Effect of thiourea on the radical polymerization of vinyl monomers. Part II. Effect of diphenyl thiourea on the polymerization of methyl methacrylate with benzoyl peroxide as initiator

The polymerization of methyl methacrylate (MMA) initiated by benzoyl peroxide (BPO) in the presence of diphenyl thiourea (DPTU) has been studied. It was found that the BPO–DPTU catalyst system was not an effective accelerating system but showed a relatively strong retarding effect. With DPTU derivatives, the polymerization rate was found to decrease with the increase in the electron-attracting forces of substituents attached to the phenyl groups of DPTU. In the polymerization of MMA initiated by AIBN, the addition of DPTU to the reaction systems affected neither the polymerization rate nor the degree of polymerization. From this fact, it might be concluded that DPTU itself serves as a radical scavenger. It seems most probable from the results of kinetic studies, iodometric titration, and from the effect of an oxidation product of DPTU (diphenyl formamidine disulfide) that the retardation effect observed is attributable to the action of the disulfide (DPFDS). By extending the Alfrey-Price scheme for the copolymerization reactions to the chain-transfer reactions, the Q and e values of DPFDS were determined. The apparent chain-transfer constants for DPTU and its derivatives were calculated by means of rate measurements and were correlated with substituent constants. The mechanism of the polymerization is discussed on the basis of these results.     

Kinetics of styrene homogeneous polymerization to atactic polypropylene

The rate of polymerization of styrene initiated by hydroperoxidized atactic polypropylene in a homogeneous toluene solution has been measured at 60 and 70°C. The reaction is first-order with respect to styrene concentration and independent of the polymeric hydroperoxide concentration above 2 × 10^?5N hydroperoxide. The individual rate constants, length and frequency of the grafted polystyrene chains along the polypropylene backbone have been calculated and their significance discussed. The initiation rate constant compares closely with values reported for the analogous tert-butyl hydroperoxide-initiated polymerization. The rate constant for the chain transfer termination elementary step at 70°C., however, is 18 times the value reported for the tert-butyl hydroperoxide-initiated polymerization of styrene. This high constant accounts for the relatively low rates of polymerization observed and high termination rates. Chain deactivation is presumably accelerated by increased collisions between growing styrene chains and inactive propylene hydroperoxide and polystyrene molecules. Distribution of polystyrene grafts on polypropylene is estimated from knowledge of effects of styrene concentration, polymeric hydroperoxide concentration, and temperature upon the rate of polymerization.     

Catalytic action of metallic salts in autoxidation and polymerization. VIII. Polymerization of methyl methacrylate by various metal acetylacetonate–cyclic ether hydroperoxides

Polymerization of methyl methacrylate by cyclic ether hydroperoxide–metal acetylacetonate systems for a number of different metals was carried out to compare with the tert-butyl hydroperoxide–metal acetylacetonate initiating systems. The rate of polymerization of methyl methacrylate with cyclic ether hydroperoxides as initiating systems was much higher than that with tert-butyl hydroperoxide. In cyclic ether hydroperoxide initiating systems, V(III), Co(II,III), Fe(III), Cu(II), and Mn(II) promoted the polymerization rate markedly, and Zn(II), Ni(II), Al(III), and Mg(II) had little or no effect; in the tert-butyl hydroperoxide initiating system only V(III), Co(II), and Mn(II) enhanced polymerization rate, and most of other metals showed little or no effect. Furthermore, noticeable differences in color of solution and appearance during polymerization, and in relation between conversion and the degree of polymerization were observed. The effect of metal acetylacetonates on hydroperoxide initiators in polymerization of methyl methacrylate was also compared with that on the decomposition of hydroperoxides.     

STUDIES ON RADICAL POLYMERIZATION OF METHYL METHACRYLATE INITIATED WITH ORGANIC PEROXIDE-AMINE SYSTEMS

Radical polymerization of methyl mcthacrylate (MMA) initiated with various diacyl peroxideamine systems was studied. Benzoyl peroxide (BPO) and lauroyl peroxide (LPO) were used as diacyl peroxide component, N,N-dimethyl aniline (DMA) and its para substituted derivatives, i.e., N,N-dimethyl-p-toluidine (DMT), p-hydroxymethyl-N,N-dimethyl aniline (HDMA), p-nitro-N,N-dimethyl aniline (NDMA) and p-dimethylamino benzaldehyde (DMAB) were used as amine components. It was found that the peroxide-DMT systems give higher rates of bulk polymerization R_p of MMA than the organic hydroperoxide-DMT systems with the following descending order BPO-DMT>LPO-DMT>CHP (cumene hydroperoxide)-DMT>TBH (tert-butyl hydroperoxide)-DMT. The aromatic tertiary amines possess obvious structural effect on the R_p values in the diacyl peroxideamine system. The overall activation energy of MMA polymerization was determined and thekinetics of polymerization of MMA initiated with BPO-DMT system was investigated.     

Effect of alcohols on the gamma-radiation-induced polymerization of ethylene

Gamma-radiation-induced polymerization of ethylene in alcohols such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, and n-pentyl alcohols was carried out under a pressure of 400 kg./cm.²at 30°C. at a dose rate of 1.4 × 10⁵ rad/hr. in a batch reactor of 100 ml. capacity. The yield and molecular weight of polymer formed in the alcohols (except tert-butyl alcohol) were much lower than those of the bulk polymerization under the same conditions, whereas the addition of tert-butyl alcohol increased the yield and reduced the molecular weight. From the infrared spectra of the polymers and those of the bromination products it was concluded that only primary OH exists in the polymer formed in methyl alcohol and that both primary and secondary OH are in the polymer formed in other primary alcohols. Both secondary and tertiary OH were observed in the polymer when the secondary alcohols were used, and only tertiary OH in the case of tert-butyl alcohol. These polymers were found to contain small amounts of vinylidene unsaturation and methyl group. On the basis of these results the roles of the alcohols in the polymerization are discussed.     

Catalytic action of metallic salts in autoxidation and polymerization. IV. Polymerization of methyl methacrylate by cobalt(II) or (III) acetylacetonate–tert-butyl hydroperoxide or dioxane hydroperoxide

Polymerization of methyl methacrylate was carried out by four initiating systems, namely, cobalt(II) or (III) acetylacetonate–tert-butyl hydroperoxide (t-Bu HPO) or dioxane hydroperoxide (DOX HPO). Dioxane hydroperoxide systems were much more effective for the polymerization of methyl methacrylate than tert-butyl hydroperoxide systems, and cobaltous acetylacetonate was more effective than cobaltic acetylacetonate in both hydroperoxides. The initiating activity order and activation energy for the polymerization were as follows: Co(acac)₂–DOX HPO (E_a-9.3 kcal/mole) > Co (acac)₃–DOX HPO (E_a = 12.4 kcal/mole) > Co(acac)₂–t-Bu HPO (E_a = 15.1 kcal/mole) > Co(acac)₃–t-Bu HPO (E_a-18.5 kcal/mole). The effects of conversion and hydroperoxide concentration on the degree of polymerization were also examined. The kinetic data on the decomposition of hydroperoxides catalyzed by cobalt salts gave a little information for the interpretation of polymerization process.     

Kinetic and ESR studies on radical polymerization of methyl methacrylate in the presence of fullerene

The effect of fullerene (C₆₀) on the radical polymerization of methyl methacrylate (MMA) in benzene was studied kinetically and by means of ESR, where dimethyl 2,2′-azobis(isobutyrate) (MAIB) was used as initiator. The polymerization rate (R_p) and the molecular weight of resulting poly(MMA) decreased with increasing C₆₀ concentration ((0–2.11) × 10⁻⁴ mol/L). The molecular weight of polymer tended to increase with time at higher C₆₀ concentrations. R_p at 50°C in the presence of C₆₀ (7.0 × 10⁻⁵ mol/L) was expressed by R_p = k[MAIB]^0.5[MMA]^1.25. The overall activation energy of polymerization at 7.0 × 10⁻⁵ mol/L of C₆₀ concentration was calculated to be 23.2 kcal/mol. Persistent fullerene radicals were observed by ESR in the polymerization system. The concentration of fullerene radicals was found to increase linearly with time and then be saturated. The rate of fullerene radical formation increased with MAIB concentration. Thermal polymerization of styrene (St) in the presence of resulting poly(MMA) seemed to yield a starlike copolymer carrying poly(MMA) and poly(St) arms. The results (r₁ = 0.53, r₂ = 0.56) of copolymerization of MMA and St with MAIB at 60°C in the presence of C₆₀ (7.15 × 10⁻⁵ mol/L) were similar to those (r₁ = 0.46, r₂ = 0.52) in the absence of C₆₀. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2905–2912, 1998     

Role of N,N-dimethyl-para-toluidine and saccharin in the radical polymerization of methyl methacrylate initiated by a redox system. I. Cumene hydroperoxide/copper saccharinate

Kinetics of methyl methacrylate polymerization initiated by a redox system [cumene hydroperoxide (CHP)/copper saccharinate] were studied in bulk at 20°C in the presence of accelerators such as N,N-dimethyl-p-toluidine (DMPT) and o-benzoic sulphimide (saccharin). Assuming a steady-state concentration of propagating radicals, the polymerization rate depends on the square root of the initiation rate and the kinetic orders with respect to each compound in the initiation step may be deduced. Initiation is first-order in CHP, copper saccharinate, and saccharin and second-order in DMPT. A reaction scheme consistent with these orders is proposed. The main features are the following: (1) CHP reduces rapidly Cu(II) to Cu(I); (2) a small fraction of Cu(I) is complexed with DMPT; (3) the complexed ions (Cu⁺, DMPT₂) are strong reductants with respect to CHP whereas uncomplexed Cu⁺ are almost inactive; (4) the decomposition of CHP is strongly catalyzed by saccharin (protonated CHP is 13000 times more reactive than free CHP). Thus both accelerators are necessary to get high polymerization rates. © 1994 John Wiley & Sons, Inc.     

Effect of triphenyl phosphite on the radical polymerization of styrene and methyl methacrylate

The effects of triphenyl phosphite (TPP) on the radical polymerization of styrene (St) and methyl methacrylate (MMA) initiated with α,α,-azobisisobutyronitrile (AIBN) was investigated at 50°C. The rate of polymerization of St and MMA at a constant concentration of TPP was found to be proportional to the monomer concentration and the square root of the initiator concentration. The rate of polymerization and the degree of polymerization of both St and MMA increased with increasing TPP concentration. The accelerating effect was shown to be due to the decrease of the termination rate constant k_t with an increase in the viscosity of the polymerization systems. The chain transfer constant C_tr of TPP in St and MMA systems was determined from the degree of polymerization system. The C_tr of TPP was almost zero in the St system and 6.5 × 10^?5 in the MMA system.     

Radiation-induced heterogeneous polymerization of ethylene in the presence of ethyl alcohol

The radiation-induced heterogeneous polymerization of ethylene in ethyl alcohol was carried out in a reactor with a capacity of 100 ml under the following reaction conditions: temperature, 24 ± 3°C; pressure, 200–400 kg/cm²; amount of ethyl alcohol, 30–70 ml; dose rate, 3.7 × 10⁴?1.05 × 10⁵ rad hr. The effects of amount of ethyl alcohol, pressure, and dose rate on the rate of polymerization at the steady state, the amount of polymerized monomer, the molecular weight of polymer, and the number of polymer chains were studied compared with the results obtained in the polymerization in tert-butyl alcohol. It was found that there is an acceleration period in the early stage of reaction followed by a steady state. The rate of polymerization was maximum when about 50 ml of ethyl alcohol was used. The molecular weight of polymer increased with a decrease in the amount of ethyl alcohol. The dependences of pressure (p) and dose rate (I) on the rate of polymerization at steady state (R_s) and the molecular weight of polymer (M?_n) were expressed as follows; R_s ∝ p^0.74, M?_n ∝ p^0.3?0.4, R_s ∝ I^0.9 and M?_n ∝ I^{?0.1 ?0.0}. The results were analyzed by a kinetic treatment based on a reaction mechanism containing both first-and second-order terminations. The rate constant of first-order termination by radical occlusion was considerably larger than that in the polymerization in tert-butyl alcohol, because the affinity of ethyl alcohol for polyethylene is smaller than that of tert-butyl alcohol. It was found that chain transfer to ethyl alcohol takes place easily and the G value of ethyl alcohol for initiation is larger than 1.5.     

Vinyl polymerization with Fe(III)–thiourea as initiator system. Part II. Kinetics: Predominant primary radical termination

The rate of polymerization R_p of methyl methacrylate initiated by Fe(CIO₄)₃ and thiourea (TU) in tert-butyl alcohol is indepenent of [Fe(III)] and [TU] in the concentration range studied. In contrast to R_p, the degree of polymerization DP changes markedly with the change in the initiator concentration. DP is overwhelmingly lower than is expected in a standard radical polymerization at the same R_p. Further, R_p is proportional to the square of the monomer concentration. Initiation efficiency is less than one. Independent experiments proved that in the azobisisobutyronitrile-initiated polymerization the R_p and DP are negligibly affected by [Fe(CIO₄)₃] or [TU], though high [TU] brings about high induction periods. The results of Fe(III)-TU-initiated polymerization have been interpreted in terms of the predominant termination of polymer radicals by primary 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.     

Gel permeation chromatographic determination of activation rate constants in nitroxide-controlled free radical polymerization, 1. Direct analysis by peak resolution

The dissociation rate constant k_d related to the homolytic cleavage of the C ON bond formed between a polystyrene (PS) and 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) is determined by adopting the gel permeation chromatography peak-resolution method to the styrene polymerization with a PS-TEMPO adduct as a probe and the radical initiator tert-butyl hydroperoxide. The result was given by the Arrhenius equation, k_d = A exp(−E/(RT)) with A = 3.0 × 10¹³ s⁻¹ and E = 124 kJ · mol⁻¹.     

Vinyl polymerization. 364. Polymerization of methyl methacrylate initiated with benzaldehyde

Benzaldehyde (PhCHO) is found to be able to initiate the radical polymerization of methyl methacrylate (MMA). The rate of polymerization is expressed by the following equation: R_p = const[PhCHO]^0.5[MMA]^1.5. The overall activation energy is estimated to be 56.3 kJ mole^?1. The mechanism of polymerization is discussed.     

Hydroperoxide-initiated copolymerization of sulfur dioxide and cyclohexene. I. Characterization of charge-transfer complex and initiation

The copolymerization of cyclohexene and sulfur dioxide to form an alternating copolymer was initiated by tert-butyl hydroperoxide. The enthalpies and entropies of formation of the cyclohexene-sulfur dioxide charge-transfer complex, which is present during the copolymerization, were determined in two solvents by means of ultraviolet spectroscopy. The reduction of ultraviolet absorption during copolymerization afforded a convenient means of investigating reaction kinetics. No evidence of the direct involvement of the complex in polymerization initiation was found. The observation that the use of unpurified cyclohexene led to spontaneous initiation appears to point to adventitiously formed hydroperoxide rather than the charge-transfer complex as providing initiating radicals which are produced by the redox reaction of the hydroperoxide with sulfur dioxide. A competing heterolytic scission reaction was found to result in the formation of tert-butyl peroxide and sulfuric acid. This reaction caused the polymerization reaction to stop after a short period of time due to a time-dependent decrease in initiator concentration.     

Effect of pressure on the radiation-induced polymerization of ethylene in tert-butyl alcohol

The effects of pressure of the radiation-induced polymerization of ethylene in tert-butyl alcohol were studied. The reaction was carried out by use of a reactor with a capacity of 100 ml under the following conditions; pressure, 60–400 kg/cm²; temperature, 24 ± 3°C; dose rate, 2.0 × 10⁴?1.6 × 10⁵ rad/hr; amount of medium (tert-butyl alcohol containing 5 vol-% water), 70 ml. The results of polymerization were analyzed by a kinetical treatment based on a reaction mechanism with both first- and second-order terminations for the concentration of propagating, radical. On the basis of the kinetical treatment the rate constants of each elementary reaction at several pressures were determined, and the activation volumes of elementary reactions were obtained and are discussed in connection with the reaction mechanism. Consequently, the rate constants of propagation, first-order termination, and second-order termination at pressure p and at 24°C were expressed by,      

Kinetics of the gamma-radiation-induced polymerization of ethylene in tert-butyl alcohol

The gamma-radiation-induced polymerization of ethylene in the presence of 13–30 ml of tert-butyl alcohol was carried out under a pressure of 120–400 kg/cm² at a dose rate of 1 × 10³ to 2.5 × 10⁴ rad/hr at 30°C with a 100 ml reactor. The polymerization rate and the molecular weight of the polymer increased with reaction time and pressure and decreased with amount of tert-butyl alcohol. The polymer yield increased almost proportionally with the dose rate, while the molecular weight was almost independent of it. These results were graphically evaluated, and the rate constants of initiation, propagation, and termination for various conditions were determined. No transfer was observed. On the basis of these results the role of tert-butyl alcohol in the polymerization is discussed.     

Role of chain transfer in heterogeneous polymerization of ethylene

The role of chain transfer was studied for the radiation-induced polymerization of ethylene in precipitating media, namely n-butyl alcohol, tert-butyl alcohol and their mixtures. The affinities of those solvents for polyethylene are similar, but the chain-transfer coefficient of n-butyl alcohol is larger than that of tert-butyl alcohol. The polymerizations were carried out in a reactor of 100 ml under a pressure of 300 kg/cm², at 60°C, dose rate of 3.07 × 10⁴–1.75 × 10⁵ rad/hr in the presence of 50 ml of solvents. The polymerization in tert-butyl alcohol shows the kinetic behavior characteristic of a heterogeneous polymerization, such as rate acceleration, high dose rate dependence of polymerization rate, and low dose rate dependence of polymer molecular weight, whereas the polymerization in n-butyl alcohol does not exhibit such behavior and gives polymer having a molecular weight much lower than that of polymer obtained in tert-butyl alcohol. The polymer formed in tert-butyl alcohol exhibits a bimodal molecular weight distribution measured by gel permeation chromatography. In mixed tert-butyl alcohol and n-butyl alcohol solvent, with increasing fraction of n-butyl alcohol, the two peaks not only shift to lower molecular weight but the higher molecular weight peak becomes relatively small. Eventually, the polymer formed in n-butyl alcohol exhibits a unimodal distribution. Those results are well explained on the basis of the proposed scheme for heterogeneous polymerization.     

Kinetics of polymerization of N-tert-butylacrylamide. Part II

The effect of ferric chloride on the kinetics of the radical polymerization of N-tert-butylacrylamide has been investigated in methanol solution at 25°C, with the use of 4,4′-dicyano-4,4′-azodipentanoic acid as initiator. A shrinkage factor of 0.193 mmole polymerized for 1 mm contraction in a capillary of 1 mm diameter has been obtained from density measurements. In the absence of ferric chloride, rates of polymerization were found to be proportional to the concentration of monomer and to the square root of the initiator concentration. With ferric chloride present, the rate of polymerization becomes directly proportional to the initiator concentration and inversely proportional to the concentration of ferric salt. From measurements of the rates of production of ferrous iron, the specific rate constant of the initiation reaction has been found to be (1.8 ± 0.4) × 10^?6sec^?1 at 25°C, compared with a value of 7.63 × 10^?8 sec^?1 calculated from the kinetic data obtained with no ferric salt present. The value of the ratio k_p/k₄. where k_p is the propagation coefficient and k₄ is the velocity coefficient for termination by ferric chloride, has been calculated to be 6.0 × 10^?4 at 25°C, which is considerably smaller than the value found for the ferric chloride-terminated polymerization of acrylamide in water. This markedly lower value of k_p/k₄ has been attributed principally to the steric effect of the tert-butyl group on the magnitude of k_p.     

Vinyl polymerization. 403. Polymerization of vinyl monomer initiated with sodium poly-p-vinylphenolate

The polymerization of vinyl monomer initiated by poly-p-vinylphenol (PVPh) in NaOH aqueous solution was carried out at 85°C with shaking. Methyl methacrylate (MMA) was polymerized, whereas styrene and acrylonitrile were not. PVPh, which is dissociated into phenolate form (PVPh^?Na⁺) in NaOH aqueous solution, was effective for the polymerization. The effects of the amounts of MMA, PVPh, NaOH, and H₂O on the conversion of MMA were studied. The rate of polymerization of MMA increased with an increase in the molecular weight of PVPh-Na. The overall activation energy was estimated as 54 kJ mol^?1. The polymerization proceeded through a radical mechanism. The addition of tetra-n-butylammonium bromide increased the rate of polymerization.