A novel synthetic method for preparing poly(2,6-dimethyl-1,4-phenylene oxide)/polystyrene alloy in reactor containing aqueous medium

Considering the defect of solution polymerization of 2,6-dimethylphenol (DMP), the low molecular weight of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) synthesized in water and difficulty in processing of PPO, a novel one-pot synthetic method for preparing PPO/PS alloy in reactor containing aqueous medium was proposed based on green chemistry. In the presence of styrene, DMP was polymerized to form PPO, and then styrene was in situ polymerized under the initiation of dibenzoyl peroxide (BPO) and dicumyl peroxide (DCP), finally thermodynamically compatible PPO/PS alloy was prepared. It was found that the introduction of styrene during the oxidative polymerization of DMP could increase the molecular weight of PPO. When styrene content was 50 wt%, for the synthesized PPO/PS alloy the yield and the weight-average molecular weight were determined to be 95% and 1.7 × 10⁵ for PPO, 93% and 2.0 × 10⁵ for PS, respectively.     

OXIDATIVE POLYMERIZATION BEHAVIOR OF 2,6-DIMETHYLPHENOL IN AQUEOUS MEDIA WITH POTASSIUM FERRICYANIDE

The effects of potassium ferricyanide,sodium n-dodecyl sulfate,sodium hydroxide and temperature on the molecular weight and the yield of poly(2,6-dimethyl-1,4-phenylene oxide)(PPO) synthesized in an aqueous medium were studied.It was found that oxygen in air had little influence on the oxidative polymerization of 2,6-dimethylphenol(DMP) in the aqueous medium,and potassium ferricyanide was only an oxidant during the oxidative polymerization of DMP.Sodium n-dodecyl sulfate could stabilize polymer particles...     

水介质中2,6-二甲基苯酚的氧化偶合聚合

聚2,6-二甲基苯醚(PPO)是重要的工程塑料,一般采用在有机溶剂中使2,6-二甲基苯酚(DMP)氧化聚合的方法合成,这就需要溶剂回收装置和防爆反应器,且污染环境.从绿色化学观点出发,以水作为反应介质,不仅对环境友好,而且PPO不溶于水,容易分离.近年来,一些学者研究了在油/水两相或全水介质中使DMP氧化聚合合成PPO的新方法.本文主要综述了该方法的研究进展,包括DMP氧化聚合的机理,油/水两相或水介质中对聚合速率、氧化偶合选择性及PPO分子量等的影响因素.     

Magnetic nanoparticle supported catalytic Cu(II)–poly(amindoamine) complexes for aerobic oxidative polymerization to form poly(2,6-dimethyl-1,4-phenylene oxide) in water

Poly(amindoamine) (PAMAM) was grafted onto magnetic Fe₃O₄ nanoparticles to produce PAMAM grafted Fe₃O₄ (shortened as Mag-PAMAM). Mag-PAMAM coordinated with Cu(II) to form the supported Cu(II)–PAMAM complex (shortened as Cu(II)/Mag-PAMAM). The stoichiometric ratio between amine groups in Mag-PAMAM and Cu(II) was found to be 4. The Cu(II)/Mag-PAMAM complexes were employed to catalyze the oxidative polymerization of 2,6-dimethylphenol (DMP) in water. The Cu(II)/Mag-PAMAM complexes demonstrated the excellent selectivity of C–O/C–C coupling and reactivity to form poly(2,6-dimethyl-1,4-phenylene oxide) (PPO). After polymerization, the Cu(II)/Mag-PAMAM complexes were recovered by an external magnetic field and used repeatedly in the next run with additional Mag-PAMAM and copper ions. After three runs of oxidative polymerization of DMP, the recovery ratio of the catalyst was about 95% and the yield of PPO maintained a relatively high value.     

Mechanistic studies of the oxidative coupling polymerization of phenols. VI. Comparison of reactivities of DMP,PPO-dimer,and -trimer in the copper-catalyzed oxidative coupling polymerization

In the oxidative coupling polymerization, catalyzed by copper-amine complexes, the oxidation rates of 2,6-dimethylphenol (DMP) and its C? O-coupled dimer [4-(2′,6′-dimethylphenoxy)-2,6-dimethylphenol] and trimer [4-(-4′-(2″,6″-dimethylphenoxy)-2′,6′-dimethylphenoxy))-2,6-dimethylphenol] have been determined. The DMP concentration dependence shows a Michaelis–Menten-type behavior. On the other hand, the dimer and trimer showed a first-order rate-dependence in the respective phenol concentrations. This indicates that the slow reaction step, following an equilibrium complex formation between DMP and copper complex, is relatively fast for both the dimer and the trimer. Therefore, coordination of dimer or trimer to the copper complex appears to be rate-determining. Furthermore, the dimer and trimer gave overall reaction rates approximately eight times higher than found for DMP. Following the Flory principle of equal reactivity for functional groups of oligomers in polycondensations, all PPO oligomers can be assumed to have equally high oxidation rates as the dimer and trimer. The yield of undesired DPQ side product is strongly reduced when starting with the dimer (0.18%), or trimer (0.17%), compared to 3.3% for DMP. This is not unexpected, since DPQ can only be formed from two monomeric DMP residues. In fact, using a 1/10 molar mixture of dimer/DMP already results in a DPQ yield of only 1.7%. Furthermore, when starting from DMP, it has been observed that DPQ was predominantly formed during the first 30% conversion. Starting from dimer (or trimer) DPQ was formed at an almost constant very low rate during the whole course of the reaction. From these experiments it can be concluded that the most important polymerization reaction involves oxidation of copper-coordinated DMP anion to its corresponding cations, followed by coupling with a copper coordinated PPO chain.     

Electron transfer between protonated and unprotonated phenoxyl radicals

The reaction of phenoxyl radicals with acids is investigated. 2,4,6-Tri-tert-butylphenoxyl radical (13), a persistent radical, deteriorates in MeOH/PhH in the presence of an acid yielding 4-methoxycyclohexa-2,5-dienone 18a and the parent phenol (14). The reaction is facilitated by a strong acid. Treatment of 2,6-di-tert-butyl-4-methylphenoxyl radical (2), a short-lived radical, generated by dissociation of its dimer, with an acid in MeOH provides 4-methoxycyclohexa-2,5-dienone 4 and the products from disproportionation of 2 including the parent phenol (3). A strong acid in a high concentration favors the formation of 4 while the yield of 3 is always kept high. Oxidation of the parent phenol (33) with PbO(2) to generate transient 2,6-di-tert-butylphenoxyl radical (35) in AcOH/H(2)O containing an added acid provides eventually p-benzoquinone 39 and 4,4'-diphenoquinone 42, the product from dimerization of 35. A strong acid in a high concentration favors the formation of 39. These results suggest that a phenoxyl radical is protonated by an acid and electron transfer takes place from another phenoxyl radical to the protonated phenoxyl radical, thus generating the phenoxyl cation, which can add an oxygen nucleophile, and the phenol (eq 5). The electron transfer is a fast reaction.     

Theoretical and experimental investigation on the oxidation of gallic acid by sulfate radical anions

By monitoring the decay of SO4*- after flash photolysis of aqueous solutions of S2O82- at different pH values, the kinetics of the reaction of SO4*- radicals with gallic acid and the gallate ion was investigated. The bimolecular rate constants for the reactions of the sulfate radicals with gallic acid and the gallate ion were found to be (6.3 +/- 0.7) x 10(8) and (2.9 +/- 0.2) x 10(9) M(-1) s(-1), respectively. On the basis of the oxygen-independent second-order decay kinetics and on their absorption spectra, the organic radicals formed as intermediates of these reactions were assigned to the corresponding phenoxyl radicals. DFT calculations in the gas phase and aqueous solution support formation of the phenoxyl radicals by H abstraction from the phenols to the sulfate radical anion. The observed recombination of the phenoxyl radicals of gallic acid to yield substituted biphenyls and quinones is also supported by the calculations. HPLC/MS product analysis showed formation of one of the predicted quinones.     

Effect of POSS on morphology and properties of poly(2,6-dimethyl-1,4-phenylene oxide)/polyamide 6 blends

Poly(2,6-dimethyl-1,4-phenylene oxide)/polyamide 6 (PPO/PA6) (50/50 w) blends filled with epoxycyclohexyl polyhedral oligomeric silsesquioxane (POSS) were prepared via melt-mixing. The reactions between POSS and PPO/PA6 blends were studied by Fourier transform infrared spectroscopy, end group and gel content tests. The morphology of PPO/PA6/POSS composites was observed by field emission scanning electron microscope and transmission electron microscope. As a chain extender and a crosslinking agent for PA6, POSS largely affected the morphology of the composites, which was mainly dependent on the melt-viscosity ratio and interfacial tension between the components. With increasing POSS content from 2 to 4 phr, the morphology of the composites transformed from droplet/matrix to co-continuous morphology. The PPO/PA6/POSS composites with co-continuous morphology had the better mechanical properties than those with droplet/matrix morphology. Dynamic mechanical thermal analysis showed that the addition of POSS increased the T_g of PA6.     

Quantitative synthesis of star-shaped poly(vinyl ether)s with a narrow molecular weight distribution by living cationic polymerization

Star-shaped poly(vinyl ether)s with narrow molecular weight distributions were obtained from polymer-linking reactions of living polymers with a divinyl compound based on living cationic polymerization. For example, living polymers (DP(n) = 50-300) of isobutyl vinyl ether (IBVE), prepared with a cationogen/EtAlCl(2) at 0 degrees C in hexane in the presence of ethyl acetate, were allowed to react with a small amount of 1,4-cyclohexanedimethanol divinyl ether (DVE-1) to give a star-shaped poly(IBVE) in quantitative yield (100%). In addition, a notable feature of this star-shaped polymer was extremely narrow molecular weight distribution (M(w)/M(n) = 1.1-1.2). The structure of divinyl compounds and reaction conditions for the linking reaction are key factors for achieving quantitative yield of star-shaped polymers. To our best knowledge, this is the first example of selective preparation of star-shaped polymers with narrow molecular weight distribution via one-pot polymer-linking reactions, which has never been achieved in any other mechanisms. The M(w) and the number of arms per molecule ranged from 6 x 10(4) to 30 x 10(4) and 9 to 44, respectively. Thermosensitive star polymers were also synthesized in quantitative yield, and the products were found to undergo sensitive phase separation and physical gelation.     

Synthesis and supramolecular association of immobilized NCN-pincer platinum(II) complexes on hyperbranched polyglycerol supports

Pertosylation of hyperbranched polyglycerol (M(n)=2000; M(w)/M(n)=1.3) followed by partial displacement of the tosyl groups with carboxylic acid functionalized NCN-pincer platinum(II) complexes [PtI-2,6-(NMe(2)CH(2))(2)C(6)H(2)-4-COOH], resulted in covalent attachment of the NCN-pincer complexes to the polyglycerol. These functionalized hyperbranched macromolecules have been characterized by (1)H, (13)C, and (195)Pt NMR, UV-visible, and IR spectroscopy. The presence of Pt and I atoms renders them directly visible by transmission electron microscopy (TEM) without staining procedures, which offers images of associated hyperbranched macromolecules. TEM micrographs show disk-shaped structures with a small size-distribution (15-20 nm), and characteristic core-shell ring structures. The thickness of the corona observed in TEM could be correlated with the substitution degree with pincer platinum moieties.     

COMPLEX AMPHIPHILIC HYPERBRANCHED FLUOROPOLYMERS BY ATOM TRANSFER RADICAL SELF-CONDENSING VINYL (CO)POLYMERIZATION

Amphiphilic hyperbranched fluorohomopolymer (M(n) = 9.06 kDa, M(w)/M(n)= 1.90) and fluorocopolymer (M(n) = 17.2 kDa, M(w)/M(n)= 2.50) with tri(ethylene glycol) units incorporated at the molecular level were synthesized by atom transfer radical self-condensing vinyl homopolymerization of an inimer, 4-[oxy(tri(ethylene glycol))bromoisobutyryl]-2,3,5,6-tetrafluorostyrene, and copolymerization of the inimer with 2,3,4,5,6-pentafluorostyrene (1:3, inimer:monomer), using 2,2'-bipyridine together with CuCl/CuCl(2) as the ligand/catalyst/deactivator system. The structure and composition of the fluoropolymers were characterized by (1)H, (13)C, and (19)F NMR spectroscopies. As detected by thermogravimetric analyses, the homopolymer and the copolymer had thermal stability up to 175 °C and 210 °C, respectively. Differential scanning calorimetry revealed a glass transition temperature of -19 °C for the homopolymer and 20 °C for the copolymer. Solubility tests indicated that both polymers were soluble in a broad range of organic solvents, and the presence of tri(ethylene glycol) units resulted in the formation of water dispersible micelles from each of the polymers.     

Model compound studies of the beta-O-4 linkage in lignin: absolute rate expressions for beta-scission of phenoxyl radical from 1-phenyl-2-phenoxyethanol-1-yl radical

Arrhenius rate expressions were determined for beta-scission of phenoxyl radical from 1-phenyl-2-phenoxyethanol-1-yl, PhC*(OH)CH2OPh (V). Ketyl radical V was competitively trapped by thiophenol to yield PhCH(OH)CH2OPh in competition with beta-scission to yield phenoxyl radical and acetophenone. A basis rate expression for hydrogen atom abstraction by sec-phenethyl alcohol, PhC*(OH)CH3, from thiophenol, log(k(abs)/M(-1) s(-1)) = (8.88 +/- 0.24) - (6.07 +/- 0.34)/theta, theta = 2.303RT, was determined by competing hydrogen atom abstraction with radical self-termination. Self-termination rates for PhC*(OH)CH3 were calculated using the Smoluchowski equation employing experimental diffusion coefficients of the parent alcohol, PhCH(OH)CH3, as a model for the radical. The hydrogen abstraction basis reaction was employed to determine the activation barrier for the beta-scission of phenoxyl from 1-phenyl-2-phenoxyethanol-1-yl (V): log(k beta)/s(-1)) = (12.85 +/- 0.22) - (15.06 +/- 0.38)/theta, k beta (298 K) ca. (64.0 s(-1) in benzene), and log(k beta /s(-1)) = (12.50 +/- 0.18) - (14.46 +/- 0.30)/theta, k beta (298 K) = 78.7 s(-1) in benzene containing 0.8 M 2-propanol. B3LYP/cc-PVTZ electronic structure calculations predict that intramolecular hydrogen bonding between the alpha-OH and the -OPh leaving group of ketyl radical (V) stabilizes both ground- and transition-state structures. The computed activation barrier, 14.9 kcal/mol, is in good agreement with the experimental activation barrier.     

Amperometric biosensor for the quantification of gentisic acid using polyphenol oxidase modified carbon paste electrode

The affinity of mushroom polyphenol oxidase (PPO) towards gentisic acid (GA), a metabolite of acetyl salicylic acid (ASA), is demonstrated by spectrophotometry and by electrochemical techniques. The enzyme can selectively recognize GA even in the presence of large excess of ASA and its metabolic derivatives (salicylic acid (SA) and salicyluric acid (SUA)). At -0.150 V, the sensitivity is (6.1+/-0.1)x10(4) NAM(-1), the response is linear up to 2.0x10(-4) M and the detection limit is 5.0x10(-5) M. The kinetic parameters, obtained from Eadie-Hofstee plots, are I(max)=51.4 nA and K(m)(app)=6.7x10(-4) M.     

Inverse miniemulsion ATRP: a new method for synthesis and functionalization of well-defined water-soluble/cross-linked polymeric particles

A new methodology for the synthesis and functionalization of nanometer-sized colloidal particles consisting of well-defined, water-soluble, functional polymers with narrow molecular weight distribution (M(w)/M(n) < 1.3) was developed, utilizing atom transfer radical polymerization (ATRP) of water-soluble monomers in an inverse miniemulsion. The optional introduction of a disulfide-functionalized cross-linker allowed for the synthesis of cross-linked (bio)degradable nanogels. Dynamic light scattering (DLS) and atomic force microscopy (AFM) measurements indicated that these particles possessed excellent colloidal stability. ATRP in inverse miniemulsion led to materials with several desirable features. The colloidal particles preserved a high degree of halogen chain-end functionality, which enabled further functionalization. Cross-linked nanogels with a uniformly cross-linked network were prepared. They were degraded to individual polymeric chains with relatively narrow molecular weight distribution (M(w)/M(n) < 1.5) in a reducing environment. Higher colloidal stability, higher swelling ratios, and better controlled degradability indicated that the nanogels prepared by ATRP were superior to their corresponding counterparts prepared by conventional free radical polymerization (RP) in inverse miniemulsion.     

HES/TiCl_4体系引发异丁烯可控正离子聚合

由六官能团引发剂环氧化角鲨烯(HES)与TiCl4组成引发体系,引发异丁烯(IB)在CH2Cl2/n-Hex(40/60,V/V)混合溶剂中进行正离子聚合,分别探讨了HES和2,6-二甲基吡啶(DMP)用量对IB正离子聚合转化率、产物分子量及其分布的影响.结果表明HES和微量水均可与TiCl4发生络合,并分别形成碳正离子和质子两种引发活性中心,导致聚合产物GPC谱图呈明显双峰分布.增加引发剂HES用量([HES]=2.64mmol/L),可以减少聚合体系中微量水的不可控引发,提高HES引发效率;在聚合体系中引入少量DMP时,可明显地减少微量水的不可控引发和提高HES的引发效率,使得即使在较低HES用量下([HES]=0.084mmol/L),也可达到主要由HES引发IB正离子聚合,制备出官能叔氯末端的六臂星形支化遥爪聚异丁烯,GPC谱图呈现单峰分子量分布,分布指数为1.5左右.     

Inactivation of horseradish peroxidase by phenoxyl radical attack

To test the hypothesis that horseradish peroxidase (HRP) can be inactivated by phenoxyl radicals upon reaction with H(2)O(2)/phenol, we probed HRP-catalyzed phenol oxidation at various phenol/H(2)O(2) concentrations. To this end the total protein, phenolic product, active protein, and iron concentrations in the aqueous phase were determined by protein assay, phenol-(14)C isotopic labeling, resonance Raman and atomic absorption spectroscopy, respectively. Additionally, resonance Raman and FTIR measurements were carried out to probe possible structural changes of the enzyme during the reaction. The data obtained provide the first experimental support for the hypothesis that HRP can be inactivated by a phenoxyl radical attack. The heme macrocycle destruction involving deprivation of the heme iron occurs as a result of the reaction. An intermediate type of the active protein was observed by Raman difference spectra at low concentrations which features a stabilization of the quantum mixed state of the heme iron and a significant amount of phenoxylphenol-type oligomers in solution and probably also in the heme pocket. This work provides a basis for evaluating the relative contributions of different HRP inactivation mechanisms and is thus critical for optimizing engineering applications involving HRP reactions.     

Size and shape of soil humic acids estimated by viscosity and molecular weight

Ultrafiltration fractions of three soil humic acids were characterized by viscometry and high performance size-exclusion chromatography (HPSEC) in order to estimate shapes and hydrodynamic sizes. Intrinsic viscosities under given solute/solvent/temperature conditions were obtained by extrapolating the concentration dependence of reduced viscosities to zero concentration. Molecular mass (weight average molecular weight (M (w)) and number average molecular weight (M (n))) and hydrodynamic radius (R(H)) were determined by HPSEC using pullulan as calibrant. Values of M (w) and M (n) ranged from 15 to 118 x 10(3) and from 9 to 50 x 10(3) (g mol(-1)), respectively. Polydispersity, as indicated by M (w)/M (n), increased with increasing filter size from 1.5 to 2.4. The hydrodynamic radii (R(H)) ranged between 2.2 and 6.4 nm. For each humic acid, M (w) and [eta] were related. Mark-Houwink coefficients calculated on the basis of the M (w)-[eta] relationships suggested restricted flexible chains for two of the humic acids and a branched structure for the third humic acid. Those structures probably behave as hydrated sphere colloids in a good solvent. Hydrodynamic radii of fractions calculated from [eta] using Einstein's equation, which is applicable to hydrated sphere colloids, ranged from 2.2 to 7.1 nm. These dimensions are fit to the size of nanospaces on and between clay minerals and micropores in soil particle aggregates. On the other hand, the good agreement of R(H) values obtained by applying Einstein's equation with those directly determined by HPSEC suggests that pullulan is a suitable calibrant for estimation of molecular mass and size of humic acids by HPSEC.     

Synthesis and antioxidant activity of [60]fullerene-BHT conjugates

Fullerene derivatives incorporating one or two 3,5-di-tert-butyl-4-hydroxyphenyl groups were synthesized by 1,3-dipolar cycloaddition of azomethine ylides to C(60). The O-H bond dissociation enthalpies (BDEs) of these compounds were estimated by studying, by means of EPR spectroscopy, the equilibration of each of these phenols and 2,6-di-tert-butyl-4-methylphenol (BHT) with the corresponding phenoxyl radicals. The antioxidant activity of the investigated phenols was also determined by measuring the rate constants for their reaction with peroxyl radicals in controlled autoxidation experiments and compared to that recorded under identical experimental settings for [60]fullerene itself and unlinked BHT. The results indicate that linking of the BHT structure to C(60) does not substantially alter the thermochemistry and kinetics of its reaction with peroxyl radicals, but such adducts may behave as interesting bimodal radical scavengers. The inherent rate constant for trapping of peroxyl radicals by C(60) per se (k(inh)=3.1+/-1.1 x 10(2) m(-1) s(-1)) indicates that, contrary to previous reports, [60]fullerene is an extremely weak chain-breaking antioxidant.     

Synthesis, spectroscopic characterization and redox reactivity of some transition metal complexes with salicylaldimines bearing 2,6-di-phenylphenol

New bidentate N-(2,6-di-phenyl-1-hydroxyphenyl) salicylaldimines bearing X=H and 3,5-di-t-butyl substituents on the salicylaldehyde ring, L(x)H, and their copper(II) complexes, M(Lx)2, (M=Cu(II), Co(II), Pd(II), Ni(II) and Zn(II)) have been synthesized and characterized by IR, UV/vis, 1H NMR, 13C NMR, ESR spectroscopy, magnetic susceptibility measurements, as well as their oxidation with PbO(2) and reduction (for Cu(Lx)2) with PPh(3) were investigated. ESR studies indicate that oxidation of M(Lx)2 produces ligand-centered M(II)-phenoxyl radical species. The Cu(Lx)2 complexes, unlike others M(Lx)2, are readily reduced by PPh3 via intramolecular electron transfer from ligand to copper(II) to give unstable radical intermediates which are converted to another stable secondary radical species. The analysis of ESR spectra of Cu(Lx)(2), Co(L1)(2) and generated phenoxyl radicals are presented.     

Size effects on miscibility and glass transition temperature of binary polymer blend films

After determining the size dependent miscibility of binary polymer blend films using molecular dynamics simulation and thermodynamics, the size dependent glass transition temperatures Tg(w,D) of several polymer blend films in miscible ranges are determined by computer simulation and the Fox equation where w is the weight fraction of the second component and D denotes thickness of films. The Tg(w,D) function of a thin film can decrease or increase as D decreases depending on their surface or interface states. The computer simulation results are consistent with available experimental results and theoretical results for polymer blend films of PPO/PS [poly(2,6-dimethyl-1,4-phenylene oxide)/polystyrene] and stereoregular PMMA/PEO [poly(methyl methacrylate)/poly(ethylene oxide)]. The physical background of the above results is related to the root of mean square displacement of thin films in their different regions.