Phospha-s-triazines. IV. Degradation studies of 1-diarylphospha-3,5-bis(perfluoroaliphatic)-2,4,6-triazines and 1,3,-bis(diarylphospha)-5-perfluoroaliphatic-2,4,6-triazines

Thermal and thermal oxidative stability evaluations were performed on mono- and diphospha-s-triazines at 235 and 316°C using sealed Pyrex ampoules. The specific compounds studied were: 1-diphenylphospa-3,5-bis(perfluoro-n-heptyl)-2,4,6-triazine, 1-diphenylphospha-3,5-bis(perfluoro-alkylether)-2,4,6-triazines, their respective pentafluorophenyl analogues, 1,3-bis(diphenylphospha)-5-perfluoro-n-heptyl-2,4,6-triazine and 1,3-bis(diphenylphospha)-5-perfluoroalkylether-2,4,6-triazine. All the compounds wherein phenyl groups were present on the phosphorous exhibited good thermal stability up to 316°C; the analogous pentafluorophenyl substituted materials were degraded extensively at these temperatures. The oxidative stability of both the mono- and diphospha-s-triazines was excellent at 235°C, but at 316°C some degradation was observed. This was more pronounced in compounds containing the perfluoroalkyl moiety on carbon than in the perfluoroalkylether substituted members of the series.     

Diphosphatetraazacyclooctatetraenes. II. Properties and degradations

1,5-Bis(diphenylphospha)-3,7-bis(perfluoroalkylether)-2,4,6,8- tetraazacyclooctatetraene and 1,3-bis(diphenylphospha)-5,7-bis(perfluoroalkylether) -2,4,6,8-tetraazacyclooctatetraene were found to decompose at 316°C to phospha-s-triazines. The symmetrical arrangement liberated perfluoroalkylether nitrile with concommitant formation of the corresponding diphospha-s-triazine; the unsymmetrical isomer eliminated the (C₆H₅)₂PN unit to give the monophospha-s-triazine. The thermal and oxidative stabilities of the two compounds differed widely, with the unsymmetrical isomer being significantly more stable than the symmetrical arrangement. Spectral data pertinent to these results are discussed. Both materials were found to be effective in arresting perfluoroalkylether fluid degradation in oxidizing atmospheres in the presence of metal alloys.     

Syntheses and degradations of fluorinated heterocyclics II. Perfluoroalkyl and perfluoroalkylether-1,2,4-oxadiazoles

3-Perfluoroalkylether-5-perfluoro-n-heptyl-1,2,4-oxadiazole and 3,5-bis(perfluoroalkylether)-1,2,4-oxadiazole were synthesized and characterized. The 3,5-bis(perfluoroalkylether)-1,2,4-oxadiazole was subjected to thermal, thermal oxidative, and hydrolytic degradations at 235 and 325°C and was found to be stable under these conditions as evidenced by practically quantitative recovery of the test samples. In the presence of Jet-A-fuel at 235°C a low degree of degradation,～4%, was observed. 3,5-Bis(perfluoro-n-heptyl)-1,2,4-oxadiazole was found to be stable to attack by water at 325°C; however in air in the presence of Jet-A at 235°C the extent of degradation was in excess of 10%.     

Effect of aromatic substitution in aniline on the properties of polyaniline

Substitution in aniline has tremendous effect in the synthesis of poly(substituted anilines) as well as in their properties. In this investigation polyaniline (PANI), poly(m-nitro aniline) (PMNA), poly(m-amino phenol) (PMAP) and poly(o-ethyl aniline) (POEA) were synthesized by oxidative polymerization under identical conditions. Different properties were measured and compared with PANI to find out the presence of electron donating -OH group, electron withdrawing -NO₂ group and less effecting ethyl group on the properties of poly(substituted anilines). It was found that presence of any type of substitution in the benzene ring of aniline increases the solubility of the resulted polymer but reduces the yield, degree of polymerization, thermal stability, electrical and thermal conductivity. The colors, bulk density, particle size, percentage of crystallinity vary considerably depending on the nature of substitution.     

Synthesis of 2- and 2,5-substituted benzoxazoles and benzothiazoles

A number of 2- and 2,5-perfluoroalkyl and perfluoroalkylether substituted benzoxazoles and benzothiazoles have been prepared. Their relative hydrolytic stability has been examined. In all cases the benzothiazoles were more stable that the benzoxazoles. Substituents in the 2-position offering steric hindrance improve hydrolytic stability.     

Optical and electrochemical properties of poly(o-toluidine) multiwalled carbon nanotubes composite Langmuir-Schaefer films

Conducting poly(o-toluidine) (POT) with multiwalled carbon nanotubes (MWNTs) nanocomposite (POT-MWNTs) was synthesized by oxidative polymerization. Chloroform solutions of the material were used for the optical characterizations by means of UV-visible spectroscopy and for the fabrication of Langmuir-Schaefer (LS) films. LS films were fabricated at the air-liquid interface by using 0.1 M HCl aqueous solution as the subphase to study the electrochemical properties of the nanocomposite by means of cyclic voltammetry and photoelectrochemical techniques. The optical characterizations gave proof that the presence of MWNTs inside the polymeric matrix produced no change in the (pi-pi*) transition of POT structure, indicating that the polymeric chains were simply wrapped around and not doped by MWNTs. The electrochemical investigations highlighted significant changes in the redox properties of POT-MWNTs LS films with respect to pure POT. The cyclic voltammetric study also revealed high electrochemical stability, confirmed by the estimation of the diffusion coefficient and the photoelectrochemical response of the nanocomposite LS films. This characteristic turned out to be more evident than that obtained in our earlier studied poly(o-anisidine)-MWNTs (POAS-MWNTs) system.     

Synthesis and characterization of polylactide functionalized polyacetylenes

The paper deals with the synthesis and polymerization of novel poly(l-lactide)-derived acetylene monomers and the analysis of the thermal properties of the formed graft copolymers. Poly(l-lactide) macromonomers with different acetylene end groups were prepared using stannous octanoate as a catalyst in the presence of various hydroxyacetylenes. Next, the well-characterized macromonomers were subjected to polymerization using [{RhCl(nbd)}₂]/Et₃N and [RuCl₂(CH–o–OiPrC₆H₄)(IMesH₂)] to obtain graft copolymers. Investigation of these graft copolymers by GPC and NMR spectroscopy revealed the presence of some poly(l-lactide) formed as a side product during the ring opening polymerization of l-lactide. The thermal stability of the polymeric materials has been studied as a function of the polyacetylene backbone substituents and the length of poly(l-lactide) side chains. Introducing polyacetylene into polyester increased the polymer stability. The thermal degradation behavior of the synthesized materials depends on the length of poly(l-lactide) chains and also on l-lactide homopolymer impurities in the graft copolymers.     

Mass spectra of some perfluoroalkyl and perfluoroalkylether substituted 1,2,4-oxadiazoles

Electron impact fragmentation patterns were obtained for 1,4-bis[(5-perfluoro-n-heptyl)-1,2,4-oxadiazolyl]-benzene, its perfluoroalkylether substituted analogue, 3,5-bis(perfluoroalkyl)-, 3,5-bis(perfluoroalkylether)- and 3-perfluoroalkylether-5-perfluoroalkyl-1,2,4-oxadiazoles. In the compounds containing the phenylene group the molecular ion constituted the base peak; the main process was the breakdown of the oxadiazole ring with concurrent liberation of the perfluoroalkyl or perfluoroalkylether nitrile molecule; cleavage of the fluorinated chain α to the oxadiazole ring was found to take place to a considerable degree. In the perfluorinated 1,2,4-oxadiazoles cleavage β to the oxadiazole ring occurred preferentially; fragmentation of the ring itself took place to a limited degree only. The 3-perfluoroalkylether-5-perfluoroalkyl-1,2,4-oxadiazole appeared to undergo the primary β-cleavage exclusively at the perfluoroalkylether sidechain.     

Note New Organic Polymers. 5. Synthesis of Poly(2-Vinyl-3-Substituted-4-Quinazolone)s

Heterocyclic polymers are well known for their outstanding thermal stability [I]. Sillion et al. [2, 31 reported that polyquinazolones prepared from 6,6′-bi(3,1-benzoxazin-4-one) substituted in the 2-position by a methyl or phenyl group and aromatic diamines are soluble in m-cresol and possess good thermal stability. The present paper deals with the synthesis of polyquinazolones from poly [l-(2-carboxyanilinocarbonyl)ethylene]. See Figs. 1 and 2.     

Inorganic coordination polymers. XVI. Zinc(II) phosphinate polymers containing polyphenylene and poly(phenylene oxide) side groups

The synthesis and characterization of a series of new phosphinic acids and the zinc polymers prepared from them are reported. These compositions are characterized by the presence of short polyphenylene and poly(phenylene oxide) chains as side groups. Some of the zinc derivatives were found to be tractable polymers with good thermal stability.     

Syntheses and degradations of fluorinated heterocyclics III. Perfluoroalkyl and perfluoroalkylether-1,3,4-oxadiazoles

2,5-Bis(perfluoro-n-heptyl)-, 2-perfluoroalkylether-5-perfluoro-n-heptyl-, and 2,5-bisperfluoroalkylether-1,3,4-oxadiazoles were synthesized and characterized. 2,5-Bis(perfluoro-n-heptyl)-1,3,4-oxadiazole was thermally and hydrolytically stable at 325°C; however, in the presence of air, degradation took place at 235°C. The perfluoroalkylether analogue exhibited thermal and hydrolytic stability at 325°C; it was found to be unaffected by Jet-A fuel and air at 235°C. At 325°C in air some degradation occured as evidenced by volatiles production, oxygen consumption, and 96% starting material recovery.     

A novel approach to prepare proton exchange membranes from fluoropolymer powder by pre-irradiation induced graft polymerization

A novel approach was developed to overcome the non-uniform distribution of grafted polystyrene (PS) chains across proton exchange membranes (PEMs) manufactured using radiation induced graft polymerization of commercialized fluoropolymer films. This process involves the three key steps of grafting of styrene into fluoropolymer powder, processing the grafted powder into membranes, and then obtaining the PEM by sulfonation of these membranes. The structure of the membranes and the PEMs were analyzed by means of infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope with energy-dispersive X-ray analysis (SEM-EDX) to demonstrate the uniform distribution of poly(styrene-sulfonic acid) (denoted as PSSA) graft-chains across the PEM. The properties of the resulting PEMs, such as their ion exchange capacity (IEC), water uptake (WU), proton conductivity, dimensional stability, oxidative stability and thermal stability, were also investigated.     

Fluoro-ketones VIII. Synthesis of some fluoroquinoxaline compounds from fluoroketones

The reaction between a perfluoroalkylether ,β-diketone or perfluoroalkyletherketoester and o-phenylenediamine yielding quinoxaline compounds was studied in detail. The various intermediate compounds leading to the formation of the quinoxalines were examined by NMR, MS, GC/MS and IR. 2,3-Perfluoroalkylether substituted quinoxaline is the major product of the reaction. In addition however, the formation of a minor product 3-perfluoro-alkylether-2(1H)-quinoxalinone, indicates an alternate reaction path.     

Photooxidative and pyrolytic degradation of methyl methacrylate-alkyl acrylate copolymers

Different compositions of poly(methyl methacrylate-co-methyl acrylate) (PMMAMA), poly(methyl methacrylate-co-ethyl acrylate) (PMMAEA) and poly(methyl methacrylate-co-butyl acrylate) (PMMABA) copolymers were synthesized and characterized. The photocatalytic oxidative degradation of all these copolymers were studied in presence of two different catalysts namely Degussa P-25 and combustion synthesized titania using azobis-iso-butyronitrile and benzoyl peroxide as oxidizers. Gel permeation chromatography (GPC) was used to determine the molecular weight distribution of the samples as a function of time. The GPC chromatogram indicated that the photocatalytic oxidative degradation of all these copolymers proceeds by both random and chain end scission. Continuous distribution kinetics was used to develop a model for photocatalytic oxidative degradation considering both random and specific end scission. The degradation rate coefficients were determined by fitting the experimental data with the model. The degradation rate coefficients of the copolymers decreased with increase in the percentage of alkyl acrylate in the copolymer. This indicates that the photocatalytic oxidative stability of the copolymers increased with increasing percentage of alkyl acrylate. From the degradation rate coefficients, it was observed that the photocatalytic oxidative stability follows the order PMMABA > PMMAEA > PMMAMA. The thermal degradation of the copolymers was studied by using thermogravimetric analysis (TGA). The normalized weight loss and differential fractional weight loss profiles indicated that the thermal stability of the copolymer increases with an increase in the percentage of alkyl acrylate and the thermal stability of poly(methyl methacrylate-co-alkyl acrylate)s follows the order PMMAMA > PMMAEA > PMMABA. The observed contrast in the order of photostability and thermal stability of the copolymers was attributed to different mechanisms involved for the scission of polymer chain and formation of different products in both the processes.     

Cyclopolycondensations. VI. Fully aromatic polybenzoxazinones from aromatic poly(amic acids)

New high temperature aromatic polybenzoxazinones of high molecular weight have been prepared by the cyclopolycondensation of 4,4′-diaminobiphenyl-3,3′-dicarboxylic acid (I) with aromatic dicarboxylic acid halides (II). The low temperature solution polymerization techniques afforded poly(amic acid) (III) of high molecular weight in the first step. An open-chain precursor subsequently underwent thermal cyclodehydration along the polymer chain at 200–350°C. in the second step, to give in quantitative yield a fully aromatic polybenzoxazinone (IV) of outstanding heat stability both in nitrogen and in air. The poly(amic acid) is soluble in N-methyl-2-pyrrolidone, and tough, transparent films can be cast from solution. Insoluble aromatic polybenzoxazinone films which possess excellent oxidative and thermal stability were obtained by the heat treatment of the polyamic acid. A detailed account of polymerization conditions in the low temperature solution polymerization of polybenzoxazinones is given, and the reaction mechanisms of cyclopolycondensation of poly(amic acids) and the formation of polybenzoxazinones are discussed.     

Thermal Degradation and Fire Behavior of High Performance Polymers

Abstract

High performance and high temperature polymers are a class of polymeric materials exhibiting high thermal stability and their resistance to fire makes them valuable assets for many applications. Those applications include as typical examples high temperature gas separation membranes, automotive and aerospace industry as well as the construction industry. The high performance polymers have been synthesized since the early 1960s, and have developed rapidly over the past few decades. Most high performance polymers comprise a highly aromatic backbone, linear chains, and strong inter-chain interactions. This review deals mostly with commercial polymeric materials. Studies regarding their thermal behavior, degradation mechanism and their reaction to fire have been synthetically combined in order to bring out potential insight concerning the effect of the thermal decomposition and thermal behavior on the fire properties of those polymers.     

Importance of bound water in hydration-dehydration behavior of hydroxylated poly(N-isopropylacrylamide)

In this study, a differential scanning calorimetric analysis was performed to investigate the role of water existing around the polymer chains on their thermoresponsive behaviors using the novel functional temperature-sensitive copolymer, poly(N-isopropylacrylamide-co-2-hydroxyisopropylacrylamide) (poly(NIPAAm-co-HIPAAm)). The HIPAAm comonomers were incorporated into the polymeric chains as hydrophilic parameters, and then the hydration states of poly(NIPAAm-co-HIPAAm) with various HIPAAm compositions were examined. Bound water, which is affected by the polymeric chains to some extent, was produced by adding the copolymers to the water, and the temperature due to the melting of the bound water decreased as the HIPAAm content increased. On the basis of this result, we considered that the interaction between the bound water and the polymeric chains is reinforced by the increasing HIPAAm composition. In addition, the cloud points of the copolymers shifted to a higher temperature, and the endothermic enthalpy for the phase transition decreased with increasing the HIPAAm content, suggesting that the number of water molecules disassociated from the polymeric chains decreased. Based on these results, we postulate that the changes in the interaction between the thermosensitive polymer and bound water exert a strong influence on its phase transition and/or separation, such as the cloud point or dehydration behavior.     

Development of Poly(Phenylene)-Based Materials for Thin Film Applications: Optical Waveguides and Low Dielectric Materials

Abstract

We have synthesized and evaluated poly(phenylene)-based materials made via spin-coatable polymeric precursors for such thin film applications as optical waveguides and low dielectric materials. Poly(phenylene) precursors were prepared by radical polymerization of cyclohexadiene-1, 2-diol derivatives containing various leaving groups. The precursors were converted into poly(phenylene) either by curing at 300°C or by deep-UV exposure in the presence of a photoacid generator. Poly(phenylene) has a number of desirable properties including good near-IR transmission, low dielectric constant, thermal and environmental stability, low water absorption, and ease of pattern fabrication using microlithographic techniques. Copolymer precursors based on 1,2-diaceto-3,5-cyclohexadiene and styrene derivatives as well as copolymers with Nsubstituted maleimide derivatives were prepared by radical copolymerization. The copolymer precursors were converted into poly(phenylene) copolymers either by annealing at 300°C or by deep-UV exposure in the presence of a photoacid generator. The results of this study indicate that copolymerization allows the incorporation of comonomers that can control dielectric and optical properties as well as glass transition temperature.     

Electrosynthesized, non-conducting films of poly(2-naphthol): electrochemical and XPS investigations

Advanced biosensors are frequently based on electrosynthesized polymeric films. In this context, the electrosynthesis mechanism underlying the electrochemical oxidation of 2-naphthol (2-NAP) in phosphate buffer at pH 7 on Pt electrodes has been investigated. The voltammetric behaviour suggested the formation of a non-conducting polymer (poly(2-NAP)) through an irreversible electrochemical process complicated by 2-NAP adsorption and fast electrode passivation. Repeat experiments showed the passive films to be strongly adherent to the Pt surface with thicknesses of approximately 10 nm, as estimated by in-situ electrochemical quartz crystal microbalance (EQCM) measurements and by X-ray photoelectron spectroscopy (XPS). The polymer structure was then investigated by XPS, which gave evidence of the presence of naphthalene rings bonded through poly(oxide) groups (C–O–C) and of quinonoid groups, probably present as the ends of polymeric chains. The polymer repeat unit and terminal groups derived by XPS analysis are in accordance with electrochemical results and with synthesis routes reported for phenol-derived compounds in aqueous solution. XPS also gave evidence of a large excess of oxygen, probably arising from water molecules entrapped by the polymeric chains, as suggested by angle-resolved XPS and thermal treatment of poly(2-NAP)/Pt film under ultra-high vacuum (UHV).