Introduction

Abstract

The initiation mechanism for spontaneous copolymerizations of vinyl sulfides (VS) with electron-accepting monomers such as maleic anhydride (MAn), diethyl fumarate (DEF), acrylonitrile (AN), and methyl acrylate (MA) was investigated by means of spin trapping technique using 2-methyl-2-nitrosopropane as a spin trapping agent. From the ESR spectrum observed from the system ethyl VS-DEF, two types of radicals, a vinyl radical (I; RSCH=CH) and an alkyl (1, 2-dicarboethoxyethyl) radical (II; C₂H₅OCOCHCH₂COOC₂H₅) which derived from VS and DEF, respectively, were detected as their nitroxides. Similar radicals, I and III (NCCH₂CH₂), were also observed from the system VS-AN, but in the system VS-MA, three types of radicals, I, IV (CH₃OCOCH₂CH₂), and V (CH₃OCOCHCH₃) were trapped as their nitroxides. In the system isopropyl VS-MAn, I and a propagating radical (VI) ～～CH₂CHSR, were detected. The system isobutyl vinyl ether-MAn also showed a weak ESR spectrum due to the nitroxide from Radical I. These initiating radicals were assumed to be produced from the charge transfer complex formed between both donor and acceptor monomers. Based on these results, the cross-initiation mechanism for spontaneous alternating copolymerization is discussed.     

Alternating copolymerizations of styrene and acrylic monomers initiated with carbanions in the presence of ZnCl2

On electrochemical initiation of alternating copolymerizations of styrene–acrylonitrile (AN) and styrene–diethyl fumarate (DEF) in the presence of ZnCl₂, radical anions of AN–ZnCl₂ and DEF–ZnCl₂ complexes produced at the cathode were assumed to initiate copolymerization. In analogy with the cathode-initiated copolymerization, the radical anions of AN–ZnCl₂ and DEF–ZnCl₂, generated with the carbanions such as sodium naphthalene, disodium α-methylstyrene tetramer dianion, and butyllithium, were also found to produce alternating copolymers of styrene–AN and styrene–DEF. On the contrary, no polymers were obtained from methyl methacrylate (MMA)–styrene and methacrylonitrile (MAN)–styrene in the presence of ZnCl₂ either with carbanions or by electrochemical reduction. Styrene–MAN–ZnCl₂ yielded an alternating copolymer with carbanions upon introduction of oxygen.     

Biobased Polymers via Radical Homopolymerization and Copolymerization of a Series of Terpenoid-Derived Conjugated Dienes with exo-Methylene and 6-Membered Ring

A series of exo-methylene 6-membered ring conjugated dienes, which are directly or indirectly obtained from terpenoids, such as β-phellandrene, carvone, piperitone, and verbenone, were radically polymerized. Although their radical homopolymerizations were very slow, radical copolymerizations proceeded well with various common vinyl monomers, such as methyl acrylate (MA), acrylonitrile (AN), methyl methacrylate (MMA), and styrene (St), resulting in copolymers with comparable incorporation ratios of bio-based cyclic conjugated monomer units ranging from 40 to 60 mol% at a 1:1 feed ratio. The monomer reactivity ratios when using AN as a comonomer were close to 0, whereas those with St were approximately 0.5 to 1, indicating that these diene monomers can be considered electron-rich monomers. Reversible addition fragmentation chain-transfer (RAFT) copolymerizations with MA, AN, MMA, and St were all successful when using S-cumyl-S’-butyl trithiocarbonate (CBTC) as the RAFT agent resulting in copolymers with controlled molecular weights. The copolymers obtained with AN, MMA, or St showed glass transition temperatures (T_g) similar to those of common vinyl polymers (T_g ~ 100 °C), indicating that biobased cyclic structures were successfully incorporated into commodity polymers without losing good thermal properties.     

Spin trapping studies of poly(methyl methacrylate) degradation in solution

Free radicals produced either by γ or ultrasonic irradiation of poly(methyl methacrylate) (PMMA) in benzene solution were stabilized by spin trapping; they were identified by analysis of ESR spectra of the trapped radicals (the spin adducts). The radical species identified after γ-irradiation were methyl, ester (COOCH₃), a pair of the chain scission radicals, ～CH₂C(CH₃)(COOCH₃) and CH₂C(CH₃)(COOCH₃)～, and phenyl radical originating from the solvent. The chain scission radicals were also detected by spin trapping after ultrasonic irradiation of the benzene solution. Taking account of the difference in the trapping rate for two spin trapping agents, 2,4,6-tri-t-butylnitrosobenzene (BNB) and penta-methyl-nitrosobenzene (PMNB) the radical species trapped by PMNB are assumed to be precursors of those trapped by BNB. Based on the radical species found by the spin trapping method, plausible degradation processes for PMMA in benzene solution are proposed.     

Synthesis of poly(methyl methacrylate)‐b‐polystyrene containing a crown ether unit at the junction point via combination of atom transfer radical polymerization and nitroxide mediated radical polymerization routes

Poly(methyl methacrylate)‐b‐polystyrene (PMMA‐b‐PS) containing a benzo‐15‐crown‐5 unit at the junction point was prepared by combining atom transfer radical polymerization and nitroxide‐mediated radical polymerization. For this purpose, 6,7,9,10,12,13,15,16‐octahydro‐5,8,11,14,17‐pentaoxa‐benzocyclopentadecene‐2‐carboxylic acid 3‐(2‐bromo‐2‐methyl‐propionyloxy)‐2‐methyl‐2‐[2‐phenyl‐2‐(2,2,6,6‐tetramethyl‐piperidin‐1‐yloxy)‐ethoxycarbonyl]‐propyl ester ( 3 ) was synthesized and used as an initiator in atom transfer radical polymerization of methyl methacrylate in the presence of CuCl and pentamethyldiethylenetriamine at 60°C. A linear behavior was observed in both plots of ln([M]₀/[M]) versus time and M_n,_GPC versus conversion indicating that the polymerization proceeded in a controlled/living manner. Thus obtained PMMA precursor was used as a macroinitiator in nitroxide‐mediated radical polymerization of styrene (St) at 125°C to give well‐defined PMMA‐b‐PS with crown ether per chain. Kinetic data were also obtained for copolymerization. Moreover, potassium picrate (K⁺ picrate) complexation of 3 and PMMA‐b‐PS copolymer was studied. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3242–3249, 2006     

Polymerization of vinyl monomers by diphenylsulfone–potassium complexes

Diphenylsulfone (DPSO₂) was found to react with an equimolar amount of potassium in tetrahydrofuran (THF), dimethoxyethane (DME), or diglyme (DG) at reflux or an elevated temperature to yield a reddish-black solution, giving an electron spin resonance (ESR) signal. The signal was attributed to the formation of relatively labile DPSO₂ anion radical. The apparent effects of solvents on the reactivity of DPSO₂ with potassium depended on the polarities and the solvation powers: benzene ? toluene ? dioxane ? tetrahydrofuran < monoglyme < diglyme. The monopotassium complex was found to react further with another molecular amount of the metal to yield a dark blue solution giving no ESR signal. The monopotassium complex initiated the polymerization of acrylonitrile (AN). It did not, however, initiate the polymerization of methyl methacrylate (MMA), styrene (St), or isoprene (IP). The active species of the monopotassium complex that initiated the polymerization of AN was found from analyses of the reaction products and the infrared spectrum of oily oligomer of AN obtained by the complex to be potassium benzenesulfinate. The dipotassium complex was found to initiate the polymerization of MMA, St, IP and AN. The active species of the dipotassium complex that initiated the polymerization of MMA, St, or IP was found from analyses of the reaction products and the infrared spectrum of the oily oligomer of MMA obtained by the complex to be phenyl potassium.     

Gas Chromatography - Mass Spectroscopy (GC/MS) of Single and Double Spin Adducts of PBN and the Hydroxylamines of Corresponding Structure

Abstract

The GC/MS spectra of the methyl adduct of PBN as the aminoxyl and as the corresponding hydroxylamine are reported. Similar results are obtained with higher alkyl analogues. With excess alkyl Grignard the O-alkyl hydroxylamine ether (PBN double adduct) is obtained if the solution is exposed to O₂ in the presence of the alkyl spin adduct of PBN. A mechanism involving radical trapping by the alkyl spin adduct is proposed.     

Spin trapping of propagating radicals derived from dialkyl fumarates

Propagating radicals of dialkyl fumarates (DRFs) and deuterated fumarate were trapped by admitting a 2-methyl-2-introsopropane (BNO) solution to the polymerization mixture containing the active radicals or by the polymerizations initiated with di-t-butyl hyponitrite in the presence of BNO. Although ESR spectra of the propagating radicals were appreciably changed with the size of the ester alkyl groups, all the nitroxyl radicals resulting from the spin trapping exhibited similar six-line spectra. The hyperfine splitting constant for the α-hydrogen of the radical moiety showed a slight dependence on the chain length, and the bulkiness of the ester alkyl group did not affect splitting of the spectra. These findings indicate that a substituted methylene radical is produced by addition of the primary radical to DRF followed by propagation throughout the polymerization and that poly(DRF) radical does not encounter severe hindrance in the reaction with BNO.     

Preparation of Photoactive Polymers and Postmodification via Nitroxide Trapping Under UV Irradiation

New types of photoactive homo and block copolymers bearing α−hydroxyalkylphenylketone (2‐hydroxy‐2‐methyl‐1‐phenylpropan‐1‐one) moieties as backbone substituents are prepared using nitroxide‐mediated radical polymerization (NMP). Such polymers can be readily activated via the Norrish‐type I photoreaction to give polymeric acyl radicals. Photolysis in the presence of a persistent nitroxide, which serves as a C‐ radical trapping reagent, leads to chemically modified polymers conjugated with nitroxide moieties. The number‐average molecular weight (M _n) of the prepolymers and the chemically modified polymers was determined by gel permeation chromatography (GPC). Structures were further confirmed by NMR spectroscopy and by attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopy.     

“Living” free radical ring-opening copolymerization of 4,7-dimethyl-2-methylene-1,3-dioxepane and conventional vinyl monomers

It is the first report on the atom transfer radical ring-opening copolymerizations of unsaturated cyclic acetal: 4,7-dimethyl-2-methylene-1,3-dioxepane (DMMDO) with conventional vinyl monomers, styrene (St), acrylonitrile (AN) and methyl acrylate (MA) in the presence of ethyl α-bromobutyrate as initiator and CuBr/2,2^′-bipyridyl as catalyst/ligand at 110 °C. ¹H, ¹³C NMR and IR data show that the copolymerizations of DMMDO with St (or AN or MA) yield the copolymers, poly(DMMDO-co-St) [or poly(DMMDO-co-AN) or poly(DMMDO-co-MA)] with narrow molecular weight distribution, and low content of DMMDO in the copolymers for electron-donor St, higher contents of DMMDO for electron-acceptor AN or MA are observed.     

Copolymerization Reactivities of α-Substituted Crotonyl Monomers

The radical copolymerizations of various α- substituted crotonyl monomers with styrene (St) and acrylonitrile (AN) were investigated, and the copolymerization parameters were determined by a least-squares procedure reported previously. The relative reactivities of the α-substituted crotonyl monomers toward polymer radicals of St and AN were found to correlate with the equation: log (relative reactivity of CH₃CH[dbnd]CXY) = ρ (σ + σ_Y) + A(Δlog Q_x + Δlog Q_Y), where Σ and Δlog Q are the polar Hammett and resonance substituent constants, respectively, and p and A are reaction constants. From the observed straight line relationships, the values of p and A were obtained to be as follows: ρ = 0.66, A = 0.75 for attack of poly-St radical, and ρ = -3.20, A = 1.3 for attack of poly-AN radical.     

Studies in Cyclocopolymerization. XII. Cyclocopolymerization of the Donor:Acceptor Pair 1,4-Diene:Monoolefin Lewis Acid Complex

Acrylonitrile (AN) is known to form a cyclocopolymer with 1,4-dienes such as divinyl ether (DVE) and 3,3-dimethyl-1,4-pentadiene with radical initiators. Since AN has a high tendency toward homopolymerization, the copolymers are not of regular structure. Lewis acids such as ZnCl₂ and Al(Et)₃ were used in this paper to increase the e-values of AN and methacrylonitrile (MAN) through complexation. AN, MAN, and 2- and 4-vinylpyridine were copolymerized with DVE and 1,4-pentadiene with Lewis acids. In all cases the rate of copolymerization was much enhanced and the alter-nating tendency of the cyclocopolymer increased with the amount of added Lewis acids. A 1:2 DVE:AN alternating cyclocopolymer was obtained spontaneously or with AIBN with Al(Et)₃ in hexane. Also 1:2 alternating cyclocopolymer was successfully obtained in acetone by using a large amount of ZnCl₂. The identification of charge-transfer (CT) complex-ation between the DVE and (AN,¹ ₂, ZnCl₂ complex, and between the 1-hexene and (AN)₂ZnCl₂ complex may supoort the par-ticipation of a CT complex formed between all 1,4-dienes studied and the monoolefin-Lewis acid complexes in the     

Interference by Desferrioxamine of Spin Trapping Oxy-Radicals For ESR Analysis

Abstract

The iron chelator desferrioxamine (DEF), commonly used to assess the involvement of iron in oxy-radical production, was examined with respect to its effect on spin trapping oxy-radicals generated independently of iron. OH. was generated by photolysis of H₂O₂- was generated by photolysis of Cds dispersions and by the hypoxanthine-xanthine oxidase system.In the presence of DEF, the amount of the radicals detected by spin trapping techniques of ESR with 5,5-dimethyl-1-pyrroline-1-oxide was greatly diminished. These results confirmed that DEF is an oxy-radical scavenger and, in addition, indicated that it should not be used to assess the involvement of iron in oxy-radical generation during spin trapping with nitrones for ESR analysis.

An additional finding was that a new radical, as yet uncharacterized, was generated by UV irraditional of DEF.     

Copolymerization and Copolymers of 2,4,5-Tribromostyrene with Styrene and Acrylonitrile

Abstract

2,4,5-Tribromostyrene (TBSt) was copolymerized with styrene (St) or acrylonitrile (AN) in toluene solution using 2,2′-azobisisobutyronitrile as free radical initiator. The copolymerization reactivity ratios were found to be for the system TBSt/St r ₁ = 1.035 ± 0.164 (TBSt) and r ₂ = 0.150 ± 0.057 (St), and for the system TBSt/AN r ₁ = 2.445 ± 0.270 (TBSt) and r ₂ = 0.133 ± 0.054 (AN). The e and Q values were also calculated. The initial copolymerization rate, R _p, for both systems linearly increases as the content of TBSt in the monomer mixture increases. However, these values are somewhat higher when AN was used as a comonomer. A similar behavior has also been established for the course of the copolymerization reactions to high conversion. The resulting copolymers and TBSt-homopolymer show similar thermal stabilities of polystyrene. However, the glass transition temperature increases markedly with increasing TBSt content.     

Polymerization of Vinyl Monomers with Binary Initiator System of N-Chlorosuccinimide and Lewis Acids

The polymerization of vinyl monomers with a binary system composed of N-chlorosuccinimide (NCS) and some Lewis acids was investigated by means of kinetic and spectral determinations. It was found that the NCS-ZnCl₂ system was the most effective as an initiator of radical polymerization of methyl methacrylate, and this polymerization was initiated by a radical produced via the reaction of NCS and ZnCl₂, and terminated bimolecularly. By applying a spin trapping technique to the reaction of NCS with ZnCl₂, it was shown that the initiating radical was N-succinimidyl radical which was obtained through a homolysis at the N-Cl bond.     

Oxidation of quinolones with peracids (an in situ EPR study)

4‐Oxoquinoline derivatives (quinolones) represent heterocyclic compounds with a variety of biological activities, along with interesting chemical reactivity. The quinolone derivatives possessing secondary amino hydrogen at the nitrogen of the enaminone system are oxidized with 3‐chloroperbenzoic acid to nitroxide radicals in the primary step while maintaining their 4‐pyridone ring. Otherwise, N‐methyl substituted quinolones also form nitroxide radicals coupled with the opening of the 4‐pyridone ring in a gradual oxidation of the methyl group via the nitrone–nitroxide spin‐adduct cycle. This was confirmed in an analogous oxidation using N,N‐dimethylaniline as a model compound. N‐Ethyl quinolones in contrast to its N‐methyl analog form only one nitroxide radical without a further degradation. Copyright © 2013 John Wiley & Sons, Ltd.     

Polymerization of vinyl monomers initiated by organoaluminium compounds/benzoyl peroxide systems

The free-radical polymerization of methyl methacrylate (MMA) initiated by systems comprizing benzoyl peroxide (BPO) and different organoaluminium compounds (OACs) has been studied. The influence of the type of OAC, concentration of components of the initiation system, temperature, and time on the reaction yield have been determined. Systems containing BPO and diethylaluminium chloride (Et₂AlCl) have been found to enable us to obtain, in high yields at room temperature, of homopolymers of MMA, methyl acrylate, acrylonitrile (AN), vinyl acetate, and the alternating AN/styrene (St) copolymer; they are, however, not very active in the homopolymerization of St and vinyl chloride. Factors affecting the polymerization yield have been discussed in terms of the mechanism of the reaction between BPO and OACs, reactivity of alkyl radicals formed in these systems, and catalytic effect of OAC in the propagation step.     

Copolymerization of Chloroprene with Methyl Methacrylate by the EtnAICI3.n (n=1, 1.5, 2)-Vanadium Compound System

Abstract

The copolymerization of chloroprene with methyl methacrylate was studied in the presence of Et_n A1C1_3-n (n=1, 1.5, 2)-vanadium compounds. Monomer reactivity ratios in various catalyst concentrations were compared with that of a usual radical initiator. The apparent monomer reactivity ratio changed with the concentration of alkylaluminum halide. In this polymerization, alternating copolymer could not be prepared by the ordinary catalyst concentration by which the alternating copolymerization of chloroprene with acrylonitrile was carried out. The addition of more than 10 mole % of the alkylaluminum halide based on two monomers was required to prepare the copolymer which had equimolar composition irrespective of the feed monomer ratio.

The configuration in the repeating unit of the copolymer was discussed by comparison with the NMR and IR spectra of the radical copolymer and the cyclic Diels-Alder adduct of chloroprene-methyl methacrylate. The high alternating tendency was clarified by ozonolysis of the copolymer which was prepared under the conditions which produced equimolar copolymer in various feed monomer ratios. The chloroprene unit of the copolymer was present in the 1, 4-trans structure in the copolymer prepared by the Et_n A1C1_3-n -vanadium compound system.     

EPR studies on H-abstraction from methylbenzenes by “magic blue” reagent

After mixing a methylbenzene 4 with “magic blue” solution in F113 (CClF₂CCl₂F) containing bis{perfluoro[1-(2-fluorosulfonyl)ethoxy]ethyl}nitroxide 2 and perfluoro-1-nitroso-1-[1-(2-fluorosulfonyl)ethoxy]ethane 3 at room temperature, benzylic H-atom of 4 could be selectively abstracted by 2, and benzyl radical 5 thus generated was immediately trapped by 3. Based on hyper-fine splitting constants (hfsc), the structure of the spin adducts perfluoro[1-(2-fluorosulfonyl)ethoxy]ethyl benzyl nitroxides 6 derived from seven methylbenzenes have been identified. The mechanism of the H-abstraction/spin trapping process is also discussed.     

Mechanism of radiation-induced degradation of poly(methyl methacrylate) as studied by ESR and electron spin echo methods

The role of radical species in the degradation of poly(methyl methacrylate) (PMMA) induced by γ-irradiation has been studied by means of electron spin resonance and electron spin echo spectroscopy. The major radical species generated initially at 77 K are assigned to main chain ? CH ? and side chain ? COOCH₂ radicals, and ? COOCH anion radical. Only the ? COOCH₂ radical converts to the scission-type ? CH₂ ? C(CH₃)COOCH₃ radical on warming the sample of >180 K. A part of the ? CH ? radical disappears on warming the sample of >265 K. It is concluded that the scission of PMMA main chain occurs by the intramolecular process from the ? COOCH₂ radical as the precursor state.