Metal-Containing Initiator Systems. IX. Radical Polymerizations of Vinyl Monomers by Various Metal Acetylacetonates

Abstract

A study of the polymerization of styrene, methyl methacrylate, acrylonitrile, vinyl acetate, and vinyl chloride initiated by various metal acetylacetonates [Me(acac)_x] has been made. It was found that Mn(acac)₃ was the most effective initiator, and Co(acac)₃, Mn(acac)₂, Cu(acac)₂, and Cr(acac)₃ showed moderate activity for the polymerization of methyl methacrylate at 60°C. However, the other, Me(acac)_x, had no effect or served as inhibitors. The addition of some additives such as halogen compounds did not accelerate polymerization of methyl methacrylate by Mn(acac)₃, From the results of polymerization and copolymerization of methyl methacrylate by Mn(acac)₃, it was concluded that the polymerization proceeded via an ordinary radical mechanism and the activation energy for initiation was 25.2 kcal/mole. The initiation mechanism of vinyl polymerization by Me(acac)_x was studied on the basis of the complex formation with the monomer.     

Free-radical polymerization of vinyl ferrocene

The results of quantitative studies of the rates of free-radical polymerization of vinyl ferrocene indicate that the latter has polymerization characteristics similar to those of styrene. The rates of homopolymerization of these two monomers in benzene at 70°C. were measured with the use of azobisisobutyronitrile as catalyst. The rate constants (k = R_p/[M][I]^1/2) are k_VF = (1.1 ? 1.8) × 10^?4, k_STY = 1.65 × 10^?4. Small amounts of vinyl ferrocene and styrene have similar effects on the rates of polymerizations of methyl methacrylate and ethyl acrylate and on the molecular weights of the resulting polymer. Polystyrene and poly(vinyl ferrocene) with similar molecular weights are isolated from polymerizations carried out under identical conditions. The rates of copolymerization of vinyl ferrocene—methyl methacrylate, vinyl ferrocene—styrene, and styrene—methyl methacrylate were determined by following the disappearance of monomers by means of gas chromatographic analyses. The relative reactivity for vinyl ferrocene is slightly lower than that for styrene.     

Synthesis of Vinyl Polymer—Poly (α-Amino Acid) Block Copolymers by End-Reactive Oligomers

In order to synthesize block copolymers consisting of segments having dissimilar properties, vinyl polymer - poly (α-amino acid) block copolymers were synthesized by two different methods. In the first method, the terminal amino groups of polysarcosine, poly(γ-benzyl L-glutamate), and poly(γ-benzyloxycarbonyl-L-lysine) were haloacetylated. The mixture of the terminally haloacetylated poly (α-amino acid) and styrene or methyl methacrylate was photoirradiated in the presence of Mo (CO)₆ or heated with Mo(CO)₆, yielding A-B-A-type block copolymers consisting of poly(α-amino cid) (the A component) and vinyl polymer(the B component). The characterization of block copolymers revealed that the thermally initiated polymerization of vinyl compounds by the trichloroacetyl poly(α-amino acid)/Mo(CO)₆ system was most suitable for the synthesis of vinyl polymer - poly-(α-amino acid) block copolymers. In the second method, poly (methyl methacrylate) and polystyrene having a terminal amino group were synthesized by the radical polymerization in the presence of 2-mercaptoethylammonium chloride. Using these polymers having a terminal amino group as an initiator, the block polymerizations of γ-benzyl L-glutamate NCA and e-benzyloxycarbonyl-L-lysine NCA were carried out, yielding A-B-type block copolymer. By eliminating the protecting groups of the side chains of poly(α-amino acid) segment, block copolymers such as poly(methyl methacrylate) with poly(L-glutamic acid) or poly(L-lysine) and polystyrene with poly(L-glutamic acid) and poly(L-lysine) were successfully synthesized.     

Mn2(CO)10‐induced controlled/living radical copolymerization of vinyl acetate and methyl acrylate: Spontaneous formation of block copolymers consisting of gradient and homopolymer segments

The controlled/living radical polymerization of vinyl acetate (VAc) and its copolymerization with methyl acrylate (MA) were investigated in bulk or fluoroalcohols using manganese complex [Mn₂(CO)₁₀] in conjunction with an alkyl iodide (R? I) as an initiator under weak visible light. The manganese complex induced the controlled/living radical polymerization of VAc even in the fluoroalcohols without any loss of activity. The R? I/Mn₂(CO)₁₀ system was also effective for the copolymerization of MA and VAc, in which MA was consumed faster than VAc, and then the remaining VAc was continuously and quantitatively consumed after the complete consumption of MA. The ¹H and ¹³C NMR analyses revealed that the obtained products are block copolymers consisting of gradient MA/VAc segments, in which the VAc content gradually increases, and homopoly(VAc). The use of fluoroalcohols as solvents increased the copolymerization rate, controllability of the molecular weights, and copolymerizability of VAc. The saponification of the VAc units in poly(MA‐grad‐VAc)‐block‐poly(VAc) resulted in the corresponding poly(MA‐co‐γ‐lactone)‐block‐poly(vinyl alcohol) due to the intramolecular cyclization between the hydroxyl and neighboring carboxyl groups in the gradient segments. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1343–1353, 2009     

Effective grafting of polymers onto ultrafine silica surface: Photopolymerization of vinyl monomers initiated by the system consisting of trichloroacetyl groups on the surface and Mn2(CO)10

The effective grafting of vinyl polymers onto an ultrafine silica surface was successfully achieved by the photopolymerization of vinyl monomers initiated by the system consisting of trichloroacetyl groups on the surface with Mn₂(CO)₁₀ under UV irradiation at 25 °C. The introduction of trichloroacetyl groups onto the surface of silica was achieved by the reaction of trichloroacetyl isocyanate with surface amino groups, which were introduced by the treatment of silica with 3‐aminopropyltriethoxysilane. During the polymerization, the corresponding polymers were effectively grafted onto the surface, based on the propagation of polymer from surface radicals formed by the interaction of trichloroacetyl groups and Mn₂(CO)₁₀. The percentage of poly(methyl methacrylate) grafting onto the silica reached 714.6% after 90 min. The grafting efficiency (proportion of grafted polymer to total polymer formed) in the polymerization of methyl methacrylate was very high, about 80%, indicating the depression of formation of ungrafted polymer. Polymer‐grafted silica gave a stable colloidal dispersion in good solvents for grafted polymer. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2157–2163, 2001     

Vapour pressure measurements on (acac)M(substituted olefin)2 and (acac)M(CO)2 (M = Rh(I), Ir(I))

Vapour pressures and enthalpies of sublimation of the complexes (acac)M (olefin)₂ and (acac)M(CO)₂ (M = Rh(I), Ir(I); olefin = ethylene, propylene, vinyl chloride, vinyl acetate and methyl acrylate) were determined by the Koudsen effusion method.     

Preparation and radical ring-opening polymerization of exo-methylene substituted cyclic ketene acetals

Preparation and radical ring-opening polymerization of the exo-methylene substituted cyclic ketene acetals, 2,4-dimethylene-1,3-dioxolane ( I ) and 2,5-dimethylene-1,3-dioxane ( II ), were carried out. Ketene acetals I and II were prepared by dehydrohalogenation of the corresponding cyclic haloacetal with potassium tert-butoxide in tetrahydrofuran at –78°C and ambient temperature, respectively. I underwent radical polymerization with essentially quantitative ring-opening with di-tert-butyl peroxide in dimethylformamide at 120°C. On the other hand, II underwent both ring-opening polymerization and vinyl polymerization under the same conditions of the polymerization of I . The differences of polymerization behavior between I and II were also discussed.     

Living cationic polymerization of α‐methyl vinyl ethers using SnCl4

Cationic polymerization of α‐methyl vinyl ethers was examined using an IBEA‐Et_1.5AlCl_1.5/SnCl₄ initiating system in toluene in the presence of ethyl acetate at 0 ～ ?78 °C. 2‐Ethylhexyl 2‐propenyl ether (EHPE) had a higher reactivity, compared to corresponding vinyl ethers. But the resulting polymers had low molecular weights at 0 or ?50 °C. In contrast, the polymerization of EHPE at ?78 °C almost quantitatively proceeded, and the number‐average molecular weight (M_n) of the obtained polymers increased in direct proportion to the EHPE conversion with quite narrow molecular weight distributions (weight‐average molecular weight/number‐average molecular weight ≤ 1.05). In monomer‐addition experiments, the M_n of the polymers shifted higher with low polydispersity as the polymerization proceeded, indicative of living polymerization. In the polymerization of methyl 2‐propenyl ether (MPE), the living‐like propagation also occurred under the reaction conditions similar to those for EHPE, but the elimination of the pendant methoxy groups was observed. The introduction of a more stable terminal group, quenched with sodium diethyl malonate, suppressed this decomposition, and the living polymerization proceeded. The glass transition temperature of the obtained poly(MPE) was 34 °C, which is much higher than that of the corresponding poly(vinyl ether). This poly(MPE) had solubility characteristics that differed from those of poly(vinyl ethers). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2202–2211, 2008     

Organometallic polymers. XXIV. Radical-initiated copolymerization of ferrocenylmethyl acrylate and methacrylate with acrylonitrile,maleic anhydride,and N-vinyl-2-pyrrolidone

Ferrocenylmethyl acrylate (I) and ferrocenylmethyl methacrylate (II) have been readily copolymerized with maleic anhydride in benzene–ethyl acetate solutions. Similarly, II has been copolymerized with both acrylonitrile and N-vinyl-2-pyrrolidone in benzene solutions to give higher molecular weight copolymers in high yields. In all cases azobisisobutyronitrile has been the initiator. Based on e values obtained, the metal carbonyl substituent acts as an electron-withdrawing group. Over a wide range of comonomers (N-vinyl-2-pyrrolidone, styrene, vinyl acetate, methyl acrylate, acrylonitrile, and maleic anhydride) I and II exhibit r₁ values lower than (and r₂ values higher than) similar copolymerizations with methyl acrylate or methyl methacrylate. Further more, the Q values found for I (0.03–0.11) and II (0.08–0.18) are smaller than those for methyl acrylate (0.46) and methyl methacrylate (0.74). Thus, I and II are less reactive than expected, presumably due to steric effects.     

The Polymerization of Free Enols with Electron-Deficient Comonomers

Abstract

The balance between kinetics and thermodynamics is illustrated herein by the first direct polymerization of vinyl alcohol, the thermodynamically unstable tautomer of acetaldehyde, at a rate faster than it can tautomerize. Vinyl alcohol was formed through the acid catalyzed hydrolysis of ketene methyl vinyl acetal. With excess water present, the kinetics of tautomerization first order dependence upon vinyl alcohol (k_obs = 2.73 × 10^?4 s^?1). Under water starved conditions, however, the kinetics now show a zero order dependence upon the concentration of vinyl alcohol (k_obs = 3.5 × 10^?6 M/s). Under these latter conditions, the half life of vinyl alcohol is nearly 24 hours at room temperature. Although cationic and homo free radical polymerization of vinyl alcohol failed, we found that this meta-stable species could be quantitatively polymerized in a copolymerization (AIBN, hυ, -10 to 25°C) with maleic anhydride. The k_obs for copolymerization was found to be 4.41 × 10^?4 sec^?1 at ?10°C. Since the rate of polymerization is far greater than that of tautomerization under these conditions (ca. 30 times faster at ?10°C), there is no significant increase in acetaldehyde concentration during polymerization.     

Organometallic modification approach to the control of push-pull architectures: Synthesis, properties and radical polymerization of chromium N-vinylcarbazole derivatives

In an effort to combine the donor character of the carbazole unit with the electron-withdrawing nature of the chromiumtricarbonyl moiety, which can be further modified by exchange of the CO ligand, a new series of vinyl-type monomers with organometallic push-pull chromophores, (N-vinylcarbazole)Cr(CO)₂L (L = CO (2), PPh₃ (4), (5)) and (N-vinylcarbazole)bisCr(CO)₃ (3), have been synthesized and isolated, wherein 2 could be converted into 3 under appropriate conditions. All compounds were characterized spectroscopically, and X-ray crystal structure analyses were performed for 2-4. The coordination-induced geometrical changes occur predominantly on the N-center and its attached double bond. PPh₃ replaces a CO group leading to the N-vinyl double bond length shortening from 1.274 (12) to 1.245 (9) Å. The distance of Cr from the carbazole plane, which allows estimates of the strength of the metal-ligand π-bonding, is shorter in 3 than in 2 as a result of an electronic communication between the two Cr(CO)₃ groups on each aryl ring of carbazole molecule. Electronic absorption and fluorescence spectral features of these complexes have been studied in terms of the electronic nature of the ligands. The change from 2 to 3 causes a subtle red-shift of the absorption bands due to the electronic transitions within dinuclear-carbazole ring system. The polymerization studies of these complexes under free-radical conditions lead to a better understanding of how the organometallic moiety affects the vinyl polymerization. The intriguing effect of the organometallic moiety on the intrachain excimer formation in the resultant polymers have been shown to be likely.     

Cyclometalated 2‐phenylpyridine complex [RuII(o‐C6H4‐py)(MeCN)4]PF6 as a tunable catalyst for living radical polymerization

The cyclometalated complex [Ru^II(o‐C₆H₄‐py)(MeCN)₄]PF₆ ( 1 ) with a σ‐Ru? C bond and four substitutionally labile acetonitrile ligands mediates radical polymerization of different vinyl monomers, viz. n‐butyl acrylate, methyl methacrylate, and styrene, initiated by three alkyl bromides: ethyl 2‐bromoisobutyrate, methyl 2‐bromopropionate, and 1‐phenylethyl bromide. The polymerization requires the presence of Al(OiPr)₃ and occurs uncontrollably as a conventional radical process. The variation of the molar ratio of the components of the reaction mixture, such as initiator, Al(OiPr)₃ and catalyst, affected the polymerization rates and the molecular weights but did not improve the control. A certain level of control has been achieved by adding 0.5 eq of SnCl₂ as a reducing agent. Tin(II) chloride decreased the rate of polymerization and simultaneously the molecular weights became conversion‐dependent and the polydispersities were also narrowed. Remarkably, the level of control was radically improved in the presence of excess of the poorly soluble catalyst ( 1 ), when the added amount of ( 1 ) was not soluble any more, i.e., under heterogeneous conditions, the system became adjustable and the living polymerization of all three monomers was finally achieved. Possible mechanisms of the ( 1 )‐catalyzed polymerization are discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4193–4204, 2008     

Vinyl ether end‐groups in poly(ethylene glycol)s from the Na2CO3‐promoted degradation of 1,3‐dioxolan‐2‐one polymers

The Na₂CO₃‐promoted polymerization of 1,3‐dioxolan‐2‐one (I) to afford poly(ethylene glycol) III was reinvestigated. The reaction appeared to involve a nucleophilic attack against the carbonyl and methylene groups of I to afford poly(carbonate) II with poly(ethylene glycol) linkages and ethylene oxide IV as a side product (10–22%). As the reaction progressed, poly(carbonate) II decreased and poly(ethylene glycol) III increased. Under some conditions, poly(ethylene glycol)s V and VI with vinyl ether terminal groups were formed unexpectedly. The formation of unsaturated products during the polymerization of I/EO (ethylene oxide) has not been reported in the literature. We believe that vinyl ethers were formed from the degradation of poly(carbonate)s and were accompanied by a reduction in molecular weight. The structures of vinyl ethers V and VI were confirmed by hydrogenation of the double bond into the ethyl ether group in VII and VIII, respectively. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 152–160, 2000     

Aspects of Living Radical Polymerization Mediated by Cobalt Porphyrin Complexes

Living radical polymerization (LRP) of methyl acrylate (MA), acrylic acid (AA), and vinyl acetate (VAc) mediated by cobalt(II) porphyrin complexes ((TMP)Co^II·, (TMPS)Co^II·) are reported. The polymeric products with relatively low polydispersity and controlled number average molecular weight (M_n) based on one polymer chain per cobalt complex demonstrate the living characters of the polymerization process. The formation of block copolymers of poly(methyl acrylate)‐b‐poly(vinyl acetate) (PMA‐b‐PVAc) and poly(methyl acrylate)‐b‐poly(vinyl pyrrolidone) (PMA‐b‐PVP) demonstrate another important feature of LRP and extend the application of cobalt porphyrin mediated radical polymerization to a wider array of functionalized monomers. Kinetic studies using ¹H NMR to follow the formation of orGano‐cobalt complexes reveal that two mechanisms, reversible termination (RT) and degenerative transfer (DT), occur during the polymerization process. MA and VAc polymerization mediated by cobalt porphyrin complexes are used to illustrate the properties of these two LRP pathways and evaluate the kinetic and thermodynamic properties for several of the central reactions.     

Über Oberflächenverbindungen von Übergangsmetallen. V. Oligomere Reaktionsprodukte bei der Polyäthylen- Synthese mit Chrom-Oberflächenverbindungen

On surface compounds of transition metals. V. Oligomeric reaction products by the polymerization of ethylene with chromium surface compounds Short time polymerization of ethylene with Cr(II) and Cr(VI) surface species on oxide carriers produces oligomeric reaction products, when followed by protonolysis, that originate, at least in part, from the decomposition of a soluble organochromium complex. Different homologous series result according to the type of heterogeneous catalyst employed: with Cr(II) contact α-olefines are obtained (in presence of O₂ the corresponding n-aldehydes are formed), Cr(VI) contacts give straightchain methylketones. Whereas the aldehyde formation occurs in secondary reactions the CH₃CO endgroup is produced evidently through the primary oxidation of C₂H₄ with surface Cr(VI). A polymerization sequence is then discussed in terms of protonolysis products wherein the alkene and acetyl endgroups are attached at that chain end which is not bound to chromium.     

Chemistry of polyfluorocarbanions 1. Nucleophilic iodofluorination of perfluoroalkyl vinyl ethers

Nucleophilic iodofluorination of perfluorovinyl methyl (I) and perfluorovinyl propyl (II) ethers by iodine chloride in nitrobenzene or sulfolan afforded 1-iodoperfluoro-1-methoxyethane (III) and 1-iodoperfluoro-l-propoxyethane in yields of 65 and 77%, respectively. In addition to compound (III), the reaction of perfluorovinyl methyl ether afforded two side products: l-iodo-2-chloroperfluoro-1-methoxyethane and 2-iodo-l-chloroperfluoro-1-methoxyethane. The latter products are formed via a radical reaction, which takes place under drastic conditions. On the basis of quantum chemical calculations of (I), (II), and the two anions formed from (I), CF₃OCFCF₃ (VI) and CF₃OCF₂CF₂ (VII), it is proposed that nucleophilic iodofluorination of perfluoroalkyl vinyl ethers involves the formation of thermodynamically more stable anions. The higher reactivity of (I) compared with (II) is in accord with the energy of the lowest unoccupied molecular orbitals and the charge density on the CF₂ carbon atoms.¹⁹F NMR spectra of the synthesized products are shown.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 669–672, March, 1991.     

Chromium Tricarbonyl η6-Complexes of (η5-Cyclopentadienyl)(η4-1,3-Diphenylcyclobutadiene)Cobalt

The reaction of (η⁵-cyclopentadienyl)(η⁴-1,3-diphenylcyclobutadiene)cobalt ( I ) with excess Cr(CO)₃py₃ in BF₃OEt₂ yielded two identified heterometallic compounds. Compounds II and III with one and two phenyl rings complcxed with Cr(CO)₃ fragment(s), respectively. These compounds were characterized by mass, infrared, ¹H and ¹³C NMR spectra and elemental analysis. The crystal structure of II was determined. The Cr(CO)₃ fragment bends inward toward the cyclobutadicne ring due to its electron-withdrawing ability, in accord with Hunter's postulate. A sharp line due to the non-complexed phenyl ring was observed in the ¹HNMR spectrum, which implies that five protons are magnetically equivalent. The chemical shifts of two protons of the cyclobutadiene ring decreased from I to II then to III , possibly because of diminished deshielding effect from the phenyl ring in (arene)Cr(CO)₃.     

Organometallic mediated radical polymerization of vinyl acetate with Fe(acac)2

The radical polymerization of vinyl acetate (VAc) is moderated by iron(II) acetylacetonate (Fe(acac)₂) by the organometallic route (OMRP), as well as by degenerative transfer polymerization (DTP) when in the presence of excess radicals, through the formation of thermally labile organometallic Fe^III dormant species. The poly(vinyl acetate) (PVAc)‐Fe^III(acac)₂ dormant species has been isolated in the form of an oligomer and characterized by ¹H NMR, EPR, and IR methods, and then used as a single‐component initiator for the OMRP of VAc. The degree of polymerization of this isolated oligomeric species demonstrates the limited ability of Fe(acac)₂, relative to the Co(acac)₂ congener, to rapidly trap the growing PVAc radical chain. Control under OMRP conditions is improved by the presence of Lewis bases, especially PMe₂Ph. On the other hand, iron(II) phthalocyanine inhibits the radical polymerization of VAc completely. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3494–3504     

Indenyl and fluorenyl transition metal complexes.: IV. Reactions of 2- and 4-azafluorenes with chromium hexacarbonyl

Reactions of 2- and 4-azafluorenes (I, II) and their methyl derivatives, 3-methyl-2-azafluorene (III) and 7-methyl-4-azafluorene (IV) with chromium hexacarbonyl in a $\text{1}\text{1}$ diglyme/heptane mixture at 140°C have been studied. A N-donor complex, C₁₂H₉NCr(CO)₅ is formed in the reaction of I with Cr(CO)₆. Compounds II–IV react to give arenechromiumtricarbonyl derivatives with benzene rather than pyridine ring bound to the metal. [η⁶-(4b,5,6,7,8,9b)-4-Azafluorene]chromiumtricarbonyl (VIII) gives the corresponding hydrochloride under the action of HCl. Methyl iodide decomposes VIII to produce 4-azafluorene iodomethylate. Deprotonation of VIII with BuLi in ether at ?20°C followed by dilution with hexane leads to precipitation of the corresponding Li salt (Xb), having η⁶-structure. Methylation of Xb with methyl iodide proceeds stereospecifically to yield the exo-methyl derivative XII. Treatment of VIII with excess t-BuOK at 25°C in THF results in a mixture of η⁶-(Xa) and η⁵-anions (XI), the former predominating.     

Neodymium Catalyst for the Polymerization of Dienes and Polar Vinyl Monomers

Ziegler–Natta catalysts have played a major role in industry for the polymerization of dienes and vinyl monomers. However, due to the deactivation of the catalyst, this system fails to polymerize polar vinyl monomers such as vinyl acetate, methyl methacrylate, and methyl acrylate. Herein, a catalytic system composed of NdCl₃⋅3TEP/TIBA is reported, which promotes a quasi‐living polymerization of dienes and is also active for the homopolymerization of polar vinyl monomers. Additionally, this catalytic system generates polymyrcene‐b‐polyisoprene and poly(myrcene)‐b‐poly(methyl methacrylate) diblock copolymers by sequential monomer addition. To encourage the replacement of petroleum‐based polymers by environmentally benign biobased polymers, polymerization of β‐myrcene is demonstrated with a catalytic activity of ≈106 kg polymer mol Nd⁻¹ h⁻¹.