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.     

Chain transfer in anionic polymerization. Determination of chain-transfer constants by using carbon-14-labeled chain transfer agents

A method is described in which ¹⁴C-labeled chain-transfer agents are employed to measure chain-transfer constants in anionic polymerization as low as 10^?6. Each chain-transfer step incorporates one molecule of the chain-transfer agent into the polymer so that measurement of the activity and conversion allows evaluation of the chain-transfer constant. This method is independent of the initiator concentration and efficiency, making the technique especially useful when problems with the initiator are encountered. The experimental procedure is described in detail for the case of chain transfer to toluene in the n-butyllithium-initiated polymerization of styrene, where C_RH was found to be 5 × 10^?6. A mathematical treatment is given showing the relationship between the degree of polymerization (DP _n) and chain transfer.     

Syndiospecific polymerization of styrene. I. Tetrabenzyl titanium/methylaluminoxane catalyst

Syndiospecific polymerization of styrene (S) was catalyzed by Bz₄Ti/MAO (tetrabenzyltitanium/methylaluminoxane). The product was separated into syndiotactic polystyrene (s-PS) and atactic polystyrene (a-PS) by extraction of the latter with boiling 2-butanone. Over the broad range of catalyst concentrations, compositions, and polymerization temperatures, the catalytic activity is 150 ± 80kg PS (mol Ti mo S h)^?1 with 89 ± 5% yield of s-PS (SY). The concentration of active species has been determined by radiolabeling. Only about 1.7% of Bz₄Ti initiates syndiospecific polymerization at 60°C with values of rate constants for propagation and for chain transfer to MAO of 1.38 (M s)^?1 and 5.2 × 10^?4s^?1, respectively. Nonspecific polymerization was initiated by 16.8% of the Ti having values of 0.056 (M s)^?1 and 6.5 × 10^?4 s^?1 for the rate constants of propagation and transfer, respectively. The effect of solvent polarity on the polymerization was studied using toluene mixed with chlorobenzene of o-dichlorobenzene as solvents. An increase of effective dielectric constant from 2.43 to 5.92 reduces the polymerization activity by a factor of two and lowers SY to mere 39%. In 1 : 1 toluene/chlorobenzene solvent mixture, it was found that 1.3% and 26% of the Bz₄Ti initiate syndiospecific and nonspecific polymerizations of styrene, respectively. The Bz₄Ti/MAO catalyst is poor in both productivity and stereoselectivity.     

Vinyl polymerization of acrylamide initiated by Thallium(III) ions in solution

Kinetics of polymerization of acrylamide initiated by Thallium(III) perchlorate was investigated in aqueous perchloric acid medium in the temperature range of 55–70°C. The rates of polymerization were measured varying the concentration of the monomer, initiator, and perchloric acid. The rate of polymerization was found to increase with increase of temperature, monomer concentration, initiator concentration, and perchloric acid concentration. The effect of additives like different solvents, surfactants, and retarders on the rate of polymerization was studied. Molecular weights of the polymer were determined by viscometry. The chain transfer constants for the monomer (C_M) and that for the solvent dioxan (C_s) were calculated to be 7.33 × 10^?3 and 6.66 × 10^?3, respectively. From the Arrhenius plot, the overall activation energy (E_a) was calculated to be 10.68 kcal/mol. The energy of initiation was calculated to be 12.36 kcal/mol. Depending on the results obtained, a suitable reaction mechanism has been suggested and a rate equation has been derived.     

Long branching in poly(vinyl acetate) and poly(vinyl alcohol). III. Kinetic study of the branching reaction in the radical polymerization of vinyl acetate

The branching reaction in the radical polymerization of vinyl acetate was studied kinetically. Branching occurs by polymer transfer as well as terminal double-bond copolymerization. The chain-transfer constants to the main chain (C_p,2) and to the acetoxy methyl group (C_p,1) on the polymer were calculated on the basis of the experimental data described in the preceding paper giving C_p,2 = 3.03 × 10^?4, C_p,1 = 1.27 × 10^?4 at 60°C, and C_p,2 = 2.48 × 10^?4, C_p,1 = 0.52 × 10^?4 at 0°C. Chain transfer to monomer is important with respect to the formation of the terminal double bond. The total values of transfer constants to the α- or β-position in the vinyl group and the acetoxymethyl group in vinyl acetate was determined to be 2.15 × 10^?4 at 60°C. The transfer constant to the acetyl group in the monomer (C_m,1) was also evaluated to be 2.26 × 10^?4 at 60°C from the quantitative determination of the carboxyl terminals in PVA. These facts suggest that the chain-transfer constant to the α- or β-position in the monomer (C_m,2) is nearly equal to zero within experimental error. Copolymerization reactivity parameters of the terminal double bond were also estimated. In conclusion, it has become clear that the formation of nonhydrolyzable branching by the terminal double-bond reaction can be almost neglected, and hence that the long branching in PVA is formed only by the polymer transfer mechanism. On the other hand, a large number of hydrolyzable branches in PVAc are prepared by the terminal double-bond reaction rather than by polymer transfer.     

Chain transfer constants for vinyl monomers polymerized in methyl oleate and methyl stearate

Chain transfer constants were obtained for styrene, methyl methacrylate, methyl acrylate and vinyl acetate, polymerized in methyl oleate and methyl stearate at 60°C. Transfer constants increased in the order: methyl methacrylate < styrene < methyl acrylate ? vinyl acetate in both solvents. Average values of the transfer parameters were: for methyl oleate, Q_tr = 2.04 × 10^?4, e_tr = 1.08; for methyl stearate, Q_tr = 0.373 × 10^?4, e_tr = 1.01. Indication that polar species predominate in the transition state is supported by the observed order of reactivity. The usual rate dependence appeared to be followed by all of the monomers except vinyl acetate, which was retarded, severely in methyl oleate. Transfer in methyl oleate was about 5.8 times greater than that found in methyl stearate for these four monomers. The internal allylic double bond of methyl oleate had about the same reactivity in transfer as had the terminal unsaturation in N-allylstearamide at 90°C. Rough estimates were obtained of the monomer transfer constants for the long side-chain homologs of these four monomers from the respective monomer transfer constants and the experimental transfer constants, corrected for transfer to the labile groups of the solvent. It was concluded that the rate of polymerization would determine in large measure the degree of polymerization for the reactive 18-carbon homologs but that the molecular weight of poly(vinyl stearate) and (oleate) will be regulated primarily by transfer to monomer.     

Rate constants for the reactions of chlorine atoms with hydrochloroethers at 298 k and atmospheric pressure

The relative rate technique has been used to determine the rate constants for the reactions Cl + CH₃OCHCl₂ → products and Cl + CH₃OCH₂CH₂Cl → products. Experiments were carried out at 298 ± 2 K and atmospheric pressure using nitrogen as the bath gas. The decay rates of the organic species were measured relative to those of 1,2‐dichloroethane, acetone, and ethane. Using rate constants of (1.3 ± 0.2) × 10^?12 cm³ molecule^?1 s^?1, (2.4 ± 0.4) × 10^?12 cm³ molecule^?1 s^?1, and (5.9 ± 0.6) × 10^?11 cm³ molecule^?1 s^?1 for the reactions of Cl atoms with 1,2‐dichloroethane, acetone, and ethane respectively, the following rate coefficients were derived for the reaction of Cl atoms (in units of cm³ molecule^?1 s^?1) with CH₃OCHCl₂, k= (1.04 ± 0.30) × 10^?12 and CH₃OCH₂CH₂Cl, k= (1.11 ± 0.20) × 10^?10. Errors quoted represent two σ, and include the errors due to the uncertainties in the rate constants used to place our relative measurements on an absolute basis. The rate constants obtained are compared with previous literature data and used to estimate the atmospheric lifetimes for the studied ethers. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 420–426, 2005     

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.     

Rates and mechanisms of oxidation of ZnTPP by CCI3O2 radicals in various solvents

Trichloromethylperoxyl radicals were produced by pulse radiolysis of air saturated solutions containing CCl₄. The rate constants for the reaction of CCl₃O₂ radicals with zinc tetraphenylporphyrin (ZnTPP) were determined in various solvents. They were found to vary between 3 × 10⁷ and 3 × 10⁹ M^?1 s^?1. The changes in rate constants result from complexation of ZnTPP with the different solvents, but did not correspond to changes in redox potential of ZnTPP. The rate constants were found to depend on the strength of the axial complexation, indicating an inner sphere mechanism whereby the radical binds to the metal prior to electron transfer.     

Anomalous solubility of polyacrylamide prepared by dispersion (precipitation) polymerization in aqueous tert‐butyl alcohol

Polyacrylamide prepared by dispersion (precipitation) polymerization in an aqueous t‐butyl alcohol (TBA) medium is only partially soluble when the TBA concentrations in the polymerization media are in the range 82 vol % < TBA < 95 vol %. Independent experiments with a soluble (linear) sample of polyacrylamide show that the polymer swells sufficiently in the aforementioned media to lower the glass‐transition temperature of the polymer below the polymerization temperature (50 °C). The anomalous solubility has been attributed to the crosslinking of polymer chains that occurs during the solid‐phase polymerization of acrylamide in the swollen polymer particles. It is postulated that some of the radical centers shift from the chain end to the chain backbone during solid‐phase polymerization by chain transfer to neighboring polymer molecules, and when pairs of such radicals come into close vicinity, crosslinking occurs. However, dispersion (precipitation) polymerization in other media such as aqueous methanol and aqueous acetone yields polymers that are soluble. This result has been attributed to the fact that the polymer radical undergoes a chain‐transfer reaction with these solvents at a much faster rate than with TBA, which overcomes the effect of the polymer‐transfer reaction. Even the addition of as little as 5% methanol to a TBA–water mixture (TBA:water = 85:10) gives rise to a soluble polymer. The chain‐transfer constants for acetone, methanol, and TBA have been determined to be 9.0 × 10^?6, 6.9 × 10^?6, and 1.48 × 10^?6, respectively, at 50 °C. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3434–3442, 2001     

Effect of metal salts on polymerization. Part I. Polymerization of vinylpyridine initiated with cupric acetate

The polymerization of vinylpyridine initiated by cupric acetate has been studied. The rate of polymerization was greatly affected by the nature of the solvent. In general polar solvents increased the rate of polymerization. Polymerization was particularly rapid in water, acetone, and methanol. The initial rate of polymerization of 4-vinylpyridine (4-VP) in a methanol–pyridine mixture at 50°C. is R_p = 6.95 × 10^?6[Cu¹¹]^1/2 [4-VP]² l./mole-sec. The activation energy of initiation by cupric acetate is 5.4 ± 1.6 kcal./mole. Polymerization of 2-vinylpyridine and 2-methyl-5-vinylpyridine with the same initiator was much slower than that of 4-VP. Dependence of R_p on monomer structure and solvent is discussed. Kinetic and spectroscopic studies led to the conclusion that the polymerization of 4-VP is initiated by one electron transfer from the monomer to cupric acetate in a complex having the structure, (4-VP)₂Cu(CH₃COO)₂.     

Kinetic model of reversible addition‐fragmentation chain transfer polymerization in microemulsions

A simplified kinetic model for RAFT microemulsion polymerization has been developed to facilitate the investigation of the effects of slow fragmentation of the intermediate macro‐RAFT radical, termination reactions, and diffusion rate of the chain transfer agent to the locus of polymerization on the control of the polymerization and the rate of monomer conversion. This simplified model captures the experimentally observed decrease in the rate of polymerization, and the shift of the rate maximum to conversions less than the 39% conversion predicted by the Morgan model for uncontrolled microemulsion polymerizations. The model shows that the short, but finite, lifetime of the intermediate macro‐RAFT radical (1.3 × 10^?4–1.3 × 10^?2 s) causes the observed rate retardation in RAFT microemulsion polymerizations of butyl acrylate with the chain transfer agent methyl‐2‐(O‐ethylxanthyl)propionate. The calculated magnitude of the fragmentation rate constant (k_f = 4.0 × 10¹–4.0 × 10³ s^?1) is greater than the literature values for bulk RAFT polymerizations that only consider slow fragmentation of the macro‐RAFT radical and not termination (k_f = 10^?2 s^?1). This is consistent with the finding that slow fragmentation promotes biradical termination in RAFT microemulsion polymerizations. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 604–613, 2010     

Effect of chlorosilanes on the radical polymerization of styrene and methyl methacrylate

Styrene (St) and methyl methacrylate (MMA) were polymerized by azobisisobutyronitrile at 50°C. in the presence of silanes such as tetramethylsilane, trimethylcholorosilane, dimethyldichlorosilane, methyltrichlorosilane, and tetrachlorosilane. The polymerization rates of both St and MMA in the presence of silanes were nearly equal to those in the absence of silanes. On the other hand, the molecular weights decreased gradually as the concentration of chlorosilane increased. The chain transfer constants of all the silanes in the polymerization of St and MMA at 50°C. were calculated by Mayo's equation. The chain transfer constants of Me₄Si, Me₃SiCl, Me₂SiCl, MeSiCl₃, and SiCl₄ were 0.31 × 10^?3, 1.25 × 10^?3, 1.78 × 10^?3, 1.92 × 10^?3, and 2.0 × 10^?3, for St and 0.13 × 10^?3, 0.22 × 10^?3, 0.245 × 10^?3, 0.27 × 10^?3, and 0.30 × 10^?3, for MMA, respectively. From these results, it was found that the Si? Cl bond was radically cleaved. The Q_tr values of the silanes, in the same order as above, were found to be 1.03 × 10^?4, 2.33 × 10^?4, 2.83 × 10^?4, 3.10 × 10^?4, and 3.35 × 10^?4, respectively and the e_tr values were +0.58, +1.30, +1.50, +1.48, and +1.43, respectively.     

Trityl salt—initiated polymerization of α-methylstyrene

The initiation reaction of the polymerization of α-methylstyrene by trityl tetrachloroferate and tritylhexachloroantimonate in 1,2-dichloroethane at 20°C was studied. The rate constants were 14 × 10^?3 and 27 × 10^?3 L mol^?1s^?1, respectively. The dissociation constants of tritylterachloroferate (K_d = 0.88 × 10^?4M^?1) and tritylhexachloroantimonate (K_d = 2.64 × 10^?4M^?1) was determined. The effect of electron acceptors and donors on the dissociation equilibrium and initiation rate was investigated. It was shown that in strongly dissociated ion pairs such as stable carbenium salts the electron donors and acceptors have no appreciable effect on the magnitude of the dissociation. The temperature dependence of the rate constants in the ?20–+20°C range yielded the following thermodynamic parameters for trityltetrachloroferate: E_i = 8.54 kcal/mol; A = 3.2 × 10⁴ mol^?1s^?1; ΔH* = 8 kcal/mol; and S* = ?39.8 eu.     

Catalytic action of metallic salts in autoxidation and polymerization. IX. Polymerization of methyl methacrylate with sodium hexanitrocobaltate(III) in mixed solvent of acetone and water

Polymerization of methyl methacrylate with some cobalt (III) complexes was carried out in various solvents and in mixed solvents of acetone and water or alcohols. Sodium hexanitrocobaltate(III) was found to be an effective initiator in mixed solvent of water and acetone. The kinetic study on the polymerization of methyl methacrylate with Na₃[Co(NO₂)₆] in a water-acetone mixed solvent gave the following over-all rate equation: R_p = 8.04 × 10⁴ exp{ ?13,500/RT} [I]^1/2[M]² (mol/1.?sec). The effects of various additives on polymerization rate and the copolymerization curve with styrene suggest that polymerization proceeds via a radical mechanism. The dependence of the polymerization rate on the square of monomer concentration and the spectroscopic data were indicative of the formation of a complex between initiator and monomer.     

Intermolecular interaction between squarylium cyanine and porphyrin

In this paper, the interaction between squarylium cyanine and porphyrin in chloroform is investigated by absorption and fluorescence spectroscopy. Emphasis has been put on the mechanism of intermolecular energy transfer. The overlap integral J between the absorption spectrum of squarylium cyanine and the fluorescence spectrum of porphyrin was calculated, which reveals that the singlet-singlet energy transfer may occur from porphyrin to squarylium cyanine in solution. In comparison of the observed rate constant [kqII=6.1 ×1013 (mol/L)-1·s-1] for fluorescence quenching of porphyrin by squarylium cyanine with the diffusion rate constant in chloroform [kdif=1.1×1010 (mol/L)-1·s-1] and the rate of energy transfer [ket≤6.7×104 (mol/L)-1·s-1 in the experimentally dilute solutions] estimated from Forster formula, the possibility of energy transfer by electron exchange or/and coulombic mechanism could be excluded. So it has been definitely convinced that the intermolecuiar energy transfer between them is     

The flash photolysis of aqueous solutions of rhodizonic and croconic acids

The flash photolysis of aqueous solutions of rhodizonic and croconic acids has been studied in the presence and absence of electron acceptors. No transient absorption which could be identified with an excited state was observed with either anion. The rate of recovery of the ground state in the absence of additives was a first-order process with both acids and gave rate constants for deactivation of the excited state, k_D, of 2.4 × 10⁵ s^?1 for rhodizonate and 2.8 × 10⁵ s^?1 for croconate. With croconate dianion in the presence of three acceptors, 4-nitrobenzylbromide, methylviologen, and biacetyl, a transient absorption was detected, with a maximum absorbance at 500 nm, and was tentatively identified with the monoanion radical, formed following electron transfer to the acceptor. From the rate of growth of the transient, rate constants for the rate of electron transfer to the acceptor were measured as follows: 4-nitrobenzylbromide: 2.8 × 10⁹ M^?1 s^?1; methyl viologen: 3.7 × 10¹⁰ M^?1 s^?1; and biacetyl: 2.0 × 10⁸ M^?1 s^?1. The significance of the measurements is discussed in relation to the mechanism proposed for the photochemical reactions of these dianions. © 1994 John Wiley & Sons, Inc.     

Photopolymerization of vinyl monomers in the presence of chlorosilane compounds

The photopolymerization of vinyl monomers (methyl methacrylate and styrene) was investigated in the presence of chlorosilane compounds. It was found that these additives acted as photosensitizers. In the case of the photopolymerization of methyl methacrylate, the rate of polymerization was found to be proportional to the concentration of methyl methacrylate and to the square root of the chlorosilane concentration. The chain-transfer constants of these photosensitizers, SiCl₄, CH₃SiCl₃, (CH₃)₂SiCl₂, (CH₃)₃-SiCl, and (CH₃)₄Si, with ultraviolet irradiation were 25.6 × 10^?3, 18.4 × 10^?3, 17.5 × 10^?3, 14.4 × 10^?3 and 0.5 × 10^?3, respectively, for methyl methacrylate.     

Solvent effects on the activation parameters of the reaction between an α‐tocopherol analogue and dpph•: The role of H‐bonded complexes

The analysis of the activation parameters for the formal H‐atom transfer reaction between 2,2,5,7,8‐pentamethyl‐6‐chromanol (ChrOH) and 2,2‐diphenyl‐1‐picrylhydrazyl (dpph^?) reveals that these parameters are effective probes of the actual reaction mechanism. Indeed, the A factors measured in various polar and apolar solvents are localized in three distinct domains according to whether the reaction occurs via outer‐sphere electron transfer (ET) from the anion ChrO^? or hydrogen atom transfer (HAT). For instance, A = 5.9 × 10⁵ M^?1 s^?1 and E_a = 2.5 kcal mol^?1 in cyclohexane where the reaction proceeds by HAT, whereas in methanol, ethanol, and their mixtures with water where there is a substantial ET contribution A > 10⁹ M^?1s^?1 and E_a > 7 kcal mol^?1. Interestingly, in nonhydroxylic polar solvents, A～ 10⁷ M^?1s^?1 and the E_a values reflect the H‐bond accepting ability of the solvent in agreement with the “standard” kinetic solvent effects on HAT reactions. Addition of small quantities of pyridine accelerates the reaction rates in these solvents. This suggests that the H‐bonded complex (ChrOH···Py) is able to react via intermolecular ET with dpph^?. It is known, in fact, that pyridine lowers the oxidation potential of phenols by ～0.5 V and the ΔG_ET of ChrOH + dpph^? consequently decreases by about 10 kcal mol^?1. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 524–531, 2012     

Transfer reaction of the polystyrene radical with electron-acceptor molecules of tetrachlorophthalanhydride

The transfer constants (C_s) of the polystyrene radical with some derivatives of phthalic acid have been determined. Among the agents used, tetrachlorophthalanhydride (TCPA) differs distinctly from other compounds by its value of C_s 3·1 × 10^?3 for thermal and 3·4 × 10^?3 for initiated polymerization of styrene. The values of C_s for phthalanhydride, dimethyl phthalate, and tetrachlorodimethyl phthalate are lower by two decimal orders. The considerable decrease in the degree of polymerization of styrene prepared in the presence of TCPA is mainly attributed to the increased reactivity of chlorine atoms in TCPA induced by the acceptor effect of anhydride ring. Participation of a TCPA-styrene complex in transfer reaction has been assumed but not proved.