Mass DSC/TG and IR ascertained structure and color change of polyacrylonitrile fibers in air/nitrogen during thermal stabilization

The structure evolution was studied by mass spectrum (MS), differential scanning calorimetry (DSC) and thermogravimetry (TG), Fourier transform infrared (FTIR) spectroscopy. The results indicated that the CN and CC groups appeared gradually with the increase of the temperature in air and nitrogen. The CO groups appeared because of oxidative reaction in air. The CN, CC and CO groups were all chromophores. The effect of conjugated CN and CC on the absorption of the visible light was shifted to longer wavelengths and indicated π‐π* transition. There was a strong bathochromic effect as the number of CC bonds were increased. The effect of CO and –NH₂ on the absorption of the visible light was shifted to longer wavelengths and indicated n‐π* transition. Oxygen could facilitate chemical reactions in air. Hence, the color of PAN in air was deeper than in nitrogen at the same temperature. The structural change of PAN in air was faster and more complex than in nitrogen. PAN fibers treated in air turned black after 230°C. However, PAN fibers turned black at 350°C in nitrogen. The MS and FTIR indicated that cyclization occurred before dehydrogenation during stabilization in air and nitrogen. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Chelation of chitosan derivatives with zinc ions. II. Association complexes of Zn2+ onto O,N‐carboxymethyl chitosan

The chelation of zinc ions onto O,N‐carboxymethyl chitosan (ONCMCh) was characterized using a Fourier transform infrared (FTIR) spectrophotometer and a scanning electron microscope (SEM). From the FTIR spectra, little change in the absorption intensities and frequencies at 3300–3600 cm⁻¹ of Zn²⁺ ONCMCh chelated specimens suggested that  OH and  NH₂ groups were not participating in the chelation reaction. The absence of absorption bands at 1755–1700 cm⁻¹ suggested that the carboxyl group CO was not ionized, and the ionized CO bands were observed at 1400–1600 cm⁻¹ for chelated specimens. Thus, the chelation sites took place at the carboxyl group rather than at the  OH and NH₂ groups. It also confirmed that water‐insoluble chelates, which were formed through the Zn O and Zn N bonds, presented a tetrahedral structure. The water‐soluble complexes where zinc ions connected with oxygen of CO and water molecules were only due to electron attraction. Formation of different microstructures on the surfaces, as revealed by SEM, provided evidence to distinguish different chelating mechanisms between water‐soluble and water‐insoluble complexes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1476–1485, 2001     

FTIR equivalent weight determination of perfluorosulfonate polymers

Fourier transform infrared (FTIR) and attenuated total reflectance (ATR) spectroscopy studies of the sulfonyl fluoride, potassium salt, and sulfonic acid forms of long and short side chain perfluorosulfonate polymers revealed bands indicative of the sidegroup and backbone compositions, endgroups on the main chain, water content, monomer concentration, and degree of salt hydrolysis. The equivalent weight (EW) of the polymer was obtained by titration and NMR measurements which were then calibrated to either the C F/C O C absorbance band ratio for thin (<1.1 mil) films or to a C F/SO₂F absorbance band ratio for thick films (5 to 25 mils). An FTIR measurement of the film thickness based on the C F group concentration was found to be both a function of the actual thickness and the EW; a method for compensating for this EW dependence is described. Esterification and fluorination of the polymers yielded FTIR measurements of the endgroup compositions on the polymer backbone which were shown to consist of  COF,  COOH,  CO₂CH₃, and  CFCF₂ groups. Thermogravimetric Analysis Infrared (TGA‐IR) spectroscopy of the acid form polymers indicates that degradation begins by the decomposition of the  SO₃H group at 320°C followed by bulk deterioration above 400°C. The FTIR techniques detailed herein have been developed for accurate, reproducible, and rapid compositional measurements of Nafion® and other perfluorosulfonate polymers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Enhanced photoreactivity of MOFs by intercalating interlayer bands via simultaneous ?NCO and ?SCu modification

Herein, we propose a novel method to enhance the photoreactivity of an MOF catalyst by grafting isocyanate bonds ( NCO) and sulfhydryl-complexed copper ( SCu) onto ZIF-8 (NIF-SCu). The grafting process intercalated interlayer bands between the conduction and valence bands of ZIF-8, thereby providing a “ladder” for facile electron transition. The extreme improvement in the photoreactivity of NIF-SCu could be attributed to the enhancement in light responses in the range of 350–450 nm by  NCO groups and the widening of the visible light range of the MOF by  SCu groups. The formation of staggered energy levels in NIF-SCu could also narrow the band gap, lower the resistance, and facilitate the transfer of photogenerated carriers, thereby generating electrons with strong reduction potential in the  SCu conduction band. This study provides a new strategy for improving or even endowing the photoactivity of environmental functional materials with wide bandgaps.     

Efficient synthesis of phosphorus containing melamine salt for enhancing flame retardancy of poly(lactic acid)/polyamide 11 blends

A tetrakis (melamine)-1-hydroxyethylidene-1,1-diphosphonic acid salt (EA-MEL) was synthesized by a straightforward acid–base neutralization reaction between 1-hydroxyethylidene-1,1-diphosphonic acid (EA) and melamine (MEL). This compound, which contains phosphorus and nitrogen elements, exhibits a 40% carbon residue at a temperature of 800°C. When combined with diethyl aluminium hypophosphite (OP1230) as a flame-retardant composite in polylactic acid (PLA)/polyamide 11 blends through melt blending, a synergistic effect between the two flame retardants is observed. Consequently, the limiting oxygen index value significantly increases to 34.3, showcasing a remarkable 64.6% improvement. Additionally, the material achieves a V-0 rating according to UL-94 standards, and the peak heat release rate drops to 269 kW∙m⁻² with the addition of just 5 wt% EA–MEL. These results demonstrate that EA-MEL and OP1230 contribute to the generation of phosphoric acid derivatives and the formation of a crosslinked ( P N )_n or ( P O N )n network. This network enables the formation of a complete, compact, and expanded char residue, effectively isolating heat and oxygen.     

1,3-Diaza-2-azoniaallene Salts as Novel N3-Building Blocks: Preparation and cycloadditions to alkenes,alkynes, carbodiimides,and cyanamides

1,3-Diaza-2-azoniaallene salts R¹-NN⁺N R² 6 represent a new functional group. 1,3-Disubstituted triazenes 8 are oxidized with tert-butyl hypochlorite to stable open-chain N-chlorotriazenes R¹ NN NCl R² 9 , which at low temperatures with Lewis acids afford the reactive intermediates 6 . The salt 6a is stable below −50 °C and was characterized by spectroscopic and analytical data. Heterocumulenes 6 behave as positively charged 1,3-dipoles undergoing cycloadditions to many different multiple bonds to furnish 1,2,3-triazolium and tetrazolium salts, e.g. to both electron-rich and electron-deficient alkenes, alkynes, to one or both double bonds of 1,3-butadienes, to carbodiimides, and cyanamides (1,3-dipolar cycloaddition with inverse electron demand). With an allene, a butatriene and a pentatetraene the 4,5-dihydro-1H-1,2,3-triazolium salts 17–19 were obtained. The constitutions of four of the products were secured by X-ray structural analyses. 4,5-Dihydro-1H-1,2,3-triazolium salts 11 and 1H-1,2,3-triazolium salts 20 are aza analogues of Arduengo's and Wanzlick's nucleophilic carbenes.     

Preparation of tetrafluoro-λ6-sulfanyl bridged-bonding perfluoroalkyl styrene and its emulsion copolymerization with acrylate monomers for cotton fabrics finishing

4-(Perfluorobutyl)styrene, 4-(Perfluorohexyl)styrene, 4-[Perfluorobutyl(tetrafluoro-λ⁶-sulfanyl)]styrene (C₄F₉ SF₄ styrene), and 4-[Perfluorohexyl(tetrafluoro-λ⁶-sulfanyl)]styrene (C₆F₁₃ SF₄ styrene) were prepared in two or three steps. The short-chain perfluoroalkyl groups are modified through the insertion of tetrafluoro-λ⁶-sulfanyl linked groups ( SF₄ ). The prepared perfluoroalkyl styrene acts as functional monomers to react with butyl acrylate, methyl methacrylate, and hydroxyethyl methacrylate for emulsion copolymerization to obtain side-chain fluoropolymers. The long-chain fluoropolymer formed in contrast to the tetrafluorosulfanyl ( SF₄ ) modified ones. The emulsions were applied on cotton fabrics to give hydrophobicity. The result showed that the fabrics treated with tetrafluorosulfanyl-modified fluoropolymers were more hydrophobic, indicating that the introduction of  SF₄ was beneficial to provide lower surface energy and obtain better water repellent performance. The water contact angles record the varying degrees of variation in polymer degradation under UV exposure. The result showed that, as the perfluoroalkyl is bonded by  SF₄ , when comparing with the carbon-chain perfluoroalkyl polymer, the tetrafluorosulfanyl-modified fluoropolymer is more degradable during UV irradiation.     

Study of microbial polyhydroxyalkanoates using two-dimensional Fourier-transform infrared correlation spectroscopy

The premelting behavior of bacterially synthesized polyester poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), abbreviated as P(HB-co-HHx), was investigated by two-dimensional Fourier-transform infrared (2D FTIR) correlation spectroscopy. The temperature-dependent dynamic spectra were measured over a temperature range of 25–300°C. We focused our study on the thermally induced intensity fluctuations of bands for CO (1700–1760 cm⁻¹), C H (2910–3010 cm⁻¹) and C O C groups (1220–1310 cm⁻¹) stretching vibrations. Changes of crystalline conformation due to the thermal perturbation could be detected by the intensity and location variations of those characteristic bands responding to the variations of dipole moments. 2D correlation analysis indicated that the appearance of fully amorphous component did not happen simultaneously with the disappearance of crystalline component, suggesting that there was an intermediate state between ordered crystalline and amorphous states in P(HB-co-HHx). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 934–940, 2001     

Rhodium(III)‐Catalyzed in situ Oxidizing Directing Group‐ Assisted C?H Bond Activation and Olefination: A Route to 2‐Vinylanilines

A new and efficient method for the synthesis of 2‐vinylanilines from the reaction of arylhydrazine hydrochlorides with alkenes and diethyl ketone via a rhodium‐catalyzed C H activation is described. The oxidant‐free olefination reaction involves the in situ generation of an  N NCR¹R² moiety as the oxidizing directing group thus providing an easy access to 2‐vinylanilines.

     

Correlation of chemical shrinkage of polyacrylonitrile fibres with kinetics of cyclization

It has been established that the most important step in the production of carbon fibres from polyacrylonitrile (PAN) precursor fibres is the oxidative thermal treatment applied. During this treatment, physical phenomena and chemical reactions take place accompanied by the shrinkage of the fibres, which has a physical or chemical origin, depending on the nitrile cyclization reactions. The aim of the present study is to establish a correlation between the chemical shrinkage of PAN fibres and the kinetics of cyclization reactions. Based on the isothermal treatment of PAN fibres, we developed a method in order to distinguish between physical and chemical shrinkages. The onset time for the chemical shrinkage follows a relationship with temperature. Chemical shrinkage versus cyclization time data were fitted with the exponential rise to the maximum of the curves. Furthermore, the cyclization kinetics was studied using differential scanning calorimetry and the kinetic parameters determined were identical to those calculated from the chemical shrinkage, demonstrating that the latter is directly related to the kinetics of the cyclization reactions. It was therefore concluded that according to the method developed to distinguish the physical from the chemical shrinkages: (1) there exists a certain onset time for a given treatment temperature to trigger the chemical shrinkage; (2) cyclization reactions do not start below a limiting temperature of 168 °C; (3) at 340 °C, the temperature where the cyclization reactions are completed, the maximum shrinkage is 24%; and (4) the oxidized PAN fibres contain mainly ladder polymer structures with approximately symmetrical sequences connected in angled positions. Copyright © 2007 Society of Chemical Industry     

Über die strukturanalystische Anwendung von „anomalen”︁ Multipletts in off-resonance entkoppelten 13C-NMR-Spektren von ?CH  CH?Fragmenten

On the Structural Analytical Application of „Anomalous”︁ Multiplets in Off-resonance Decoupled ¹³C NMR Spectra of  CH  CH Fragments The theoretical background of “anomalous” splitting of signals of molcular fragments  CHCH in off-resonance decoupled ¹³C NMR spectra is described. The use of these splitting phenomena on the determination of vicinal H,H and geminal C,H coupling constants is demonstrated using simple examples. The possibilities to determine the configuration of double bonds are shown by other examples from the field of natural constituents chemistry.     

Relation between hydrophilicity and cell culturing on polystyrene Petri dish modified by ion‐assisted reaction

Polystyrene Petri dishes were modified by an ion‐assisted reaction to supply a suitable surface for culturing cells. Wettability was measured by a contact anglometer after surface modification of polystyrene. Contact angles of water on the polystyrene were not reduced much by Ar⁺ ion irradiation only, but dropped rapidly to a minimum of 19°, when polystyrene surface was modified by Ar⁺ ion irradiation with flowing oxygen gas. X‐ray photoelectron spectroscopy analyses showed that hydrophilic groups were formed on the surface of polystyrene by a chemical reaction between unstable chains induced by the ion irradiation and the blown oxygen gas. Newly formed hydrophilic groups were identified as C O,  (CO) and  (CO) O bonds. The influence of the ion beam modification in growth of the rat pheochromocytoma cells was investigated. The results showed exclusively preferential cell growth in the polystyrene Petri dish that was treated by the ion‐assisted reaction. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 41–46, 1999     

Solid-phase synthesis,reaction mechanism of biomass glycerol metal chelates and its thermal stability property for polyvinyl chloride

To explore the simple preparation method of glycerol metal chelates and effectively expand the application field of glycerol metal chelates and biomass glycerol, the micro-nanopowders such as glycerin zinc (Gly-Zn), and glycerin bismuth (Gly-Bi) were prepared by the solid-phase reaction, using sodium benzene sulfonate as a catalyst and template. Theoretical calculation of deprotonation reaction energy of glycerol and zinc chloride, bismuth nitrate was performed with the framework of DFT, and their structures were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscope and X-ray photoelectron spectroscopy. The thermal stability of Gly-Zn and Gly-Bi for polyvinyl chloride (PVC) is discussed by TG. The results show that the deprotonation reaction of glycerol with zinc chloride or bismuth nitrate mainly occurs in the dehydrogen of secondary hydroxyl ( O_secH) and primary hydroxyl ( O_primH) of glycerol molecules, and the H of  O_secH is more active than that of the  O_primH. The obtained Gly-Zn and Gly-Bi have good micromorphology with the rod-like and bar-like respectively. Applied them as thermal stabilizers to PVC processing, the reaction kinetic constant (k, s⁻¹) is an order of k_PVC > k_PVC/Gly-Zn > k_PVC/Gly-Bi. After the additions of 10% Gly-Zn and 10% Gly-Bi, the thermal stability time (min) of PVC, PVC/Gly-Zn and PVC/Gly-Bi is 45, 54.43 and 71.47, respectively.     

Effect of cupric ion on thermal degradation of chitosan

The thermal degradation of chitosan and chitosan–cupric ion compounds in nitrogen was studied by thermogravimetry analysis and differential thermal analysis (DTA) in the temperature range 30–600°C. The effect of cupric ion on the thermal degradation behaviors of chitosan was discussed. Fourier transform-infrared (FTIR) and X-ray diffractogram (XRD) analysis were utilized to determine the micro-structure of chitosan–cupric ion compounds. The results show that FTIR absorbance bands of  N H,  C N ,  C O C etc. groups of chitosan are shifted, and XRD peaks of chitosan located at 11.3, 17.8, and 22.8° are gradually absent with increasing weight fraction of cupric ion mixed in chitosan, which show that there are coordinating bonds between chitosan and cupric ion. The results of thermal analysis indicate that the thermal degradation of chitosan and chitosan–cupric ion compounds in nitrogen is a two-stage reaction. The first stage is the deacetylation of the main chain and the cleavage of glycosidic linkages of chitosan, and the second stage is the thermal destruction of pyranose ring of chitosan and the decomposition of residual carbon, in which both are exothermic. The effect of cupric ion on the thermal degradation of chitosan is significant. In the thermal degradation of chitosan–cupric ion compounds, the temperature of initial weight loss (T_st), the temperature of maximal weight loss rate (T_max), that is, the peak temperature on the DTG curve, and the peak temperature (T_p) on the DTA curve decrease, and the reaction activation energy (E_a) varies with increasing weight fraction of cupric ion. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Dyeability of cellulose fibers using dyestuff from African rosewood (Pterocarpus erinaceous)

Methanol extracted from the “heart wood” of the plant Pterocarpus erinaceous (African rosewood) gave a brick red dyestuff. Chromatographic separation of the dye produced a single homogenous component with an Rf value of 0.78, a yield of about 17.3% and a melting point of 86°C. IR spectrum of the purified dye showed the presence of an aromatic CC double bond band at 1620–1470 cm⁻¹ and NH₂ absorption characteristic of an aromatic amine N H stretch at 3590–3400 cm⁻¹, while para‐disubstitution on aromatic nucleus was observed at 850–840 cm⁻¹. A wavelength of maximum absorbance, λ_max, of 500 nm was recorded on a UV/visible scan for the solvent soluble dye. The dye, which was substantive to cotton, was applied quantitatively to it and reed fibers by exhaust dyeing technique from locally distilled alcohol. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 746–751, 2000     

UV‐induced crosslinking and cyclization of solution‐cast polyacrylonitrile copolymer

An alternative, rapid stabilization route for polyacrylonitrile (PAN) precursors is reported based on UV‐induced crosslinking and cyclization reactions. Two mechanisms of photoinitiation were investigated: homolytic cleavage and hydrogen abstraction. Solution‐cast PAN copolymer samples were irradiated for different durations (100, 300, and 600 s) and temperatures (～65 and 100°C, below and above glass transition temperature respectively). FTIR spectra show the formation of carbon–oxygen, carbon–nitrogen, and carbon–carbon double bonds (1450–1700 cm^?1 region) attributed to the development of cyclized structure. Conversion indices estimated from the FTIR spectra indicate samples containing hydrogen abstraction photoinitiator show higher extents of cyclization among the three main set of samples. This observation was also confirmed by higher gel percentages measured on the same set of samples. FTIR conversion indices of samples UV‐treated above glass transition temperature were higher compared with that for the same specimens UV‐treated below glass transition temperature. DSC results show that samples containing hydrogen abstraction photoinitiator enable a higher extent of post‐UV thermal cyclization. FTIR spectra of the UV treated samples were compared with conventional thermal stabilized specimens. This comparison confirms that the addition of 1 wt % photoinitiator to PAN followed by 5 min of UV treatment increases the rate of the cyclization reaction and reduces the thermal oxidation time by over an hour, which could significantly reduce the conventional stabilization time by half. These results indicate the potential for an energy‐efficient, cost‐effective route for producing carbon fibers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermal decomposition of poly(glycidyl azide) as studied by high-temperature FTIR and thermogravimetry

Thermal decomposition of poly(glycidyl azide) (PGA) has been studied by using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and high-temperature FTIR spectrometry. By using DSC and TGA techniques, the first stage weight loss of PGA due to exothermic decomposition of pendant azide ( N₃) groups was explained in terms of the energy released at every stage of decomposition. From the glass transition temperature (T_g) measurements, it was observed that T_g values of PGA increased with increasing quantity of decomposed  N₃ groups. The course of the decomposition reaction was also studied by taking successive FTIR spectra. It was observed that during the first stage weight loss process of PGA, the main chain was not decomposed thermally; inter- and intramolecular linking reactions accompanied the side chain decompositions. © 1996 John Wiley & Sons, Inc.     

Chain-Extended bismaleimides. I. Preparation and characterization of maleimide-terminated resins

Starting from aromatic diamines, a series of bismaleimides (BMIs) and maleimide-terminated structural resins were prepared in solution and characterized. Maleimide-terminated resins were prepared through Michael addition reaction with 3/2 molar ratio of bismaleimide and aromatic diamine as reactants. The structural analysis was performed by FTIR and ¹H-NMR spectroscopy. Thermal properties are investigated by TGA, DTA, and DSC. Number-average molecular-weights of the resins were determined by cryoscopy. The presence of methylene ( CH₂ ) and ether ( O ) groups in the starting materials affect the reactivity and the degree of chain extension of the resins. From the viscosity measurements it was also found that thermal polymerization of BMIs could be taking place together with the Michael addition. © 1996 John Wiley & Sons, Inc.     

Structure evolution mechanism of polyacrylonitrile films incorporated with graphene oxide during oxidative stabilization

Oxidative stabilization is a key process for polyacrylonitrile (PAN)-based carbon materials. During this process, oxygen has a significant influence on the formation of cyclization structure and crosslinking structure of PAN matrix. Here, graphene oxide (GO) was used as filler in PAN matrix, the structure evolution of GO/PAN composite was studied during oxidative stabilization. Solubility measurement revealed that the crosslinking degree increased, while the cyclization degree of stabilized films decreased after GO incorporation. The effect of GO on the structure of PAN film was characterized by XRD, DSC, DMA, FTIR, and XPS. These results verified that GO could initiate the cyclization reaction of PAN at a lower temperature. The carboxylic groups on GO sheets might take part in the cyclization reactions during the heat treatment. Moreover, the oxygen-containing molecules released from GO decomposition during the heat treatment were beneficial to the formation of crosslinking structure. The possible mechanism of the structure evaluation was proposed in this article. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47701.     

Phosphorus-Containing polyurethanes based on bisphenol-AF,prepared by N-alkylation

Phosphorus-containing polyurethanes (PU-P) based on bisphenol-AF were synthesized by N-alkylation in a two-step process. First, the polymer was metalated with sodium hydride; then the prepared urethane polyanion was treated with diethyl 2-bromoethyl phosphate. IR spectra exhibited characteristic absorptions at 1303 cm⁻¹ (PO stretch), 1015 cm⁻¹ (CH stretch), 1646 cm⁻¹ (CO stretch), 1231 cm⁻¹ (CNH), and 1053 cm⁻¹ (CO O C stretch). In the ¹H-NMR spectrum of the maximum substituted PU-P, the signal of the urethane proton (NH  CO O) at 9.87 ppm virtually disappeared as expected; new signals appeared at 1.20–1.24 ppm (POCH₂CH ₃) and 3.79 ppm (POCH ₂CH₃). Physical and thermal properties of the N-alkylated polymer were also investigated with differential scanning calorimetry (DSC), solubility, X-ray diffraction, thermogravimetric analysis (TGA), limiting oxygen index (LOI), and reduced viscosity. DSC analysis showed that T_g values were decreased from 81 to 43°C. The reduced viscosities of the PU-Ps were observed in the range of 0.23–0.18 dL g⁻¹. The results of TGA revealed that the thermal stability was decreased, because the phosphorus moiety in the PUs is readily dissociated thermally. The PU-Ps exhibited enhanced fire resistance because phosphorus simultaneously promoted carbonization of the polymer and inhibited combustion. The X-ray diffraction patterns of the PU-Ps showed that with increasing phosphorus content, the degree of crystallinity of the PUs decreased. N-alkylated PUs are soluble, not only in polar solvents such as N,N-dimethylformamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, and H₂SO₄, but also in less polar solvents such as phenol, toluene, THF, and trichloroethylene. © 1996 John Wiley & Sons, Inc.