Effect of pyridine on the kinetics of polymerization of methyl methacrylate initiated by benzoyl peroxide and azobisisobutyronitrile at 60°C

Solution polymerization of MMA, with pyridine as the solvent and BZ₂O₂ and AIBN as thermal initiators, was studied kinetically at 60°C. The monomer exponent varied from 0.45 to 0.91 as [BZ₂O₂] was increased from 1 × 10^?2 to 30 × 10^?2 mole/liter in a concentration range of 8.3-4.6 mole/liter for MMA. For AIBN-initiated polymerization the monomer exponent remained constant at 0.69 as [AIBN] varied from 0.4 × 10^?2 to 1.0 × 10^?2 mole/liter in the same concentration range for MMA. The k²_p/k_t Value increased in both cases with an increase in pyridine concentration in the system. This was explained in terms of an increase in the k_p value, which was due presumably to the increased reactivity of the chain radicals by donor-acceptor interaction between the molecules of solvent pyridine and propagating PMMA radicals and in terms of lowering the k_t value for the diffusion-controlled termination reaction due to an increase in the medium viscosity and pyridine content.     

New coordination catalysts based on rare earth compounds for polymerization of 1-octene

The study of rare earth coordination catalysts for polymerization of 1-octene has been successfully carried out for the first time. Some features and kinetic behavior of polymerization of 1-octene by Nd(naph)₃–AIEt₃ catalyst system in tetrachloro-methane are described. The overall polymerization activation energy E_a measured was 74.5 kJ/mol and the rate equation could be expressed as R_p = k_p [Nd] [M] (k_p = 3.21 × 10^?3 L/mol s, at 50°C). The catalytic activity of various rare earth elements in Ln (naph)₃ and ligands in NdL₃ for the polymerization was compared. A 1-octene oligomer with double bonds was obtained. It is either a white or pale yellow waxy semi-solid. Its number-average molecular weight is about 10³ and the molecular weight distribution is less than 2.     

A novel tridentate nitrogen donor as ligand in copper catalyzed ATRP of methyl methacrylate

A tridentate ligand, BPIEP: 2,6‐bis[1‐(2,6‐diisopropyl phenylimino) ethyl] pyridine, having central pyridine unit and two peripheral imine coordination sites was effectively employed in controlled/“living” radical polymerization of MMA at 90°C in toluene as solvent, Cu^IBr as catalyst, and ethyl‐2‐bromoisobutyrate (EBiB) as initiator resulting in well‐defined polymers with polydispersities M_w/M_n ≤ 1.23. The rate of polymerization follows first‐order kinetics, k_app = 3.4 × 10^?5 s^?1, indicating the presence of low radical concentration ([P*] ≤ 10^?8) throughout the reaction. The polymerization rate attains a maximum at a ligand‐to‐metal ratio of 2:1 in toluene at 90°C. The solvent concentration (v/v, with respect to monomer) has a significant effect on the polymerization kinetics. The polymerization is faster in polar solvents like, diphenylether, and anisole, as compared to toluene. Increasing the monomer concentration in toluene resulted in a better control of polymerization. The molecular weights (M_n,SEC) increased linearly with conversion and were found to be higher than predicted molecular (M_n,Cal). However, the polydispersity remained narrow, i.e., ≤1.23. The initiator efficiency at lower monomer concentration approaches a value of 0.7 in 110 min as compared to 0.5 in 330 min at higher monomer concentration. The aging of the copper salt complexed with BPIEP had a beneficial effect and resulted in polymers with narrow polydispersitities and higher conversion. PMMA obtained at room temperature in toluene (33%, v/v) gave PDI of 1.22 (M_n = 8500) in 48 h whereas, at 50°C the PDI is 1.18 (M_n = 10,300), which is achieved in 23 h. The plot of lnk_app versus 1/T gave an apparent activation energy of polymerization as (ΔE^≠_app) 58.29 KJ/mol and enthalpy of equilibrium (ΔH⁰_eq) to 28.8 KJ/mol. Reverse ATRP of MMA was successfully performed using AIBN in bulk as well as solution. The controlled nature of the polymerization reaction was established through kinetic studies and chain extension experiments. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4996–5008, 2005     

Charge transfer polymerization of 2-vinyl pyridine initiated by n-butyl amine and carbon tetrachloride

2-Vinyl pyridine (2-VP) can be initiated by a charge-transfer complex formed by the interaction of aliphatic amines such as n-butylamine (nBA) and carbon tetrachloride (CCl₄) in a solvent like NN-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). This article describes the polymerization of 2-VP by n-butylamine (nBA) in the presence of carbon tetrachloride in DMSO at 60°C. The rate of polymerization R_p increases rapidly with carbon tetrachloride (CCl₄) up to a concentration of 3.93 mol/L, but for a higher concentration it is almost independent of the carbon tetrachloride concentration; R_p is proportional to [nBA]^0.5 and [2-VP]^1.5 when [CCl₄]>[nBA]. The average rate constant k is 1.03 × 10^?5 L/mol s. When [CCl₄] < [nBA] the rate constant in terms of [2-VP] was 1.06 × 10^?5 s^?1 at 60°C and the overall rate constant was 1.035 × 10^?5 L/mol s at 60°C.     

Polymerization of diallyl phthalate in solution by γ-radiation

The polymerization of diallyl phthalate has been studied in two solvents, benzene (G_Radical = 0.7) and chloroform (G_R = 11.2), γ-radiation being used to investigate the effect of the solvent on the rates of polymerization and also chain transfer to the solvent. Kinetic analysis shows that in benzene solution the initiating species come almost exclusively from the monomer, but in chloroform they arise only from the solvent. The latter was further confirmed from the chlorine analysis of the polymer wherein chloroform appears to have telomerized with diallyl phthalate. In neither of the solvents was high molecular weight polymer obtained. The k_p/k_t^1/2 for the polymerization of DAP was found to be 3.3 × 10^?4 and 1.17 × 10^?3 in benzene and chloroform solutions, respectively. The chain-transfer constant C_S was 11.25 × 10^?3 and 9.75 × 10^?3 for benzene and chloroform, respectively.     

Kinetics and mechanism of the cationic polymerization of tetrahydrofuran in solution. I. THF–CCI4 system

Polymerization of THF in CCl₄ solvent was initiated with 1,3-dioxolan-2-ylium eations with AsF₆^?, PF₆^?, and SbF₆^? anions as well as with esters of fluorosulfonic and trifluoromethanesulfonic acids. With these esters polymerization proceeds with a marked acceleration period, due to slow initiation. The corresponding rate constants of initiation and their dependence on the polarity of the THF/CCl₄ mixture were determined. The rate constant of propagation on the macroion-pairs (k_p^±) of the polytetrahydrofurylium cation with AsF₆^?, PF₆^?, and SbF₆^? and CF₃SO₃^?, anions was found to be independent in CCl₄ solvent on the anion structure and given by the expression: k_p^± = 2.93 × 10^?2 exp {?4.7 × 10³/T} at [THF]₀ = 8.0M. This constant depends on the polarity of the polymerization mixture, and at 25°C for the THF-CCl₄ system, k_p^± = 1.78 × 10^?2 exp {?4.9/D}; thus, in CCl₄ at [THF]₀ = 8.0M, and at 25° k_p^± = 4.0 × 10^?21/mole-sec. In the polymerization with derivatives of CF₃SO₃H (able to form the corresponding macroester) the overall polymerization rate is much lower than that with complex anions because of the reversible conversion of the macroion-pairs into the macroester (internal return). The macroester is much less reactive than the macroionpair (10²–10³ times) in the monomer addition reaction. At [THF]₀ = 8.0M and at 25°C, 96.5% of the growing species exists in the macroester form. Polymerization of THF initiated with derivatives of CF₃SO₃H is a subject of a strong special salt-effect. At a sufficiently high ratio of [AgSbF₆] to [I]₀, where the initiator I is C₂H₅OSO₂CF₃, the overall polymerization rate is equal to that observed for the polymerization of THF on the macroion-pairs, since the internal return within the triflate ion-pair (the macroester formation) is eliminated and polymerization proceeds on the macroion-pairs with SbF₆- anions exclusively.     

A triangular palladium(II) supramolecular coordination complex based on 1,4‐bis(1H‐imidazol‐1‐yl)benzene and (2,2′‐bipyridyl)palladium(II) nitrate: synthesis and crystal structure

The self‐assembly of ditopic bis(1H‐imidazol‐1‐yl)benzene ligands ( L ^H) and the complex (2,2′‐bipyridyl‐κ²N,N′)bis(nitrato‐κO)palladium(II) affords the supramolecular coordination complex tris[μ‐bis(1H‐imidazol‐1‐yl)benzene‐κ²N³:N^3′]‐triangulo‐tris[(2,2′‐bipyridyl‐κ²N,N′)palladium(II)] hexakis(hexafluoridophosphate) acetonitrile heptasolvate, [Pd₃(C₁₀H₈N₂)₃(C₁₂H₁₀N₄)₃](PF₆)₆·7CH₃CN, 2 . The structure of 2 was characterized in acetonitrile‐d₃ by ¹H/¹³C NMR spectroscopy and a DOSY experiment. The trimeric nature of supramolecular coordination complex 2 in solution was ascertained by cold spray ionization mass spectrometry (CSI–MS) and confirmed in the solid state by X‐ray structure analysis. The asymmetric unit of 2 comprises the trimetallic Pd complex, six PF₆^? counter‐ions and seven acetonitrile solvent molecules. Moreover, there is one cavity within the unit cell which could contain diethyl ether solvent molecules, as suggested by the crystallization process. The packing is stabilized by weak inter‐ and intramolecular C—H…N and C—H…F interactions. Interestingly, the crystal structure displays two distinct conformations for the L ^H ligand (i.e. syn and anti), with an all‐syn‐[Pd] coordination mode. This result is in contrast to the solution behaviour, where multiple structures with syn/anti‐ L ^H and syn/anti‐[Pd] are a priori possible and expected to be in rapid equilibrium.     

Kinetics and mechanism of oxidation of the binary and ternary complexes of chromium(III) involving inosine and glycine by N -bromosuccinimide

The kinetics of oxidation of the chromium(III) complexes, [Cr(Ino)(H₂O)₅]³⁺ and [Cr(Ino)(Gly)(H₂O)₃]²⁺ (Ino?=?Inosine and Gly?=?Glycine) involving a ligands of biological significance by N-bromosuccinimide (NBS) in aqueous solution to chromium(VI) have been studied spectrophotometrically over the 25–45°C range. The reaction is first order with respect to both [NBS] and [Cr], and increases with pH over the 6.64–7.73 range in both cases. The experimental rate law is consistent with a mechanism in which the hydroxy complexes [Cr(Ino)(H₂O)₄(OH)]²⁺ and [Cr(Ino)(Gly)(H₂O)₂(OH)]⁺ are significantly more reactive than their conjugate acids. The value of the intramolecular electron transfer rate constant, k ₁, for the oxidation of the [Cr(Ino)(H₂O)₅]³⁺ (6.90?×?10^?4?s^?1) is lower than the value of k ₂ (9.66?×?10^?2?s^?1) for the oxidation of [Cr(Ino)(Gly)(H₂O)₂]²⁺ at 35°C and I?=?0.2?mol?dm^?3. The activation parameters have been calculated. Electron transfer apparently takes place via an inner-sphere mechanism.     

Radical heterogeneous polymerization behavior of N‐methyl‐α‐fluoroacrylamide in benzene

The polymerization of N‐methyl‐α‐fluoroacrylamide (NMFAm) initiated with dimethyl 2,2′‐azobisisobutyrate (MAIB) in benzene was studied kinetically and with electron spin resonance. The polymerization proceeded heterogeneously with the highly efficient formation of long‐lived poly(NMFAm) radicals. The overall activation energy of the polymerization was 111 kJ/mol. The polymerization rate (R_p) at 50 °C is given by R_p = k[MAIB]^0.75±0.05 [NMFAm]^0.44±0.05. The concentration of the long‐lived polymer radical increased linearly with time. The formation rate (R_p?) of the long‐lived polymer radical at 50 °C is expressed by R_p? = k[MAIB]^1.0±0.1 [NMFAm]^0±0.1. The overall activation energy of the long‐lived radical formation was 128 kJ/mol, which agreed with the energy of initiation (129 kJ/mol), which was separately estimated. A comparison of R_p? with the initiation rate led to the conclusion that 1‐methoxycarbonyl‐1‐methylethyl radicals (primary radicals from MAIB), escaping from the solvent cage, were quantitatively converted into the long‐lived poly(NMFAm) radicals. Thus, this polymerization involves completely unimolecular termination due to polymer radical occlusion. ¹H NMR‐determined tacticities of resulting poly(NMFAm) were estimated to be rr = 0.34, mr = 0.48, and mm = 0.18. The copolymerization of NMFAm(M₁) and St(M₂) with MAIB at 50 °C in benzene gave monomer reactivity ratios of r₁ = 0.61 and r₂ = 1.79. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2196–2205, 2001     

Kinetics of the Copolymerization of Methyl Vinyl Ketone and Acrylamide Initiated by the Adduct of Methyl Vinyl Ketone and Imidazole

N-(Butyl-3-one)imidazole acts as an initiating adduct which is formed in the anionic polymerization of methyl vinyl ketone (MVK) induced by imidazole (Im) and is directly formed from Im and the MVK monomer. The kinetics of the anionic homopolymerization of MVK and acrylamide (AAm) under argon in the presence of the adduct were investigated in tetrahydrofuran (THF). The rate of polymerization for the MVK system is expressed as R_p = k[Adduct] [MVK], where k = 3.1 × 10^?6 L/(mol·s)in THF at 30°C. The overall activation energy, E_a , was found to be 5.34 kcal/mol. The R_p for the AAm system is expressed as R_p = k[Adduct] [AAm], where k = 6.8 × 10^?6 L/(mol·s) in THF at 30°C, with E_a 7.78 kcal/mol. The mechanism of the polymerization induced by the initiator adduct is discussed on the basis of these results.     

Polystyrene bis[N-(2-pyridyl) sulfonamide] palladium(II): Synthesis,characterization as a catalyst for coupling reactions

The [N-(2-pyridyl)] para-styrene sulfonamide (PSS) was prepared as a monomer, from the reaction of para-styrene sulfonyl chloride and 2-amino pyridine in the presence of potassium hydroxide solution 0.5 M as a base, and CH₃Cl. Polystyrene [N-(2-pyridyl) sulfonamide] (PPSS) was synthesized from the polymerization of [N-(2-pyridyl)] para-styrene sulfonamide (PSS). The Polystyrene bis [N-(2-pyridyl) sulfonamide] palladium (II) as a polymer- supporting palladium complex was also prepared from the reaction of PdCl₂ (CH₃CN)₂ with PPSS in the presence of KOH 0.5 M. Polystyrene bis [N-(2-pyridyl) sulfonamide] palladium (II) is produced as a novel heterogeneous catalyst for coupling reactions for C-C bond formation. This method includes higher yield and has an easier work-up procedure. The structures of the monomer, polymer and its Pd complex were confirmed by using FT-IR and ¹H-NMR spectroscopy. Elemental analysis of Pd by inductively coupled plasma (ICP) technique and hot filtration test showed loading of the metal into solution from the catalyst The heterogeneous catalyst was recycled without any loss in its properties.     

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     

Free-radical polymerization of vinyl ferrocene

The results of quantitative studies of the rates of free-radical polymerization of vinyl ferrocene indicate that the latter has polymerization characteristics similar to those of styrene. The rates of homopolymerization of these two monomers in benzene at 70°C. were measured with the use of azobisisobutyronitrile as catalyst. The rate constants (k = R_p/[M][I]^1/2) are k_VF = (1.1 ? 1.8) × 10^?4, k_STY = 1.65 × 10^?4. Small amounts of vinyl ferrocene and styrene have similar effects on the rates of polymerizations of methyl methacrylate and ethyl acrylate and on the molecular weights of the resulting polymer. Polystyrene and poly(vinyl ferrocene) with similar molecular weights are isolated from polymerizations carried out under identical conditions. The rates of copolymerization of vinyl ferrocene—methyl methacrylate, vinyl ferrocene—styrene, and styrene—methyl methacrylate were determined by following the disappearance of monomers by means of gas chromatographic analyses. The relative reactivity for vinyl ferrocene is slightly lower than that for styrene.     

Alkylaluminum activator effects on polyethylene branching using a N,N′‐nickel precatalyst appended with bulky 4,4′‐dimethoxybenzhydryl groups

Ten unsymmetrical N,N'‐bis (imino) acenaphthene‐nickel (II) halide complexes, [1‐[2,6‐{(4‐MeOC₆H₄)₂CH}₂–4‐MeC₆H₂N]‐2‐(ArN)C₂C₁₀H₆]NiX₂, each appended with one N‐2,6‐bis(4,4'‐dimethoxybenzhydryl)‐4‐methylphenyl group, have been synthesized and characterized. The molecular structures of Ni1 , Ni3 , Ni5 and Ni6 highlight the variation in steric protection afforded by the inequivalent N‐aryl groups; a distorted tetrahedral geometry is conferred about each nickel center. On activation with diethylaluminum chloride (Et₂AlCl) or methylaluminoxane (MAO), all complexes showed high activity at 30°C for the polymerization of ethylene with the least bulky bromide precatalysts ( Ni1 and Ni4 ), generally the most productive, forming polyethylenes with narrow dispersities [M_w/M_n: < 3.4 (Et₂AlCl), < 4.1 (MAO)] and various levels of branching. Significantly, this level of branching can be influenced by the type of co‐catalyst employed, with Et₂AlCl having a predilection towards polymers displaying significantly higher branching contents than with MAO [T_m: 33.0–82.5°C (Et₂AlCl) vs. 117.9–119.4°C (MAO)]. On the other hand, the molecular weights of the materials obtained with each co‐catalyst were high and, in some cases, entering the ultra‐high molecular weight range [M_w range: 6.8–12.2 × 10⁵ g mol^?1 (Et₂AlCl), 7.2–10.9 × 10⁵ g mol^?1 (MAO)]. Furthermore, good tensile strength (ε_b up to 553.5%) and elastic recovery (up to 84%) have been displayed by selected more branched polymers highlighting their elastomeric properties.     

Room temperature polymerization of alkyl isocyanates catalyzed by rare earth Schiff base complexes

The polymerization of alkyl isocyanates catalyzed by rare earth chloride salen complexes/triisobutyl aluminum (Ln(H₂salen)₂Cl₃·2C₂H₇OH/Al(i-Bu)₃) at room temperature was investigated. The influences of ligand structure, catalyst composition, polymerization temperature, polymerization time, the concentration of catalyst and monomer, and the polymerization solvent on the polymerization of isocyanates were studied. It was found that under the polymerization conditions, examined La(H₂salen_A)₂Cl₃·2C₂-H₇OH/Al(i-Bu)₃ (H₂salen_A= N,N′-disalicylideneethylene diamine) is a fairly high efficient catalyst for the polymerization of n-hexyl isocyanate (n-HexNCO) to prepare high molecular weight poly(n-hexyl isocyanate) (PHNCO) with narrower molecular weight distribution at room temperature. PHNCO could be prepared with yield of 74.0%, number-average molecular weight (M _n) of 40.20×10⁴ and MWD of 1.79 under the following optimum conditions: [Al]/[La] = 30 (molar ratio), [n-HexNCO]/[La] = 100 (molar ratio), [n-HexNCO] = 3.43 mol/L polymerization at 20°C for 12 h in toluene. In the same polymerization conditions, poly (n-octyl isocyanate) (PONCO) with yield of 67.3%, and poly(n-butyl isocyanate) (PBNCO) with yield of 45.5%, could be prepared respectively. The kinetics of the polymerization of n-HexNCO was also investigated and found to be first-order with respect to both monomer and catalyst concentrations.     

Chromocene-based catalysts for ethylene polymerization: Kinetic parameters

The chromocene catalyst for ethylene polymerization shows a high response to hydrogen which leads directly to highly saturated polyethylenes containing methyl groups as the major terminal functionality in the polymers. At a polymerization temperature of 90°C the ratio of termination rate constants for hydrogen (k_H) and ethylene (k_M) is k_H/k_M = 3.60 × 10³. The ratio of k_H to the chain propagation constant (k_p) is k_H/k_p = 4.65 × 10^?1 A simple relation that can be derived from polymerization kinetics and the Quackenbos equation exists between melt index and hydrogen–ethylene ratio. A deuterium isotope effect (k_H/k_D) = 1.2 was calculated for the termination reaction. The overall polymerization process has an apparent activation energy of 10.1 kcal/mole. Oxygen addition studies show catalyst activity is proportional to initial divalent chromium content.     

Radical-initiated homo- and copolymerization of methoxymethyl methacrylate

The kinetics of methoxymethyl methacrylate (MOMA) homopolymerization has been investigated in benzene, using azobis(isobutyronitrile) as an initiator. The rate of polymerization (R_p) could be expressed by R_p = k[AIBN]^0.5 [MOMA]^1.19. The overall activation energy was calculated to be 73.2 kJ/mol. Kinetic constants for MOMA polymerization were obtained as follows: k_p/k_t^1/2 = 0.091 L^1/2 · mol^?1/2 · s^?1/2; 2fk_d = 1.37 × 10^?5 s^?1. The values of K and a in the Mark–Houwink equation, [η] = KM^a, where K = 5.89 × 10^?5 and a = 0.82 when M = M _n and the solvent was benzene. The relative reactivity ratios of MOMA (M₂) copolymerizations with styrene (r₁ = 0.40, r₂ = 0.58) were obtained. Applying the Q-e scheme led to Q = 0.78 and e = 0.67. The glass transition temperature (T_g) of poly(MOMA) was observed to be 64°C by DSC. Thermogravimetry of poly(MOMA) showed a 10% weight loss at 230°C in air.     

Radical and cationic polymerizations of 3‐ethyl‐3‐methacryloyloxymethyloxetane

3‐Ethyl‐3‐methacryloyloxymethyloxetane (EMO) was easily polymerized by dimethyl 2,2′‐azobisisobutyrate (MAIB) as the radical initiator through the opening of the vinyl group. The initial polymerization rate (R_p) at 50 °C in benzene was given by R_p = k[MAIB]^0.55 [EMO]^1.2. The overall activation energy of the polymerization was estimated to be 87 kJ/mol. The number‐average molecular weight (M?_n) of the resulting poly(EMO)s was in the range of 1–3.3 × 10⁵. The polymerization system was found to involve electron spin resonance (ESR) observable propagating poly(EMO) radicals under practical polymerization conditions. ESR‐determined rate constants of propagation (k_p) and termination (k_t) at 60 °C are 120 and 2.41 × 10⁵ L/mol s, respectively—much lower than those of the usual methacrylate esters such as methyl methacrylate and glycidyl methacrylate. The radical copolymerization of EMO (M₁) with styrene (M₂) at 60 °C gave the following copolymerization parameters: r₁ = 0.53, r₂ = 0.43, Q₁ = 0.87, and e₁ = +0.42. EMO was also observed to be polymerized by BF₃OEt₂ as the cationic initiator through the opening of the oxetane ring. The M?_n of the resulting polymer was in the range of 650–3100. The cationic polymerization of radically formed poly(EMO) provided a crosslinked polymer showing distinguishably different thermal behaviors from those of the radical and cationic poly(EMO)s. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1269–1279, 2001     

Kinetics of the gas‐phase reactions of cyclo‐CF2CFXCHXCHX – (X = H,F, Cl) with OH radicals at 253–328 K

Rate constants were determined for the reactions of OH radicals with halogenated cyclobutanes cyclo‐CF₂CF₂CHFCH₂? (k₁), trans‐cyclo‐CF₂CF₂CHClCHF? (k₂), cyclo‐CF₂CFClCH₂CH₂? (k₃), trans‐cyclo‐CF₂CFClCHClCH₂? (k₄), and cis‐cyclo‐CF₂CFClCHClCH₂? (k₅) by using a relative rate method. OH radicals were prepared by photolysis of ozone at a UV wavelength (254 nm) in 200 Torr of a sample reference H₂O? O₃? O₂? He gas mixture in an 11.5‐dm³ temperature‐controlled reaction chamber. Rate constants of k₁ = (5.52 ± 1.32) × 10^?13 exp[–(1050 ± 70)/T], k₂ = (3.37 ± 0.88) × 10^?13 exp[–(850 ± 80)/T], k₃ = (9.54 ± 4.34) × 10^?13 exp[–(1000 ± 140)/T], k₄ = (5.47 ± 0.90) × 10^?13 exp[–(720 ± 50)/T], and k₅ = (5.21 ± 0.88) × 10^?13 exp[–(630 ± 50)/T] cm³ molecule^?1 s^?1 were obtained at 253–328 K. The errors reported are ± 2 standard deviations, and represent precision only. Potential systematic errors associated with uncertainties in the reference rate constants could add an additional 10%–15% uncertainty to the uncertainty of k₁–k₅. The reactivity trends of these OH radical reactions were analyzed by using a collision theory–based kinetic equation. The rate constants k₁–k₅ as well as those of related halogenated cyclobutane analogues were found to be strongly correlated with their C? H bond dissociation enthalpies. We consider the dominant tropospheric loss process for the halogenated cyclobutanes studied here to be by reaction with the OH radicals, and atmospheric lifetimes of 3.2, 2.5, 1.5, 0.9, and 0.7 years are calculated for cyclo‐CF₂CF₂CHFCH₂? , trans‐cyclo‐CF₂CF₂CHClCHF? , cyclo‐CF₂CFClCH₂CH₂? , trans‐cyclo‐CF₂CFClCHClCH₂? , and cis‐cyclo‐CF₂CFClCHClCH₂? , respectively, by scaling from the lifetime of CH₃CCl₃. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 532–542, 2009     

Effect of LiClO4 on the radical polymerization of Di-2-[2-(2-methoxyethoxy)ethoxy]ethyl itaconate

The effect of LiClO₄ on the polymerization of di-2-[2-(2-methoxyethoxy)ethoxy]ethyl itaconate (DMEI) with dimethyl 2,2′-azobisisobutyrate (MAIB) was investigated in methyl ethyl ketone (MEK) kinetically and by ESR. The polymerization rate (R_p) at 50°C, where the concentrations of DMEI and MAIB were 1.00 and 5.00 × 10⁻² mol/L, increased with increasing [LiClO₄]. Marked acceleration was observed at higher [LiClO₄]s than 1.0 mol/L. The molecular weight of resulting polymer (ca. 10,000) was relatively insensitive to [LiClO₄], indicating occurrence of chain transfer. IR analysis of mixtures of LiClO₄/DMEI and LiClO₄/poly(DMEI) indicated complexation of LiClO₄ with DMEI and its polymer. The rate constants of propagation (k_p) and termination (k_t) were determined by ESR. k_p (1.7–10.5 L/mol s at 50°C) increased with [LiClO₄]. k_t (5.2–1.0 × 10⁴ L/mol s at 50°C) showed remarkable decrease at higher [LiClO₄]s than 1.0 mol/L. R_p of polymerization of equimolar complex of LiClO₄/DMEI with MAIB at 50°C in MEK was expressed by R_p = k[MAIB]^0.5[DMEI]^2.4. k_p increased and k_t decreased with [DMEI]. The activation energies of overall polymerization, propagation and termination were estimated to be 34.5, 8.0, and 59.4 kJ/mol. Copolymerization of DMEI with styrene was also profoundly affected by the presence of LiClO₄. Such large effects of LiClO₄ on the homo- and copolymerization of DMEI are explicable in term of association of LiClO₄-complexed DMEI monomers. © 1997 John Wiley & Sons, Inc.