Chain Transfer Constants Research Articles

Controlled radical polymerization of styrene mediated by dithiobenzoates as reversible addition-fragmentation chain-transfer agents

The radical polymerization of styrene at 60 and 80°C mediated by benzyl dithiobenzoate and poly(styrene dithiobenzoate) as reversible addition-fragmentation chain-transfer agents has been studied. It has been shown that both agents are characterized by high chain-transfer constants and provide control over molecular-mass characteristics of polymerization products. The number-average molecular mass of polystyrene linearly grows with conversion, and the polymers are characterized by low values of polydispersity indexes. It has been demonstrated that the rate of polymerization significantly decreases with an increase in the concentration of reversible addition-fragmentation chain-transfer agents. This effect is typical of styrene polymerization mediated by dithiobenzoates. The possible reasons for this phenomenon are discussed.

Synthesis of poly(methyl methacrylate- co-styrene)- block-polysulfide- block-poly(methyl methacrylate- co-styrene) copolymers by free radical polymerization combined with oxidative coupling

Poly(methyl methacrylate- co-styrene)- block-polysulfide- block-poly(methyl methacrylate- co-styrene) triblock copolymers were synthesized for the first time by the free radical copolymerization of methyl methacrylate (MMA) and styrene (St) in the presence of a thiocol oligomer as a chain transfer agent, followed by chemical oxidation of the remaining SH-end groups. The apparent chain transfer constant of the thiocol SH groups in the copolymerization reaction was estimated from the rate of consumption of the thiol groups versus the overall rate of consumption of the monomers ( C T = 1.28). Based on this value, the chain transfer constant of the thiocol SH groups in St polymerization was calculated ( C T St = 8.4 ) . The triblock copolymers synthesized were characterized by SEC and 1H NMR measurements.

Chain transfer in pulsed laser polymerization of methylmethacrylate in the presence of different cobalt (II) [Co(dmg-2H) 2 (BF 2) 2] and [Co(afdo-2H) 2 (BF 2) 2] complexes

Methylmethacrylate (MMA) was polymerized at 25 °C with excimer laser ( λ = 308 nm) in the presence of different Co(II) chain transfer agents, bis(boron difluorodimethylglyoximate) cobaltate(II) [Co(dmg-2H) 2 (BF 2) 2] (henceforth called catalyst (1)) and bis(boron difluorodialphafurilglyoximate) cobaltate(II) [Co(afdo-2H) 2 (BF 2) 2] (henceforth called catalyst (2)) used separately, with 2,2′-Azobis-(2-methylpropionitrile) [AIBN] as an initiator. The polymer (PMMA) formed in this study was characterized using GPC, 1H NMR, 13C NMR, and DEPT 135. The value of chain transfer constant ( C s) was higher for catalyst (1) than catalyst (2) by a factor of 5. The higher character of “living free radical polymerization”, as evident from the low values of polydispersity index (PDI), was observed mainly for catalyst (2). Both steric and electronic factors supported by IR and UV–vis spectra for the two catalysts indicate that catalyst (2) is a weaker nucleophile as compared to catalyst (1) forming a weaker Co–C bond between this catalyst and growing polymer chain indicating more living polymerization for the catalyst (2).

NMR Spectroscopy and MALDI‐TOF MS Characterisation of End‐Functionalised PVP Oligomers Prepared with Different Esters as Chain Transfer Agents

Ester-functionalised poly(1-vinylpyrrolidin-2-one) (PVP) oligomers obtained by radical polymerisation in methyl propionate, diethyl malonate and diethyl 2-methylmalonate were characterised by NMR spectroscopy, and MALDI-TOF mass spectrometry. The chain-transfer constants were determined as 5.54 x 10(-4), 1.22 x 10(-3) and 1.70 x 10(-2), respectively, by measuring the variation of the number-average molecular weight on conversion. These values were compared with those of methyl isobutyrate (1.65 x 10(-3)) and ethyl lactate (1.03 x 10(-2)), which had been previously determined. A clear dependence was found on the reactivity of the mobile hydrogen atoms alpha with the ester group. All of the macromolecules carried a single ester function. Therefore, the re-initiation step by the CTA-derived radicals overwhelmingly prevailed over initiation by the primary radicals.

Determination of the kinetic parameters of pseudoliving radical polymerization by linearizing the chain length distribution of macromolecules

A new approach is proposed for determination of quantitative kinetic parameters of pseudoliving radical polymerization proceeding in the mode of reversible termination, which include the reversible-termination rate constant, the length of the elementary step (number of growth events beginning from chain initiation to termination), and the number of steps that compose the chain during its growth. The method is based on the linearization of the chain length distribution of macromolecules and constitutes further development of the previously known approach to the determination of the chain transfer constant in nonliving polymerization. The applicability of the method was theoretically substantiated and experimentally verified using, as an example, some systems with reversible inhibition by nitroxides.

THE EVOLUTION OF THE CHAIN TRANSFER CONSTANT DURING THE CATALYTIC CHAIN TRANSFER POLYMERIZATION OF 2-HYDROXYPROPYL METHACRYLATE

Using cobaloxime boron fluoride (COBF) and AIBN as catalyst and initiator respectively,the catalytic chain transfer bulk polymerization of 2-hydroxyporpyl methacrylate (HPMA) was carried out at 60℃ and the low molecular weight polymer with a terminal double bond was prepared.The evolution of the apparent chain transfer constant (C~app _S) of COBF during the polymerization was determined by the Mayo equation and the CLD (chain length distribution) equation respectively.At the beginning of the reaction,the chain transfer constant showed values of up to about 2000,but with the increasing of the monomer conversion,the chain transfer constant decreases and keeps at a value of about 600 for sometime and then decreased again.The most likely cause for the catalyst deactivation is the stable cobalt-carbon bond formed at the first period of the reaction and then reached equilibrium point.When the polymerization proceeds up to middle and high conversion,the chain transfer polymerization is further manipulated by diffusions of polymeric propagating chain and catalyst molecules,and the apparent chain transfer constant fell to value of below 300. It has been found also,that the data determined by the CLD equation are usually lower than those by the Mayo equation,especially at high conversion stage.It is because that both original equations are available for the instantaneous produced polymer or the case of very lower conversion stage.However,the GPC measurements give molecular weight distributions of the cumulated products rather than the instantaneous produced polymer.The number-average polymerization degrees for the instantaneous produced polymers were obtained from the GPC data,and used in the Mayo equation method together with the modification of the monomer concentration.It was believed that the apparent chain transfer constants from the modified Mayo equation method are more available for the middle and high conversion cases.

Effect of dielectric and structural properties of solutions on the polymerizability of diallylammonium-type monomers

New polymerization systems— N , N -diallyl- N -methylammonium trifluoroacetate (D1TFA) and N , N -diallylammonium trifluoroacetate (D2TFA)—exhibit phenomena that distinguish their behavior during radical polymerization (Scheme 1) from the known cases, in particular, from the quaternary N , N -diallyl- N , N -dimethylammonium chloride (D3C). These phenomena are evidence of a substantial effect of the medium on the basic polymerization characteristics of new cationogenic monomers: the initial polymerization rate V , the average length of the polymer chain P n , and the constant of chain transfer to the monomer C m [1].

Poly(methyl methacrylate)-block-polysulfide-block-poly(methyl methacrylate) copolymers obtained by free-radical polymerization combined with oxidative coupling

Poly(methyl methacrylate)-block-polysulfide-block-poly(methyl methacrylate) copolymers were synthesized for the first time through a new method involving the free radical polymerization of MMA in the presence of a thiocol oligomer as a chain transfer agent, followed by chemical oxidation of the remaining SH end-groups. The chain transfer constant of the SH end-groups of the thiocol was estimated from the rate of consumption of the thiol groups versus the rate of consumption of the monomer (CT=0.67). The triblock copolymers synthesized were characterized by SEC and 1H NMR measurements.

Catalytic chain transfer polymerisation of CO 2-expanded methyl methacrylate

The catalytic chain transfer polymerisation of methyl methacrylate expanded with dense CO 2 is reported. Experimental values of the chain transfer constant ( C s) are presented at 50 °C and in the range of pressure from 0.1 to 6 MPa, using a cobaloxime complex as the chain transfer catalyst. The effect of small quantities of poly(methyl methacrylate) on the volumetric expansion of the monomer with CO 2 is considered. Experimental data are presented on the pressure limit for homogeneous expansion as a function of the molecular weight of the polymer. It is shown that the values of C s in CO 2-expanded methyl methacrylate are significantly higher than that in bulk monomer. This effect is mainly attributed to the enhancement of the chain transfer rate coefficient, arising from the reduction in the viscosity of the medium, and is consistent with a diffusion-controlled rate-determining step in the chain transfer process.

Efficient Synthesis and Copolymerization of Poly(acrylic acid) and Poly(acrylic ester) Macromonomers: Manipulation of Steric Factors

AbstractSummary: Macromonomers have been prepared by polymerization of acrylic acid (AA) and tert‐butyl acrylate (tBA) in the presence of the addition‐fragmentation chain transfer (AFCT) agents, ethyl α‐(bromomethyl)acrylate (EBMA) and tert‐butyl α‐(bromomethyl)acrylate (BBMA). Chain transfer constants of 1.25 (EBMA) and 1.14 (BBMA) in the AA polymerization, and 2.42 (EBMA) and 1.75 (BBMA) in the tBA polymerization were obtained. The reduction in molecular weight with increasing concentration of AFCT agent and efficient introduction of 2‐carbalkoxy‐2‐propenyl ω‐end group was indicative of macromonomer formation. Polymerizations were retarded with increasing concentrations of AFCT agent and increases in the absolute concentration of EBMA slowed down the polymerization of AA but not tBA. The difference between EBMA and BBMA was less significant with tBA; more efficient macromonomer synthesis was indicated by less retardation and greater double bond retention at higher conversions. Copolymerizations of poly(AA) and poly(tBA) macromonomers with styrene indicated that the former was more reactive towards the St propagating radical. The results are rationalized in terms of the steric hindrance imposed by the tert‐butyl group. Poly(tBA) macromonomer was successfully hydrolyzed to give an alternative route to the poly(AA) macromonomer.Reaction mechanism for macromonomer synthesis using AFCT.magnified imageReaction mechanism for macromonomer synthesis using AFCT.

Radical polymerization behavior of trimethoxyvinylsilane

AbstractTrimethoxyvinylsilane (TMVS) was quantitatively polymerized at 130 °C in bulk, using dicumyl peroxide (DCPO) as initiator. The polymerization of TMVS with DCPO was kinetically studied in dioxane by Fourier transform near‐infrared spectroscopy. The overall activation energy of the bulk polymerization was estimated to be 112 kJ/mol. The initial polymerization rate (Rp) was expressed by Rp = k[DCPO]0.6[TMVS]1.0 at 120 °C, being closely similar to that of the conventional radical polymerization involving bimolecular termination. The polymerization system involved electron spin resonance (ESR) spectroscopically observable polymer radicals under the actual polymerization conditions. ESR‐determined apparent rate constants of propagation and termination were 13 L/mol s and 3.1 × 104 L/mol s at 120 °C, respectively. The molecular weight of the resulting poly(TMVS)s was low (Mn = 2.0–4.4 × 103), because of the high chain transfer constant (Cmtr = 4.2 × 10−2 at 120 °C) to the monomer. The bulk copolymerization of TMVS (M1) and vinyl acetate (M2) at 120 °C gave the following copolymerization parameters: rl = 1.4, r2 = 0.24, Q1 = 0.084, and e1 = +0.80. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5864–5871, 2005

Thiophenols as chain transfer agents in the polymerization of vinyl monomers

The behaviour of a series of 4-substituted thiophenols as chain transfers in the photopolymerization of the acrylamide and methyl methacrylate was studied. The addition of concentrations lower than 1 mM of thiophenols to the polymerization of acrylamide in aqueous solutions reduces slightly the polymerization rate but decreases markedly the polymer molecular weight. Chain transfer constants were determined by a modified Mayo equation that consider the variation of the polymerization rate with the chain transfer agent. The addition of thiophenols to the polymerization of methyl methacrylate in organic media reduced considerably the polymer molecular weight without variations in the polymerization rate. The chain transfer rate constants for both monomers are well correlated with the electron donor-acceptor ability of the 4-substitutents, increasing with electron donating groups. An amino substituent in the 4-position increases 10 times the chain transfer constant with respect to the unsubstituted compound. No correlations were found with reported data on stability of the thiyl radicals or the addition rate to the monomer. The electron-donating effect of 4-substituents on the chain transfer constant is related to polar structures in the transition state, and suggests that the main controlling chain transfer step by thiophenols is the H-abstraction from the S–H.

The use of radical polymerization in the synthesis of telechelic oligomers

The following is a review of the newer methods that are available for the synthesis of telechelic oligomers using radical polymerizations. We detail advances in the field since John Ebdon’s review published in 1995 [J.R. Ebdon, Eastmond, New Methods of Polymer Synthesis, Blackie Academic, 1995, ISBN 0751402427]. The available methods are categorized into sections on: chain cleavage techniques; controlled polymerizations; dead end polymerizations and transfer methods. We also introduce a new mathematical technique for determining chain transfer constants that is applicable when transfer to solvent is the dominant termination mechanism. In this new method, we differentiate the Mayo equation with respect to solvent concentration ([ S]) and then plot ∂(1/ X n )/∂[ S] against 1/[ M]. This procedure then gives C s as the gradient.

Measurement of Chain Transfer Constants to Polymer Using Oligomers and Model Compounds: Chain Transfer to Poly[11-(4‘-cyanophenyl-4‘ ‘-phenoxy)undecyl acrylate] in Radical Polymerization

The chain transfer constant to polymer (CP) for poly[11-(4‘-cyanophenyl-4‘ ‘-phenoxy)undecyl acrylate] was measured directly by the Mayo method by following the decrease in molecular weight at low monomer conversion by gel permeation chromatography of poly(methyl acrylate) generated in the presence of increasing amounts of 11-(4‘-cyanophenyl-4‘ ‘-phenoxy)undecyl propionate (CP = (6.62 ± 0.476) × 10-3) and 11-(4‘-cyanophenyl-4‘ ‘-phenoxy)undecyl isobutyrate (CP = (4.27 ± 0.858) × 10-3) as model compounds that mimic one repeat unit of the polymer and oligo[11-(4‘-cyanophenyl-4‘ ‘-phenoxy)undecyl acrylate] with nine repeat units (CP = (5.54 ± 0.608) × 10-3) synthesized by atom transfer radical polymerization. The mean chain transfer constant, CP = 5.48 × 10-3, was used to calculate the extent of branching (ρ) in poly[11-(4‘-cyanophenyl-4‘ ‘-phenoxy)undecyl acrylate] (DPn = 37) synthesized by conventional radical polymerization: ρ = 0.0042−0.020 at 72−99% conversion, which corresponds to one branch per 6.4−1.4 chains, respectively, of 37 repeat units.

Use of Organohydridodisilanes for Controlling the Molecular-Weight Distribution of High-Conversion Polymers

The polymerization of methyl methacrylate to high conversion in the presence of a series of disilanes as chain-transfer agents was studied, and the chain-transfer constants at low and high conversions were determined. The molecular-weight characteristics of the polymers were estimated by gel permeation chromatography.

Investigation of the Telomerization Kinetics of N-Isopropylacrylamide Using 3-Mercaptopropionic Hydrazide as Chain Transfer Agent

The telomerization (chain transfer polymerization) kinetics of N-isopropylacrylamide were investigated in various (hydro)organic solvents using 3-mercaptopropionic hydrazide as chain transfer agent (telogen). Except for the dioxane/water system telogen consumption rates were similar for all cases, while solvent effects could be observed for the monomer consumption rates. Chain transfer constants, as defined by the ratio of the rate constants for chain transfer and chain propagation (CT = ktr,/kp), were highest in DMF (10.3), a solvent unable to form hydrogen bonds or dipole−dipole interactions with the monomer, while a more promising value of CT = 1.7 was found for the 6:4 methanol/water mixture. The highest monomer consumption rates were observed for the 1:1 dioxane/water mixture. However, in this particular case the telogen consumption was also found to increase, as we propose due to a “hydrophobic effect” whereby polymer microaggregates serve to locally increase the concentration of telogen and/or mono...

Polymerization of vinyl acetate in fatty acids and properties of poly (vinyl alcohols) derived from the poly (vinyl acetates)

Polymerization of vinyl acetate (VAc) in various fatty acids (carbon numbers 4–18) was carried out. Chain transfer constants to the acids were determined to be 20–35×10−4, from which the constant to a methylene group was obtained to be 0.73×10−4. Viscometry in aqueous solution of derived poly (vinyl alcohol) (PVA) showed the usual behavior in terms of Huggins’ constant obtained by the Schulz–Blaschke’s equation for PVAs derived from fatty acid systems lower than hexadecanoic acid. PVA derived from octadecanoic acid system showed abnormality, indicating association of alkyl groups. Contact angles on surfaces of PVAs cast from aqueous solutions were measured. While those of PVA derived from lower acid systems were 62°, those of PVAs derived from higher aids were higher and increased to 92° with increase in carbon number to octadecanoic acid. Alkyl groups in the PVAs were estimated to appear on the surfaces. Surface tension of aqueous solution of the PVA derived from octadecanoic acid showed high surface activity, and depended on pH of the solution, indicating the presence and cleavage of lactone ring at the combined portion between PVA and the acid.

Effect of alkylaluminum on ethylene polymerization catalyzed by 2,6-bis(imino)pyridyl complexes of Fe(II)

In the presence of tetraethylaluminoxane (TEAO), iron complexes were used to catalyze ethylene polymerizations with extremely high activities and generally produced polyethylene with a bimodal molecular weight distribution (MWD). This bimodal MWD of polyethylene was mainly derived from residual triethylaluminum in TEAO and was produced through a mechanism of chain transfer to aluminum. Ethylaluminoxane and tetraisobutylaluminoxane also were used to polymerize ethylene with high activities in the presence of iron complexes, and only polyethylene with a unimodal MWD was produced. The ratio of the rate constant of chain transfer to aluminum (k trA ) to the rate constant of chain propagation (k p ) was determined to be 0.12 for {[ArN=C(Me)] 2 C 5 H 3 N}FeCl 2 when Ar was 2,6-diisopropylphenyl (1) and 2.48 for {[ArN=C(Me)] 2 C 5 H 3 N}FeCl 2 when Ar was 2,6-dimethylphenyl (2); these values are far larger than those for metallocene-based catalysts. This explains why an iron complex usually produces polyethylene with a broader MWD than metallocene-based catalysts. Additionally, it can be concluded from the great difference between 1 and 2 with respect to k trA /k p that an iron complex with less congested aryl substituents is subjected to chain transfer to aluminum.

Studies on chain transfer reaction in butadiene polymerization initiated withn-butyl lithium and novel promoter potassiumpara-methylphenoxide

The chain transfer reaction was examined in the anionic telomerization of butadiene with n-BuLi as the initiator, potassium para-methylphenoxide (ROK) as the novel promoter, mixed xylene as the transfer agent as well as a solvent in the presence of diglyme as the polar modifier. Effects of ROK, diglyme, and the polymerizing temperature were studied. It was demonstrated that they all promote the chain transfer reaction. The relative constant of chain transfer to the solvent was also calculated. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1215–1218, 2005

Free Radical Polymerization of Acrylonitrile in Green Ionic Liquids

AbstractFree radical polymerization of acrylonitrile (AN) in ionic liquid, 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([bmim][BF4]), 2,2;m1‐azobisisobutyronitrile (AIBN) as initiator was investigated. Early investigations on polymerizations using ionic liquids indicate that they serve as especially good solvents to achieve high molecular weight polymers. Free radical polymerizations result in higher molecular weight polymers, for ionic liquids have low chain transfer constants and act to stabilize the active radical during the process of polymerization. The thermal stability of polymers synthesized in ionic liquids have be improved obviously than that in traditional solvents.