Modification of fluoropolymers by means of electron beam irradiation

High molecular weight polytetrafluoroethylene (PTFE) is transformed to free-flowing micropowder by treatment with electron beams. In case of irradiation in presence of air carboxylic acid fluoride groups are incorporated which rapidly hydrolyze to carboxylic groups in the surface-near regions due to atmospheric humidity. These polar groups reduce the hydrophobic and oleophobic properties so much that homogeneous compounding with other materials becomes possible. In addition to PTFE, copolymers of tetrafluoroethylene with hexafluoropropylene (FEP) and perfluoropropylvinylether (PFA) were modified. In case of identical irradiation conditions, the concentration of carboxylic groups is much higher in FEP and PFA than in PTFE, which is due to the lower crystallinity of the copolymers.

Electron beam irradiation of PTFE was performed in vacuum at elevated temperature above the melting point. The changes in the chemical structure were studied. The concentration of CF₃ branches was found to be much higher as compared to room temperature irradiation.

In a practical test PTFE micropowders functionalized by electron irradiation were compounded with epoxy resins, with polyoximethylene and with polyamides. Such compounds are characterized by very good frictional and wearing behaviour in dry-running tests.     

Perfluorocyclobutyl (PFCB) aromatic polyethers: Synthesis and characterization of new sulfonimide containing monomers and fluoropolymers

The synthesis and thermal cyclopolymerization of aryl trifluorovinyl ether monomers containing novel sulfonimide acid functionalities are described. The monomers are prepared starting from commercially available 4-bromophenol in five steps. These novel polymers explore a new versatile class of partially fluorinated polymers for potential use in fuel cells and other electrochemical applications.     

Electron beam irradiation effects on poly(ethylene terephthalate)

Changes in poly(ethylene terephthalate) subjected to electron beam irradiation at doses up to 15 MGy and dose rate of 1.65 MGy/h, were investigated by differential scanning calorimetry, molecular weight measurement, X-ray photoelectron spectroscopy, and scanning electron microscopy. Irradiated samples showed a decrease of molecular weight with a minimum at 5 MGy, which is attributed to chain scission of the macromolecules and then an increase at further doses due to branching and some degradation effect. Irradiation in air is not an important factor because the high dose rate of irradiation inhibits oxygen diffusion in the samples.     

Electron beam forming system for irradiation of large diameter cylindrical products

The report describes electron beam electromagnetic forming system, which is destined for irradiation of cylindrical long goods, specifically for PE tubes 160 mm diameter. System consists of electromagnet, power supply units, beam distributions control units, etc. for use at an electron accelerator at 5 MeV and 50 kW. The particular geometry of the magnet poles and their mutual arrangement are creating an irradiation field that allows the electrons to irradiate the surface of the product close to 90°.     

Electron beam irradiation of bamboo chips: degradation of cellulose and hemicelluloses

Electron beam irradiation (EBI) can degrade lignocellulosic materials and thus be used as a pretreatment method for efficient enzymatic hydrolysis. This research is mainly concerned with the degradation of cellulose and hemicelluloses when bamboo chips are exposed to various doses of EBI. The results show that cellulose degradation occurred continuously but without a gradual drop of the crystalline index with irradiation dose ranging from 0 to 50 kGy; meanwhile, no significant changes were observed in the molecular weight of hemicelluloses. An obvious relationship was found between irradiation dose and cellulose degradation, which could be used to control cellulose degradation by adjusting the EBI dose. Furthermore, the difficulty of cellulose depolymerization [G(s)] in bamboo chips by exposure to EBI was calculated as 0.052 µmol/J.     

Treatment of pharmaceutical wastewater containing clofibric acid by electron beam irradiation

In this study, clofibric acid (CA) degraded by the electron beam (EB) irradiation was investigated at CA initial concentration of 10 mg L^?1. Results showed that more than 90% CA degradation is achieved at 0.5 kGy. The acid conditions (pH 3.00) and the addition of N₂ remarkably improved the CA degradation efficiency. The addition of CO₃^2?, HCO₃^? anions and H₂O₂ reduced the CA degradation efficiency. It showed that ·H had a primary role to play in the EB degradation of CA. The determination of byproducts showed hydrosilylation reaction of CA molecules. The byproducts were clofibric acid, chlorophenol, phenol, hydroquinone, benzoquinone and dihydroxybenzene. These results suggested that electron beam irradiation (EBI) can be used to eliminate CA.

     

Crosslinking study of polyethers containing pendent double bonds

This article studies the crosslinking reactions of some polyethers containing double bonds on the side chains. Thermal crosslinking takes place in all cases, but is overlapped by the degradation process. So, a catalyst has to be used to obtain the cured material and avoid degradation. The best initiator appears to be dicumyl peroxide and the maximum cross-linking degree is achieved only with 5% (w/w). Thermogravimetric analyses are used to test the quality of the cured materials. IR spectroscopy shows that crosslinking actually takes place by polymerizing pendent double bonds. Furthermore, activation energies for thermal and radical initiated crosslinking are determined by means of dynamic DSC studies. © 1995 John Wiley & Sons, Inc.     

Effect of gamma irradiation on molecular weight of fluorinated aromatic polyethers

A series of fluoropolymer films was synthesized by reacting 1,3-bis(1,1,1,3,3,3-hexafluoro-2-pentafluorophenylmethoxy-2-propyl)benzene (12F-FBE) with a series of bisphenol monomers via a polycondensation reaction. The biphenols used included a diphenol-substituted spirodilactam, biphenol, bisphenol A, bisphenol AF, bisphenol F and bisphenol O. Polymers films from these new fluoropolyaryl ethers were irradiated by a Gamma Beam 657-PT at a dose rate of 9 kGy/h; the absorbed dose was varied between 30 and 150 kGy. The effect on the chemical structure upon radiation was studied by DSC, TGA, FTIR-ATR, NMR, and GPC, both before and after irradiation. The data obtained allowed the determination of the degradation radiochemical yield (G _s), between 0.24 and 7.43 crosslinking radiochemical yield (G _x), from 0.03 to 1.47 and the ratio of G _s/G _x was between 2.89 and 8.28. There was no apparent physical change, from 30 to 150 kGy; the films continue to be flexible and transparent after irradiation.     

Synthesis of polyethers containing cyclodipeptide moiety in the main chain

The dichlorodihydropyrazines derived from 2,5‐diketopiperazine were treated with diols in a basic condition to afford polyethers containing cyclodipeptide moiety in the main chain, which were found to be degraded into amino acid components in an acidic condition. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 927–933, 2001     

Electron impact induced fragmentation of pyridyl macrocyclic polyethers (crown ethers)

The mass spectra of pyridyl-18-crown-6 and pyridyl-15-crown-5 were determined. The spectra of five deuterium labeled analogues of pyridyl-18-crown-6 coupled with high resolution data, allowed formulation of fragmentation pathways, which are dominated by several series involving the loss of C₂H₄O units.     

Electron beam irradiation of poly(vinyl methyl ether) films. 2. Temperature-dependent swelling behavior

Temperature-sensitive hydrogel films were synthesized by electron beam irradiation of poly(vinyl methyl ether) (PVME) on silicon (Si/SiO(2)) substrates and gold (Au) coated glass slides. The temperature-dependent swelling behavior of the films in aqueous solution was characterized by in situ spectroscopic ellipsometry and a combination of surface plasmon resonance (SPR) and optical waveguide spectroscopy (OWS). The results of both techniques are compared. The suitability of both techniques for the characterization of the swelling behavior of thin hydrogel films is demonstrated. The volume swelling degree in the swollen state decreases with increasing radiation dose D. This is explained by the fact that the number of formed polymeric radicals, and hence cross-linking density, increases with D. Above the phase-transition temperature, the swelling degrees were independent of D, slightly above 1. The swelling/deswelling process was fully reversible and is mainly directed perpendicular to the substrate surface. The phase-transition temperature was determined to be T(cr) approximately 33 degrees C. However, T(cr) slightly decreases with increasing D and increasing film thickness d.     

Synthesis of polyethers containing viologen moiety and their application to electron-transfer catalyst

Polyethers containing viologen moieties were prepared by the reaction of tosylated polyethers with bipyridine. Viologen moieties of these polymers having ? ((CH₂)₂? O? )_n ? chains were reduced into the cation radicals by sodium dithionite in dichloromethane, methanol, and benzene. The reduction of vicinal dibromide, ethyl 2,3-dibromo-3-phenylpropionate using these polymers as electron-transfer catalyst (ETC) was performed in dichloromethane to obtain ethyl cinnamate in good yield.     

Electron beam irradiation of poly(vinyl methyl ether) films: 1. Synthesis and film topography

Temperature-sensitive hydrogel layers on silicon (Si) substrates were synthesized by electron beam irradiation of spin-coated poly(vinyl methyl ether) (PVME) films. The influences of the used solvent, the polymer concentration, and the spinning velocity on the homogeneity and the thickness of the PVME film were investigated. In the range of concentration c(p) = 1-15 wt% PVME in ethanol solution, homogeneous films with a thickness between d = 50 nm and 1.7 mum were obtained. The films were cross-linked by electron beam irradiation under inert atmosphere and analyzed by sol-gel-analysis. The results were compared with bulkgels formed by electron beam irradiation of PVME in the dry state. The film topography was analyzed by high-resolution field emission scanning electron microscopy and atomic force microscopy. An islandlike structure in the dry, swollen, and shrunken state of the hydrogel films was observed.     

The degradation mechanism using TG-MS technique of some aromatic polyethers containing flexible spacers

The paper presents a thermogravimetric study of some aromatic poly- and copolyethers, using mass spectrometry technique combined with thermogravimetric analysis. The polymers were synthesized by phase transfer catalysis technique, using bis(2-chloroethyl)-ether or 1,6-dichlorohexane as flexible spacers and various bisphenols (4,4'-dihydroxydiphenyl, 4,4'-dihydroxyazobenzene and bisphenol A). The presence of azobenzenic moieties in the chain induces a liquid crystalline behavior, but, due to the high values of the transition temperature, some precautions during the thermal characterisation are necessary. In the case of azobenzenic samples, the degradation reactions begin, as a function of the chemical structure, around 230-250°C. A degradation mechanism based on chain transfer reactions was proposed. The chain flexibility influences the thermal degradation mechanism, in the case of rigid polymers the chain transfer reactions being less probable. For the flexible chains, the thermal stability is not essentially influenced by the copolymerisation ratio between the two aromatic bisphenols. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structure–property relationship of photoactive liquid crystalline polyethers containing benzylidene moiety

A series of main chain photoactive liquid crystalline polyethers, containing rigid bisbenzylidene photoactive mesogen and flexible methylene spacers, were synthesized by polycondensation of bisbenzylidene diols and dibromoalkanes. The polyethers were characterized with ¹H NMR, gel permeation chromatography (GPC), differential scanning calorimeter (DSC), thermo gravimetric analyzer (TGA), and polarized light optical microscopy. The individual and combined effects of spacer length and number of methoxy substituents on mesogenic and photoactive properties were investigated. Both first order and second order transition temperatures decreased with increased spacer length and the number of substituents. The combined effect of spacers and substituents drastically reduced the transition temperatures. All monomers and polymers showed mainly the smectic mesophase. In a few cases, nematic droplets along with the smectic phase were observed. The width of the liquid crystalline phase reduced with an increasing number of methoxy substituents on mesogenic unit. Variation of spacer length has a negligible effect on photocycloaddition. However, steric hinderance caused by the substituents decreased the photoactivity as the number of substituents increased. Total energies of crosslinked dimers calculated from modeling studies supported the above findings. Intermolecular photocycloaddition was also confirmed by photoviscosity measurement. The refractive index change was found to be in the range of 0.017–0.031. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2143–2155, 2009     

Electron beam curing with glycerol methacrylate

Glycerol methacrylate and hydroxyethyl methacrylate in combination with glycerol dimethacrylate as crosslinker were applied with electron beam irradiation to consolidate the color painting of the terracotta army of the first Chinese Emperor Qin Shihuangdi. The described mixture allowed reducing the necessary irradiation dose for consolidation to 40 kGy. The formation of glossy spots could be suppressed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6660–6663, 2008