Alkyl halide/tertiary amine as novel initiators for free radical polymerizations of methyl methacrylate,methyl acrylate and styrene

A series of combinations of alkyl halide with tertiary amine such as ethyl α-bromophenylacetate/tris[2-(dimethylamino)ethyl)]amine (αEBP/Me₆TREN), ethyl 2-bromoisobutyrate/triethylamine (EBiB/TEA), and ethyl 2-chloropropionate/N,N,N′,N′,N′′-pentamethyldiethylenetriamine (ECP/PMDETA) have been developed as novel free radical initiators and used for the polymerizations of methyl acrylate (MA), methyl methacrylate (MMA) and styrene (St). The effects of the structure of alkyl halide and tertiary amine on the polymerization of MA were investigated. Gel permeation chromatograph (GPC) and proton nuclear magnetic resonance (¹H NMR) have been utilized to analyze the end group of the obtained poly(methyl acrylate). Electron spin resonance (ESR) spectroscopy was employed to identify the structure of the radicals produced by αEBP/Me₆TREN, and the results indicated that αEBP reacted with Me₆TREN via a single electron transfer (SET) nucleophilic mechanism to produce corresponding ethyl α-phenylacetate radicals which subsequently initiated the polymerization of MA. As both alkyl halide and tertiary amine are commercially available at low cost, non-explosive, and ease of use and storage in comparison with conventional azo, peroxide or persulfate initiators, the combination of alkyl halide and tertiary amine as a free radical initiator is promising for large-scale practical applications.     

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     

Kinetics of ε-caprolactone polymerization on dialkylaluminum alkoxides

Polymerization of ε-caprolactone initiated with dialkylaluminum alkoxides is a living system; formation of macrocyclics is fully depressed. Polymerization initiated with diethylaluminum alkoxide and diisobutylaluminum alkoxide proceeds on monomeric (deaggregated) active species, reversibly aggregating into trimers for the former and into dimers for the latter initiator. Kinetic treatment of this system allowed to determine simultaneously the aggregation-deaggregation equilibrium constant and the rate constant of propagation. Propagation most probably proceeds with insertion (pseudoanionically). Application of amines, complexing the growing species, allowed to break down the aggregates; polymerization became firstorder in initiator. Only secondary amines complexed strongly enough with growing species, the tertiary ones did not affect polymerization, at least up to the ratio 2:1 ([amine]/[initiator]^o). Rate constants of propagation in all of the studied^o systems, whether aggregated or not, have been found to be the same and equal to 0, 04 1·mol⁻¹·s⁻¹ at 25° in THF solvent. This value is approx. 10² times lower than for ion-pairs at these conditions. Moreover, rate constants are almost the same for the growing species …-OAl(C₂H₅)₂ and …-OAl(i-C₄H₉)₂, although aggregation is very much influenced by the size of the alkyl groups.     

STUDIES ON ORGANIC PEROXIDE/N, NDI (2-α-METHYL-ACRYLOYLOXY PROPYL)-PARA-TOLUIDINE BINARY SYSTEMS

The polymerization of methyl methacrylate (MMA) initiated by organic peroxide and polymerizable aromatic tertiary amine such as N, N-di (2-α-methylacryloyloxy propyl)-p-toluidine (MP)_2PT binary system has been studied. It was found that the (MP)_2PT promotes MMA polymerization, and the kinetics of MMA polymerization fits the radical polymerization rate equation. Based on the ESR studies and the end-group analysis the initiation mechanism is proposed.     

NMR spectroscopic investigation on polymerization mechanisms of amino acid NCAS

Polymerizations of α-aminoacid N-carboxyanhydrides (α-NCAs) can be initiated by nucleophilic or basic reagents. Depending on the nature of the reagent, nucleophilic attack at the carbonyl group C-5 or deprotonation of the N-H group may be the first reaction step. ¹H NMR spectroscopy is best suited to detect incorporation of initiator fragments. In the case of primary aliphatic amines quantitative endgroup analyses may even allow the calculation of the average degree of polymerization (DP). In the case of base-initiated polymerization the formation of N-acyl-NCA endgroups or the incorporation of the basic initiator is detectable. Furthermore, the role of electrophilic co-catalysts, such as isocyanates or N-acyl-NCAs, can be elucidated. ¹³C- and ¹⁵N NMR spectroscopy are better suited than ¹H NMR spectroscopy for stereosequence analyses of poly(D,L-amino acid)s. The results of both methods agree in that primary amine-initiated polymerizations of D,L-NCAs yield nearly random stereosequences. Trialkylamine initiated polymerizations of α-helix forming D,L-NCAs favour the formation of isotactic blocks, whereas in the case of non-helicogenic NCAs (e.g. D,L-Val-NCA) syndiotactic blocks are preferentially formed. ¹⁵N NMR spectroscopy also enables the sequence analysis of binary copolypeptides, and in favourable cases even ternary copolypeptides can be analyzed. ¹³C NMR crosspolarization/magic angle spinning (CP/MAS) spectroscopy of solid polypeptides enables the qualitative and quantitative determination of their secondary structure. Such investigations revealed that primary amine and tertiary amine-initiated polymerizations may yield different ratios of crystallites built up by β-sheets or α-helices and thereby bimodal molecular weight distributions (MWDs).     

Effect of amines on the ceric ion-initiated polymerization of vinyl monomers. II. Polymerization of acrylonitrile by ceric ion in presence of various substituted amines

The effect of various substituted amines on the polymerization of acrylonitrile initiated by ceric ammonium sulfate has been studied in aqueous solution at 30°C. It was found that the secondary and tertiary amines considerably increased the rate of polymerization, whereas the primary amines seemed to have no effect at all. From the kinetic studies it was found that the overall polymerization rate R_p is independent of ceric ion concentration and can be expressed by the equation: R_p = k₁ [amine] [monomer] + k₂[monomer]², where k₁ and k₂ are constants (involving different rate constants). The accelerating effect of the amines was attributed to a redox reaction between the ceric ion and the amine involving a single electron transfer, the relative activity of the different amines being thus dependent on the relative electron-donating tendency of the substituents present in the amine. The mechanism of the polymerization is discussed on the basis of these results, and various kinetic constants are evaluated.     

A Novel One‐Pot Conversion of Allyl Alcohols into Primary Allyl Halides Mediated by Acetyl Halide

A new and simple method for the synthesis of the primary allyl chlorides and bromides 9 – 16 from the secondary or tertiary allyl alcohols 3 – 8 and acyl halide was developed (Scheme 2, Table 1). Non‐commercially available secondary and tertiary allyl alcohols were synthesized from the related ketones and aldehydes via the addition of vinylmagnesium chloride. Mechanistic studies indicate that the alcohols were first acetylated by the acetyl halide and then protonated prior to substitution by the halide, Cl^? or Br^?, via an S_N2′ reaction, to yield the primary halides (Scheme 5).     

Isomerism and fluxional behaviour in η2 -vinyl complexes resulting in inversion of configuration at an asymmetric carbon atom. The crystal and molecular structures of two isomeric forms of [MoCl{η2 -C(CF3)C(CF3)(PEt3)} (CF3CCCF3)(η5 -C5H5)]

η² -Vinyl complexes [MCl{η² -C(CF₃)C(CF₃)L} (CF₃CCCF₃)(η⁵ -C₅H₅)] (M = Mo, W: L = tertiary phosphine or phosphite or pyridine) have been shown by NMR and X-ray diffraction studies to exist in two distinct isomeric forms which exhibit (a) different orientations of the η² -vinyl ligand (b) different configurations at the asymmetric carbon atom of the η² -vinyl ligand: variable temperature NMR studies reveal fluxional behaviour thought to involve reversible inversion of configuration at this carbon atom.     

Some studies of the reaction of μ-dichlorotetracarbonyldirhodium with dimethylphenylphosphine

The addition of PMe₂Ph to solutions of Rh₂Cl₂(CO)₄ has been studied by infrared and ¹H NMR spectroscopy, by measurement of conductance and of the carbon monoxide evolved. Under an atmosphere of CO the dominant course of the reaction is chloride bridge cleavage followed by CO substitution, whereas in refluxing cyclohexane substitution occurs initially. The formation of RhCl(CO)(PMe₂Ph)₂ on addition of PMe₂Ph (2 mol/mol Rh) is independent of solvent whereas addition of more tertiary phosphine leads to very different behaviour, depending upon the solvent and whether the solution is under CO or N₂. ¹H NMR studies show that all species with no more than one PMe₂Ph coordinated to a rhodium atom are in rapid equilibrium leading to averaged NMR signals.     

Characterization of polyelectrolyte solutions by analytical ultracentrifugation

In this paper some applications of ultracentrifugation on characterizing cationic polypeptides are reviewed. Especially the influence of α-helix favoring, water-structure breaking (chaotropic) anions (e.g. ClO₄⁻) as well as that of strongly hydrated, water structure-making anions (e.g. sulfate) on the sedimentation behaviour of (Lys)n and (Arg)n is considered. Moreover ultracentrifuge studies on the interaction between DNA and strong basic nucleoproteins (protamines) and on the solubilisation of the basic polypeptides mentioned before in reverse micelles are presented.     

Long‐Lived Excited States of Zwitterionic Copper(I) Complexes for Photoinduced Cross‐Dehydrogenative Coupling Reactions

Four heteroleptic copper(I) complexes containing phenanthroline and monoanionic nido‐carborane‐diphosphine ligands have been prepared and structurally characterized by various spectroscopic techniques and X‐ray diffraction. These complexes exhibit intense absorptions in the visible range and excited‐state lifetimes on the microsecond scale. Their application in visible‐light‐induced cross‐dehydrogenative coupling reactions was investigated. Preliminary studies showed that one of the four copper(I) complexes is an efficient catalyst for photoinduced oxidative C?H functionalization using oxygen as oxidant. Furthermore, α‐functionalized tertiary amines were obtained in good‐to‐excellent yields by light irradiation (λ>420 nm) of a mixture of our Cu^I complex, tertiary amines, and a variety of nucleophiles (nitroalkane, acetone, or indoles) under aerobic conditions. Electron paramagnetic resonance measurements provided evidence for the formation of superoxide radical anions (O₂^??) rather than singlet oxygen (¹O₂) during these photocatalytic reactions.     

Mechanisms and kinetics of the thermal decompositions of trichlorosilane,dichlorosilane, and monochlorosilane

Decomposition studies of trichlorosilane, dichlorosilane, and monochlorosilane at 921 K, 872 K, and 806 K, respectively, are reported. The studies were made at fixed reactant pressures over a range of total pressures in a wall conditioned, quartz reactor connected to a quadrupole mass-spectrometer. Products were monitored sequentially and continuously in time. The dichlorosilane decomposition was also studied by the comparative-rate single-pulse shock-tube method at temperatures around 1250 K. Two mechanisms of decomposition are considered: a silylene based mechanism initiated by molecular elimination reactions (Scheme I), and a free radical based mechanism initiated by bond fission reactions (Scheme V). Modeling tests of these mechanisms show that only the former is consistent with the experimental data. The decompositions are shown to be essentially nonchain processes initiated by the following pressure dependent reactions: HSiCl₃(SINGLEBOND)4→ SiCl₂+HCl, H₂SiCl₂(SINGLEBOND)1→ SiCl₂+H₂ and H₃SiCl(SINGLEBOND)5→ HSiCl+H₂. High pressure Arrhenius parameters recommended for these reactions are A_4,∞=A_1,∞=A_5,∞=10^14.5±0.5 s⁻¹, E_4,∞=71.9±2.1 kcal/mol, E_1,∞=69.2±2.0 kcal/mol, and E_5,∞=60.6±1.8 kcal/mol. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 69–88, 1998.     

Frontispiz: Mild and Versatile Nitrate‐Promoted C?H Bond Fluorination

A novel and facile C H bond fluorination proceeds under remarkably mild conditions (close to room temperature in most cases). Both aromatic and olefinic C(sp²) H bonds with a wide range of electronic properties are selectively fluorinated in the presence of a catalytic amount of simple, cheap, and nontoxic nitrate as the promoter. A Pd^II/Pd^IV catalytic cycle that is initiated by an in situ generated cationic [Pd(NO₃)]⁺ species was proposed based on preliminary mechanistic studies.     

SYNTHESIS AND POLYMERIZATION OF ALIPHATIC TERTIARY AMINO-GROUP N-SUBSTITUTED ACRYLAMIDES

Aliphatic tertiary amino-group N-substituted acrylamides, N-acryl-N′-methylpiperazine (AMP)and N-methacryl-N′-methylpiperazine (MAMP) were synthesized directly from N-methylpiperazinewith corresponding acryloyl chlorides and characterized by elementary analysis of their picrates,~1H-NMR, IR and MS. AMP did not polymerize with benzoyl peroxide (BPO), but could poly-merize with lauroyl peroxide (LPO). The rate equation of the polymerization was given as R_P=K_P [AMP]~(1.5)[LPO]~(0.5) and the overall activation energy of this polymerization system was 10.8Kcal/mol. The redox nature of LPO with the monomer itself was suggested. Even though AMP and MAMP hardly proceed the polymerization initiated with BPO, butunder lower concentration would form redox system with BPO to initiate the polymerization of MMAreadily. The rate equation of the polymerization of MMA initiated with MAMP-BPO systemwas given as R_P=K_P [MMA] [MAMP}~(0.5) [BPO]~(0.5) and the overall activation energy was 10.2Kcal/mol. The analysis of the obtained polymers confirmed that MAMP not only initiated the poly-merization of MMA by combining with BPO, but also took part in the polymer chains impartingthem with better biocompatibility.     

Protonation of metal carbonyl complexes : VI. Protonation of manganese π-cyclopentadienylphosphine complexes studied by 13C and 31P NMR techniques

¹³C and ³¹P NMR techniques have been applied to the complexes CpMn(CO)L₂ and CpMn(CO)₂ L (where L₂ is a bidentate tertiary phosphine, L is a monodentate tertiary phosphine, and Cp is cyclopentadienyl). It is shown that the complexes are protonated reversibly, when dissolved in CH₂Cl₂ in the presence of CF₃COOH, with the proton attacking the manganese atom.     

Evidence for a Proton-Coupled Electron Transfer Mechanism in a Biomimetic System for Monoamine Oxidase B Catalysis

Mechanistic studies with 5-ethyl-3-methyllumiflavinium (Fl⁺) perchlorate, a biomimetic model for flavoenzyme monoamine oxidase B (MAO-B) catalysis, and the tertiary, allyl amine 1-methyl-4-(1-methyl-1 H-pyrrol-2-yl)-1,2,3,6-tetrahydropyridine (MMTP) reveal that proton-coupled electron transfer (PCET) may be an important pathway for MAO catalysis. The first step involves a single-electron transfer (SET) leading to the free radicals Fl^. and MMTP^., the latter produced by deprotonation of the initially formed and highly acidic MMTP^.+. Molecular oxygen (O₂) is found to play a hitherto unrecognized role in the early steps of the oxidation. MMTP and several structurally similar tertiary amines are the only tertiary amines oxidized by MAO, and their structural/electronic properties provide the key to understanding this behavior. A general hypothesis about the role of SET in MAO catalysis, and the recognition that PCET occurs with appropriately substituted substrates is presented.     

Studies on tetrahydrofuran solutions of manganese(II) dihalides and tertiary phosphines and their reactions with dioxygen

Solutions of Mn(THF)₂Br₂ and MnI₂ and tertiary phosphines in tetrahydrofuran at 0°C are oxidised by dioxygen or electrochemically giving deep blue-purple solutions which have identical electronic spectra. The principal band with λ_max at 570 nm has ?>9000 1 cm^?1 mol^?1. Tertiary phosphines have been shown to be oxidised to the corresponding tertiary phosphine oxides. No evidence was found for the reversible formation of dioxygen-manganese complexes.     

Polymerization and copolymerization of 2-phthalimidomethyl 1,3-butadiene. I. Preliminary studies of free radical polymerization and polymerizations initiated by various transition metal allyl complexes

2-Phthalimidomethyl 1,3-butadiene was homopolymerized and copolymerized with butadiene by free radical initiators; r₁ and r₂ were close to 1. All the attempts to polymerize 2PMB anionically have been unsuccessful. Preliminary studies of various η³-allylic catalysts showed that η³-allyl M₀(CO)₃OOCCF₃ initiates the polymerization of butadiene and is not sensitive to N-methyl phthalimide (NMP); neither does it initiate the copolymerization of butadiene and 2PMB. On the other hand, a catalyst that results from the reaction of allyl trifluoroacetate with nickel tetracarbonyl is efficient for the copolymerization of butadiene and 2PMB. η³-Allyl nickel trifluoroacetate was prepared in heptane or benzene and used in benzene or methylene chloride. In all cases it initiated the copolymerization of butadiene with 2PMB     

Mild and Versatile Nitrate‐Promoted CH Bond Fluorination

A novel and facile C? H bond fluorination proceeds under remarkably mild conditions (close to room temperature in most cases). Both aromatic and olefinic C(sp²)? H bonds with a wide range of electronic properties are selectively fluorinated in the presence of a catalytic amount of simple, cheap, and nontoxic nitrate as the promoter. A Pd^II/Pd^IV catalytic cycle that is initiated by an in situ generated cationic [Pd(NO₃)]⁺ species was proposed based on preliminary mechanistic studies.     

Photochemical and Electrochemical Reduction of Carbon Dioxide to Carbon Monoxide Mediated by (2,2′-Bipyridine)tricarbonylchlororhenium(I) and Related Complexes as Homogeneous Catalysts

[fac-Re(bpy) (CO)₃Cl] (bpy = 2,2′-bipyridine) is an efficient homogeneous catalyst for the selective and sustained photochemical or electrochemical reduction of CO₂ to CO. A quantum yield of 14% and a faradic efficiency of 98% were measured in the presence of excess Cl^? ions. The photochemical process took place under visible-light irradiation and consumed a tertiary amine as electron donor. A formato-rhenium complex was isolated in the absence of excess Cl^? ions. Substitution by Cl^? ion generated free formate, but no CO was detected. Luminescence measurements showed that the tertiary amine quenches the metal-to-ligand charge-transfer excited state of the rhenium complex via a reductive mechanism, with a rate constant of 3.4 × 10⁷M^?1S^?1. The 19e-complex [Re(bpy) (CO)₃X]^? produced either photochemically or electrochemically appears to be the active precursor in the CO-generation process. Detailed spectroscopic studies on ¹³C-enriched carbonyl-rhenium and formato-rhenium complexes derived from ¹³C-enriched CO₂ were performed in order to confirm the origin of the products and to study the exchange of the ligands. A mechanism for the present CO₂ photoreduction process is presented; it involves separate pathways for CO and formate generation, in which the [Re(bpy) (CO)₃X] complex plays the role of both the photoactive and the catalytic center.