Long-lived polymer radicals. IV. Reactions of poly(N-methylacrylamide) and poly(N-methylmethacrylamide) radicals with binary mixtures of vinyl monomers

N-methylacrylamide (NMAAm) and N-methylmethacrylamide (NMMAm) were polymerized to give polymer microspheres containing living propagating radicals. The microsphere polymer radicals were allowed to react with some binary mixtures of vinyl monomers including alternating copolymerization combinations. The reaction processes were investigated by ESR spectroscopy. In the poly(NMMAm) radical/methyl methacrylate (MMA)/styrene (St) system, the propagating radical from MMA was mainly observed at the higher MMA concentration, while polySt radical prevailed at the lower MMA concentration. In the poly(NMMAm) radical/α-methylstyrene (α-MeSt)/diethyl fumarate system, the α-MeSt radical was exclusively observed, while the maleic anhydride (MAn) radical was predominantly observed in the α-MeSt/MAn system. In the MAn/diphenylethylene system, the propagating radicals from both monomers were observed at comparable concentrations. The poly(NMAAm) microsphere radical behaved differently in the reaction with the MMA/St mixture. The poly(NMAAm) microsphere was found to incorporate preferentially St, leading to formation of the St radical. The St preference was enhanced in the St/cyclohexyl methacrylate (CHMA) system. These results were in agreement with those of block copolymerization via the reaction of poly(NMAAm) radical with the MMA/St or CHMA/St mixture, where the compositions of the resulting polymers were analyzed by pyrolysis gas chromatography.     

Long-lived polymer radicals. VI. Polymerization of N-methylmethacrylamide with formation of living propagation radicals

The polymerization of N-methylmethacrylamide (NMMAm) with azobisisobutyronitrile (AIBN) was investigated kinetically in benzene. This polymerization proceeded heterogeously with formation of the very stable poly(NMMAm) radicals. The overall activation energy of this polymerization was calculated to be 23 kcal/mol. The polymerization rate (R_p) was expressed by: R_p = k[AIBN]^0.63-0.68[NMMAm]^1?2.5. Dependence of R_p on the monomer concentration increased with increasing NMMAm concentration. From an ESR study, cyanopropyl radicals escaping the solvent cage were found to be converted to the living propagating radicals of NMMAm in very high yields (ca. 90%). Formation mechanism of the living polymer radicals was discussed on the basis of kinetic, ESR spectroscopic, and electron microscopic results.     

Long-lived polymer radicals. III. Synthesis of block copolymer by the reaction of living poly(N-methylacrylamide) radical with some vinyl monomers

N-Methylacrylamide (NMAAm) was polymerized quantitatively by using di-tert-butyl peroxide as photosensitizer to be, for the most part, incorporated in living poly(NMAAm) radical. The living polymer radical reacted effectively with acrylate monomers to yield block copolymer. Longer alkyl chain of the acrylate monomer caused a decrease in the conversion of the second monomer. Methacrylate monomers, such as methyl methacrylate and cyclohexyl methacrylate, showed relatively low reactivities in comparison with acrylates. Styrene exhibited a much lower conversion. The resulting block copolymers showed different thermochromic behaviors in methyl benzoate from that of poly(NMAAm). This is explained on the basis of the difference between refractive indexes of the block copolymers and poly(NMAAm).     

Reactions of tert-butoxy radicals with vinyl monomers

Tert-butoxy radicals generated in the photolysis of di-tert-butyl peroxide in benzene at 25°C react with vinyl monomers by double-bond addition and, in most cases, also by competitive hydrogen abstraction. The rate constant for the double-bond addition changes by a factor of 17 between isoprene, which shows the highest reactivity, and the methacrylate derivatives, which are the least reactive of the monomers considered. The fraction of tert-butoxy radicals that react by hydrogen abstraction varies considerably with the monomer structure, ranging from 0.9 (cyclohexyl methacrylate) to less than 0.05 (styrene and conjugated diolefins). In the methacrylate derivatives, most of the hydrogen abstraction takes place, not in the α-methyl group, but in the alkyl chain.     

The oxidation of methyl radicals at room temperature

Using the technique of molecular modulation spectrometry, we have measured directly the rate constants of several reactions involved in the oxidation of methyl radicals at room temperature: k₁ is in the fall-off pressure regime at our experimental pressures (20–760 torr) where the order lies between second and third and we obtain an estimate for the second-orderlimit of (1.2 ± 0.6) × 10^?12 cm³/molec · sec, together with third-order rate constants of (3.1 ± 0.8) × 10^?31 cm⁶/molec² · sec with N₂ as third body and (1.5 ± 0.8) × 10^?30 with neopentane; we cannot differentiate between k_2a and k_2c and we conclude k_2a + (k_2c) = (3.05 ± 0.8) × 10^?13 cm³/molec · sec and k_2b = (1.6 ± 0.4) × 10^?13 cm³/molec · sec; k₃ = (6.0 ± 1.0) × 10^?11 cm³/molec · sec.     

Synthesis of ordered polymer by direct polycondensation. VIII. Ordered polymer from two nonsymmetric monomers

The ordered (-aacdbbdc-) polymer was prepared by the direct polycondensation of a pair of symmetric monomers (XabX), 4,4′-(oxydi-p-phenylene)dibutanoic acid (XaaX) and 2-methoxyisophthalic acid (XbbX), with a nonsymmetric monomer (YcdY), 4-aminobenzhydrazide, using the condensing agent diphenyl (2,3-dihydro-2-thioxo-3-benzoxazolyl)phosphonate ( 1 ). The polymerization was carried out by a one-pot procedure, that is, mixing the dicarboxylic acids, condensing agent 1 and triethylamine in NMP for 2 h at room temperature, followed by the addition of 4-aminobenzhydrazide. This polymerization proceeded smoothly, yielding the ordered polymer with an inherent viscosity of 0.34 dL g⁻¹. The microstructure of the ordered polymer was confirmed by comparing the authentic ordered polymer in their ¹³C-NMR spectrum. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2309–2314, 1998     

Sulfur-containing vinyl monomers. XIII. Cationic copolymerizations of vinyl sulfides with some vinyl monomers

Cationic copolymerizations of vinyl sulfides (VS) with some vinyl monomers with boron tri-fluoride-diethyl etherate catalyst were investigated to evaluate their monomer reactivities. The effects of VS on the copolymer yield and viscosity of the resulting copolymers revealed the inhibition or retardation mechanism which was explained in terms of the formation of a stable vinylsulfonium salt by the reaction between a propagating carbonium ion and VS monomer. From the results of copolymerizations of phenyl vinyl sulfide (PVS) with isobutyl vinyl ether (IBVE), β-chloroethyl vinyl ether (CEVE), α-methylstyrene (α-MeSt), and styrene (St), the relative reactivities of these monomers were found to be in the following order: IBVE > CEVE > PVS > α-MeSt > St. The relatively higher reactivity of PVS than St derivatives was explained on the basis of the conjugative and electron-donating nature of the VS monomer. The effects of alkyl and para-substituted phenyl groups in vinyl sulfides on their reactivities toward the propagating carbonium ion were correlated with polar factors and compared with those of the hydrolysis of α-mercaptomethyl chlorides. The transition state for the propagation reaction in cationic polymerization of VS was proposed to be a π-complex type structure.     

Electron spin resonance studies of propagating radicals in polymerization. I. Methacrylate propagating radicals

Ferric chloride-photosensitized free-radical initiation was used to generate propagating radicals in polymerization of methacrylic acid (MAA), allyl methacrylate (AMA), methyl methacrylate (MMA), 1,3-butylene dimethacrylate (1,3-BDMA), hydroxypropyl methacrylate (HPMA), lauryl methacrylate (LMA), hexyl methacrylate (HMA), and methacrylamide (MA) in rigid glasses of methanol or acetone at near liquid nitrogen temperatures. The formation and conformational changes of these propagating radicals at different temperatures were studied by electron spin resonance (ESR) spectroscopy. When methanol was the rigid glass, ·CH₂OH radicals were formed initially and were stable below ?160°C. As the temperature of the rigid glass was increased, the ·CH₂OH radicals reacted with monomer to yield propagating radicals. With the exception of the propagating radical for methacrylamide, the propagating radicals of the methacrylates examined initially generated five-line ESR spectra which gradually changed to nine-line spectra, as temperature of the rigid glass was increased. It was concluded that one type of propagating radical was formed in all cases. However, when the temperature of the rigid glass was increased, the single structural conformation that initially allowed one of the methylene hydrogens and methyl group to interact with the unpaired electron to generate only a five-line spectrum was changed to yield a second conformation that allowed interaction to generate an additional four-line spectrum. Finally, a mixture of the propagating radical for methacrylate monomer in two structural conformations was obtained, and an ESR spectrum consisting of nine lines (5 + 4 lines) was generated. In the case of the propagating radical for methacrylamide this change to yield two structural conformations evidently was hindered, so that only an ESR spectrum consisting of five lines was generated.     

Electron spin resonance studies of propagating radicals in polymerization. II. Acrylate propagating radicals

Ferric chloride-photosensitized free-radical initiation was used to generate propagating radicals in polymerization of acrylic acid (AA), methyl acrylate (MA), ethyl acrylate (EA), butyl acrylate (BA), acrylamide (A), and diacetone acrylamide (DAA) in rigid glasses of methanol, ethanol, n-propanol, isopropanol, or acetone at near liquid nitrogen temperatures. When the temperatures of the glasses were increased, primary radicals derived from the solvents reacted with the monomers to yield propagating radicals. Formation and conformational changes of the propagating radicals at different temperatures were studied by electron spin resonance (ESR) spectroscopy. It was concluded that one type of propagating radical was formed in all cases. However, when the temperature of the rigid glass was increased, the structural conformation of the radical that initially allowed the near-equivalent interaction of the α-hydrogen and one of the β-hydrogens with the unpaired electron generated a three-line spectrum.     

Cationic polymerization of vinyl monomers initiated by 10-methylphenothiazine cation radicals

A small quantity of 10-methylphenothiazine cation radical (MPT^.+), electrochemically prepared and stocked in acetonitrile solution, initiated cationic polymerizations of n-butyl, t-butyl, and 2-methoxyethyl vinyl ethers and p-methoxystyrene, while no initiation occurred for phenyl vinyl ether, styrene, methyl methacrylate, and phenyl glycidyl ether. ¹H-NMR studies of oligomers and low molecular weight compounds isolated from the reaction mixture for the polymerization of t-butyl vinyl ether in the presence of a small amount of D₂O indicated that electron transfer from the monomer to MPT^.+ was involved in the initiation step. ¹H- and ¹³C-NMR and MO calculation implied that monomers with higher electron densities on the vinyl groups and with lower ionization potentials were more susceptible to the initiation of MPT^.+. © 1994 John Wiley & Sons, Inc.     

Molecular probe for a fluorous medium: long-lived phosphorescence of alpha-diketones in perfluoromethylcyclohexane at room temperature.

We found that alpha-diketones (2,3-butanedione (BD) and 1-phenyl-1,2-propanedione (PPD)) were very suitable luminescence probes for studying the properties of a perfluorinated solvent (i.e., fluorous solvent; perfluoromethylcyclohexane (PFMC)), since these compounds were soluble in PFMC and showed long-lived phosphorescence even at room temperature. The phosphorescence lifetime (tau(p)) of BD in PFMC (650 micros) was much longer than that in cyclohexane (CH, 270 micros). The longer tau(p) value of BD in PFMC was ascribed to the variation of the intersystem crossing rate constant (k(isc)) from the excited triplet state (T1) to the ground state (S0) with the solvent. Some possible reasons for the change in k(isc) were discussed in terms of solute-solvent interactions. Furthermore, by utilizing phosphorescence quenching of BD by pyrene, we, determined a rate constant of the diffusion-controlled reaction in PFMC. Characteristic behaviors of mixing/separation processes between PFMC and a common organic solvent observed by Schlieren photographs were also reported.     

Photochemical synthesis of nitroxyl free radicals in the presence of vinyl monomers

The photochemical formation of an inhibitor in the presence of monomers and a photoinitiator offers the possibility of producing positive two-step photoresists. As inhibitor precursor sterically hindred amines have been used in the presence of air oxygen and Rose Bengal as oxidation photosensitizer. On irradiation with visible light (546 nm). stable nitroxyle radicals are formed, which act as strong inhibitors of free radical polymerization. Hexanediol diacrylate and 2-acryloxy-2′-propionyl oxydiethylether were used as monomers. The photoinitiator required for the second step polymerization is benzoin isopropyl ether, which photolyzes on irradiation at 340 n,. The quantum yield of nitroxyl radical formation has been determined in solution and in polymeric films. Polymerization inhibition experiments were carried out with methyl methacrylate in solution and with neat monomers. Though the quantum yield Φ_NO° is low, especially in the last case, the experiments confirm the possibilities of this two-step procedure.     

Radiation grafting of vinyl monomers to wool. III. Location of the grafted polymer

Studies of properties such as water sorption of grafted wool have shown the importance of the location of the polymer in the fiber. Electron microscopy and low-angle x-ray diffraction studies have been used to determine the location of grafted polystyrene in wool. Samples grafted from 15 to 800% (dry weight increase) all exhibit a large increase in contrast in the cell membranes (IR) and nuclear-remnant regions (NR) in the electron micrographs. This is considered to be due in part to an unevenness in mechanical response to sectioning and in part to the deposition of ungrafted homopolymer in IR and NR, particularly at grafts of greater than about 100%. Analysis of the change in the 83 A. equatorial x-ray reflection suggests that most of the grafted polymer resides in the keratinous matrix regions between the microfibrils within the cortical cells. At larger grafts the wool still retains its basic histological character, but the increase in this spacing is no longer proportional to the amount of graft, and the desposition of polymer becomes very inhomogeneous.     

Experimental observation on multiaxial ratchetting of polycarbonate polymer at room temperature

Multiaxial stress-controlled and mixed stress-strain-controlled cyclic tests were carried out to investigate the multiaxial ratchetting of polycarbonate (PC) polymer at room temperature. The effects of applied mean stress, stress amplitude, loading rate, loading path and loading history on the ratchetting are discussed. The results show that the multiaxial ratchetting mainly occurs in the direction of non-zero mean stress. In the multiaxial stress-controlled cases, the ratchetting strain increases with increasing mean stress and stress amplitude and decreasing stress rate. Different values of ratchetting strain were obtained in the multiaxial cyclic tests with seven different loading paths, and prior cyclic loading with higher stress level resulted in decreased ratchetting in the subsequent cyclic loading with lower stress level. In the multiaxial mixed stress-strain-controlled tests, the ratchetting increased with increasing axial (or equivalent shear) stress and torsional-angle (or axial-displacement) amplitude and decreasing applied deformation rate.     

Alloy formation at the deposition of palladium on gold at room temperature

Palladium is shown to be deposited underpotentially on gold electrodes in 1 M H₂OSO₄. The deposit forms an alloy according to a t^1/2 law. The rate of alloy formation is strongly dependent on the potential. The diffusion coefficient is about 10^?16 cm² s^?1. This value is discussed in comparison with earlier measurements on gold-palladium alloys at higher temperatures.     

Millisecond long-lived charge separated state at room temperature in a flexibly linked diphenylaminopolyene-C60 dyad

Long-lived photoinduced charge separation involving one-step electron transfer is achieved in diphenylaminopolyene based C60-donor dyads with a short, flexible linkage.     

Relationships of graft polymerization of vinyl monomers onto cellulose. Reaction kinetics and polymer structure

Graft polymerization of acrylamide and sulfuric salt of 2-methyl-5 vinylpyridine onto cellulose using CO(III) salts was studied. It was shown that graft polymerisation of water-soluble polymers can be described by general relationships of radical reaction. The relation between elementary reaction constants of the formation and termination of active centers in cellulose, as well as relation between constants of the propagation, transfer and termination of chains were determined for different cellulose materials and monomers. The translational diffusion, sedimentation, viscosity, and flow birefringence of copolymers have been investigated in different solvents. Experimental data showed that the copolymers obtained are graft copolymers with two to five grafted chains onto macromolecules. The minimum distance between the branch points is 100 ± 20 glucoside units. The peculiarity of these copolymers is relatively low polydispersity. The conformation of macromolecules of such copolymers in solution depends on the compatibility of the copolymer components and the thermodynamic properties of the solvent.