On the copolymerization of acrylonitrile with styrene in the presence of Lewis acid, 3. Photoinitiated copolymerization

The rate of the acrylonitrile (AN)-styrene (St) copolymerization (R_p) photoinitiated (λ=365 nm) by the St? AN? ZnCl₂ complex at 30°C is proportional to the square root of the intensity of radiation. The limiting viscosity number [η] of alternating copolymers increases with the intensity of radiation. The 1/[η] vs. R_p relationship for the St? AN copolymers is similar as has been found for the initiation of copolymerization by thermal decomposition of 2,2-azoisobutyronitrile. Provided benzophenone combined with 2-propanol is used as a photosensitizer, the rate of the St? AN copolymerization in acetone—at constant concentrations of both comonomers, zinc chloride, and benzophenone—decreases with 2-propanol concentration in the reaction mixture. If benzophenone alone (e.g. without 2-propanol) is used as a photosensitizer under equal conditions, the observed values of the rate of copolymerization are lower in comparison with the system where the ternary molecular complex is empolyed as a photosensitizer. Moreover, R_p decreases with increasing concentration of benzophenone in the system. These findings are interpreted as a result of the termination reactions of ketyl radicals (hydroxydiphenylmethyl radicals) with macroradicals of copolymer.     

On the copolymerization of acrylonitrile with styrene in the presence of Lewis acid, 1. Effect of zinc chloride concentration

The copolymerization of acrylonitrile (AN) with styrene (St) is studied in the presence of Lewis acid (LA) (zinc chloride and zinc nitrate) in homogeneous reaction system. It is revealed that the rate of copolymerization (R_p) only slightly increases with the concentration of Lewis acid in the range of ratios [LA]/[AN]≦0,01 at constant concentrations of comonomers and source of radicals, i. e. 2,2′-azoisobutyronitrile (AIBN). An increase in R_p appears when the ratio [LA]/[AN]≧0,05 is reached. The dependence of log R_p on log [AIBN] is not linear in the systems containing Lewis acid, but is a function of both the total concentration of Lewis acid and AIBN in the reaction system. For the system St-AN-Zn(NO₃)₂ the dependence of the reciprocal value of molecular weight of copolymer on the rate of copolymerization is linear and does not exhibit the minimum found for the system St-AN-ZnCl₂. The results of kinetic investigations are interpreted from the view-point of the present ideas on the mechanism of copolymerization in the presence of Lewis acid.     

Photoinitiation, 6. Copolymerization of styrene with maleic anhydride photoinitiated by the excited charge-transfer complex styrene-maleic anhydride

The kinetics of styrene (St) copolymerization with maleic anhydride (MA) initiated by light (at λ = 365 nm) was studied in acetone, acetonitrile, chloroform, and N,N-dimethyl formamide at 30°C. With the exception of the chloroform containing system, the copolymerizations took place in homogeneous reaction media. The copolymerization rate R_p = ?d([St] + [MA])/dt was found to be a function of the mole ratio of the comonomers in the reaction mixture. For a given ratio of comonomers R_p and the molecular weight of the resulting copolymer were found to be a function of the donor number of the solvent used for a given rate of initiation. Due to the dependence of R_p on the concentration of an equimolar mixture of both comonomers in acetone on [St] (at constant [MA]), and on [MA] (at constant [St]) the participation of the exciplex {St…acetone}^* in the initiation reaction can be expected. The ratio of the overall rate constants for the propagation (k?_p) and termination (k?_t) reactions, k?_p/2k?_t, determined by a rotating sector technique, was found to depend on the composition of the comonomer mixture. The copolymerization rate is proportional to the square root of the intensity of incident light, which, together with the observed inhibition effect of oxygen points to a radical mechanism of the photoinitiated copolymerization of St with MA. In the presence of the photosensitizer benzophenone in the system St/MA/acetone an increase in R_p was observed, accompanied by a decrease in molecular weight of the copolymer in comparison with the system without benzophenone.     

Discussion on the mechanism of alternating copolymerization of styrene and maleic anhydride

To clear up the detailed mechanism of the alternating copolymerization of styrene (St) and maleic anhydride (MAn) concerning the initiation species, the propagation species, the tendency of the chain transfer reaction as well as the directional tendency of the reaction between copolymer radicals and monomer complexes, the role of the charge transfer complexes, characterization of end groups and additional donor effects were examined. The equilibrium constant of the St/MAn (1 : 1) complex was determined to be 0.31 by NMR spectroscopy, that suggested considerable amounts of complexes existing in the system. As expected, a small quantity of initiator (¹⁴C-azobisisobutyronitrile (AIBN)) was incorporated into the St/MAn copolymer. Chlorine atoms were scarcely incorporated into the copolymer synthesized in CCl₄ with AIBN or benzoyl peroxide (BPO) as an initiator. Hence the copolymerization was considered to be induced only by attacke of initiator radicals to the monomer or the complexes, contrary to the usual conception of telomerization. When the electron donor monomer was added to the system, the terpolymerization could be treated as a copolymerization of the two complexes, i.e., St/MAn and Donor/MAn. By adding naphthalene the rate maximum point shifted from higher concentration of MAn to the equivalent concentration of St and MAn. Degradative chain transfer to N.N-dimethylaniline was observed, confirming the existance of poly-MAn radicals. It was suggested from these results that the charge transfer complex and uncomplexed MAn took part in the copolymerization of St and MAn. This was proved kinetically. The whole mechanism was discussed.     

Phase separation in random copolymers from high conversion free radical copolymerization, 1

The phase separation of random copolymers during free radical copolymerization to high conversion was studied. In order to prepare in situ high impact thermoplastics during the copolymerization process, the attention was focussed on systems in which the more reactive comonomers form thermoplastics, whereas the less reactive components form elastomeric homopolymers. The studied systems (A, B) were (AN, EA), (AN, VA), (CHMA, MA) and (S, BA) (AN: acrylonitrile, EA: ethyl acrylate, VA: vinyl acetate, CHMA: cyclohexyl methacrylate, MA: methyl acrylate, S: styrene, BA: butyl acrylate). These copolymers display varying compositional heterogeneity depending on the different radical reactivity ratios and the feed composition used. Curves of instantaneous copolymer composition versus fractional conversion and the distribution functions of chemical composition were calculated for the various systems. In addition, miscibility diagrams of corresponding low conversion copolymers A_xB_1−x and A_yB_1−y, derived from the same monomer pair (A, B) but differing in composition, were recorded at high temperatures. Phase separation was detected by light microscopy and differential scanning calorimetry (DSC) using cast films. The onset of phase separation depending on the actual stage of copolymerization was recorded. The composition of the copolymers at the onset of phase separation was compared with the miscibility of low conversion copolymer blends. A satisfactory prediction of the start of phase separation during copolymerization is presented.     

Die Copolymerisation von Natriumäthylensulfonat mit Acrylnitril

To elucidate the contradictions in the published values of reactivity ratios of the comonomers sodium ethylenesulfonate (NaAS) and acrylonitrile (AN), a series of radical compolymerizations was carried out in conc. solutions of zinc chloride. The results of the calculation of the reactivity ratios, r_NaAS=0,13 and r_AN=8,10, showed that both comonomers represent an ideal system for which r_AN. r_NaAS ≈ 1.     

Copolymerization of styrene with acrylonitrile initiated by 2-methyl-2-undecanethiol

The copolymerization of styrene (St) with acrylonitrile (AN) initiated with 2-methyl-2-undecanethiol (RSH) was investigated. Kinetic studies revealed that the initial rate of the copolymerization, which does not occur spontaneously in the absence of RSH, obeys the following expression: R_p ∝? [RSH]^x, where x is 0,5 when [RSH] ranges from 3,4.10^?4 to 3,4.10^?3 mol/l and 0 when [RSH] is larger than 3,4.10^?3 mol/l. The initial copolymerization rate, R_p, increases with increasing percentage of AN in the monomer feed. From the slope of ln R_p vs. 1/T, the apparent activation energy, E_app, was calculated to be 17 kJ/mol in the temperature range of 30°C to 50°C. RSH is the only initiating species, and it also plays a role as chain-transfer agent. The value of M _w/M _n, which varies from 1,5 to 2,0, is typical of a free-radical poymerization. The reactivity ratios were calculated to be r_St = 0,42 ± 0,04 and r_AN = 0,02 ± 0,03. It seems to be unnecessary to introduce a penultimate effect for explaining the experimental data.     

Alternating copolymerization of acrylonitrile with butadiene in the presence of binary and ternary catalytic systems of Lewis acids type

Acrylonitrile (AN) and butadiene (BD) were copolymerized in the presence of binary C₂H₅AlCl₂? MtX_n (MtX_n = metal halide or metal alkoxide) and ternary ZnCl₂? R_mMtX_n? VOCl₃ (R_mMtX_n = metal alkyl or alkylmetal chloride) catalytic systems. The yield of the copolymer (mole ratio of units AN/BD = 1:1) formed in the presence of the above systems, and the effects of the molar proportion of catalyst components, of the reaction temperature and time on the copolymer yield in some systems were determined. The role of individual components of binary and ternary catalytic systems in the copolymerization is discussed.     

Kinetic and ESR studies on radical polymerization. ESR and kinetic evidences for the penultimate effect in the radical-initiated copolymerization of N-cyclohexylmaleimide and bis(2-ethylhexyl) itaconate in benzene

The copolymerization of N-cyclohexylmaleimide ( 1 ) (M₁) and bis(2-ethylhexyl) itaconate ( 2 ) (M₂) with dimethyl 2,2′-azoisobutyrate ( 3 ) as an initiator was carried out at 50°C in benzene. Monomer reactivity ratios were estimated as r₁ = 0,34 and r₂ = 0,38. The copolymerization rate (R_p) and the molecular weight of the resulting copolymer increased with increasing concentration of 1 when the total concentration of comonomers was fixed at 1,00 mol. L^?1. R_p was proportional to [ 3 ]^0,5, indicating a usual bimolecular termination in the copolymerization. An electron spin resonance (ESR) spectrum of the propagating polymer radicals was observable in the actual copolymerization system at 50°C. The spectrum of the copolymerization system is inexplicable in terms of any superposition of spectra observed in the corresponding homopolymerization systems, revealing that some penultimate monomeric unit causes a change in the ESR spectrum, that is, the structure of propagating polymer radical. The apparent rate constant of propagation (k_p) and termination (k_t) were estimated by ESR. The k_p values (1,5–50 L · mol^?1 · s^?1) are fairly higher than those estimated on the basis of the terminal model, affording another piece of evidence for the penultimate effect. The k_t value (1,8–5,4·10³ L · mol^?1 · s^?1) shows a behaviour similar to that of the intrinsic viscosity of the resulting copolymer on varying the monomer feed composition, which seems to reflect diffusion-control of termination reactions.     

Cationic copolymerization of norbornadiene with styrene by AlEtCl2/tert-butyl chloride catalyst system, 1. Effect of norbornadiene/styrene feed ratio

The cationic copolymerization of norbornadiene (NBD) and styrene (St) was carried out with the AlEtCl₂/tert-butyl chloride catalyst system in CH₂Cl₂ at ?50°C, and the effect of NBD/St feed ratio on the solubility, the glass trtansition temperature (T_g) and the molecular weight of the copolymers was investigated. A soluble copolymer was prepared at 40 mol-% (or above) of St in the feed, although the NBD homopolymer comprised an insoluble fraction which might have been formed by a crosslinking reaction between the double bonds in the NBD units of the polymer. The copolymer has a statistically random sequence distribution of the two monomeric units not only in the polymer chain but also over the whole molecular weight range (from 10³ to 10⁶). The T_g of the amorphous copolymer is controlled by the NBD/St composition in the range from 100°C through 290°C. A soluble copolymer with highest T_g (ca. 170°C) could be prepared at a NBD/St feed ratio of 60/40 mol-%.     

Polymerizations of 1-(9-anthryl)ethyl methacrylate and charge-transfer complex formations with its polymers

1-(9-Anthryl)ethyl methacrylate (9AEMA) was prepared by condensation of 1-(9-anthryl)ethanol with methacryloyl chloride. The rate of AIBN initiated polymerization of 9AEMA in benzene at 60°C was intermediate between the polymerization rates of styrene and methyl methacrylate. 9AEMA/styrene copolymerization studies at 60°C resulted in the copolymerization parameters r_9AEMA = 0,42±0,07 and r_st = 0,37 ± 0,08. Charge transfer complexes are formed between p- chloranil and the 9AEMA homo- and copolymers. The absorption maxima of the CT-complexes shifted to higher wavelengths with increasing 9AEMA content of the copolymers, whereas the equilibrium constant of the CT-complex formation was independent of copolymer composition. Both the complex formation enthalpies and entropies decreased with increasing 9AEMA content of the copolymers.     

Solvent effects on radical polymerization of cyclododecyl acrylate, 2. Copolymerization

The radical copolymerization of cyclododecyl acrylate (CDA) with styrene (St) or acrylonitrile (AN) was studied in bulk, benzene, tetrahydrofuran, or dioxane at 60°C, and was compared with that of cyclohexyl acrylate (CHA). In the copolymerization with St, the change in the ester groups or the used solvents influenced the reactivity of both acrylates in the same manner as their homopolymerization rates. Approximately, CDA and CHA behaved like methyl methacrylate in the copolymerization with St. Contrary, in the cases of copolymerization of CDA with AN, peculiar results were obtained and interpreted in terms of characteristic association states of the monomers in the solutions. In benzene solution both the monomer reactivity ratios, r₁ and r₂, are larger than unity (M₁ = AN, M₂ = CDA; r₁ = 1,7, r₂ = 2,0).     

Synthesis and characterization of some acrylic monomer/sulfur dioxide copolymers

The copolymerization of acrylic monomers (M) [acrolein (AL), methyl acrylate (MA), acrylamide (AM) and acrylonitrile (AN)] with liquid sulfur dioxide (S) at low temperature and high dilution in the presence of tert-butyl hydroperoxide gives high SO₂ incorporation into the resulting copolymers. Analysis of the composition of these polysulfones, by elemental analyses and ¹³C NMR, shows that they consist mostly of the MMM, SMM, MMS and MSM triad monomer sequences. Thermal (TG) analyses of selected samples demonstrate that their thermal stability, up to 30% weight loss, increases for different acrylic comonomers as follows: AL < AM < MA < AN. Preliminary flammability tests revealed that flame retardancy increases with increasing SO₂ content in the copolymer.     

Synthesis and characterization of homo- and co-oligomers of tetracyclo[4.4.0.12,5.17,10]dodecene-3 by cationic polymerization

Cationic homopolymerization of tetracyclo[4.4.0.1^2,5.1^7,10]dodecene-3 (TCD) and its copolymerization with styrene (St) were carried out with the catalyst system Al(C₂H₅)Cl₂/tert-butyl chloride, and the effects of temperature and TCD/St feed ratio, on polymer solubility, molecular weight and glass transition temperature (T_g) were investigated. A soluble oligomer with a molecular weight of 1000 was prepared by homopolymerization of TCD at +10°C or by copolymerization with St (>4 mol-% in the feed) at ?50°C. ¹³C NMR analysis of the TCD homo- and TCD/St copolymers revealed both 3,4- and 3,11-additions for the repeating units from TCD. A polymerization mechanism including initiation, propagation, termination (deprotonation), and further crosslinking reactions is proposed. Moreover, it was demonstrated that a TCD/St copolymer with a controlled T_g in the range of 100 to 260°C can be prepared by selecting the TCD/St composition.     

Terpolymérisation acrylonitrile/styrène/acrylate de méthyle, 3. Etude du mécanisme de la copolymérisation en emulsion

Emulsion copolymerization appears to be very suitable for mechanistic investigations in emulsion polymerization. A study of the emulsion copolymerization under various conditions (batch, semi-continuous, composition controlled reactor) of the styrene (S)/acrylonitrile (A) system is presented, which may have model character due to the very different monomer solubilities both in water and in their polymers. Comparison of copolymer composition with monomer mixture composition in the various phases (determine by gas chromatography analysis after the emulsion has been centrifuged) confirms that the monomer/polymer particles are the main loci of polymerization. The monomier / water ratio and the amount of emulsifier sodium dodecylsulfate influence the polymerization rate (R_p) as well as the particle size (D?_p). The existance of a monomer droplet phase seems also to be determinant for many features of such as a copolymerization as, e. g., the evolution of R_p, D?_p, number of particles (N_p) etc. In addition, in a batch process, the composition drift versus conversion modified the monomer solubilities within the particles, the emulsifier adsorption, the particle growth which appeared to reach a limiting size, mainly due to electrostatic hindrance. It is also observed, Whatever may be the emulsion polymerization process, that R_p is not proportional towards N_p, but towards dN_p/dt; this might be related to the particle growth rate. A. mechanism is derived, based on experimental data and thermodynamic considerations, which allows to take into account molecular interactions (χ), coplymer composition, D_p, interfacial tension (γ), and above all, the actual monomer feed composition within the polymerization loci, as the copolymerization proceeds.     

Copolymer-monomer miscibility during copolymerization

Significant drift in the compositions of copolymer and of unreacted monomer mixture is predicted to occur during the bulk copolymerization of N-vinyl-2-pyrrolidone (VP) with butyl acrylate (BA), when the inital feed mixture contains 75 wt.-% VP. The drift in copolymer composition has been confirmed by 1 the optical appearance and glass transition (T_g) behaviour of the products of the γ-ray initiated copolymerization at various fractional conversions (C) and 2 the T_g behaviour of low-conversion samples of poly(VP-co-BA) blended in propertions so as to simulate the overall composition of material that would be present cumulatively at selected values of C during an actual copolymerization. The compositions of unreacted monomer mixtures co-existing with copolymer at selected conversions have been calculated and intrinsic viscosities [η] of blends dissolved in these VP/BA mixtures have been measured. Theta conditions for the blends have been established turbidimetrically in chloroform/heptane and the corresponding values of [η]_Θ measured. The chain expansion factors thereby derived from [η] and [η]_Θ show a decreasing affinity of copolymer for residual monomer during the course of copolymerization.     

Copolymerization of styrene and butadiene with Co(acac)3‐methylaluminoxane catalyst

The copolymerization of Styrene (St) and butadiene (Bd) with Co(acac)₃‐MAO catalyst was investigated. The copolymers consisting of St and Bd with highly cis‐1,4‐structure could be synthesized with Co‐(acac)₃‐MAO catalyst without formation of homopolymer, although the St contents in the copolymer were not high. The copolymer composition curve for copolymerization of St and Bd with the Co(acac)₃‐MAO is different from that obtained with the Ni(acac)₂‐MAO catalyst. The additive effects of triphenylphosphine (TPP) and trifluoroacetic acid (TFA) on the copolymerization of St and Bd with the Co(acac)₃‐MAO catalyst were also investigated. The copolymer yields increased by adding TPP to the Co‐(acac)₃‐MAO catalyst, although the St contents in the copolymer did not change. In the microstructure of the Bd units in the copolymers, 1,2‐contents increased remarkably. The copolymer yields and the microstructure of the copolymer did not change by addition of TFA.     

Charge-transfer complex between p-oxathiene and maleic anhydride and its relative reactivity in alternating copolymerization

Charge-transfer complex formation and alternating copolymerization of p-oxathiene (POT)-maleic anhydride (MAnh) system were studied. Relative reactivity of POT-MAnh complex was obtained from three kinds of terpolymerizations. For example, in terpolymerization of POT, MAnh and acrylonitrile (AN), monomer reactivity ratios of POT-MAnh complex and AN were found as r₁ (complex)=55,8 and r₂ (AN)=0,0176 at 60°C. POT-MAnh, p-dioxene-MAnh and vinyl ether-MAnh systems were compared in relative reactivity and some physical properties concerning charge-transfer complex. The reactivity of those MAnh complexes was found to be controlled more significantly by some properties related to electron-donating power of donors rather than by resonance and polarity terms of separate donor monomers.     

Tailored rigid-flexible block copolymers, 2. Intrinsic viscosity behavior

The determination of single-chain properties for heterogeneous molecules such as a rigid-flexible block copolymer requires the use of solvents capable of reducing selective interactions involving the blocks and the diluent. Molecular dispersion is displayed by a two-block copolymer of benzoyl-terminated poly(p-benzamide) (poly(imino-1,4-phenyl-enecarbonyl) and anilino-terminated poly(m-phenyleneisophthalamide) in 96 wt.-% sulfuric acid. For a series of such copolymers, intrinsic viscosities were measured avoiding degradation effects due to H₂SO₄. The intrinsic viscosity ([η]) of the copolymers was found to decrease with increasing length of the flexible block, but [η] remained larger than the value corresponding to an equimolar blend of rigid and flexible homopolymers. These results are explained by theoretical considerations within the framework of the hydrodynamic behavior of single rodlike and single coiled macromolecules.     

High conversion copolymerization, 1. Kinetics of the copolymerization of styrene and maleic anhydride

The copolymerization of styrene (S) with maleic anhydride (MAn) in 1,4-dioxane at 60, 70 and 80°C up to high conversion (≈ 98%) was followed by differential scanning calorimetry. The rate of copolymerization increases up to 20 – 40% conversion of both monomers and then gradually decreases to zero. The increase in the copolymerization rate is more pronounced for equimolar ratios [S]/[MAn] as compared to ratios with an excess of S. For a given mole ratio of S and MAn the copolymerization rate in 1,4-dioxane is higher at higher total monomer concentrations and/or at higher temperatures. The heat of copolymerization is 81,6 kj · mol^?1 for the equimolar [S]/[MAn] mixture. For mixtures with [S]/[MAn] > 1 the heat of reaction is between 70 and 80 kj · mol^?1. The limitingconversion of styrene for [S]/[MAn] = 1 is about 98%, and for [S]/[MAn] > 1 it is a function of the [S]/[MAn] ratio. Assuming exclusively the formation of an alternating S/MAn copolymer the following relation is derived. for the ratio of the apparent rate constants of propagation k?_p, and termination k?</_t.