Kinetic and ESR studies on the radical polymerization. radical-initiated copolymerization of the diethyl itaconate-SnCl4 complex and styrene

The copolymerization of diethyl itaconate (1) (M₁) and styrene (2) (M₂) with dimethyl 2,2′-azoisobutyrate ( 3 ) was performed in benzene at 50°C, and the following copolymerization parameters were obtained: r₁ = 0,34, r₂ = 0,35, Q₁ = 0,93 and e_l = +0,66. The copolymerization system was found to involve ESR 1

1 Electron spin resonance.

-observed propagating polymer radicals at low monomer feed composition (f₂) of 2 . The apparent rate constant of termination increased rapidly with f₂. The ESR-determined values of the apparent propagation rate constant of the copolymerization were lower than those calculated on the basis of the Mayo-Lewis model, suggesting a significant penultimate effect in the copolymerization. On the other hand, the copolymerization of the 1 -SnCl₄ complex (M₁) and 2 (M₂) at 50°C yielded a nearly alternating copolymer independently of the monomer feed composition. The propagating polymer radicals were ESR-observable even up to f₂ = 0,8. The ESR-determined apparent rate constant (k_p) of propagation showed a maximum near f₂ = 0,5. From the relationship between k_p and f₂, the rate constants of cross-propagations of the present alternating copolymerization were evaluated as k₁₂ = 483 and k₂₁ = 510 L. mol^?1 · s^?1. Comparison of the k₂₁ value and the reported propagation rate constant (209 L · mol^?1 · s^?1) of homopolymerization of 2 leads to the conclusion that the alternating copolymerization via free-monomer propagation mechanism originates from a pronounced penultimate effect suppressing homopropagation of 2 , but not from enhanced cross-propagation.     

Solvent effect on the propagation rate constant in the radical polymerization of bis(2-ethylhexyl) itaconate

Polymerization of bis(2-ethylhexyl) itaconate ( 1 ) with dimethyl azobis(isobutyrate) ( 2 ) was carried out at 50°C in various solvents. Polar solvents caused a significant decrease in the polymerization rate (R_p) and the molecular weight of resulting poly( 1 ). The propagating poly( 1 ) radical could be observed as a five-line ESR spectrum in the actual polymerization systems used. The stationary concentration of poly( 1 ) radical was determined by ESR to be 4,2–6,4 · 10^?6 mol · L^?1 at 50°C when the concentrations of 1 and 2 were 1,03 and 3,00 · 10^?2 mol · L^?1. Using R_p the monomer concentration and the polymer radical concentration, the propagation rate constant (K_p) was estimated to be 1,4–6,8 L · mol^?1 · s^?1, depending on the solvents used. The k_p value was smaller in more polar solvents. The solvent effect is explained in terms of the solvent affinity for the propagating polymer chain.     

Kinetic and ESR studies on radical polymerization. Radical polymerization behavior of N-octadecylmaleimide in benzene

The polymerization of N-octadecylmaleimide ( 1 ) initiated with azodiisobutyronitrile ( 2 ) was investigated kinetically in benzene. The overall activation energy of the polymerization was calculated to be 94,2 kJ·mol^?1. The polymerization rate (R_p) at 50°C is expressed by the equation, R_p = k[ 2 ]^0,6[ 1 ]^1,7. The homogeneous polymerization system involves ESR-detectable propagating polymer radicals. Using R_p and the polymer radical concentration determined by ESR, the rate constants of propagation (k_p) and termination (k_t) were evaluated at 50°C. k_p (33 L · mol^?1 · s^?1 on the average) is substantially independent of the monomer concentration. On the other hand, k_t (0,3 · 10⁴ – 1,0 · 10⁴ L · mol^?1 · s^?1) is fairly dependent on the monomer concentration, which is ascribable to a high dependence of k_t on the chain length of rigid poly( 1 ). This is the predominant factor for the high order with respect to the monomer concentration in the rate equation. In the copolymerization of 1 (M₁) and St (M₂) with 2 in benzene at 50°C, the following copolymerization parameters were obtained: r₁ = 0,11, r₂ = 0,09, Q₁ = 2,1, and e₁ = +1,4.     

Kinetic and ESR studies of the radical-initiated polymerization of N-(2,6-dimethylphenyl)itaconimide

The polymerization of N-(2,6-dimethylphenyl)itaconimide (1) with azoisobutyronitrile (2) was studied in tetrahydrofuran (THF) kinetically and spectroscopically with the electron spin resonance (ESR) method. The polymerization rate (R_p) at 50°C is given by the equation: R_p = K [2] ^0,5 · [1] ^2,1. The overall activation energy of the polymerization was calculated to be 91 kJ/mol. The number-average molecular weight of poly (1) was in the range of 3500–6500. From an ESR study, the polymerization system was found to involve ESR-observable propagating polymer radicals of 1 under the actual polymerization conditions. Using the polymer radical concentration, the rate constants of propagation (k_p) and termination (k_t) were determined at 50°C. k_p (24–27 L · mol^?1 · s^?1) is almost independent of monomer concentration. On the other hand, k_t (3,8 · 10⁴–2,0 · 10⁵ L · mol^?1 · s^?1) increases with decreasing monomer concentration, which seems mainly responsible for the high dependence of R_p on monomer concentration. Thermogravimetric results showed that thermal degradation of poly (1) occurs rapidly at temperatures higher than 360°C and the residue at 500°C was 12% of the initial polymer. For the copolymerization of 1 (M₁) with styrene (M₂) at 50°C in THF the following copolymerization parameters were found; r₁ = 0,29, r₂ = 0,08, Q₁ = 2,6, and e₁ = +1,1.     

Effect of SnCl4 on the radical-initiated polymerization of diethyl itaconate: Kinetical and ESR studies

The effect of SnCl₄ on the polymerization of diethyl itaconate ( 1 ) with dimethyl 2,2′-azoisobutyrate ( 2 ) in benzene was investigated kinetically and ESR spectroscopically. The polymerization rate (R_p) at 50°C shows a flat maximum on varying the SnCl₄ concentration. The molecular weight of the resulting polymer decreases with increasing SnCl₄ concentration. The overall activation energy of the polymerization is lowered from 52 to 33 kJ · mol^?1 by the presence of SnCl₄, (0,342 mol · L^?1). An NMR study revealed that 1 and SnCl₄ form 1:1 and 2:1 complexes with a large stability constant in benzene. The propagating polymer radicals in the absence and presence of SnCl₄ are ESR-observable as a five-line spectrum under the actual polymerization conditions. The complexed polymer radicals show further three-line splitting due to two methylene hydrogens of the ethyl ester group. The polymer radical concentration increases with the SnCl₄ concentration. The rate constant (k_p) of propagation was determined using R_p and the polymer radical concentration. k_p (6,3–2,9 L · mol^?1 · s^?1 at 50°C) decreases with increasing SnCl₄ concentration. The presence of SnCl₄ (0,342 mol · L^?1) reduces the activation energy of propagation from 29 to 21 kJ · mol^?1. The rate constant (k_t) of termination was estimated from the decay curve of the polymer radicals, k_t (3,1–1,1 · 10⁵ L · mol^?1 s^?1) also decreases with the SnCl₄ concentration. The activation energies of termination in the absence and presence of SnCl₄ (0,342 mol · L^?1) are 30 and 24 kJ · mol^?1, respectively. Suppression of propagation and termination by SnCl₄ seems to be explicable in terms of an entropy factor.     

Kinetic and electron paramagnetic resonance studies on radical polymerization. Radical copolymerization of p-tert-butoxy-styrene and dibutyl fumarate in benzene

The copolymerization of p-tert-butoxystyrene ( 1 ) (M₁) and dibutyl fumarate ( 2 ) (M₂) initiated with dimethyl 2,2′-azobisisobutyrate ( 3 ) was studied in benzene at 60°C kinetically and by means of electron paramagnetic resonance (EPR) spectroscopy. The monomer reactivity ratios were determined to be r₁ = 0,18 and r₂ = 0,01, indicating that homopropagation of M₂ is almost negligible in the copolymerization. The copolymerization system was revealed to involve EPR-observable propagating polymer radicals under practical copolymerization conditions. The apparent rate constants of propagation (k_p) and termination (k_t) determined by EPR show a rapid increase in the range from 0,9 to 1,0 of feed composition (f₁ = {[M₁]/([M₁] + [M₂])}) of M₁. From the relationship between k_p and f₁ based on Fukuda's penultimate model, the rate constants of propagation of copolymerization were evaluated; k₁₁₁ = 140 L · mol^?1 · s^?1, k₂₁₁ = 4,3 L · mol^?1 · s^?1, k₁₁₂ = 778 L · mol^?1 · s^?1, k₂₁₂ = 24 L · mol^?1 s^?1 and k₁₂₁ = 19 L · mol^?1 · s^?1, suggesting a pronounced penultimate effect.     

Kinetic and electron paramagnetic resonance studies on radical polymerization. Radical-initiated polymerization of methyl N-phenylitaconamate in N,N-dimethylformamide

The polymerization of methyl N-phenylitaconamate(methyl 2-methylenesuccinanilate ( 1 )) with dimethyl 2,2′-azodiisobutyrate ( 2 ) was studied in N,N-dimethylformamide (DMF) kinetically and by means of electron paramagnetic resonance (EPR) spectroscopy. The polymerization rate (R_p) at 55°C is given by the equation: R_p = k[ 2 ]^0,58 · [ 1 ]^1,6. The overall activation energy of the polymerization was calculated to be 54,2 kJ/mol. The number-average molecular weight of poly( 1 ) was in the range between 5000 and 17000. From an EPR study, the polymerization system was found to involve the EPR-detectable propagating polymer radical of 1 at practical polymerization conditions. Using the concentration of polymer radicals, the rate constants of propagation (k_p) and termination (k_t) were determined for 55°C. The rate constant of propagation k_p (between 8,4 and 12 L · mol^?1 · s^?1) tends to somehow increase with increasing monomer concentration. On the other hand, k_t (between 1,9. 10^?5 L · mol^?1 · s^?1) increases with decreasing monomer concentration, which results from a considerable dependence of k_t on the polymer-chain length. Such monomer-concentration-dependent k_p and k_t values are responsible for the high dependence of R_p on the monomer concentration. Thermogravimetric results showed that thermal degradation of poly( 1 ) occurs rapidly at temperatures higher than 200°C and the residue at 500°C amounts to 26% of the initial polymer. For the copolymerization of 1 (M₁) with styrene (M₂) at 55°C in DMF the following copolymerization parameters were found: r₁ = 0,52, r₂ = 0,31, and Q, e values Q₁ = 1,09 and e₁ = +0,55.     

The thiol/dimethyl sulfoxide system as initiator of polymerization in benzene medium, 2. Kinetic studies

The kinetics of butanethiol/dimethylsulfoxide (DMSO) initiated polymerization of methyl methacrylate in benzene medium was studied gravimetrically. The thiol acts as the reducing component of the initiator system and also as a transfer agent. The order with respect to [Butanethiol] is 0,48. In the lower concentration region between 4,69.10^?4 and 9,38.10^?2mol 1^?1, DMSO behaves simply as the oxidant of the initiator system, and the rate of polymerization has the usual square root dependence on [DMSO]. But above the concentration of 9,38.10^?2mol 1^?1 and up to 1,40mol 1^?1, DMSO acts both as an oxidizing agent and as a retarder, forming an adduct with the growing radicals, which propagates the reaction with a retarded rate. The order with respect to monomer concentration is 1,04, when DMSO is used in the lower concentration range and it increases to 1,25 when [DMSO] is higher than 9,38.10^?2mol 1^?1. Thiols of different structures affect the rate significantly. The rate of polymerization is also dependent on the polarity and viscosity of the solvent being a maximum in benzene and a minimum in ethyl acetate. The efficiency of initiation of the initiator system is 60–80% and the overall activation energy is 72,45 kJ mol^?1. An appropriate kinetic expression was derived to explain the results.     

Cationic polymerization of bis(1-alkylvinyl)benzene and related monomers, 7. Copolymers

Polyindanes with long alkyl side chains have been prepared by reaction of 1,4-bis(2-hydroxy-2-propyl)benzene ( 3 ) and 1,4-bis(2-hexadecen-2-yl)benzene ( 4 ) in various ratios. All copolymers are soluble in common organic solvents and have been characterized by NMR, IR, GPC, DSC and TG. The variation of the glass transition temperature T_g with the composition of the copolymers can be described satisfactorily by Couchman's equation, which describes the dependence of the T_g's of copolymers on the T_g's and heat capacities of the homopolymers and the weight fractions of the comonomers in the copolymers. A very important feature of this step-growth copolymerization is the ability of all possible end-groups of monomers and oligomers to react with each other. Therefore the composition of the copolymers is not governed by the composition of the feed, because there is no need for high conversion to obtain high molar mass. It was found that 3 was twice as reactive as 4 . The experimentally determined composition of the copolymers is in good agreement with the calculations based on the differences in the reactivity of the monomers.     

Free radical polymerization of unconjugated dienes. IX. Kinetic evidence of formation of five and six membered rings in the free radical polymerization of divinylether

Some kinetic relationships between the monomer concentration and the composition of the polymers from 1.4-dienes, in terms of monomeric and structural units, are derived taking into account all the cyclization reactions which can occur in the course of the chain growth. These relationships are applied to the results of the analytical determination of the residual unsaturations in the products of the free radical polymerization at 70°C of divinylether in benzene solutions. It is shown that the chain growth takes place exclusively by addition of cyclic radicals onto monomer molecules. Evidence is given that both five and six membered rings are formed in the cyclization steps.     

Studies on the polymerization of ethylene using a high-yield MgCl2-supported titanium catalyst, 2. Kinetic studies

Polymerization of ethylene was carried out in a batch process under pressure with an optimized high-yield Ti/Mg-catalyst. It was shown through gas chromatography analysis as well as by educt/product mass balances that no side-reactions take place, and therefore, the monomer is quantitatively converted to polyethylene. It is demonstrated that influences of diffusion are excluded under the described experimental condition. The dependence of the overall polymerization rate on time shows that the rate at constant pressure is constant from the beginning over a certain period of time. The rate of polymerization under isobaric as well as isochoric conditions was determined to be first order with respect to monomer concentration and catalyst concentration. The overall activation energy obtained for this catalytic system was determined to be 32 kJ · mol^?1.     

Adjuvant effect of di-(2-ethylhexyl) phthalate on asthma-like pathological changes in ovalbumin-immunised rats

Pollution of phthalates, including di-(2-ethylhexyl)phthalate (DEHP), is widespread because of their use in plastics and other daily consumer products. Epidemiological studies have shown that the largest source of general population exposure to DEHP is on dietary. Studies have suggested an association between exposure to phthalate plasticisers, and increased prevalence of asthma. To investigate the adjuvant effect of DEHP on asthmatic pathological changes in ovalbumin-immunised rat model. Wistar rats were randomly divided into five groups (eight rats of each group): (1) saline; (2) ovalbumin (OVA); (3) OVA+DEHP 0.7mg·kg^?1·d^?1; (4) OVA+DEHP 70 mg·kg^?1·d^?1; and (5) DEHP 70 mg·kg^?1·d^?1. DEHP treatment groups which were administered to 0.7 mg and 70 mg DEHP/kg/d by gastric gavage for 30d before and during the process of OVA immunisation or saline treatment. The in vivo pulmonary function analysis, bronchoalveolar lavage (BAL) fluid collection and section histological observation were conducted. DEHP exposure could significantly increase airway hyperresponsiveness, airway remolding, and eosinophil infiltration in the OVA-immunised rats. But the DEHP exposure alone group does not show significant airway structural change and inflammatory cell infiltration, compared with control group. DEHP administered by gastric gavage play an adjuvant effect on respiratory systems in ovalbumin-immunised rat model.     

Retardation effect of 1,1,4,4-tetraphenyl-2-tetrazene in the radical polymerization of methyl methacrylate

The decomposition of 1,1,4,4-tetraphenyl-2-tetrazene (TPT) was carried out in four aprotic solvents [acetonitrile, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and benezene]. ΔH≠ was found to decrease with increasing polarity of the solvent. The effect of TPT on the polymerization of methyl methacrylate (MMA) was also studied in the same solvents. TPT was found to be a retarder for the radical polymerization of MMA. The induction period is affected by the polarity of the medium. In addition, the chain-transfer constant of TPT (C_TPT) was calculated to be 5,40, 4,00, 2, 78, and 3, 96 for the polymerization of MMA in acetonitrile, DMSO, DMF, and benzene, respectively. The transition state of the chain-transfer reaction seems to be influenced by the polarity of the solvent.     

The laser flash-initiated polymerization as a tool of evaluating (individual) kinetic constants of free radical polymerization, 1. Outline of method and first results

A method is presented which allows the determination of k_p/k_t-values in free radical polymerization. It is based on measurements of the (average) rate of polymerization under pseudostationary conditions, the polymerization being initiated by laser flashes of short duration. For ρk_t t₀ ? 1 (ρ being the additional polymer radical concentration produced by each laser flash, k_t the bimolecular termination constant between polymer radicals, k_p the rate constant of chain propagation, t₀ the time separating two successive laser flashes) k_p/k_t may be obtained as the slope of a linear plot of the fractional conversion per flash vs. ln t₀. Dividing the intercept by the slope yields ln (pk_t). Thus, if p is accessible, separation of k_p/k_t-data into its individual constituents may be accomplished without making any use of stationary polymerization data. Application of this method to the polymerization of styrene sensitized by benzoin or AIBN at 25°C gives k_p/k_t-values of 1,0 · 10^?6 which are in fair agreement with those obtained by other methods.     

Kinetic studies in ethylene polymerization with Ziegler type catalysts. V. Evaluation of fractionation data for simultaneous polymerization on trivalent and tetravalent titanium sites

A method is described which allows the individual characterization (M_w, M_n) of the two ethylene polymers formed simultaneously on Ti(III) and Ti(IV) sites of a Ziegler catalyst system. The method is based on the evaluation of the CH₃ or CHD group distributions in fractionated polymers prepared in the absence or the presence of deuterium, respectively.     

Polymer conformation and viscometric behaviour, 3. Synthesis,characterization and conformational studies in poly(mono-n-octyl itaconate)

The unperturbed dimensions and the steric factor σ of poly(mono-n-octyl itaconate) (poly-(1-carboxy-1-octyloxycarbonylmethylethylene)) were determined from the intrinsic viscosities in two solvents, using the semiempirical equation of Stockmayer and Fixman. Evidence for the existence of specific effects was found. The irregular behaviour observed, can be interpreted in terms of conformational changes and conformational transitions of the polymeric chain, induced both by solvent and temperature. The effect of the structure of the monomeric unit on the flexibility of the macromolecule is discussed.     

Polymerization of macromonomers, 3. Monomer reactivity ratios in radical copolymerization of poly(tetrahydrofuran) macromonomers with 2-vinylnaphthalene

Methacrylate-terminated poly(tetrahydrofuran) (MA-PTHF) and acrylate-terminated poly-(tetrahydrofuran) (A-PTHF) macromonomers (M₂) were radically copolymerized with 2-vinylnaphthalene (2-VN, M₁). The composition of copolymers was determined by UV spectroscopy taking advantage of the very high absorption coefficient (UV) of the monomeric units of 2-VN in copolymer. The monomer reactivity ratios r₁ and r₂ evaluated are as follows. MA-PTHF: r₁ =1,3 ± 0,21, ± 0,05; A-PTHF: r₁ = 2,5 ± 0,35, r₂ = 0,10 ± 0,05. These reactivity ratios were compared with those in the copolymerizations of 2-VN with the corresponding small monomers and were discussed in terms of polymer (hindering) effect and the concept of equal reactivity of growing chain.