The influence of steric factors on the mechanism of copolymerization of phenylvinyl alkyl ethers and maleic anhydride

By assuming that the initial rate of copolymerization (R_p) of phenylvinyl alkyl ether (I) and maleic anhydride (MAn) equals the sum of the rate of polymerization of free monomers R_p(f) and CT complex monomers R_p(CT) the reactivity ratios k_1c/k₁₂ and k_2c/k₂₁ were calculated for copolymerization of I(R = Me, n-Pr, iso-Pr, and sec-Bu) and MAn from the change of copolymerization rate with monomer feed at a constant total monomer concentration. From the equation R_p = R_p(f) + R_p(CT) were calculated R_p(f) and R_p(CT) by applying the generalized model described by Shirota and coworkers and it was found that the participation of CT complex monomers increases with an increase in total monomer concentration in the feed. It was also found that the degree of CT complex monomer participation depends largely on the steric factors. In the copolymerization of I which contains bulky isopropyl or sec-butyl group even in the dilute solutions, copolymerization proceeds by the addition of CT complex monomers.     

Alternating copolymerization of β-methylstyrene and maleic anhydride

Alternating copolymers of β-methylstyrene and maleic anhydride were prepared by free-radical-initiated polymerization in bulk and in toluene as a solvent. The reactivity ratios k_1c/k₁₂ and k_2c/k₂₁ were calculated from the change of copolymerization rate with a monomer feed at a constant total monomer concentration according to the generalized model of Shirota and coworkers. From the equation R_p = R_p(f) + R_p(CT) were calculated R_p(f) and R_p(CT), and it was found that in toluene the copolymerization proceeds predominantly by the addition of CT-complex monomers. Termination occurs predominantly by homotermination of β-methyl-styrene macro free radicals, k_t22, but the cross termination k_t21 is also operative.     

Free-Radical-Initiated Copolymerization of A-Methylstyrene with Maleimide

Alternating copolymers of α-methylstyrene (α-MeSt) and maleimide (MI) were prepared by free-radical initiated polymerization at different monomer-to-monomer concentrations in the feed in CHCl₃, as solvent. The equilibrium constant of -MeSt and MI was determined by the transformed Benesi-Hildebrand NMR method in CDCl₃, and has a value of 0.03 L/mol. From the equation R_p = R_p(f) + R_p(CT) proposed by Shirota and coworkers, R_pf) and R_pCT) were calculated, and it was found that the copolymerization of -MeSt with MI proceeds predominantly through participation of the CT complex. Alternating copolymers have a glass transition temperature of 567 K (DSC method). Alternating copolymer decomposes via a one-step reaction at 350°C.     

Elementary reaction analysis of the radical polymerization of α‐ethyl β‐N‐(α′‐methylbenzyl)itaconamates carrying (RS)‐ and (S)‐α‐methylbenzylaminocarbonyl groups

The polymerizations of α‐ethyl β‐N‐(α′‐methylbenzyl)itaconamates carrying (RS)‐ and (S)‐α‐methylbenzylaminocarbonyl groups (RS‐EMBI and S‐EMBI) with dimethyl 2,2′‐azobisisobutyrate (MAIB) were studied in methanol (MeOH) and in benzene kinetically and with electron spin resonance (ESR) spectroscopy. The initial polymerization rate (R_p) at 60 °C was given by R_p = k[MAIB]^{0.58 ± 0.05}[RS‐EMBI]^{2.4 ± 0.l} and R_p = k[MAIB]^{0.61 ± 0.05}[S‐EMBI]^{2.3 ± 0.l} in MeOH and R_p = k[MAIB]^{0.54 ± 0.05}[RS‐EMBI]^{1.7 ± 0.l} in benzene. The rate constants of initiation (k_df), propagation (k_p), and termination (k_t) as elementary reactions were estimated by ESR, where k_d is the rate constant of MAIB decomposition and f is the initiator efficiency. The k_p values of RS‐EMBI (0.50–1.27 L/mol s) and S‐EMBI (0.42–1.32 L/mol s) in MeOH increased with increasing monomer concentrations, whereas the k_t values (0.20?7.78 × 10⁵ L/mol s for RS‐EMBI and 0.18?6.27 × 10⁵ L/mol s for S‐EMBI) decreased with increasing monomer concentrations. Such relations of R_p with k_p and k_t were responsible for the unusually high dependence of R_p on the monomer concentration. The activation energies of the elementary reactions were also determined from the values of k_df, k_p, and k_t at different temperatures. R_p and k_p of RS‐EMBI and S‐EMBI in benzene were considerably higher than those in MeOH. R_p of RS‐EMBI was somewhat higher than that of S‐EMBI in both MeOH and benzene. Such effects of the kinds of solvents and monomers on R_p were explicable in terms of the different monomer associations, as analyzed by ¹H NMR. The copolymerization of RS‐EMBI with styrene was examined at 60 °C in benzene. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1819–1830, 2003     

Study on kinetics of copolymerisation of styrene and maleic anhydride in dioxane

Kinetics of the copolymerisation of styrene and maleic anhydride have been studied in dioxane at 50° using azobisisobutyronitrile as initiator. Explanation of the kinetic behaviour has been attempted in terms of the participation in propagation of a charge-transfer complex between the monomers along with propagation via free monomers. It is found that the complex model is able to explain most features of the copolymerisation of these monomers. It has been possible to determine the constants δ₁, δ₂, k_1c/k₁₂, k_2c/k₂₁ and Φ where k_1c/k₁₂ and k_2c/k₂₁ represent the specific rate constants of reaction of a particular type of radical with a dissimilar monomer site of the complex relative to that with a dissimilar free monomer. They are reviewed on the basis of available literature data. The cross-termination factor Φ is found to play an important role in the present system. An approximate value of $\text{k}{}_{\mathrm{t}}{}^{0.5}\text{k}{}_{\mathrm{p}}$ for maleic anhydride could also be found and this probably represents the first reported value for this constant from copolymerisation. The applicability of the generalised penultimate model is also briefly discussed.     

Determination of absolute rate constants for free radical polymerization of ethyl α-fluoroacrylate and characterization of the polymer

The absolute rate constants for propagation (k_p) and for termination (k_t) of ethyl α-fluoroacrylate (EFA) were determined by means of the rotating sector method; k_p = 1120 and k_t = 4.8 × 10⁸ L/mol.s at 30°C. The monomer reactivity ratios for the copolymerizations with various monomers were obtained. By combining the k_p values for EFA from the present study and those for common monomers with the monomer reactivity ratios, the absolute values of the rate constants for cross-propagations were also evaluated. Reactivities of EFA and poly(EFA) radical, being compared with those of methyl acrylate and its polymer radical, were found to be little affected by the α-fluoro substitution. Poly(EFA) prepared with the radical initiator was characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Although the glass transition temperature obtained by DSC for poly(EFA) resembled that of poly(ethyl α-chloroacrylate), its TGA thermogram showed fast chain de polymerization to EFA that was distinct from complicated degradation of poly(ethyl α-chloroacrylate).     

Some probability relations in multicomponent copolymers

It was previously shown that for a stationary random copolymer of A, B, and C, we have in general p(AB) + p(AC) = p(BA) + p(CA), etc., in place of p(AB) = p(BA) which is valid for a stationary binary copolymer. Here, p(AB) for example, is the probability that a randomly picked pair of consecutive comonomers in the polymer consists of an A followed by a B. For a stationary ternary copolymer produced by a first-order Markovian addition mechanism, we show that P_ABP_BCP_CA/P_ACP_CBP_BA = k, where k is a constant characteristic of a particular set of three monomers but independent of its composition. Here, P_AB is the conditional probability of finding a monomer of B given that its immediate predecessor is an A. We further show that if the individual rate constants of the monomer additions involved take a special form such as used in the Alfrey-Price Q–e scheme, then we have k = 1 irrespective of the kinds of monomers, and in addition we have p(AB) = p(BA), p(AC) = p(CA), etc. Thus, although these latter results were previously proposed by Ham as an alternative basis to supplant the Q–e scheme, they may rather be regarded as mathematical consequences of special assumptions adopted for the form of the individual rate constants. For a stationary random copolymer of four components A, B, C, and D, we have p(AB) + p(AC) + p(AD) = p(BA) + p(CA) + p(DA), etc., in general. For a first-order Markovian four-component copolymer, we show that there are seven different combinations of the conditional probabilities that are constants (k1, k2,…, k1) independent of the monomer composition. Again, if we assume the same special form for the rate constants involved, we find that all the seven constants k1, k2, …, k7 reduce to unity and p(XY) = p(YX) for X,Y, = A, B, C, D.     

Radical polymerization behavior of ethyl ortho-formylphenyl fumarate involving intramolecular hydrogen abstraction

The radical polymerization behavior of ethyl ortho-formyl-phenyl fumarate (EFPF) using dimethyl 2,2′-azobisisobutyrate (MAIB) as initiator was studied in benzene kinetically and ESR spectroscopically. The polymerization rate (R_p) at 60°C was given by R_p = k[MAIB]^0.76[EFPF]^0.56. The number-average molecular weight of poly(EFPF) was in the range of 1600–2900. EFPF was also easily photopolymerized at room temperature without any photosensitizer probably because of the photosensitivity of the formyl group of monomer. Analysis of ¹H? and ¹³C-NMR spectra of the resulting polymer revealed that the radical polymerization of EFPF proceeds in a complicated manner involving vinyl addition and intramolecular hydrogen-abstraction. The polymerization system was found to involve ESR-observable poly(EFPF) radicals under the actual polymerization conditions. ESR-determined rate constant (2.4–4.0 L/mol s) of propagation at 60°C increased with decreasing monomer concentration, which is mainly responsible for the observed low de-pendency of R_p on the EFPF concentration. Copolymerizations of EFPF with some vinyl monomers were also examined. © 1995 John Wiley & Sons, Inc.     

Kinetic and ESR studies on the radical polymerization of α‐n‐(α′‐methylbenzyl) β‐ethyl itaconamates derived from racemic and (s)‐α‐methylbenzylamines

The polymerization of α‐N‐(α′‐methylbenzyl) β‐ethyl itaconamate derived from racemic α‐methylbenzylamine (RS‐MBEI) by initiation with dimethyl 2,2′‐azobisisobutyrate (MAIB) was studied in methanol kinetically and with ESR spectroscopy. The overall activation energy of polymerization was calculated to be 47 kJ/mol, a very low value. The polymerization rate (R_p ) at 60 °C was expressed by R_p = k[MAIB]^0.5±0.05[RS‐MBEI]^2.9±0.1. The rate constants of propagation (k_p ) and termination (k_t ) were determined by ESR. k_p was very low, ranging from 0.3 to 0.8 L/mol s, and increased with the monomer concentration, whereas k_t (4–17 × l0⁴ L/mol s) decreased with the monomer concentration. Such behaviors of k_p and k_t were responsible for the high dependence of R_p on the monomer concentration. R_p depended considerably on the solvent used. S‐MBEI, derived from (S)‐α‐methylbenzylamine, showed somewhat lower homopolymerizability than RS‐MBEI. The k_p value of RS‐MBEI at 60 °C in benzene was 1.5 times that of S‐MBEI. This was explicable in terms of the different molecular associations of RS‐MBEI and S‐MBEI, as analyzed by ¹H NMR. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4137–4146, 2000     

Kinetic study on the radical polymerization of 2‐methacryloyloxyethyl phosphorylcholine

Polymerization of 2‐methacryloyloxyethyl phosphorylcholine (MPC) was kinetically investigated in ethanol using dimethyl 2,2′‐azobisisobutyrate (MAIB) as initiator. The overall activation energy of the homogeneous polymerization was calculated to be 71 kJ/mol. The polymerization rate (R_p) was expressed by R_p = k[MAIB]^0.54±0.05 [MPC]^1.8±0.1. The higher dependence of R_p on the monomer concentration comes from acceleration of propagation due to monomer aggregation and also from retardation of termination due to viscosity effect of the MPC monomer. Rate constants of propagation (k_p) and termination (k_t) of MPC were estimated by means of ESR to be k_p = 180 L/mol · s and k_t = 2.8 × 10⁴ L/mol · s at 60 °C, respectively. Because of much slower termination, R_p of MPC in ethanol was found at 60 °C to be 8 times that of methyl methacrylate (MMA) in benzene, though the different solvents were used for MPC and MMA. Polymerization of MPC with MAIB in ethanol was accelerated by the presence of water and retarded by the presence of benzene or acetonitrile. Poly(MPC) showed a peculiar solubility behavior; although poly(MPC) was highly soluble in ethanol and in water, it was insoluble in aqueous ethanol of water content of 7.4–39.8 vol %. The radical copolymerization of MPC (M₁) and styrene (St) (M₂) in ethanol at 50 °C gave the following copolymerization parameters similar to those of the copolymerization of MMA and St; r₁ = 0.39, r₂ = 0.46, Q₁ = 0.76, and e₁ = +0.51. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 509–515, 2000     

THE OVERALL KINETICS OF FREE RADICAL (CO)POLYMERIZATION WITH HIGHLY DIFFUSION CONTROLLED TERMINATION

The overall reaction rate kinetics of polymerization of diethyleneglycol dimethacrylate and copolymerization of it with styrene in bulk and in the presence of inert diluents were investigated. Theresults indicated that these reactions can be treated as free radical polymerization with highly diffu-sion controlled termination reaction in which the termination rate constant is an empirically derivedfunction of monomer conversion: K_t=K_(to)(1-c ln[M]/ [M_0])~(-1) in which K_(to) is the initial terminationrate constant and c is a factor related to the magnitude of diffusion co?re The following equationof monomer conversion as a function of time could then be derived: U=1-exp {1/c [1-(1+ckt/2)~2]}in which k=K_P(R_i/2K_(to))~(1/2) and t is the time of reaction. Excellent agreement between the theoreticaland experimental overall reaction kinetic curves was obtained. The equation is valid for crosslinkingand noncrosslinking free radical polymerizations in which the self-acceleration effcct is effective fromthe very beginning of the reaction. The equation can be expressed in a more generally applicableform: U=1--exp{1/e[1--(1+?t/n)~n] in which n≥0.     

A comparison of the absolute reactivity of vinyl monomers. I. Kinetic studies on radical polymerization of vinyl monomers initiated by a Mn3+–diglycolic acid redox system

The kinetics of polymerization of acrylamide (AM), acrylic acid (AA), and acrylonitrile (AN) initiated by the redox system Mn³⁺–diglycolic acid (DGA) was studied. All three systems followed the same mechanism; namely, initiation by an organic free radical arising from the oxidation of diglycolic acid and termination by the interaction of polymer radicals with Mn³⁺ ion. The rate coefficients k_i/k₀ and k_p/k_t were related to monomer and polymer radical reactivity, respectively. An inverse relation between monomer and polymer radical reactivity was observed. Monomers with higher Q values gave higher k_i/k₀ values but lower k_p/k_t values. The e values of the monomers were important in determining the reactivities of monomers with nearly the same Q values.     

Propagation kinetics in free-radical polymerizations

The combination of pulsed laser initiated polymerizations (PLP) with analysis of the generated polymer by size-exclusion chromatography (SEC) yields reliable individual rate coefficients for polymerizations of a large number of monomers in bulk and in solution. PLP-SEC experiments carried out in the presence of scCO₂ as a solvent show no unambiguous trend: while a significant reduction of k_p is seen for some monomers, e.g. acrylates, k_p for monomers such as vinyl acetate and styrene is not affected. It is suggested that the influence of CO₂ on acrylate k_p is not a true kinetic effect and that the experimental findings may be understood in terms of the occurrence of local monomer concentrations in the vicinity of the propagating radical. It is discussed that such local monomer concentrations may also contribute to a better understanding of why k_p increases with ester size within the acrylate or within the methacrylate family, and why k_p frequently is influenced by the initiating laser pulse repetition rate.     

Vinyl polymerization. 275. Polymerization of vinyl monomers photosensitized by tetramethyltetrazene

A study of the photopolymerization of vinyl monomers in the presence of tetramethyltetrazene (TMT) was made. TMT was found to act as an effective sensitizer. In the photopolymerization of vinyl monomers such as methyl methacrylate or styrene the rate of polymerization was expressed by the equation: R_p = k[TMT]^1/2[monomer]. The chain-transfer constant of TMT under ultraviolet irradiation was estimated to be 3.8 × 10^?2 for the above monomers. A linear correlation was found to exist between the reactivity of dimethylamino radical toward the vinyl monomers and e values for the corresponding monomers.     

Modeling Termination Kinetics of Non‐Stationary Free‐Radical Polymerizations

Pulsed‐laser induced polymerization is modeled via an approach presented in a previous paper.^[1] An equation for the time dependence of free‐radical concentration is derived. It is shown that the termination rate coefficient may vary significantly as a function of time after applying the laser pulse despite of the fact that the change in monomer concentration during one experiment is negligible. For the limiting case of t ≫ c^–1 (k_pM)^–1, where c is a dimensionless chain‐transfer constant, k_p the propagation rate coefficient and M the monomer concentration, an analytical expression for k_t is derived. It is also shown that time‐resolved single pulse‐laser polymerization (SP–PLP) experiments can yield the parameters that allow the modeling of k_t in quasi‐stationary polymerization. The influence of inhibitors is also considered. The conditions are analyzed under which M (t) curves recorded at different extents of laser‐induced photo‐initiator decomposition intersect. It is shown that such type of behavior is associated with a chain‐length dependence of k_t.     

Sulfur-containing vinyl monomers. XIII. Cationic copolymerizations of vinyl sulfides with some vinyl monomers

Cationic copolymerizations of vinyl sulfides (VS) with some vinyl monomers with boron tri-fluoride-diethyl etherate catalyst were investigated to evaluate their monomer reactivities. The effects of VS on the copolymer yield and viscosity of the resulting copolymers revealed the inhibition or retardation mechanism which was explained in terms of the formation of a stable vinylsulfonium salt by the reaction between a propagating carbonium ion and VS monomer. From the results of copolymerizations of phenyl vinyl sulfide (PVS) with isobutyl vinyl ether (IBVE), β-chloroethyl vinyl ether (CEVE), α-methylstyrene (α-MeSt), and styrene (St), the relative reactivities of these monomers were found to be in the following order: IBVE > CEVE > PVS > α-MeSt > St. The relatively higher reactivity of PVS than St derivatives was explained on the basis of the conjugative and electron-donating nature of the VS monomer. The effects of alkyl and para-substituted phenyl groups in vinyl sulfides on their reactivities toward the propagating carbonium ion were correlated with polar factors and compared with those of the hydrolysis of α-mercaptomethyl chlorides. The transition state for the propagation reaction in cationic polymerization of VS was proposed to be a π-complex type structure.     

Kinetic and EPR studies on radical polymerization. Radical polymerization of di-2[2-(2-methoxyethoxy)ethoxy]ethyl itaconate

The polymerization of di-2[2-(2-methoxyethoxy)ethoxy]ethyl itaconate (1) with dimethyl 2,2-azobisisobutyrate (2) was studied, in benzene, kinetically and spectroscopically with the electron paramagnetic resonance (EPR) method. The polymerization rate (R _p) at 50°C is given by the equation:R _p=k[2]^0.48 [1]^2.4. The overall activation energy of polymerization was calculated to be 34 kJ·mol^–1. From an EPR study, the polymerization system was found to involve EPR-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. With increasing monomer concentration,k _p(1.54.3 L·mol^–1·s^–1 at 50°C) increases andk _t (1.0·10⁴4.2·10⁴ L·mol^–1·s^–1 at 50°C) decreases, which seems responsible for the high dependence ofR _p on the monomer concentration. The activation energies of propagation and termination were calculated to be 11 kJ·mol^–1 and 84 kJ·mol^–1, respectively. For the copolymerization of 1(M ₁) and styrene (M ₂) at 50°C in benzene the following copolymerization parameters were found:r ₁=0.2,r ₂=0.53, Q₁=0.57, ande ₁=+0.7.     

Effect of zinc salts on the spontaneous copolymerization of 4-vinylpyridine with various electron-rich vinyl monomers

The spontaneous copolymerization of 4-vinylpyridine (4-VP) complexed with three different zinc salts (chloride, acetate, and triflate) with various electron-rich vinyl monomers (p-methoxystyrene, MeOSt; p-methylstyrene, MeSt; α-methylstyrene, α-MeSt; p-tert-butylstyrene, BuSt; styrene, St) was investigated in methanol at 75°C. Increasing the zinc salt concentration or the nucleophilicity of the electron-rich monomer increased the copolymer yields. All obtained copolymers are characterized by high molecular weight (10⁵) and broad molecular weight distribution. Both ¹H-NMR and elemental analyses confirmed the almost 1 : 1 copolymer structure. Changing the anion of the zinc salt does not have a considerable effect either on the copolymerization rate or on the molecular weight. The proposed mechanism exhibits the formation of a σ-bond between the β-carbons of the two donor–acceptor monomers. This creates the 1,4-tetramethylene biradical intermediate which can initiate the copolymerization reaction. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2787–2792, 1997     

REACTIVITY RATIOS FOR COPOLYMERIZATION WITH THE PARTICIPATION OF A CHARGE-TRANSFER COMPLEX

The complexation between styrene (St) and N-phenylmaleimide (PMI) was investigated by ~1H-NMR spectroscopy,and the existence of a complex was proved. The equilibrium constant of St/PMI in chloroform at 50℃ was determined to be0.27. New elementary propagation reactions were proposed. On the basis of the propagation elementary reactions forcopolymerization with the participation of a charge-transfer complex (CTC), a method for measuring the reactivity ratios ispresented. Four reactivity ratios and relative reactivities of free monomer and CTC were obtained. They are r_(12)=0.034. r_(21)=0.012, r_(1C)=0.0030, r_(2C)=0.0034, and k_(1C)/k_(12)=11.34, k_(2C)/k_(21)=3.42.     

Kinetic and ESR studies on the radical polymerization of Di-n-butyl itaconate in benzene

The polymerization of di-n-butyl itaconate (DBI) intiated with AIBN was kinetically investigated in benezene. The polymerization rate (R_p) was expressed by: R_p = k[AIBN]^0.5[DBI]^1.7. The polymerization showed a considerably low overall activation energy of 15.3 kcal/mol. The initiator efficiency of AIBN in this system decreased with increasing DBI concentration, ranging from 0.34 to 0.55°C, which is ascribable to viscosity effect due to the monomer. From an ESR study, the polymerization system was found to involve two kinds of persistent radicals, namely, primary propagating ( III ) and propagating ( I ) radicals. The relative concentration of III to I increased with decreasing monomer concentration. Azo-nitrile initiators such as AVN and ACN similarly produced two persistent radicals, while MAIB, DBPO, and PBO yielded only propagating radical I as persistent. The MAIB-initiated polymerization of DBI was also performed in benzene. Similar kinetic features were observed, that is, a higher dependence of R_p on the DBI concentration and a low overall activation energy (14.4 kcal/mol). The following rate equation was obtained at 50°C:R_p = k[MAIB]^0.5[DBI]^1.6. The initiator efficiency of MAIB decreased with increasing DBI concentration, ranging from 0.32 to 0.53 at 50°C. The concentration of propagating radical I was determined by ESR at 50 and 61°C, from which k_p and k_t were estimated. The k_p value increased with increasing monomer concentration, while the k_t one decreased with the DBI concentration. These values are much lower compared with those of MMA.