymerization of methyl methacrylate by use of quinoline–bromine charge-transfer complex as photoinitiator

Photopolymerization of MMA was carried out at 40°C in diluted systems by use of quinolinebromine (Q–Br₂) charge-transfer complex as the initiator and chloroform, carbon tetrachloride, chlorobenzene, dioxane, THF, acetone, benzene, toluene, quinoline, and pyridine as solvents. The results showed variable monomer exponents ranging from 1 to 3. For chloroform, carbon tetrachloride, and chlorobenzene, the monomer exponent observed was unity; for other solvents used, the value of the same exponent was much higher (between 2 and 3). Initiation of polymerization is considered to take place through radicals generated in the polymerization systems by the photodecomposition of (Q–Br₂)–monomer complex (C) formed instantaneously in situ on addition of the Q–Br₂ complex in monomer. The kinetic feature of high monomer exponent is considered to be due to higher order of stabilization of the initiating complex (C) in presence of the respective solvents. In the presence of the retarding solvents, very low or zero initiator exponents were also observed, depending on the nature and concentration of the solvents used. The deviation from the square-root dependence of rate on initiator concentration becomes higher at high solvent and initiator concentrations in general. This novel deviation is explained on the basis of initiator termination, probably via degradative chain transfer involving the solvent-modified initiating complexes and the propagating radicals.     

Kinetic and ESR studies on the radical polymerization of Di-n-butyl itaconate in benzene

The polymerization of di-n-butyl itaconate (DBI) intiated with AIBN was kinetically investigated in benezene. The polymerization rate (R_p) was expressed by: R_p = k[AIBN]^0.5[DBI]^1.7. The polymerization showed a considerably low overall activation energy of 15.3 kcal/mol. The initiator efficiency of AIBN in this system decreased with increasing DBI concentration, ranging from 0.34 to 0.55°C, which is ascribable to viscosity effect due to the monomer. From an ESR study, the polymerization system was found to involve two kinds of persistent radicals, namely, primary propagating ( III ) and propagating ( I ) radicals. The relative concentration of III to I increased with decreasing monomer concentration. Azo-nitrile initiators such as AVN and ACN similarly produced two persistent radicals, while MAIB, DBPO, and PBO yielded only propagating radical I as persistent. The MAIB-initiated polymerization of DBI was also performed in benzene. Similar kinetic features were observed, that is, a higher dependence of R_p on the DBI concentration and a low overall activation energy (14.4 kcal/mol). The following rate equation was obtained at 50°C:R_p = k[MAIB]^0.5[DBI]^1.6. The initiator efficiency of MAIB decreased with increasing DBI concentration, ranging from 0.32 to 0.53 at 50°C. The concentration of propagating radical I was determined by ESR at 50 and 61°C, from which k_p and k_t were estimated. The k_p value increased with increasing monomer concentration, while the k_t one decreased with the DBI concentration. These values are much lower compared with those of MMA.     

Polymerization of acrylonitrile with VCl4–Al(C2H5)3 catalyst system in presence of acetonitrile

The polymerization of acrylonitrile with the homogeneous catalyst system of VCl₄–AlEt₃ in acetonitrile at 40°C has been investigated. The rate of polymerization is found to be first-order with respect to monomer and inversely proportional to the catalyst concentration. The overall activation energy for this catalyst system is 10.97 kcal/mole. The inverse proportionality of rate of polymerization with the catalyst concentration is attributed to the permanent complex formation between the catalyst complex and acrylonitrile, and a reaction scheme is proposed.     

Polymerization of acrylonitrile initiated by ceric ion–citric acid redox system

Heterogeneous polymerization of acrylonitrile initiated by ceric ammonium sulfate–citric acid (C.A.) redox system is reported at 35 ± 0.2°C under nitrogen atmosphere. The rate of monomer disappearance is found to be proportional to [C.A.]⁰, [Ce⁴⁺]^0.63, and [Monomer]^1.59. The rate of ceric ion disappearance is directly proportional to ceric ion concentration but independent of monomer concentration. The initial rate was independent of [H₂SO₄]. The molecular weight of polyacrylonitrile increases with increasing monomer concentration and decreasing ceric ion concentration. Activation energy was found to be 27.9 kJ/mol.     

Kinetics of copolymerization—I. Kinetic investigation of the polymerization of acrylonitrile in homogeneous phase

A detailed study was made of the kinetics of initiated homopolymerization of acrylonitrile in dimethylformamide and dimethylsulphoxide at 40–60°. The rate of polymerization was found to be proportional to the (initiator concentration)^1/2. The rate of initiation of polymerization was determined by the inhibition method, using three stable free radicals. Trends in the average rate of polymerization were also studied for various initial monomer and solvent concentrations. The overall rate constant (K) was strongly dependent on monomer concentration decreasing with decrease of monomer concentration. It has been shown that the hot radical theory describes accurately, without physical contradiction, the solvent dependence of rate constants of polymerization systems.     

Radical polymerization and copolymerization of methyl α-(2-carbomethoxyethyl)acrylate,a dimer of methyl acrylate,as a polymerizable α-substituted acrylate

Polymerization and copolymerization of methyl α-(2-carbomethoxyethyl)acrylate (MMEA), which is known as a dimer of methyl acrylate, were studied in relation to steric hindrance-assisted polymerization. The propagating polymer radical from MMEA was detected as a five-line spectrum and quantified by ESR spectroscopy during the bulk polymerization at 40–80°C. The absolute rate constants of propagation and termination (κ_p and κ_t) for MMEA at 60°C (κ_p = 19 L/mol s and κ_t = 5.1 × 10⁵ L/mol s) were evaluated using the concentration of the propagating radical at the steady state. The balance of the propagation and termination rates allows polymer formation from MMEA. The polymerization rate of MMEA at 60°C was less than that of MMA by a factor of about 4 at a constant monomer concentration. Although no influence of ceiling temperature was observed at a temperature ranging from 40 to 70°C, addition-fragmentation in competition with propagation reduced the molecular weight of the polymer. The content of the unsaturated end group was estimated to be 0.1% at 60°C to the total amount of the monomer units consisting of the main chain. MMEA exhibited reactivities almost similar to those of MMA toward polymer radicals. It is concluded that MMEA is one of the polymerizable acrylates bearing a substituted alkyl group as an α-substituent. Characterization of poly(MMEA) was also carried out. © 1996 John Wiley & Sons, Inc.     

Radical polymerization of vinyl thiocyanatoacetate: Participation of group‐transfer mechanism

Vinyl thiocyanatoacetate (VTCA) was synthesized, and its radical polymerization behavior was studied in acetone with dimethyl 2,2′‐azobisisobutyrate (MAIB) as an initiator. The initial polymerization rate (R_p) at 60 °C was expressed by R_p = k[MAIB]^0.6±0.1 [VTCA]^1.0±0.1 where k is a rate constant. The overall activation energy of the polymerization was 112 kJ/mol. The number‐average molecular weights of the resulting poly (VTCA)s (1.4–1.6 × 10⁴) were almost independent of the concentrations of the initiator and monomer, indicating chain transfer to the monomer. The chain‐transfer constant to the monomer was estimated to be 9.6 × 10^?3 at 60 °C. According to the ¹H and ¹³C NMR spectra of poly (VTCA), the radical polymerization of VTCA proceeded through normal vinyl addition and intramolecular transfer of the cyano group. The cyano group transfer became progressively more important with decreasing monomer concentration. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 573–582, 2002; DOI 10.1002/pola.10137     

Chain transfer for vinyl monomers polymerized in N-allylstearamide

Apparent transfer constants have been determined for styrene, methyl methacrylate vinyl acetate, and diethyl maleate polymerized in N-allylstearamide at 90°C. Regression coefficients for transfer were: methyl methacrylate, 0.301 × 10^?3; styrene, with no added initiator, 0.582 × 10^?3; styrene, initiated with benzoyl peroxide, 0.830 × 10^?3; vinyl acetate, 62.01 × 10^?3; and diethyl maleate, 2.24 × 10^?3. Rates of polymerization were retarded for both styrene and methyl methacrylate. Vinyl monomer and comonomer disappearance followed an increasing exponential dependence on both initiator and monomer concentration. Although degradative chain transfer probably caused most of the retardation, the cross-termination effect was not eliminated as a contribution factor. Rates for the vinyl acetate copolymerization were somewhat retarded, even though initiator consumption was large because of induced decomposition. The kinetic and transfer data indicated that the reactive monomers added radicals readily, but that rates were lowered by degradative chain transfer. Growing chains were terminated at only moderate rates of transfer. Unreactive monomers added radicals less easily, producing reactive radicals, which transferred rapidly, so that molecular weights were lowered precipitously. Although induced initiator decomposition occurred, rates were still retarded by degradative chain transfer. A simple empirical relation was found between the reciprocal number-average degree of polymerization, 1/X?_n1 and the mole fraction of allylic comonomer entering the copolymer F₂, which permitted estimation of the molecular weight of copolymers of vinyl monomers with allylic comonomers. This equation should be applicable when monomer transfer constants for each homopolymer are known and when osmometric molecular weights of one or two copolymers of low allylic content have been determined.     

Solid-State Polymerization in Binary Component Systems at Low Temperature

Abstract

Radiation-induced polymerization in binary component systems of acrylonitrile-methacrylonitrile and acrylonitrile-vinyl acetate was studied at ?196°C. A mixture of two-component homopolymers was obtained from the acrylonitrile-methacrylonitrile system, which forms a eutectic mixture. When the mixture of acrylonitrile with vinyl acetate is cooled quickly from room temperature, a glassy state can be obtained. It was found that the copolymerization is possible in the glassy state at ?196°C, and the monomer reactivity ratios were determined as r ₁ = 6.0 and r ₂ = 0.2 (M ₁ = acrylonitrile), which coincides with the reported values on the radical copolymerization at room temperature.     

Aminobutadienes. VI. Polymerization and Copolymerization of 2-Phthalimido-1,3-butadiene

2-Phthalimido-1,3-butadiene (2-PB) was polymerized either radically or thermally in bulk and in solution. While the polymer obtained by solution polymerization was soluble in some solvents such as halogenated hydrocarbons, dioxane, and dimethylformamide and had a softening point in the range of 160–170°C., that obtained by polymerization in bulk was insoluble in any solvent and only swollen on being immersed in such solvents as above. The reduced viscosity of the soluble polymer obtained by solution polymerization was approximately 1.0, and this value remained almost unchanged with varying polymerization time. Likewise the cationic polymerization in acetylene tetrachloride or in chloroform at 20°C. with the use of cationic catalysts such as boron trifluoride and stannic chloride was attempted, but no formation of polymer was observed. This monomer preferentially reacted with acrylonitrile, methyl methacrylate, styrene, and N-vinylphthalimide to form the respective copolymers; it reacted somewhat less readily with vinyl acetate. The monomer reactivity ratios in the copolymerization with styrene were calculated by the Fineman and Ross method and found to be r₁ (2-PB) = 5.2 and r₂ (styrene) = 0.11, respectively, from which the Q, e parameters were successively evaluated to be Q = 5.0 and e = ?0.05. The fact that e value is close to zero, easily explains why this monomer can copolymerize well both with acrylonitrile, which has a highly positive value of e (1.2) and with styrene, for which e is considerably negative (-0.8).