Chain transfer for vinyl monomers polymerized in N-allylstearamide

Apparent transfer constants have been determined for styrene, methyl methacrylate vinyl acetate, and diethyl maleate polymerized in N-allylstearamide at 90°C. Regression coefficients for transfer were: methyl methacrylate, 0.301 × 10^?3; styrene, with no added initiator, 0.582 × 10^?3; styrene, initiated with benzoyl peroxide, 0.830 × 10^?3; vinyl acetate, 62.01 × 10^?3; and diethyl maleate, 2.24 × 10^?3. Rates of polymerization were retarded for both styrene and methyl methacrylate. Vinyl monomer and comonomer disappearance followed an increasing exponential dependence on both initiator and monomer concentration. Although degradative chain transfer probably caused most of the retardation, the cross-termination effect was not eliminated as a contribution factor. Rates for the vinyl acetate copolymerization were somewhat retarded, even though initiator consumption was large because of induced decomposition. The kinetic and transfer data indicated that the reactive monomers added radicals readily, but that rates were lowered by degradative chain transfer. Growing chains were terminated at only moderate rates of transfer. Unreactive monomers added radicals less easily, producing reactive radicals, which transferred rapidly, so that molecular weights were lowered precipitously. Although induced initiator decomposition occurred, rates were still retarded by degradative chain transfer. A simple empirical relation was found between the reciprocal number-average degree of polymerization, 1/X?_n1 and the mole fraction of allylic comonomer entering the copolymer F₂, which permitted estimation of the molecular weight of copolymers of vinyl monomers with allylic comonomers. This equation should be applicable when monomer transfer constants for each homopolymer are known and when osmometric molecular weights of one or two copolymers of low allylic content have been determined.     

Transfer reactions in radical polymerization of styrene in acetone–chloroform mixture

The study of chain-transfer reactions in thermal and AIBN-initiated polymerization of styrene is aimed at the determination of transfer constants to the solvents at 60°C. For thermal polymerization the transfer constants C_s to acetone, chloroform, and chloroform mixed with acetone are 3.2 × 10^?5, 4.1 × 10^?5, and 4.4 × 10^?5, respectively. In the case of AIBN-initiated polymerization, the transfer constant of chloroform in the mixture acetone–chloroform is C_s = 3.3 × 10^?4. All these transfer constants are average values. It has been found that neither acetone nor chloroform satisfies the Mayo equation in the presence of transfer agent very well. These anomalies can be explained by assuming a complexation phenomenon. The changes in the polarity and resonance are taken into account. It is considered that in the chain-transfer reactions under investigation, the association or complex-forming ability of solvent and monomer or polymer play a role. In studying the chain-transfer reaction in the acetone–chloroform solvent mixture another phenomenon affecting the determination of the chain transfer constant is assumed. This phenomenon consists in formation of associates in which both solvents participate.     

Degradative chain transfer in vinyl acetate polymerizations using toluene as solvent

In this work, we propose that retardation in vinyl acetate polymerization rate in the presence of toluene is due to degradative chain transfer. The transfer constant to toluene (C_trs) determined using the Mayo method is equal to 3.8 × 10^?3, which is remarkably similar to the value calculated from the rate data, assuming degradative chain transfer (2.7 × 10^?3). Simulations, including chain‐length‐dependent termination, were carried out to compare our degradative chain transfer model with experimental results. The conversion–time profiles showed excellent agreement between experiment and simulation. Good agreement was found for the M_n data as a function of conversion. The experimental and simulation data strongly support the postulate that degradative chain transfer is the dominant kinetic mechanism. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3620–3625, 2007     

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     

Chain transfer to solvent in two-state anionic polymerization, 1. Fast exchange between propagating species

A theoretical consideration of molecular weights and molecular weight distribution (MWD) of polymers formed in anionic polymerization proceeding via active centres of two different types under conditions of chain transfer to solvent with a fast exchange between propagating species is presented. Analytical expressions for number-and weight-average degrees of polymerization are obtained. Expressions for P_n and P_w are shown to be the same as in a one-centre process with the apparent intensity of chain transfer proportional to the weight fraction of the polymer formed via “transferring” centres. The polymers formed possess a moderately wide unimodal MWD. The dependence of the polydispersity index on the effective intensity of chain transfer goes through a maximum; for M₀/I₀ = 10³ the maximum value of P_w /P_n is ca. 4,6. The method is suggested for the estimation of the relative reactivity in chain propagation of two active centres from the dependence of molecular weight on initiator mixture composition. The effects of association of active centres on the average molecular weights are analyzed. The case when one of the centres is dormant is also considered.     

Studies on polymerization of vinyl acetate using ylide as an initiator and degradative transfer agent

The polymerization of vinyl acetate initiated by β-picolinium-p-chlorophenacylide was carried out at 30, 35, and 40°C, using the conventional dilatometric technique. The initiator and the monomer exponent values were 0.80 ± 0.15 and unity, respectively. The polymerization was inhibited in the presence of hydroquinone, but was favored by nonpolar solvent and polymerization temperature. The energy of activation was 90.3 kJ mol^?1. An average value of k/k_t for the present system was found to be 0.37 × 10^?2 L mol^?1 s^?1. The results are explained in terms of radical mode of polymerization with degradative initiator transfer; the principal mode of termination, however, was biomolecular.     

SET–LRP of N‐isopropylacrylamide in the presence of chain transfer agent

In this study, single electron transfer‐living radical polymerization (SET–LRP) of N‐isopropylacrylamide (NIPAM) in the presence of 2‐mercaptoethylamine chain transfer agent (CTA) was carried out by Cu(0) generated in situ from the disproportionation of CuBr/2,2′‐bipyridine (2,2′‐bpy) in N,N‐dimethylformamide (DMF) at 90 °C. Analysis of polymerization kinetics in the presence of CTA showed that the premature termination of growing polymer chains leads to retardation. The apparent rate constant of polymerization (k) decreased from 4.49 × 10^?4 to 2.59 × 10^?4 min^?1 with increasing CTA concentration. The initiator efficiency (I_eff) and the chain transfer constant (C_s) were found to be 0.524 and 0.286, respectively. The molecular weights of poly(N‐isopropylacrylamide) [poly(NIPAM)] produced were significantly higher than the predicted values, and the polydispersities were less than 1.22. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

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.     

The role of chain transfer agents in the emulsion polymerization of styrene

The effect of chain transfer agents on the nucleation and growth of polymer particles in the emulsion polymerization of styrene were examined extensively. The chain transfer agents used are carbon tetrachloride, carbon tetrabromide, and four primary mercaptans (C₂, n-C₄, n-C₇, and n-C₁₂). It is shown that with an increase in the amount of chain transfer agents charged the rate of polymerization per particle decreases progressively. The number of polymer particles formed, on the other hand, increases initially then decreases. These effects can be enhanced by using a chain transfer agent with higher values of chain transfer constant and solubility in water. It is also demonstrated that with increasing radical desorption from the particles, aided by chain transfer agents, the emulsifier dependence exponent for the number of polymer particles formed increases from 0.6 to 1.0 and the initiator dependence exponent decreases from 0.4 to 0. The effect of chain transfer agents on the nucleation and growth of polymer particles in the emulsion polymerization of styrene can be explained in terms of desorption of chain-transfered radicals from the polymer particles.     

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     

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.     

Anionic polymerization of norbornene trisulfide (exo-3,4,5-trithia-tricyclo[5.2.1.02.6]decane)

The anionic polymerization of norbornene trisulfide initiated with sodium thiophenoxide (sodium cation solvated with dibenzo-18-crown-6 ether) was studied. Polymers with high molecular weights were obtained (M _n up to 10⁵, osmometrically). Molecular weights calculated for living polymerization conditions (i.e., one molecule of initiator yields one macromolecule) agree well with M _n measured by osmometry. ¹H-NMR, ¹³C-{¹H}-NMR, and Raman spectra of the polymer are given. Thermodynamics of polymerization in toluene solvent is described. Enthalpy ΔH_ss = ?(1.39 ± 0.17) kcal mol^?1 and entropy ΔS_ss = ?(7.52 ± 0.55) cal mol^?1 deg^?1 coefficients of polymerization were evaluated from the temperature dependence of the equilibrium monomer concentration determined dilatometrically.     

Kinetics of polymerization initiated by peroxides containing heterocyclic groups. I. Kinetics of bulk polymerization of styrene and vinyl acetate initiated by difuroyl peroxide

The rate and degree of bulk polymerization of styrene and vinyl acetate initiated by difuroyl peroxide and, for comparison, by dilauroyl and dibenzoyl peroxides were measured at several temperatures as a function of the initiator concentration. Also the rates of initiation were determined by the inhibition method with Banfield's radicals. The rate of polymerization initiated by difuroyl peroxide appears to be lower than could be expected from the rate of initiation determined by the inhibition method and from the decomposition of difuroyl peroxide. In the case of polymerization of vinyl acetate there are significant deviations from the proportionality between R_p and the square root of the initiator concentration, which follows from the conventional kinetic scheme. The degrees of polymerization are also low, and the plots of P _n^?1 versus R_p are not linear. These deviations can be accounted for by postulating a retardation effect of the furan cycle and chain transfer to difuroyl peroxide.     

Non-ideal polymerization. Treatment of non-ideality due to primary radical termination and degradative chain transfer

A method is proposed for analysing the problems associated with non-ideal polymerizations reflected mainly in the variability of R_p/[I]^0·5[M] where R_p is the rate of polymerization and [I] and [M] are the initiator and monomer concentrations, respectively. Primary radical termination and degradative chain transfer are treated jointly and the entirely different mathematical natures of the two processes are described. The method could dispense with the need to use the uninhibited rate of polymerization which does not lend itself to reliable measurements for many systems. It is found to be efficient in detecting the active species in a polymerization system that leads to non-ideality due to degradative chain transfer.This method is applied to vinyl chloride polymerization data from the literature, the values of constants obtained therefrom are found to agree well with the existing values.     

Role of chain transfer in heterogeneous polymerization of ethylene

The role of chain transfer was studied for the radiation-induced polymerization of ethylene in precipitating media, namely n-butyl alcohol, tert-butyl alcohol and their mixtures. The affinities of those solvents for polyethylene are similar, but the chain-transfer coefficient of n-butyl alcohol is larger than that of tert-butyl alcohol. The polymerizations were carried out in a reactor of 100 ml under a pressure of 300 kg/cm², at 60°C, dose rate of 3.07 × 10⁴–1.75 × 10⁵ rad/hr in the presence of 50 ml of solvents. The polymerization in tert-butyl alcohol shows the kinetic behavior characteristic of a heterogeneous polymerization, such as rate acceleration, high dose rate dependence of polymerization rate, and low dose rate dependence of polymer molecular weight, whereas the polymerization in n-butyl alcohol does not exhibit such behavior and gives polymer having a molecular weight much lower than that of polymer obtained in tert-butyl alcohol. The polymer formed in tert-butyl alcohol exhibits a bimodal molecular weight distribution measured by gel permeation chromatography. In mixed tert-butyl alcohol and n-butyl alcohol solvent, with increasing fraction of n-butyl alcohol, the two peaks not only shift to lower molecular weight but the higher molecular weight peak becomes relatively small. Eventually, the polymer formed in n-butyl alcohol exhibits a unimodal distribution. Those results are well explained on the basis of the proposed scheme for heterogeneous polymerization.     

Photopolymerization of methyl methacrylate initiated by sulphur dioxide

In catalytic concentrations (10^?5?10^?4 mol l^?1) sulphur dioxide induces polymerization of MMA, particularly on photoactivation. The effective initiating species appears to be the monomer-SO₂ complex rather than free SO₂. A mechanism involving biradical initiation by decomposition of the initiating species, linear propagation in two directions, and significant termination of growing chains by chain transfer with initiating species has been suggested. The initiator transfer constant is 1.6 at 40°.     

Radiation polymerization of methacrylates controlled by a chain transfer catalyst

The effect of γ-radiation dose and chain transfer catalyst on polymerization of methyl methacrylate (MMA) and copolymerization of MMA with hydroxyethyl methacrylate or triethylene glycol dimethacrylate has been investigated. The addition of 5 × 10^?4?10^?3 mol/L of bis[(difluoroboryl) isopropylpyridine dimethylglyoximato]cobalt(II) (Co(II)) makes it possible to produce macromonomers MM _n ⁼⁼ bearing terminal double bonds and having a degree polymerization of n = 2?40 and a polydispersity index of 1.05?1.15. It has been found that the degree polymerization of the macromonomers increases with the increasing γ-radiation dose and monomer conversion through the mechanism of the reversible β-cleavage of the terminal unit: R _k ^? + MM _n ⁼ ? MM _k+1 ⁼ + R _n-1 ^? followed by the living polymerization of both radicals. This reaction may compete with the catalytic chain transfer reaction and have a significant effect on the evolution of the molecular weight characteristics of the macromonomers during the course of MMA (co)polymerization.     

Studies on polymers containing functional groups. VI. Kinetics of the polymerization and copolymerization behaviors of o-hydroxystyrene

Some kinetic studies were made of the homopolymerization of o-hydroxystyrene and its copolymerization behavior with styrene and methyl methacrylate in tetrahydrofuran using azobisisobutyronitrile as initiator were done. The rate of polymerization experimentally obtained is given by R_p = K[M][I]^0.72. Accordingly, it is likely that the growing chain radicals are terminated not only by mutual termination but also by a chain-transfer mechanism, the latter occupying a considerable portion. The latter is mostly attributed to the transfer to monomer, i.e., C_m for o-hydroxystyrene was 1.3 × 10^?2. Some transfer mechanisms were assumed, although it is difficult to elucidate the mechanism in detail, owing to its complexity. Effects of solvent on the rate of polymerization were examined, dioxane, methyl ethyl ketone, ethanol, and tetrahydrofuran being used. However, no differences were found among the solvents. The apparent activation energy of polymerization was found to be 21.5 kcal./mole. Monomer reactivity ratios and Alfrey-Price Q–e values for o-hydroxystyrene were determined. The Q–e values (Q = 1.41, e = ?1.13) are rather similar to those of p-methoxystyrene. Thus, the e value for o-hydroxystyrene is more negative than that for styrene.     

Phase transfer catalyzed single electron transfer–degenerative chain transfer mediated living radical polymerization (PTC‐SET–DTLRP) of vinyl chloride catalyzed by sodium dithionite and initiated with iodoform in water at 43 °C

To accelerate the living radical polymerization (LRP) of vinyl chloride (VC) in water the phase transfer catalyzed single electron transfer–degenerative chain transfer mediated living radical polymerization (SET–DTLRP) of VC mediated by sodium dithionite (Na₂S₂O₄) was investigated. The fastest polymerization reaction that still produces thermally stable poly(vinyl chloride) (PVC) takes place at 43 °C with the ratio [PTC]₀/[Na₂S₂O₄]₀ = 0.0075/1. Cetyltrimethylammonium bromide (nC₁₆H₃₃(CH₃)₃N⁺Br^?, CetMe₃NBr) was the phase‐transfer catalyst (PTC) of choice. Under these conditions the first, fast stage of SET–DTLRP of VC was accomplished within 7–8 h when the initial ratio monomer/initiator [VC]₀/[CHI₃]₀ was 800. The number‐average molecular weight (M_n) of the resulting PVC was in good agreement with the theoretical molecular weight (M_th). When the [VC]₀/[CHI₃]₀ ratio was 4800, the fast step of the reaction was accomplished within 17 h, to produce 72% monomer conversion. A deviation of the M_n from the M_th was observed in this case. Possible mechanistic explanations for this deviation as well as for the phase transfer catalyzed SET–DTLRP of VC were suggested. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 779–788, 2005     

RAFT polymerization of tertiary sulfonium zwitterionic monomer in aqueous media for synthesis of protein stabilizing double hydrophilic block copolymers

The reversible addition-fragmentation chain-transfer (RAFT) polymerization of a tertiary sulfonium-containing zwitterionic monomer (N-acryloyl-L-methionine methyl sulfonium salt: A-Met[S⁺]-OH) was performed in aqueous media in the presence of a water-soluble chain-transfer agent (CTA). Several parameters, such as the radical initiator, nature of the salt used as an additive, polymerization temperature, and solvent (water, buffer solution, and mixed solvents), were studied. The polymerization of A-Met(S⁺)-OH in acetate buffer using a trithiocarbonate-type CTA having two carboxylic acid moieties proceeded in a controlled fashion at 45°C, as confirmed by the low polydispersity of the products (M _w/M _n < 1.1) and pre-determined molecular weights. Poly(ethylene glycol)-based macro-CTA was also employed for the polymerization of A-Met(S⁺)-OH in mixed solvents (H₂O/EtOH and H₂O/DMF = 70/30 vol%) to afford novel nonionic-zwitterionic double hydrophilic block copolymers. The chain extension of the hydrophilic poly(N,N-dimethylacrylamide) macro-CTA with A-Met(S⁺)-OH was well controlled in pure water under the appropriate conditions, resulting in the formation of block copolymers with “as-designed” chain structures and relatively low dispersities (M _w/M _n < 1.3). The resulting sulfonium-containing double hydrophilic block copolymers having optimal nonionic/zwitterionic balance were efficient protein-stabilizing agents.