Selective initiation of nonconjugated dienes containing electron donor–electron acceptor systems. IV. Polymerization of vinyl ether–styrene monomers

Three isomeric nonconjugated dienes, o-, m- and p-(2-vinyloxyethoxy)styrenes, were selectively polymerized by anionic or radical initiators through the styryl double bond while leaving the vinyl ether moiety intact. The anionic-initiated polymeric products are of high molecular weight and narrow molecular weight distribution as characterized by membrane osmometry and gel-permeation chromatography, respectively. These polymers were subsequently crosslinked by cationic initiators via the vinyl ether moiety on the polymer side chains. Acid-catalyzed hydrolysis of the poly(2-vinyloxyethoxy)styrenes yielded their respective hydroxy-containing polymers, polyvinylphenoxyethanols. The latter were physically and spectroscopically identical to authentic samples prepared by radical polymerization of the corresponding vinylphenoxyethanols, which, in turn, were synthesized by hydrolysis of the (2-vinyloxyethoxy)styrenes. The polyvinylphenoxyethanols were shown to undergo many chemical transformations, such as esterification with 3,5-dinitrobenzoyl chloride, cyanoethylation, and urethane formation.     

Selective initiation of nonconjugated dienes containing electron donor–electron acceptor systems. III. Synthesis of vinyl ether–styrene monomers

In a continuation of our studies on nonconjugated dienes containing electron donor–electron acceptor systems which may function as model crosslinking monomers, we here report the synthesis of the series, 2-, 3-, and 4-(2-vinyloxyethoxy)styrenes. The dipole moments μ, infrared and ultraviolet absorption properties, refractive indices n_D³⁰, molar refractions (MR_D), and optical exaltations of the compounds were determined. In order to establish whether any intramolecular electronic interactions, e.g., intramolecular charge-transfer complexes, contribute to the structure and properties of these compounds, 2- and 4-(2-ethoxyethoxy)styrenes were also prepared, and their properties compared with those of the vinyloxy series. While there are differences in certain of the properties of these two groups of monomers, these differences are not sufficiently large to permit definite correlations with the proposed interactions.     

Selective initiation of nonconjugated dienes containing electron donor–electron aceptor systems. I. Synthesis of vinyl ether–β-nitrostyrene monomers

The objectives of this work were to synthesize, characterize, and conduct a polymerization study on a set of ideal crosslinking monomers. The monomers studied are the three isomers of (2-vinyl-oxyethoxy)-β-nitrostyrene. Such monomers contain both the electron-donating vinyl ether moiety and the electron-accepting β-nitrostyrene moiety. A study of the spectral properties of these monomers was carried out in an effort to determine whether there was a contribution to the structure through an intramolecular interaction of the nature of a charge-transfer complex. Such studies have led to little or no support for such an interaction. As model compounds for comparison of spectral properties, the monomer series, o-, m-, and p-(2-ethoxyethoxy)-β-nitrostyrenes were synthesized and characterized as above. A comparison of the spectral and physical properties of these two series of compounds show that there are significant differences suggestive of the interactions proposed. However, since these discrepancies are small in most cases, it is not possible at present to correlate them specifically with the postulated intramolecular interactions.     

Photo and thermal polymerizations sensitized by donor–acceptor interaction. II. Photopolymerization and electronic spectroscopy of the isobutyl vinyl ether–acrylonitrile system

Photopolymerization of acrylonitrile (AN), an acceptor monomer, was found to be accelerated in the presence of isobutyl vinyl ether (IBVE), a donor monomer. The propagation is completed by a radical mechanism as judged by copolymer compositions; in contrast to the N-vinylcarbazole–AN system studied previously. This photopolymerization system is entirely stable if kept in the dark. The comparison of the relation between R_p and [IBVE]/[AN] ratio in the monomer feed found for the spontaneous photopolymerization with that for radical polymerization initiated by azobisisobutylonitrile in the dark leads to the conclusion that the rate of photoinitiation is enhanced by the interaction between AN and IBVE, whereas the propagation step by a radical mechanism is retarded by increasing concentration of IBVE. The contact charge-transfer complex between IBVE and AN was confirmed by electronic spectroscopy of the polymerization system, which showed photosensitization by charge-transfer interaction. The spectroscopic study of other weak donor–weak acceptor systems is also discussed.     

Polymerization initiated by an electron donor–acceptor complex. VI. Polymerization of methyl methacrylate initiated by a liquid SO2–nicotine complex and carbon tetrachloride

A kinetic study has been made of polymerization of methyl methacrylate initiated by an electron donor–acceptor complex of liquid SO₂ (electron acceptor) and nicotine (donor) in the presence of carbon tetrachloride. It is concluded that the polymerization proceeds through free-radical intermediates similar to the cases of liquid SO₂–pyridine and liquid SO₂–poly(2-vinylpyridine) complexes. The overall rate of polymerization is proportional to the square root of both liquid SO₂ and nicotine concentrations, and the values of k_p/k_t^½ under various polymerization conditions are in satisfactory agreement with the literature values. For the activation energy of initiation, 13.6 kcal/mole is estimated from the k_p/k_t^½ values obtained at temperatures ranging from 0 to 80°C.     

Anionic-initiated polymerization of β-nitrostyrenes

β-Nitrostyrene and many of its derivatives have been shown to yield high polymers via anionic initiation with alkoxide ions in protic solvents, e.g., alcohols. A study was conducted to determine the effect of certain substituents on the polymerization characteristics of representative monomers of this series and the properties of their polymers. A kinetic study was conducted and the relative rates of propagation were unexpectedly found to correlate well with brown's σ⁺ values. The rates of initiation of two representative monomers, β-nitrostyrene and p-methoxy-β-nitrostyrene, with sodium ethoxide were found to be 3.51 and 2.86 liter/mole sec, respectively. The rate of chain transfer in ethanol was studied qualitatively by using gel-permeation chromatography (GPC) to obtain molecular weight distribution (MWD) curves. The low values of the M _w/M _n ratios indicated little chain transfer in the protic solvent.     

Polymerization of vinyl monomers initiated by KO2–charge transfer agent systems. II

Vinyl monomers having electron acceptor groups such as nitroethylene, acrylonitrile, and acrolein were polymerized by KO₂–charge transfer agent initiator systems in dimethylsulfoxide (DMSO) at 25°C. The new initiator systems were found to be stable for almost 1 month under nitrogen atmosphere. The initial rate of polymerization was so fast that both conversion and molecular weight of the polymers obtained were high. Especially their molecular weight distribution was observed to be very narrow by means of gel permeation chromatography (GPC). The anion radicals generated by one electron transfer from potassium superoxide (KO₂) to charge transfer agents such as naphthalene, benzoquinone, azobenzene, etc., were suitable as initiator for the anionic polymerization of electron acceptor monomers. Study on block copolymerization of nitroethylene with acrylonitrile or acrolein was also attempted.     

Theory of electron transfer in donor–acceptor pairs

The wave functions of donor–acceptor pairs before and after electron transfer are written as a product of the electron-vibrational wave functions of the donor and acceptor with allowance for the change in the number of electrons on these particles by one after transition. In this approximation, the energy of the initial state is represented as a sum of the electron-vibrational levels of the donor and acceptor and that of the final state as a sum of donor cation and acceptor anion levels. Formulas for the electron transfer probability of symmetrical and nonsymmetrical donor–acceptor pairs have been derived that express the dependence of this process on the ionization potential difference of the donor and the electron affinity of the acceptor, on the vibrational frequencies of these particles, and on temperature.     

Polymerization with TMA-protected polar vinyl comonomers. II. Catalyzed by nickel complexes containing α-diimine-type ligands

α-Diimine Ni complexes (7, 8) were used as catalyst precursors with MAO in co- and terpolymerization of ethylene/propylene/α-olefins with OH and COOH functional groups. Trimethylaluminium was used to protect the functional group of polar monomers. The presence of 5-hexen-1-ol seems to have no effect on the polymerization rate at all for the N,N′-bis(2,6-diisopropylphenyl) derivative 8 but caused activity decreases of about fivefold in copolymerization and around two times in terpolymerization for the N,N-dimesityl derivative 7. The effect levels off at higher polar comonomer concentration. This system, (7)/MAO, also incorporates well both 10-undecen-1-ol and 10-undecen-1-oic acid. The activities obtained with these α-diimine Ni complexes in co- and terpolymerization are three to twenty times higher than those obtained with group 4 Cp based complexes especially at concentrations of polar monomer in the feed higher than 80 mM. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2471–2480, 1999     

γ-Radiolysis of ketone polymers. II. γ-Irradiation of styrene–methyl vinyl ketone copolymers

γ-Radiolysis of copolymers of styrene and methyl vinyl ketone shows that the introduction of pendant carbonyl groups markedly increases the G(s) value as compared to the homopolymer of styrene. The G(x) value is only slightly affected. These efficiencies are determined by employing an established statistical theory for random crosslinking and scission coupled with gel-permeation chromatography as the analytical tool required to follow the changes in the MWD of polymers. Also the G(H₂) values are unaltered by the introduction of carbonyl groups in polystyrene. These results are in marked contrast to the effects of carbonyl groups in polyethylene when subjected to γ-radiolysis and can be attributed to the protective role played by the aromatic phenyl groups in polystyrene.     

Theoretical study of novel porphyrins bearing electron donor–acceptor groups

This research project is focused on molecules that comprise a series of asymmetrically A₃B‐type meso‐substituted free‐base porphyrins and their related Zn‐metalloporphyrins. A and B were taken as electron‐donor and electron–acceptor groups. Full geometry optimizations without symmetry constrains were performed with B3LYP/6‐31G(d,P) methodology. Time‐dependent density functional theory calculations of the optimized structures indicate that there is a good agreement with the available experimental results. The highest occupied molecular orbital–lowest occupied molecular orbital (LUMO) gaps (ranging between 2.62 and 2.80 eV) are similar to those reported before for other porphyrins (2.29 eV). Also, the LUMO is situated close to the conduction band of titanium oxide, increasing the possibility of a charge transfer process. As porphyrins may act as electron transfer systems, the electron donor–acceptor capacity of these systems is characterized using two parameters; electrodonating (χ?) and electroaccepting (χ+) electronegativity. The main goal of this investigation is to analyze the electronic structure and the donor–acceptor properties of these porphyrins to see if these compounds could be useful for further applications related to the design of solar cells. © 2012 Wiley Periodicals, Inc.     

α-Trifluoromethyl vinyl acetate. II

Low conversion, low molecular weight homopolymers of α-trifluoromethyl vinyl acetate have been obtained by pyridine initiation and also by employing very large amounts of benzoyl peroxide. Since allylic hydrogens are not present, it appears that the limiting factor in the polymerization of isopropenyl esters is a slow rate of chain growth rather than degradative chain transfer. Copolymerization of the fluoromonomer (M₂) with vinyl acetate (M₁) yields values of r₁ = 0.25 and r₂ = 0.20, and for the fluoromonomer values of 0.069 and 1.51, respectively, for Q and e. Whereas ultraviolet initiation of equimolar mixtures of α-trifluoromethyl vinyl acetate and vinyl acetate yields low molecular weight copolymers, diisopropyl percarbonate-initiated room temperature bulk copolymerizations and emulsion copolymerizations yield polymers of high DP . Differential thermal analysis of an equimolar copolymer of vinyl acetate and the fluoromonomer surprisingly yields a sharp endotherm reminiscent of crystalline polymers. The unhydrolyzed copolymers in acetone and the alcoholyzed copolymers in 0.1N alkali exhibit Huggins k′ values of 0.3–0.4. Like ordinary poly(vinyl alcohol), the polyfluoroalcohols lose viscosity in dilute alkali due to retrograde aldol condensations. The solubilities of the polyfluoroalcohols, together with their thermal behavior, NMR spectrum, polarized infrared spectrum, refractive index, abilities to form visible polarizers, and other properties are also described.     

Polymerization of methyl methacrylate using bis(β‐ketoamino)nickel(II)–MAO catalytic systems

The polymerization of methyl methacrylate (MMA) was investigated using a series of bis(β‐ketoamino)nickel(II) complexes in combination with methylaluminoxane in toluene solution. The binary catalyst is necessary for initiating MMA polymerization and producing PMMA with high molecular weights but broad molecular weight distributions. The effects of reaction temperature and Al:Ni molar ratios on the polymerization of MMA were examined in detail. Both steric bulk and electronic effects of the substituents around the imino group in the ligand on MMA polymerization activities could be observed. Relative to electronic effects, the steric hindrance of the ligands displayed a more significant effect on the catalytic activities, with the catalytic activity sequence observed in the order 4 > 1 > 2 > 3 > 5 > 6. Structural analyses of the polymers by ¹³C NMR spectra indicate that polymerization yields PMMA with a syndiotactic‐rich atactic microstructure. Copyright © 2006 John Wiley & Sons, Ltd.     

Polymerization of methyl methacrylate using isatoic anhydride–bromine donor–acceptor complex as the photoinitiator

Isatoic anhydride (IA) alone did not initiate photopolymerization of methyl metacrylate (MMA) at 40°C when exposed to visible light for about 180 min. But IA, when used in combination with bromine (Br₂) as the initiator, initiated the photopolymerization of MMA readily under the same conditions. This behavior was explained by the formation of a donor-acceptor type of complex between IA and Br₂ in the presence of MMA. The polymerization was found to proceed via a free radical mechanism and the radical generation process was considered to follow an initial complexation reaction between the initiator components and monomer. The complex initiator showed nonideal kinetics for the present system (initiator exponent < 0.5) and was analyzed. The monomer exponents varied from 0.83 to 1.15 normally depending on the nature of solvent used. Initiator-dependent chain termination was significant as well as the bimolecular mode of chain termination. © 1993 John Wiley & Sons, Inc.     

Polymerization of β-cyanopropionaldehyde. IV. Polymerization by the adducts of β-cyanopropionaldehyde with triethylaluminum

Adducts (X, Y, and Z) between triethylaluminum and β-cyanopropionaldehyde (CPA) have been prepared and characterized. It was found that an equimolar amount of triethylaluminum undergoes Grignard type addition reaction with aldehyde group of CPA to give aluminum alkoxide and that another equimolar quantity of triethylaluminum undergoes coordination with the nitrile group of CPA (adduct X, in which the molar ratio of CPA to aluminum is 1:2). The coordinated triethylaluminum in adduct X may be changed to aluminum alkoxide by the addition of further equimolar amount of CPA (adduct Y, molar ratio = 1:1); on the other hand, heating at 130°C affords mixtures of aluminum aldimine and aluminum ketenimine structures (adduct Z, molar ratio = 1:2). From the cryoscopic measurement, adduct Z may be regarded as a coordinated polymer joined through bridged structures I and II. In the polymerization of CPA at ?78°C, the stereoregularity of the resulting poly-(cyanoethyl)oxymethylene was found to increase in the order: X < triethylaluminum < Y < Z. The polymerizations with triethylaluminum, X, and Y are considered to be initiated by NCCH₂CH₂CH(C₂H₅)? O? Al(C₂H₅)₂. The degree of association of the species may influence the stereoregularity of the polymer.     

Cocrystals of 6‐methyl‐2‐thiouracil: presence of the acceptor–donor–acceptor/donor–acceptor–donor synthon

The results of seven cocrystallization experiments of the antithyroid drug 6‐methyl‐2‐thiouracil (MTU), C₅H₆N₂OS, with 2,4‐diaminopyrimidine, 2,4,6‐triaminopyrimidine and 6‐amino‐3H‐isocytosine (viz. 2,6‐diamino‐3H‐pyrimidin‐4‐one) are reported. MTU features an ADA (A = acceptor and D = donor) hydrogen‐bonding site, while the three coformers show complementary DAD hydrogen‐bonding sites and therefore should be capable of forming an ADA/DAD N—H...O/N—H...N/N—H...S synthon with MTU. The experiments yielded one cocrystal and six cocrystal solvates, namely 6‐methyl‐2‐thiouracil–2,4‐diaminopyrimidine–1‐methylpyrrolidin‐2‐one (1/1/2), C₅H₆N₂OS·C₄H₆N₄·2C₅H₉NO, (I), 6‐methyl‐2‐thiouracil–2,4‐diaminopyrimidine (1/1), C₅H₆N₂OS·C₄H₆N₄, (II), 6‐methyl‐2‐thiouracil–2,4‐diaminopyrimidine–N,N‐dimethylacetamide (2/1/2), 2C₅H₆N₂OS·C₄H₆N₄·2C₄H₉NO, (III), 6‐methyl‐2‐thiouracil–2,4‐diaminopyrimidine–N,N‐dimethylformamide (2/1/2), C₅H₆N₂OS·0.5C₄H₆N₄·C₃H₇NO, (IV), 2,4,6‐triaminopyrimidinium 6‐methyl‐2‐thiouracilate–6‐methyl‐2‐thiouracil–N,N‐dimethylformamide (1/1/2), C₄H₈N₅⁺·C₅H₅N₂OS⁻·C₅H₆N₂OS·2C₃H₇NO, (V), 6‐methyl‐2‐thiouracil–6‐amino‐3H‐isocytosine–N,N‐dimethylformamide (1/1/1), C₅H₆N₂OS·C₄H₆N₄O·C₃H₇NO, (VI), and 6‐methyl‐2‐thiouracil–6‐amino‐3H‐isocytosine–dimethyl sulfoxide (1/1/1), C₅H₆N₂OS·C₄H₆N₄O·C₂H₆OS, (VII). Whereas in cocrystal (I) an R₂²(8) interaction similar to the Watson–Crick adenine/uracil base pair is formed and a two‐dimensional hydrogen‐bonding network is observed, the cocrystals (II)–(VII) contain the triply hydrogen‐bonded ADA/DAD N—H...O/N—H...N/N—H...S synthon and show a one‐dimensional hydrogen‐bonding network. Although 2,4‐diaminopyrimidine possesses only one DAD hydrogen‐bonding site, it is, due to orientational disorder, triply connected to two MTU molecules in (III) and (IV).     

Living regioselective copolymerization of ethylene with nonconjugated bicyclic dienes using (salicylaldiminato)(β‐enaminoketonato) titanium catalysts

A series of heteroligated (salicylaldiminato)(β‐enaminoketonato)titanium complexes [3‐^tBu‐2‐OC₆H₃CH?N(C₆F₅)] [PhN?C(CF₃)CHCRO]TiCl₂ [ 3a : R = Ph, 3b : R = C₆H₄Cl(p), 3c : R = C₆H₄OMe(p), 3d : R = C₆H₄Me(p), 3e : R = C₆H₄Me(o)] were synthesized and characterized. Molecular structures of 3b and 3c were further confirmed by X‐ray crystallographic analyses. In the presence of modified methylaluminoxane as a cocatalyst, these unsymmetric catalysts displayed favorable ability to incorporate 5‐vinyl‐2‐norbornene (VNB) and 5‐ethylidene‐2‐norbornene (ENB) into the polymer chains, affording high‐molecular weight copolymers with high‐comonomer incorporations and alternating sequence under the mild conditions. The comonomer concentration in the polymerization medium had a profound influence on the molecular weight distribution of the resultant copolymer. At initial comonomer concentration of higher than 0.4 mol/L, the titanium complexes with electron‐donating groups in the β‐enaminoketonato moiety mediated room‐temperature living ethylene/VNB or ENB copolymerizations. Polymerization results coupled with density functional theory calculations suggested that the highly controlled living copolymerization is probably a consequence of the difficulty in chain transfer of VNB (or ENB)‐last‐inserted species and some characteristics of living ethylene polymerization under limited conditions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Polymerization of β-carbomethoxypropionaldehyde

High molecular weight crystalline poly(carbomethoxyethyl)oxymethylene was prepared from β-carbomethoxypropionaldehyde with the use of organometallic compounds. The characterization, fractionation, x-ray analysis, and viscosity measurement were carried out. Degradation by hydrochloric acid gave a highly crystalline but soluble polymer of a lower molecular weight. It was interesting to note the high solubility character of the polymer in organic solvents in contrast to the poor solubility of the isomeric poly(acetoxyethyl)oxymethylene. From the relationship among the intrinsic viscosity, Huggins' constant, and the solubility parameter of solvent, the solubility parameter of the polymer was determined to be 9.3 (cal/ml)^1/2.     

Polymerization of β-cyanopropionaldehyde

A new class of polyacetals, poly(cyanoethyl)oxymethylene, was obtained by the polymerization of β-cyanopropionaldehyde at ?78°C. with use of ionic initiators including boron trifluoride diethyl etherate, diethylzinc, triethylaluminum, and triethylaluminumtitanium tetrachloride complexes. The influence of temperature, initiator, and solvent upon the polymerization was studied. Infrared spectra of polymers obtained from different initiators are also illustrated. An attempt was made to fractionate the polymer by means of solvent extraction. The acetone-soluble polymer is an elastomeric material having a low solution viscosity. The acetone-insoluble, dimethylformamide-soluble polymer obtained as a white powder was found to have extremely high solution viscosity. Some amounts of insoluble fraction could be also separated. The latter two fractions were observed to have a reasonable stability.     

Polymerization of β-isovalerolactone

The polymerization of β,β′-dimethyl-β-propiolactone with various catalysts was investigated. A detailed study on the heterogeneous polymerization initiated by triethyl aluminum was carried out. A reaction mechanism is suggested on the basis of chemical analysis of the polymer.