Inhibition of polymerization of methyl methacrylate by an ortho-benzoquinone-amine system

The kinetic features of the bulk polymerization of MMA in the presence of sterically hindered ortho-benzoquinones and the tertiary amines N,N-dimethylaniline and N,N-dimethylisopropanolamine have been studied. The irradiation of solutions of quinones and amines in MMA with visible light causes inhibition of the thermal polymerization of MMA, with the effects of quinones and amines being synergistic. The effect of inhibition is enhanced as the steric shielding of carbonyl groups of ortho-benzoquinone by substituents becomes weaker. The dependence of the induction period on the redox potentials of quinones passes through a maximum. It is shown that inhibition involves oxyphenoxyl radicals arising from the interaction of the original quinone with the product of its photoreduction in the presence of amines, pyrocatechol. The inhibiting effect depends on the concentration ratio of quinone and pyrocatechol and the nature of amine. When quinone is in excess with respect to pyrocatechol, additional inhibition of polymerization is observed and the rate of quinone consumption during the induction period is increased.     

Reactions of poly(methyl methacrylate) radicals with some <Emphasis Type="Italic">p</Emphasis>-quinones in the presence of tri-<Emphasis Type="Italic">n</Emphasis>-butylboron in methyl methacrylate polymerization

The polymerization of methyl methacrylate initiated by dicyclohexyl peroxydicarbonate at 30 °C was studied in the presence of tri-n-butylboron and a series of quinones, namely, p-benzoquinone, chloranil, and 2,5-di-tert-butyl-p-benzoquinone, whose concentration changed from 0.25 to 2.00 mol.%. The initial polymerization rate and molecular weight of poly(methyl methacrylate) depend on the structure and concentration of quinone. The growth radicals react with p-benzoquinone and chloranil predominantly at the C=C bond, while they react at the C=O bond of 2,5-di-tert-butyl-p-benzoquinone. The terminal stable oxygen-centered radicals that formed react with alkylborane, terminating reaction chains and generating alkyl radicals into the bulk. The latter are involved in chain initiation.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2114–2119, October, 2004.     

π-π Molecular complexes with nitrones,II. Complexation between heterocyclic nitrones and tetracyanoethylene as well as 1,4-benzoquinones

Characteristic charge-transfer absorption bands of some heterocyclic nitrones as electron donor with tetracyanoethylene, 2,3-dichloro-5,6-dicyanobenzoquinone and chloranil as electron acceptor have been measured in methylene chloride solution. The stoichiometry, apparent formation constants and transition energies of the charge-transfer complexes formed as well as the effect of solvent and the stability of these complexes are discussed.     

Miniemulsion polymerization of styrene using well-defined cationic amphiphilic comblike copolymers as the sole stabilizer

Well-defined, positively charged, amphiphilic copolymers containing long alkyl side chains were used as stabilizers in the miniemulsion polymerization of styrene. The copolymers were prepared by controlled free-radical copolymerization of styrene and vinyl benzyl chloride using either the reversible addition-fragmentation chain transfer method or TEMPO-mediated polymerization. The benzyl chloride moities were modified by two different long alkyl chain tertiary amines (N,N-dimethyldodecyl amine and N,N-dimethylhexadecyl amine) to yield the amphiphilic copolymers with vinylbenzyl dimethyl alkyl ammonium chloride units. Owing to their high structural quality, only a small amount of these copolymers was required to stabilize the latex particles (0.5–2 wt% vs styrene). Moreover, in the absence of any hydrophobic agent, the amphiphilic comblike copolymer preserved the colloidal stability of both the initial liquid miniemulsion and the final latex. Ill-defined, analogous copolymers were synthesized by conventional free-radical polymerization and in comparison, exhibited poor stabilization properties.     

Thioxanthone–carbazole as a visible light photoinitiator for free radical polymerization

A thioxanthone (TX) derivative with the additional carbazole chromophore, namely thioxanthone‐carbazole (TX‐C) was synthesized and characterized. The photophysical properties and its efficiency to polymerize methyl methacrylate both in the presence and absence of N,N‐dimethylaniline (DMA) as coinitiator was investigated and compared with that of the commercially available TX. TX‐C was found to display better photophysical properties and in both cases initiate polymerization more efficiently. Detailed real‐time Fourier transform infrared studies revealed that high polymerization rates can be obtained when TX‐C in conjunction with DMA was used. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Solid-state polymerization of acrylamide and its derivatives complexed with some lewis acids. II. Radiation-induced in-source polymerization

Radiation-induced solid-state polymerizations of complexes of N-tert-butylacrylamide, N-tert-amylacrylamide, and N-tert-hexylacrylamide with zinc chloride and zinc bromide have been studied. An accelerating effect of temperature and an inhibiting effect of oxygen on the polymerization process were observed. The activation energies have been established. The influence of monomer structure as well as the halide used on the polymerization rate have been discussed and some regularities have been pointed out. The polymers obtained show good solubilities in common solvents, which proves that they are not crosslinked.     

Solid matrix polymerization and stereoisomeric complexes of poly(methyl methacrylate)

The polymerization of methyl methacrylate within solid matrices of stereoregular poly(methyl methacrylate) has been studied by proton NMR and wide angle X-ray diffraction. The semi-crystalline isotactic (i-) PMMA matrix was synthesized in the laboratory by anionic polymerization initiated by phenylmagnesium bromide, and the syndiotactic (s-) PMMA matrix was synthesized through a Ziegler–Natta reaction. Matrix polymerization of the monomer was initiated through the redox activation of benzoyl peroxide with N,N-dimethyl-p-toluidine. NMR measurements of triad distributions in matrix-polymerized chains suggest that the well-known stereospecific replica polymerization in PMMA (syndiotactic sequences promote isotactic sequences and vice versa) plays only a limited role in the systems studied. Experimental results indicate that chains grown within the i-PMMA or s-PMMA solid matrices have greater degrees of configurational disorder. The greater concentration of atactic triads in these chains could be the result of limited free volume or steric effects during polymerization in a highly condensed environment. X-ray diffraction studies of solution cast blends of isotactic PMMA and PMMA with conventional tacticity reveal some crystallinity with a structure characteristic of the stereocomplex formed by isotactic and syndiotactic PMMA from suitable solvents. Evidence was obtained for the presence of this complex in solidified mixtures of the i-PMMA solid matrix and liquid monomer. This observation is an example of special intermolecular structures that can form under conditions of in situ growth of chains within a pre-polymerized matrix.     

Sulfobetaine‐containing diblock and triblock copolymers via reversible addition‐fragmentation chain transfer polymerization in aqueous media

A novel bifunctional acrylamido‐based reversible addition–fragmentation chain transfer (RAFT) chain‐transfer agent (CTA), N,N′‐ethylenebis[2‐(thiobenzoylthio)propionamide] (CTA2), has been synthesized and used for the controlled free‐radical polymerization of N,N‐dimethylacrylamide (DMA). A comparative study of CTA2 and the monofunctional CTA N,N‐dimethyl‐s‐thiobenzoylthiopropionamide (CTA1) has been conducted. Polymerizations mediated by CTA1 result in poly(N,N‐dimethylacrylamide) (PDMA) homopolymers with unimodal molecular weight distributions, whereas CTA2 yields unimodal, bimodal, and trimodal distributions according to the extent of conversion. The multimodal nature of the PDMAs has been attributed to termination events and/or chains initiated by primary radicals. The RAFT polymerization of DMA with CTA2 also results in a prolonged induction period that may be attributed to the higher local concentration of dithioester functionalities early in the polymerization. A series of ω‐ and α,ω‐dithioester‐capped PDMAs have been prepared in organic media and subsequently employed as macro‐CTAs for the synthesis of diblock and triblock copolymers in aqueous media with the zwitterionic monomer 3‐[2‐(N‐methylacrylamido)‐ethyldimethylammonio] propane sulfonate (MAEDAPS). Additionally, an ω‐dithioester‐capped MAEDAPS homopolymer has been used as a macro‐CTA for the block polymerization of DMA. To our knowledge, this is the first example of a near‐monodisperse, sulfobetaine‐containing block copolymer prepared entirely in aqueous media. The diblock and triblock copolymers form aggregates in pure water that can be dissociated by the addition of salt, as determined by ¹H NMR spectroscopy and dynamic light scattering. In pure water, highly uniform, micellelike aggregates with hydrodynamic diameters of 71–93 nm are formed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1262–1281, 2003     

The charge-transfer polymerization of nitroethylene in electron-donating solvents

The anionic polymerization of nitroethylene was studied in N,N-dimethylformamide (DMF) and in dimethyl sulfoxide (DMSO) at 0–40°C. The polymerization proceeds spontaneously when monomer is mixed with solvent in the absence of light. From the observed results of the rate of polymerization, the molecular weight of polymer, the effects of additives and solvents, the copolymerization with acrylonitrile, and the optical absorption spectra it is concluded that the polymerization is initiated by the nitroethylene radical anion generated by the slow dissociation of the electron donor–acceptor (EDA) complexes between the solvent molecule and the monomer. The activation energy for the rate of polymerization was 50 and 29 kJ/mole in DMF and DMSO, respectively, which seems to be determined primarily by the dissociation of the EDA complexes. The significant features of this polymerization are that the initiation proceeds slowly and there is essentially no termination.     

Sulfonated salicylidene thiadiazole complexes with Co (II) and Ni (II) ions as sustainable corrosion inhibitors and catalysts for cross coupling reaction

Condensation of 2,5‐dihydrazinyl thiadiazole with 5‐sodium sulfonate salicylaldehyde afforded dibasic tetradentate pincer N,O,O,N‐salicyldiene thiadiazole ligand (H₂Sanp). The novel dipolar ligand formed para‐magnetic pincer complexes within Co (II) and Ni (II) ions (Co‐Sanp and Ni‐Sanp) under sustainable conditions. The water‐soluble ligand and its metal‐complexes were estimated by mass, IR and UV–Visible spectroscopy, EA (elemental analyses), TGA (Thermogravimetric analyses), magnetic susceptibility, and conductivity measurements. The catalytic reactivity of Co‐Sanp and Ni‐Sanp were evaluated in the Suzuki and Buchwald‐Hartwig cross coupling reaction in aqueous‐methanol binary mixtures. Both reactions of boronic acid or aryl amines with aryl halides gave high chemoselective yield of C―C or C―N product. The inhibition characteristics of H₂Sanp and its Ni‐ and Co‐complexes were performed for the C‐steel corrosion in 1.0 M HCl using electrochemical measurements and surface analysis methods. These methods indicated that the synthesized compounds have served as efficient mixed‐type corrosion inhibitors and their adsorption on the steel surface obeyed isotherm model of Langmuir. Co‐Sanp inhibitor displays the best corrosion inhibition efficiency, and the capacity is up to 97.11% at of 250 mg L^?1. Surface analysis confirms formation of protective layer on the C‐steel surface.     

Group 4 complexes bearing alkoxide functionalized N‐heterocyclic carbene ligands as catalysts in the polymerization of olefins

Novel octahedral zirconium complexes bearing alkoxide functionalized N‐heterocyclic carbene ligands have been synthesized and characterized. NMR analysis showed that more than one species was obtained during synthesis. The synthesized complexes were able to polymerize ethylene and propylene giving rise to a linear polyethylene with high M_w and polydispersity index often bimodal with molecular weight distribution (MDI) > 2, and highly isotactic polypropylene together with an atactic fraction. Density functional theory (DFT) studies on the complex stability indicate the possible species active during the polymerization reaction. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Semiconducting polymers based on charge-transfer complexes. IV. Electrical properties and structure of polymeric charge-transfer complexes

Model electron donor molecules, 10-methylphenothiazine and 4-(methylthio)anisole, and polymeric electron donors which contained these molecules on the side chains of N-acyl-substituted polyethylenimines, were complexed with the electron acceptors, dichlorodicyanoquinone (DDQ), tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE), and tetranitrofluorenone (TNF). The model donors formed 1:1 complexes with all the acceptors except TCNE. The polymeric donors formed amorphous complexes with DDQ, TCNQ, and TCNE. Crystalline complexes were formed with TNF which had low melting points (lower than the model complexes and the pure polymer). This is apparently due to poor lateral packing of the polymer chains. Electrical resistivities were lower for all the polymer complexes than for the corresponding model complexes. Electrical resistivity also decreased with increase in complex crystallinity. In the best case the polymer complex was two hundred times as conducting as the model. The concentration of unpaired electrons measured by EPR was nearly independent of temperature. Most of the electrons seen are trapped and do not participate in conduction. Thermal activation energies for conduction were in the range of 0.5–1.8 eV and were nearly equal for the model and corresponding polymeric complexes. Elongation of polymer complex with TCNQ by rolling produces a decrease in resistivity in the roll direction, although the complex is amorphous. This reinforces the hypothesis that conduction is parallel to the polymer backbone. A polymer–tetranitrofluorenone complex was photoconducting, though the photoconductivity was smaller than the dark conductivity at the level of illumination used. Dember and Seebeck effects indicated that the major carrier in the complex was holes.     

Ultra‐High Molecular Weight Alpha‐Amino Poly(Methyl Methacrylate) with High Tg through Emulsion Polymerization by Using Transition Metal Cation–Tertiary Amine Pairs as a Mono‐Centered Initiator

As some complexes of transition metal cations in high oxidation state can oxidize tertiary amines under proper conditions into aminoalkyl radicals to initiate polymerization of electron‐deficient vinylic monomers, they form mono‐centered redox‐initiation pairs for preparation of 100% alpha‐amino telechelic polymer. Radical emulsion polymerization of methyl methacrylate (MMA) is performed by using water‐soluble amines as a reducing agent and Fe^III or Cu^II as an oxidizing agent. Tertiary amines such as 2‐(N,N‐dialkylamino)ethanol and N,N,N′,N′‐tertramethylethylenediamine exhibit a higher initiation activity. Monomer conversion can reach 80% in 8 h and 95% in 16 h, leading to PMMA with an absolute weight‐average molecular weight above 1.5 × 10⁶ g mol^?1. The alpha‐amino terminal functionality is verified by ultraviolet‐induced diarylketone‐initiated radical bock polymerization by using these PMMA chains as the macro‐sensitizer. Such a facile heterogeneous technique results in syndiotactic‐rich high‐T_g PMMA (rr > 50%, T_g = 124–127 °C). PMMA chains may be oxidized by Fe^II–O₂ complexes to initiate further radical polymerization, leading to PMMA with a long‐chain branched architecture.

     

Spectroscopic study of chloranil charge-transfer complexes of amino acids and related compounds

The absorption maxima, molar absorptivities, infrared spectra, compositions, formation constants, and pH dependence of amino acid—chloranil complexes have been determined with purified chloranil The n-π charge-transfer interaction depends on the presence of an unprotonated amino group; pH 9 is optimal for complex formation, but once formed, the complex is stable in a highly acidic medium and may be quantitatively extracted by hexanol. The molar absorptivities of the chloranil complexes of glycine, iminodiacetic acid, NTA, EDTA, DTPA and TTHA were measured. There is a linear relationship between the logarithm of the molar absorptivities of their chloranil complexes and the number of carboxylic groups in the molecule. There is an inverse linear relationship between the molar absorptivities of chloranil—metal—EDTA complexes and the logarithm of the stability constants of the EDTA chelates. This leads to a new method of determining the stability constants of complexes involving a nitrogen-donating group.     

The interaction between polymerization initiators and inhibitors in solutions—VIII. The mechanism of the reaction of azobisisobutyronitrile with p-benzoquinone and chloranil in polar and nonpolar solvents

The reactions of azobisisobutyronitrile (AIBN) with p-benzoquinone (BQ) and chloranil in toluene, chlorobenzene and acetonitrile, have been investigated by isolation and identification of the reaction products. In toluene and chlorobenzene, isobutyroylamino hydroquinone together with tetramethyl dioxazinobenzene are formed in the case of (BQ); the corresponding mono- and dioxazinobenzene derivatives are formed in the case of chloranil. In acetonitrile, however, only polyquinonoid resinous derivatives of the quinones are obtained. The crystalline derivatives as well as the resinous products have no nitrile groups in their structures and the nitrogen atom is directly attached to the parent quinone nucleus. This fact indicates that the radicals from AIBN react with quinones exclusively in the ketenimine form. A mechanism based on the possibility of electron-transfer from the radical to the quinone molecule to form charged species has been suggested. The degree of separation of these species is determined by the polarity of the solvent. Combination of the charged entities produces nuclear-substituted intermediates which may be eventually isolated as hydroquinones or subjected to further radical reactions with the ketenimine substituent to form the oxazinobenzene derivatives. The formation of ether derivatives of hydroquinone and tetrachlorohydroquinone in the reaction of BQ and chloranil with AIBN is accordingly excluded.     

Copolymer with long chain alkyl group as stabilizer in the preparation of biodegradable polyester particle

Poly(eicosyl methacrylate‐co‐2‐hydroxyethyl methacrylate) is synthesized by free radical polymerization of eicosyl methacrylate and 2‐hydroxyethyl methacrylate by using 2,2′‐azobisisobutyronitrile as initiator in N,N‐dimethylformamide at 80°C. Copolymers of different molecular weights are synthesized and well characterized by different analytical techniques and used as a stabilizer in the preparation of polycaprolactone and polylactic acid particles by solvent evaporation method. The formation of the polymer particles and its morphology with respect to the stabilizer molecular weights, concentration, and reaction time are studied. Well dispersed poly(caprolactone) and poly(lactic acid) particles are formed, which demonstrated the efficiency of the copolymeric stabilizer. Polymer particle sizes and its stability depend on the molecular weights and concentration of the stabilizer. The surface morphology and particle sizes of the prepared particles are characterized by field emission scanning electron microscope.     

Cuso4‐amine redox‐initiated radical polymerization of methyl methacrylate mediated by a CuCl2 complex: Homogeneous reverse ATRP

Kinetic results of CuSO₄/2,2'‐bipyridine(bPy)‐amine redox initiated radical polymerization of methyl methacrylate (MMA) at 70 to 90 °C in dimethylsulfoxide suggest that such initiation is characteristic of a slow rate and a low initiator efficiency, but tertiary amines exhibit a relatively higher rate. UV‐Vis spectroscopy confirms the alpha‐amino functionality of PMMA chains. CuCl₂/bPy successfully mediates the redox‐initiated radical polymerization of MMA with aliphatic tertiary amines in a fashion of slow‐initiated reverse atom transfer radical polymerization (ATRP), i.e. both the initiator efficiency of aliphatic tertiary amines and the average molecular weight of PMMA increase gradually, while the molecular weight distribution remains narrow but become broader with the conversions. As the PMMA chains contain alpha amino and omega C‐Cl moieties, UV‐induced benzophenone‐initiated radical polymerization and Cu^ICl/bPy‐catalyzed ATRP initiated from PMMA lead to block copolymers from terminal functionalities. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2562‐2578     

Metal complexes with ligands—organic phosphites as polyolefin antioxidants. III. Kinetics and mechanism of the inhibiting action of individual stable Cu(i)-complexes with phosphites

The general features of behavior of kinetically labile complexes (metal phosphite) revealed earlier ^1,2 provide the basis for the prediction of the activity of a new class of oxidation inhibitors. These are individual, stable metal complexes with organic phosphites as main ligands. The remarkable feature of these complexes, as shown as in this article on Cu(I) complexes, is the significant increase in the stoichiometric coefficient of inhibition f due to the suppression of the additional chain consumption of phosphite in the complex. The study of the initiated oxidation of styrene and solid isotactic polypropylene has proved that the phosphite complexes with Cu(I) ion are more effective than free, noncoordinated phosphites; quantitative characteristics of the inhibiting action of these complexes have been calculated. It is proved that termination of oxidation kinetic chains on the inhibitor molecules includes oxidation of coordinated phosphite without changing the oxidation degree of the central ion of metal. During inhibition of the oxidation of the substrate with mixtures of phosphite complexes of Cu(I) and phosphites (in styrene) or with aromatic amines (in polypropylene), the phenomenon of nonadditive strengthening (synergism) was discovered and the mechanism and kinetic regularities of synergism were revealed. This investigation of the phosphite complexes of the ions of Cu(I) presents new opportunities for controlled stabilization of polymers in uncontrolled conditions.     

π-π* Molecular charge transfer complexes of antipyrineSchiff bases with 1,4-benzoquinone derivatives as π-acceptors

Summary Spectrophotometric studies of compounds formed by several substituted antipyrineSchiff bases as electron donors with 2,3-dichloro-5,6-dicyano-benzoquinone, chloranilic acid, and chloranil as electron acceptors have given results that are consistent with 1:1 charge transfer complexes. Transition energies, oscillator strengths, and dipole moments of the complexes as well as the effect of solvent upon their stability are discussed. Also their free energies and absorption cross sections have been determined.

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Charge-transfer-KomplexeSchiffscher Basen vom Antipyrintyp mit 1,4-Benzochinon-Akzeptoren

Zusammenfassung Spektrophotometrische Untersuchungen von ausSchiffschen Basen des Antipyrintyps als Elektronendonatoren und 2,3-Dichlor-5,6-dicyanobenzochinon, Chloranilsäure und Chloranil als Elektronenakzeptoren gebildeten Verbindungen zeigen die Entstehung vonCharge-transfer-Komplexen der Stöchiometrie 1:1. Neben der Berechnung von freien Energien und Absorptionsquerschnitten werden Übergangsenergien, Oszillatorstärken, Dipolmomente und der Einfluß des Lösungsmittels auf die Stabilität der Komplexe diskutiert.

     

Effect of phenol and derivatives on atom transfer radical polymerization in the presence of air

The various phenolic compounds in conjunction with Cu(II) or Cu(I)‐N,N,N′,N″,N″‐pentamethyl diethylenetriamine (PMDETA) complexes are used to initiate atom transfer radical polymerization (ATRP) of methyl methacrylate, styrene, and methyl acrylate in the presence of a limited amount of air at temperatures in the range of 80–110 °C. Meanwhile, an effort is directed toward the elucidation of the role of phenol and derivatives in ATRP catalyzed by Cu(II)/PMDETA. The catalytic sequence involves the formation of Cu(I) by electron transfer from phenol to Cu(II); Cu(I) so formed can then react in two distinctly different ways: with organic halide to form a propagating radical or with oxygen to form copper salt in its higher oxidation state; and regeneration of Cu(I) by excess phenol. Such regeneration of Cu(I) would be expected to lead to polymerization as a result of the consumption of oxygen and phenol as well. The phenols with electron releasing groups tended to increase the conversion of the polymerization. In this respect, sodium phenoxide, a more effective additive was found, whereas p‐nitro phenol was the least effective. The obtained polymers displayed the common features of a controlled polymerization such as molecular weight control and low polydispersity index value (M_w/M_n < 1.5). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 351–359, 2004