Living cationic polymerization of vinyl ethers

The cationic polymerization of vinyl ethers initiated by CH₃-CH(OR)(I) / R₄N⁺A⁻ (R = Alkyl, A⁻ = ClO₄⁻, BF₄⁻, PF₆⁻, I⁻, NO₃⁻) shows the characteristics of a living polymerization. The rate of polymerization is a function of the solvent polarity, the temperature, the type and concentration of the ammonium salt. The experimental data can be explained on the basis of the secondary salt effect overlapped by some dipol-dipol interactions of the chain end and the added salt. Functionalization of the chain end with thermolabile azo functions yields polymeric initiator which was applied for the synthesis of blockcopolymers. Vinyl ethers functionalized with furylacrylic ester groups were polymerized and crosslinked via [2+2] cycloaddition.     

Radical polymerization behavior of vinyl phenylsufonylacetate

Vinyl phenylsulfonylacetate (VPSA) was prepared by the reaction of vinyl chloroacetate with sodium benzenesulfinate in acetone in the presence of a phase-transfer catalyst. VPSA showed a high radical homopolymerizability similar to vinyl acetate in spite of the fact that VPSA carries a phenyl group. The polymerization of VPSA with 2,2^′-azobisisobutyrate (MAIB) was kinetically investigated in acetone. The overall activation energy of the polymerization was 27.6 kcal/mol. The polymerization rate (R_p) at 50 °C was expressed by R_p=k[MAIB]^0.67[VPSA]^1.1. Poly(VPSA) showed exothermic (27 °C) and endothermic (57 °C) peaks in its DCS curve, corresponding to crystallization and melting. The tacticity of poly(VPSA) was estimated to be rr=29, mr=49, and mm=22.     

Photoinitiation of vinyl polymerization by polysilanes

Polysilanes were found to photoinitiate the polymerization of a variety of vinyl monomers including methyl methacrylate, styrene, ethyl acrylate and acrylic acid. Polymerization initiated by polysilane photolysis is rather insensitive to oxygen inhibition, which may make it especially suitable for polymerization of thin films. The initiation efficiency of poly(phenylmethylsilylene) in styrene was determined from dilatometry data to be 1 × 10^?3. This rather low efficiency is counterbalanced by the very high extinction coefficient of polysilane polymers, ca. 4–8 × 10³ per silicon atom. Possible reasons for the low initiation efficiency and reduced oxygen inhibition of polysilane photoinitiators are discussed.     

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.     

Photoinitiated free radical polymerization of vinyl compounds in aqueous solution

A new method for the photochemical initiation of polymerization of vinyl compounds in aqueous solution is described. The photochemically active species is an ion pair complex of the formula Fe³⁺X⁻(X⁻ = OH⁻, CI⁻, N⁻₃, etc.). The light absorption by the ion pair leads to an electron transfer causing reduction of the cation and oxidation of the anion to an atom or free radical X. The latter leads to the initiation of polymerization in accordance with X + CH₂CHR→XCH₂ CHR . The kinetics of the reaction were studied by the measurement of: (a) ferrous ion formed (colorimetrically), (b) monomer disappearance (by titration and by weighting the polymer), (c) the chain length of the polymer (in the case of methyl methacrylate). The dependence of the quantum yield on the light intensity, light absorption fraction, and the concentration of vinyl monomer and ferrous ion added initially was investigated. A complete mechanism, both with regard to the formation of free radicals and the polymerization reaction, was put forward involving: (1) light absorption, (2) a primary dark back reaction, (3) dissociation of the primary product, (4) a secondary dark back reaction, (5) initiation of polymerization by free radicals, (6) propagation of polymerization, and (7) termination by recombination of active polymer endings. The mechanism was verified by the experimental results and some constant ratios were estimated quantitatively.     

Decomposition of peroxycarbamates and their initiation of vinyl polymerization

A review is given of the synthesis, physical properties, and decomposition kinetics of organic peroxycarbamates. The activity of these compounds in initiating free-radical vinyl polymerization is discussed. The decomposition of hexamethylene N,N′-bis-(α-cumyl peroxycarbamate) has been measured in different solvents between 65 and 95°C and found to be a first-order reaction governed by the specific rate constant k_d = 2.21 × 10¹⁶ exp {?34 100/RT}. The initiator exhibits normal free-radical polymerization kinetics and in polymerization of styrene at 80°C shows an initiating efficiency of 0.53. Cobalt naphthenate can act as both accelerator and retarder of styrene polymerization, depending upon its concentration and the temperature of the polymerization.     

Effect of solvent for vinyl acetate polymerization on microstructure of poly(vinyl alcohol)

The solution polymerization of vinyl acetate was carried out in several solvents at 0 to 100°C, using 2,2′-azobisisobutyronitrile as initiator. For the resulting poly(vinyl alcohol) (PVA), iodinecoloration, 1,2-glycol structure and tacticity were observed. The pentad tacticity of PVA was estimated from its methine carbon spectra by means of ¹³C-FTNMR spectrometer. Iodine-coloration ability of PVA varied markedly with the type of polymerization solvent and decreased in the following order: phenol > aq. phenol > methyl alcohol > ethyl acetate > DMSO, ethylene carbonate. The syndiotactic fraction in PVA also decreased with polymerization solvent in the same order as that of iodine coloration, while 1,2-glycol content of PVA was not almost affected by polymerization solvent except for phenol and aq. phenol. In solution polymerization performed, effect of polymerization temperature on tacticity was less than that of solvent.     

Effects of acids on vinyl polymerization initiated by chromous acetate-alkyl halide

Effects of various acids, i.e., acetic, chloroacetic, hydrochloric, and sulfuric acids on the polymerization of styrene initiated by Cr²⁺–CHCl₃ in DMF was studied. These acids reduced the rates of polymerization by Cr²⁺–CHCl₃ initiator systems. This phenomenon could be explained by a decrease of the reducing power of Cr²⁺ for alkyl halide. On the other hand, chloroacetic acids could initiate the polymerization of styrene without CHCl₃ because these acids have active chlorine in the molecule for Cr²⁺. It was found that the polymer obtained by this initiator system had an endgroup containing chromium carboxylate, therefore this polymer was green in color and insoluble in benzene.     

Effect of fullerene on radical polymerization of vinyl acetate

The effect of fullerene (C₆₀) on the radical polymerization of vinyl acetate (VAc) with dimethyl 2,2′‐azobisisobutyrate (MAIB) in benzene was investigated kinetically and by means of ESR. C₆₀ was found to act as an effective inhibitor in the present polymerization. All C₆₀ molecules used were incorporated into poly(VAc) during polymerization. The relationship of induction period and initiation rate reveals that a C₆₀ molecule can trap 15 radicals formed in the polymerization system. The polymerization rate (R_p) after the induction period is given by R_p = k [MAIB]^0.6 [VAc]^2.0 (60 °C), which is similar to that observed in the absence of C₆₀. Stable fullerene radical (C) was observed in the polymerization system by ESR. The C concentration increased with time and was then saturated. The saturation time well corresponds to the induction period observed in the polymerization. About 20% of C₆₀ molecules added could survive as stable C. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2572–2578, 2000     

Vinyl polymerization. 403. Polymerization of vinyl monomer initiated with sodium poly-p-vinylphenolate

The polymerization of vinyl monomer initiated by poly-p-vinylphenol (PVPh) in NaOH aqueous solution was carried out at 85°C with shaking. Methyl methacrylate (MMA) was polymerized, whereas styrene and acrylonitrile were not. PVPh, which is dissociated into phenolate form (PVPh^?Na⁺) in NaOH aqueous solution, was effective for the polymerization. The effects of the amounts of MMA, PVPh, NaOH, and H₂O on the conversion of MMA were studied. The rate of polymerization of MMA increased with an increase in the molecular weight of PVPh-Na. The overall activation energy was estimated as 54 kJ mol^?1. The polymerization proceeded through a radical mechanism. The addition of tetra-n-butylammonium bromide increased the rate of polymerization.     

Radiation-induced ionic polymerization of isobutyl vinyl ether in bulk

The radiation-induced ionic polymerization of isobutyl vinyl ether was investigated under conditions where the monomer was dried with molecular sieves. The investigation covered the temperature range from ?16°C to 90°C, and the dose-rate range from 10¹⁵ to 10²⁰ eV/g-sec, using both γ-rays and electrons. A very high overall activation energy of 15.9 kcal/mole was found for the process below 30°C. Above 30°C, however, the value of the overall activation energy dropped to 4.9 kcal/mole, a phenomenon which is ascribed to the solvation of the propagating carbonium ion below 30°C. The dose-rate dependence of the rate of polymerization was found to be 0.58 over the entire dose-rate range investigated. The molecular weight of the polymer was found to be far less sensitive to trace amounts of water than the rate of polymerization. The molecular weight of the polymer depended strongly on the irradiation temperature, reaching a maximum value of about 120,000 at 35°C. It is shown that at temperatures above 20°C regenerative chain transfer processes play an important role in determining the molecular weight of the polymer.     

Radiation-induced polymerization at high dose rate. I. Isobutyl vinyl ether in bulk

Bulk polymerization of isobutyl vinyl ether was studied at 25°C in a wide dose rate range, 8.2-277 rad/sec by γ rays and 8.8 × 10³-2.2 × 10⁵ rad/sec by electron beams. At low dose rate, 8.2-277 rad/sec, only the radical polymerization took place. At high dose rate exceeding 8.8 × 10³ rad/sec, cationic polymerization was found to occur in addition to the radical polymerization. DP _n of the product at high dose rate was 9-10. Further drying of the monomer increased R_p, and molecular weight of the product formed by cationic mechanism also increased.     

Vinyl polymerization. 416. Polymerization of vinyl monomer initiated by polyethyleneglycol

The polymerization of vinyl monomer initiated by polyethyleneglycol (PEG) in aqueous solution was carried out at 85°C with shaking. Acrylonitrile (AN), methyl methacrylate (MMA), and methacrylic acid were polymerized by PEG–300 (M?_n = 300), whereas styrene was not. The effects of the amounts of monomer and PEG, the molecular weight of PEG, and the hydrophobic group at the end of PEG molecule on the polymerization were studied. The selectivity of vinyl monomer and the effect of the hydrophobic group are discussed according to “the concept of hard and soft hydrophobic areas and monomers.” The kinetics of the polymerization was investigated. The overall activation energy in the polymerization of AN was estimated as 37.9 kJ mol^?1. The polymerization was effected by a radical mechanism.     

Cycloalkyl-substituted salicylaldimine-nickel(II) complexes as mediators in controlled radical polymerization of vinyl acetate

Abstract

Nickel(II) complexes of Schiff base derived from cycloalkylamines (cycloalkyl?=?cyclopentyl (cpen), cyclohexyl (chex), and cycloheptyl (chep)) were synthesized: [Ni^II(L^cpen)₂] (1), [Ni^II(L^chex)₂] (2), and [Ni^II(L^chep)₂] (3). The Schiff base-Ni^II complexes 1-3 were characterized by FTIR, UV–Vis, elemental analysis, and computational methods. Electrodeposited films of complexes 1–3 were obtained by potential cycling CH₂Cl₂ on platinum electrode, and their electrochemical behavior were characterized by cyclic voltammetry. The polymerization of vinyl acetate (VAc) initiated by azobisisobutyronitrile (AIBN) at 55?°C were conducted according to an organometallic-mediated radical polymerization (OMRP) mechanism. The best conversions were obtained using a ratio of [VAc]/[AIBN]/[Ni]?=?542/3.25/1, reaching 50, 69 and 85% in 12?h for 1, 2 and 3, respectively. The kinetic of polymerization mediated by complex 1 exhibited a linear dependence of ln([VAc]₀/[VAc]) versus time, supporting a constant radical concentration; while for the complexes 2 and 3, the radical concentration was constant for a short period of time. The increase of molecular weights with the conversion coupled with low polydispersities indicate a certain level of control of the polymerization when using the complexes [Ni^II(L^R)₂] as controlling agents.     

Free-ionic polymerization of isobutyl vinyl ether by radiation

Radiation-induced free-ionic polymerization of isobutyl vinyl ether in bulk system has been studied by dilatometry and electrical conductivity measurement. Some refinements in kinetic treatment of estimate the propagation rate constant k_p from the rate of polymerization and steady-state conductivity were attempted. Polymerization of superdried monomer which gave a half-power dose-rate dependence of R_p was carried out at 0, 25, and 50°C. The k_p value obtained at 25°C and an activation energy for propagation were estimated as 1.2 ± 0.4 × 10⁵ I./mole-sec and 9.6 ± 2.8 kcal/mole, respectively. In isobutyl vinyl ether, a propagation reaction in free-ionic mechanism was found to be characterized with a high frequency factor and presumably higher activation energy, compared with ion-pair mechanism. Discussions were also made as to several contrasting behaviors between the polymerization of alkyl vinyl ethers and other vinyl monomers as styrene both in free-ion and ion-pair mechanisms.     

Nickel N‐heterocyclic carbene complexes in the vinyl polymerization of norbornene

Vinyl polymerized norbornene has some useful properties such as good mechanical strength, optical transparency and heat resistance. Several transition metal complexes have been described in the literature as active catalysts for the vinyl polymerization of norbornene. We now report the use of three types of nickel(II) complexes with N‐heterocyclic carbene (NHC) ligands in the catalytic vinyl polymerization of norbornene under a range of conditions. Specifically, two nickel complexes bearing a chelating bis(NHC) ligand, two nickel complexes bearing two chelating anionic N‐donor functionalized NHC ligands as well as one diiodidonickel(II) complex with two monodentate NHC ligands were tested. The solid‐state structure of bis(1,3‐dimethylimidazol‐2‐ylidene)diiodidonickel(II), as determined by X‐ray crystallography, is presented. The highest polymerization activity of 2.6 × 10⁷ g (mol cat)^?1 h^?1 was observed using the latter nickel complex as catalyst, activated by methylaluminoxane. The norbornene polymers thus obtained are of high molecular weight but with rather low polydispersity. Copyright © 2010 John Wiley & Sons, Ltd.     

ESR studies on radical polymerization of vinyl ethers

ESR studies on the radical polymerization of vinyl ethers were performed from ?50°C to room temperature using di-tert-butylperoxide as a photoinitiator. Well resolved ESR spectra were assigned to propagating radicals of vinyl ethers. Their hyperfine splitting constants due to α-proton were about 16 G, being smaller than those of ethyl acrylate and vinyl acetate. The smaller constants is ascribed to a deviation of the propagating radicals from sp² hybrid structure. The reason why high polymers are not obtained from vinyl ethers by radical polymerization is discussed on the basis of information from the ESR studies.     

Oxoaminium salts as initiators for cationic polymerization of vinyl monomers

Oxoaminium salt ( 1 ), derived from 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO, 2 ) by one-electron oxidation, could be an initiator for cationic polymerization of vinyl monomers such as isobutyl vinyl ether (IBVE), 2,3-dihydrofuran, p-methoxystyrene, N-vinyl pyrrolidone, etc., to give the corresponding polymers, when 1 had a low nucleophilic counter anion. Formation of the adducts of 1 and IBVE as well as ¹H-NMR and IR data suggested the formation of polymers containing N? O? C structure as the polymer head group. In the polymerization of IBVE, the effects of solvent and concentration of 1 were little observed, however the polymerization rate was dependent on temperature. Furthermore, the thermal reaction of the polymers obtained, which were regarded as prepolymers for block copolymerization and polymeric initiators for radical polymerization, was studied. For example, poly(2-benzylidene-1,3-dioxane) obtained by the polymerization of 2-benzylidene-1,3-dioxane with oxoaminium hexafluoroantimonate ( 1, X = SbF₆) was employed as an initiator for radical polymerization of MMA to give its block copolymer with PMMA. © 1993 John Wiley & Sons, Inc.     

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