Effect of solvent on radical polymerization of vinyl benzoate

Absolute rate constants of the vinyl benzoate polymerization have been measured by use of the intermittent illumination method in various aromatic solvents and ethyl acetate at 30°C. The determination of absolute rate constants showed that effects of solvent on the polymerization rate of vinyl benzoate were mainly ascribed to the variation of k_p values with solvents rather than that of k_t values. The k_p values for solvents used increased in the order: benzonitrile < ethyl benzoate < anisole < chlorobenzene < benzene < fluorobenzene < ethyl acetate. There was an eightfold difference between the largest and the smallest values The large variation among k_p values was explained neither by the copolymerization through solvents nor the chain transfer to solvents, but by a reversible complex formation between the propagating radical and aromatic solvents. This explanation was supported by a correlation between k_p values and calculated delocalization stabilizations for the complexes.     

Role of dimethyl sulfoxide as a solvent for vinyl polymerization

Dimethyl sulfoxide has been used as a solvent in the polymerization of methyl methacrylate and styrene. The chain-transfer coefficients of the solvent and the values of δ [i.e., (2k_t)^1/2/k_p] in solvent-monomer mixtures of various compositions were determined. δ was observed to be dependent on the solvent concentration in the case of methyl methacrylate but remained constant in case of styrene. The lowering of the values of δ with increasing solvent concentration in case of methyl methacrylate has been attributed to an interaction between the solvent and poly(methyl methacrylate) radical resulting in lower termination rate.     

Ionic Liquids - New Solvents in the Free Radical Polymerization

Summary: The analysis of the influence of ionic liquids (ILs) in polymer synthesis as an alternative for common organic solvents is still an active field of research. 1 Using ILs as solvents for free radical polymerizations implies a significant increase in polymerization rates and molecular weights which can be observed. In this work we examined the copolymerization behaviour of styrene (S) and methyl methacrylate (MMA), glycidyl methacrylate (GMA) and 2-hydroxypropyl methacrylate (HPMA) with acrylonitrile (AN) in 1-etyhl-3-methylimidazolium ethylsulfate ([EMIM]EtSO₄). ILs are liquids with comparable high polarities and viscosities. These two characteristic properties are strongly correlated with the rate coefficients of propagation k_p and termination k_t. 2 - 4 The rate constant of termination k_t decreases when the IL concentration and therefore the viscosity of the reaction mixture is increased, whereas the propagation rate coefficient k_p increases with increasing IL content. The viscosity of the IL can be varied by either working with mixtures of IL with conventional organic solvents – here the IL [EMIM]EtSO₄ was mixed with DMF – or by variation of the temperature. The influence of the viscosity of the IL ([EMIM]EtSO₄) on polymerization kinetics of methyl methacrylate (MMA) and styrene/acrylonitrile (S/AN) was investigated.     

Studies on the polymerization of methyl methacrylate activated by azobisisobutyramidine

Kinetic studies on methyl methacrylate polymerization were carried out with watersoluble 2,2′-azobisisobutyramidine (ABA). The rate of polymerization was proportional to the square root of the initiator concentration in the solvents chloroform, methanol, and dimethyl sulfoxide (DMSO), which confirms the bimolecular nature of the termination reaction. The monomer exponent was unity in chloroform but in methanol and DMSO the rate of polymerization passed through a maximum when plotted against the monmer concentration. This behavior in methanol has been attributed to be due to the enhanced rate of production of radical with increasing proportion of methanol. The rate of decomposition of the ABA has been observed to be faster in methanol than in chloroform. The situation becomes more complicated with DMSO, which was found to reduce the value of δ = (2k_t)^1/2/k_p in methyl methacrylate polymerization. The rate of polymerization was observed to be highly dependent on the nature of the solvent, the rate increasing with increased electrophilicity of the solvent. The dependence of R_p on the solvent has been explained in the light of the stabilization of the transition state due to increased solvation of the basic amidine group of the initiator with the increased electrophilicity of the solvent.     

Modeling termination kinetics in free‐radical polymerization using a reduced number of parameters

An approach for modeling chain‐length dependent termination rate coefficients is presented. The method is based on the assumption that free‐radical chain length may be considered as a continuous variable. As compared to discrete numerical methods, in continuous modeling the number of independent dimensionless parameters can be significantly reduced. As a consequence, for a wide variety of monomers the conversion dependence of k_t can be predicted without extensive numerical calculations. The method may also be used to determine polymerization conditions under which simpler models of k_t (which neglect effects arising from the dependence of k_t on chain length) may be applied. Calculations for methyl methacrylate, styrene, and butyl acrylate bulk polymerizations up to high degrees of monomer conversion show that the impact of chain length on termination varies with conversion and strongly depends on the type of monomer.     

Synthesis of aromatic polyethersulfone‐based graft copolyacrylates via ATRP catalyzed by FeCl2/isophthalic acid

The atom transfer radical polymerization (ATRP) catalyzed by the FeCl₂/isophthalic acid system was used for the preparation of novel aromatic polyethersulfone (PSF)‐based graft copolymers in N,N‐dimethylformamide (DMF), such as aromatic PSF‐graft‐poly(methyl methacrylate), aromatic PSF‐graft‐polymethylacrylate, and aromatic PSF‐graft‐poly(butyl acrylate). The route consisted of two steps. The first step included the chloromethylation of aromatic PSF, and the second step involved the ATRP of acrylate monomers using chloromethylated aromatic PSF as the macroinitiator and FeCl₂/isophthalic acid as the catalyst in DMF. Characterization data by gel permeation chromatography, DSC, IR, ¹H NMR, and thermogravimetric analysis confirmed that the graft copolymerization was successful. Only one glass‐transition temperature (T_g) was observed for aromatic PSF‐graft‐poly(methyl methacrylate), and two T_g's were detected for aromatic PSF‐graft‐methyl acrylate and aromatic PSF‐graft‐poly(butyl acrylate). © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2943–2950, 2001     

Solvent effect on the radical polymerization of di-n-butyl itaconate

Solvent effect on the polymerization of di-n-butyl itaconate (DBI) with dimethyl azobisisobutyrate (MAIB) was investigated at 50 and 61°C. The solvents used were found to affect significantly the polymerization. The polymerization rate (R_p) and the molecular weight of the resulting polymer are lower in more polar solvents. The initiation rate (R_i) by MAIB, however, shows a trend of being rather higher in polar solvents. The stationary state concentration of propagating poly(DBI) radical was determined by ESR in seven solvents. The rate constants of propagation (k_p) and termination (k_t) were evaluated by using R_p, R_i, and the polymer radical concentration observed. The k_p value decreases fairly with increasing polarity of the solvent used, whereas k_t is not so influenced by the solvents. The solvent effect on k_p is explained in terms of a difference in the environment around the terminal radical center of the growing chain. Copolymerization of DBI with styrene (St) was also examined in three solvents with different physical properties. The poly(DBI) radical shows a lower reactivity toward St in a more polar solvent.     

Radical polymerization of methyl methacrylate in the presence of isotactic poly(methyl metacrylate). VII. Determination of the rate constants for template polymerization

The separate rate constants k_p and k_t for propagation and termination of radical template polymerization of methyl methacrylate along isotactic poly(methyl methacrylate) as a polymer template have been determined. The polymerizations were carried out in the strongly complexing solvent dimethylformamide at 5°C. For the evaluation of k/k_t from stationary kinetic experiments, the rates of initiation were determined by employing a scavenger method. The nonstationary experiments yielding k_p/k_t were performed by means of the rotating sector technique. As the template rate effects increased with decreasing initiator concentration, the rotating sector curves were corrected for variation in light intensity. It appeared that the radical lifetime increases from 8.4 sec for normal or blank polymerization to 64 sec for template polymerization. The calculated values of k_p are 26.6 and 5.9 l./mole-sec and of k_t 140 × 10⁴ and 1.7 × 10⁴ l./mole-sec for blank and template polymerization, respectively. The changes in k_p and k_t, due to the presence of template polymer, are explained in terms of an extra loss of activation entropy in the stereoselective propagation step and a strong hindrance of segmental diffusion for the termination reaction of the chains growing along the polymer template.     

Synthesis of miktoarm star and miktoarm star block copolymers via a combination of atom transfer radical polymerization and stable free‐radical polymerization

A trifunctional initiator, 2‐phenyl‐2‐[(2,2,6,6‐tetramethyl)‐1‐piperidinyloxy] ethyl 2,2‐bis[methyl(2‐bromopropionato)] propionate, was synthesized and used for the synthesis of miktoarm star AB₂ and miktoarm star block AB₂C₂ copolymers via a combination of stable free‐radical polymerization (SFRP) and atom transfer radical polymerization (ATRP) in a two‐step or three‐step reaction sequence, respectively. In the first step, a polystyrene (PSt) macroinitiator with dual ω‐bromo functionality was obtained by SFRP of styrene (St) in bulk at 125 °C. Next, this PSt precursor was used as a macroinitiator for ATRP of tert‐butyl acrylate (tBA) in the presence of Cu(I)Br and pentamethyldiethylenetriamine at 80 °C, affording miktoarm star (PSt)(PtBA)₂ [where PtBA is poly(tert‐butyl acrylate)]. In the third step, the obtained St(tBA)₂ macroinitiator with two terminal bromine groups was further polymerized with methyl methacrylate by ATRP, and this resulted in (PSt)(PtBA)₂(PMMA)₂‐type miktoarm star block copolymer [where PMMA is poly(methyl methacrylate)] with a controlled molecular weight and a moderate polydispersity (weight‐average molecular weight/number‐average molecular weight < 1.38). All polymers were characterized by gel permeation chromatography and ¹H NMR. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2542–2548, 2003     

Synthesis of amphiphilic star block copolymers via diethyldithiocarbamate‐mediated living radical polymerization

(AB)_f star block copolymers were synthesized by the radical polymerization of a poly(t‐butyl acrylate)‐block‐poly(methyl methacrylate) diblock macroinitiator with ethylene glycol dimethacrylate in methanol under UV irradiation. Diblock macroinitiators were prepared by diethyldithiocarbamate‐mediated sequential living radical copolymerization initiated by (4‐cyano‐4‐diethyldithiocarbamyl)pentanoic acid under UV irradiation. The arm number (f) was controlled by the variation of the initial concentration of the diblock initiator. It was found from light scattering data that such star block copolymers (f ≥ 344) not only took a spherical shape but also formed a single molecule in solution. Subsequently, we derived amphiphilic [arm: poly(acrylic acid)‐block‐poly(methyl methacrylate)] star block copolymers by the hydrolysis of poly(t‐butyl acrylate) blocks. These amphiphilic star block copolymers were soluble in water because the external blocks were composed of hydrophilic poly(acrylic acid) chains. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3321–3327, 2006     

Tricarbonylchromium complexes of styrenes in radical copolymerization

The organometallic monomers styrenetricarbonylchromium and p‐methylstyrenetricarbonylchromium were copolymerized in ethyl acetate solutions with methyl methacrylate and butyl acrylate using azobisisobutyronitrile at 50 °C and a binary system including di‐tert‐butylperoxytriphenylantimony at 30 °C as the free‐radical initiators. Comonomers are proposed to form a molecular complex based on the results of ultraviolet and electron spin resonance spectroscopy. A kinetic study shows that chromium‐containing monomers at high concentrations in the mixture reduce the rate of copolymerization. The addition of styrenetricarbonylchromium to butyl acrylate significantly slows down the autoacceleration. The reactivity ratios of the comonomer pairs, namely, styrenetricarbonylchromium–methyl methacrylate, styrenetricarbonylchromium–butyl acrylate and p‐methylstyrenetricarbonylchromium–methyl methacrylate, were determined using the method of Kelen–Tudos for low conversion polymerizations.Copyright © 2001 John Wiley & Sons, Ltd.     

4-N,N-Dimethylamino-4'-Isopropylbenzophenone as polymerization photoinitiator. Effect of solvent and photoinitiator concentration on its photoreactivity and on the polymerization process

Several kinetics aspects of the methyl methacrylate (MMA) polymerization using 4-dimethylamino-4'-isopropylbenzophenone (PI) as photoinitiator have been studied. The order of the polymerization reaction with respect to monomer and initiator concentrations have been investigated, as well as the polymerization behavior under well-stirred and unstirred conditions; values of initiation quantum yield (?_i) and k_p/k_t^1/2 have also been determined. It has been found that the nature of the polymerization-initiating radicals depends on the type of solvent and the photoinitiator concentration ([PI]). In cyclohexane solution and at low [PI] (< 5 x 10^-5M), the cyclohexyl radical is practically the only polymerization initiating radical, while at higher [PI] both radicals, cyclohexyl and the aminoalkyl derived from PI, participate in the initiation step, increasing the participation of the later as the [PI] increases. When benzene is used as solvent both phenyl and aminoalkyl radicals participate in the initiation step at any [PI] employed. Efficiencies of the radicals derived from solvent and photoinitiator have been determined.     

Kinetics of emulsion polymerization of methyl methacrylate

The kinetics of the emulsion polymerization of methyl methacrylate at 50°C have been studied in seeded systems using both chemical initiation and γ-radiolysis initiation. Both steady-state rates and (for γ-radiolysis) the relaxation from the steady state were observed. The average number of free radicals per particle was quite high (e.g., ～0.7 for 10^?3 mol dm^?3 S₂O²₈ initiator). The data are quantitatively interpreted using a generalized Smith–Ewart–Harkins model, allowing for free radical entry, exit, biomolecular termination within the latex particles, and aqueous phase hetero-termination and re-entry. From this treatment, there results (i) the dependence of the termination rate coefficient (k_t) on the weight fraction of polymer (w_p), (ii) lower bounds for the dependence of the entry rate coefficient on initiator concentration, and (iii) the conclusion that most exited free radicals undergo subsequent re-entry into particles rather than hetero-termination. The results for k_t(w_p) are consistent with diffusion control at temperatures below the glass transition point. Comparisons are presented of the behavior of methyl methacrylate, butyl methacrylate, and styrene in emulsion polymerization systems.     

Solvent effects on radical homo- and copolymerizations of methacryloyl fluroride

The effect of solvent in homo- and copolymerizations of methacryloyl fluoride (MAF) was investigated in various aromatic solvents. In these solvents, there is a significant effect on the rate of polymerization, on the tacticity of the resulting poly(methacryloyl fluoride), and on the copolymerization of MAF with methyl methacrylate (MMA). The equilibrium constants between MAF and aromatic solvents were determined from NMR spectroscopic measurements. These results indicated that the solvent effect on the MAF polymerization stems from changes in reactivity of MAF induced by the strong MAF–solvent interaction as well as stabilization of the MAF radical by solvents. Copolymerization of MAF with both p-methoxystyrene (MSt) and p-nitrostyrene (NSt) was also studied.     

Vinyl polymerization with a binary system of p‐chlorobenzenediazonium salt and sodium tetraphenylborate

A combined system of sodium tetraphenylborate (STPB) and p‐chlorobenzenediazonium tetrafluoroborate (CDF) serves as an effective initiator at low temperatures for acrylate monomers such as methyl methacrylate (MMA), ethyl acrylate, and di‐2‐ethylhexyl itaconate. The polymerization of MMA with the STPB/CDF system has been kinetically investigated in acetone. The polymerization shows a low overall activation energy of 60.3 kJ/mol. The polymerization rate (R_p) at 40 °C is given by R_p = k[STPB/CDF]^0.5[MMA]^1.6, when the molar ratio of STPB to CDF is kept constant at unity, suggesting that STPB and CDF form a complex with a large stability constant and play an important role in initiation and that MMA participates in the initiation process. From the results of a spin trapping study, p‐chlorophenyl and phenyl radicals are presumed to be generated in the polymerization system. A plausible initiation mechanism is proposed on the basis of kinetic and electron spin resonance results. A large solvent effect on the polymerization can be observed. The largest R_p value in dimethyl sulfoxide is 11 times the smallest value in N,N‐dimethylformamide. The copolymerization of MMA and styrene with the STPB/CDF system gives results somewhat different from those of conventional radical copolymerization. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4206–4213, 2001     

The effect of polymer side chains on vapor sorption in polyacrylate and polymethacrylate solutions

The segment fraction Ψ₁ activity coefficients, a₁/Ψ₁, of solvents have been determined by the piezoelectric sorption method for 0.1 ≤ Ψ₁ ≤ 0.5 in binary solutions of chlorinated methanes [carbon tetrachloride (CCl₄), chloroform (CHCl₃), and dichloromethane (CH₂Cl₂)] with aromatic hydrocarbons (benzene and toluene) in poly(methyl methacrylate), poly(methyl acrylate), poly(ethyl methacrylate), and poly(n-butyl acrylate) at 23.5°C. The present results for toluene in PMMA agree with previously published values obtained by gas-liquid chromatography. For CCl₄ and the aromatic hydrocarbons, the polymer–solvent interaction parameter χ is positive and constant, while for the polar solvents (CHCl₃ and CH₂Cl₂), χ is negative and increases with increasing Ψ₁. The effect of the polymer side chains on vapor sorption in nonpolar and polar solvent systems is discussed in terms of the χ parameter.     

Fluorinated and ring‐substituted bisbenzimidazole copper complexes for ethylene/acrylate copolymerization

Bisbenzimidazole copper dichloride complexes (CuBBIMs), when activated with methylaluminoxane, catalyze the random copolymerization of ethylene with acrylates to produce highly linear functional copolymers. To probe the sensitivity of the copolymerization to the catalyst structure, a series of CuBBIM catalysts with various steric, electronic, and geometric ligand characteristics was prepared, including CuBBIMs having benzimidazole ring substituents and ligand backbones of various lengths. Four different acrylates were also evaluated as comonomers (t‐butyl acrylate, methyl acrylate, t‐butyl methacrylate, and methyl methacrylate). Although no obvious ligand‐based influences on copolymerization were identified, the structure of the acrylate comonomer was found to exert significant effects. Copolymers prepared with t‐butyl methacrylate comonomer exhibited the highest ethylene contents (31–63%), whereas those prepared with methyl acrylate contained only minor amounts of ethylene (<15%). Copolymerizations carried out at lowered acrylate feed levels generally had increased ethylene contents but showed smaller yields, lowered molecular weights, and increased branching. Unusual ketoester structures were also observed in the methyl acrylate and methyl methacrylate containing copolymers, suggesting that the acrylate ester group size may be an important controlling factor for copolymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1817–1840, 2006     

Photopolymerization of Methyl Methacrylate Using the Benzil-Dimethylaniline Combination as the Photoinitiator

Benzil (BZL)-dimethylaniline (DMA) exciplex interaction has been utilized to initiate the photopolymerization of methyl methacrylate at 40°C in bulk and in solution. Depending on the nature of the solvent used, the monomer exponent values varied between 0.47 to 2.76. Initiator exponent values were found to be 0.29 and 0.15 with respect to [BZL] and [DMA], respectively. A low value of k_p ²/k_t and the high initiator transfer constant values indicated significant initiator-dependent termination. The semipinacol radical formed during irradiation is thought to be mainly responsible for primary radical termination while the generated ion radicals are presumed to participate in degradative initiator transfer.     

Photopolymerization of styrene,p-chlorostyrene,methyl methacrylate,and butyl methacrylate with polymethylphenylsilane as photoinitiator

The rates of photochemical polymerization of styrene (St), p-chlorostyrene (Cl-St), methyl methacrylate (MMA), and butyl methacrylate (BMA) with polymethylphenylsilane (PMPS) as an initiator were measured. Polymethylphenylsilane is photodegrated to form silyl radicals that may initiate polymerization of vinyl monomers. Rate constants k_p and k_t have been determined for these systems. A good correlation (log P = α + βμ) of the resonance stabilization (P) of the chain radicals and the dipole moment (μ) of the monomers is observed for these polymerization systems. This equation may be used to estimate the resonance stabilization (P) of a monomer and the polymerization rate constant (k_p). © 1996 John Wiley & Sons, Inc.     

Synthesis and characterization of fluorine‐containing PAA‐b‐PTPFCBPMA amphiphilic block copolymer

A series of perfluorocyclobutyl (PFCB) aryl ether‐based amphiphilic diblock copolymers containing hydrophilic poly(acrylic acid) (PAA) and fluorophilic poly(p‐(2‐(p‐tolyloxy)perfluorocyclobutoxy)phenyl methacrylate) segments were synthesized via successive atom transfer radical polymerization (ATRP). 2‐MBP‐initiated and CuBr/N,N,N′,N′,N″‐pentamethyldiethylenetriamine‐catalyzed ATRP homopolymerization of the PFCB‐containing methacrylate monomer, p‐(2‐(p‐tolyloxy)perfluorocyclobutoxy)phenyl methacrylate, can be performed in a controlled mode as confirmed by the fact that the number‐average molecular weights (M_n) increased linearly with the conversions of the monomer while the polydispersity indices kept below 1.38. The block copolymers with narrow molecular weight distributions (M_w/M_n ≤ 1.36) were synthesized by ATRP using Br‐end‐functionalized poly(tert‐butyl acrylate) (PtBA) as macroinitiator followed by the acidolysis of hydrophobic PtBA block into hydrophilic PAA segment. The critical micelle concentrations of the amphiphilic diblock copolymers in different surroundings were determined by fluorescence spectroscopy using N‐phenyl‐1‐naphthylamine as probe. The morphology and size of the micelles were investigated by transmission electron microscopy and dynamic laser light scattering, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010