Complex formation and degradation in poly(acrylonitrile‐co‐vinyl acetate) containing copper nitrate

The pyrolysis of polymers containing metal nitrates may provide a relatively simple, rapid, and advantageous method of producing high‐temperature superconductors (HTSCs). The advantage lies in the ability to use conventional polymer processing or microlithographic patterning before pyrolysis. A copolymer of acrylonitrile and vinyl acetate [P(AN‐VA)], a well‐known fiber‐forming polymer, was investigated as a potential HTSC precursor. Complex formation with the highly polar acrylonitrile groups was expected to enhance atomic‐level mixing and hinder nitrate recrystallization. The metal nitrates were found to have a profound effect on P(AN‐VA) pyrolysis. P(AN‐VA) containing copper nitrate (CuN) exhibited complex formation and an exothermic decomposition that began at about 170 °C (reaction 1‐CuN). Reaction 1‐CuN had a heat of about 3.5 kJ/g_NO3 and a mass loss of about 0.99 g/g_NO3. As reaction 1‐CuN also involved the nitrile groups, it disrupted the nitrile cyclization reaction at about 290 °C. For a P(AN‐VA)/CuN ratio of 2/1, there was no nitrile cyclization, and the thermooxidative degradation temperature was reduced by approximately 200 °C. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1023–1032, 2004     

Thermal stability of modified telechelic polystyrenes

The thermal stability of telechelic polystyrenes bearing quaternary ammonium iodide or ammonium sulfonate end groups is presented. It appears that the ammonium iodide functions are stable below 200°C. Above that temperature, the polystyrene irreversibly looses its functional end groups. The weight loss then observed leads to the conclusion that a Hofmann-type degradation mechanism is likely to take place. In contrast, the ammonium sulfonate-terminated polystyrene begins to degrade at 180°C and leads to a polymer which is no longer end-capped with sulfonic acid or sulfonate groups. This behavior is of importance, especially for the study of multiblock ionic copolymers which are prepared by blending two telechelic polymers, one of them bearing sulfonic acid end groups and the other one tertiary amine functional groups. © 1993 John Wiley & Sons, Inc.     

Complexation of sequence-ordered methacrylic acid copolymers with poly(4-vinylpyridine)

The complexation of three kinds of sequence-ordered acid (co)polymers with a base homopolymer was studied. The acid polymers used are poly(methacrylic acid) 1 , alternating (1:1) ethylene-methacrylic acid copolymer 2 , and periodic (2:1) ethylene-methacrylic acid copolymer 3 , and the base polymer is poly(4-vinylpyridine) 4. When mixing a methanol solution of 1, 2 , or 3 with that of 4 (0.1 M of each functional group), precipitate was formed immediately for all polymer pairs. All the precipitates contained carboxyl and pyridyl groups in ca. 1:1 molar ratio and showed IR spectra indicating the hydrogen bonding between carboxyl and pyridyl groups. When mixing dilute methanol solutions (10⁻⁴M) of the above polymer pairs, no precipitation was observed, but the extinction coefficient (ϵ_B) at 255 nm of pyridyl groups in 4 was found to increase with an increasing acid polymer concentration. This is ascribed to hydrogen bonding between carboxyl and pyridyl groups in methanol. Based on the ϵ_B variation, the order of complexation constants for acid/base polymer pairs was estimated as follows: 1/4 pair ∼ 2/4 pair ≫ 3/4 pair. © 1996 John Wiley & Sons, Inc.     

Synthesis of polybenzimidazoles with sulfonic acid groups

2-Sulfoterephthalic acid (STA) and disulfoisophthalic acid (DSIA) were synthesized through the sulfonation and the oxidation of m- and p-xylene. The polycondensation reactions of STA and DSIA with aromatic tetraamines gave polybenzimidazoles which contained one or two sulfonic acid groups for each repeating unit. The polymer obtained was soluble in sulfuric acid, some organic solvents, and aqueous strong alkaline solution. The polymers were stable up to 400°C, but they gave polybenzimidazoles above 400°C by eliminating sulfonic acid groups, instead of ring closure.     

Synthesis and properties of novel benzimidazole‐containing sulfonated polyethersulfones for fuel cell applications

A novel series of benzimidazole‐containing sulfonated poly(arylene sulfones)s with controllable amount of basic 2,6‐bis(benzimidazol‐2‐yl)pyridine (BIP) and sulfonic acid groups have been prepared by the copolycondensation of a new BIP‐containing arylene difluoride monomer (DFSBIP) with a sulfonated arylene difluoride (DSDFS) and 4,4′‐biphenol (BP). All the resulting polymers have high molecular weights, good thermal stability, and can form uniform and tough membranes by simple solution casting. Because of the strong acid–base interaction between BIP and sulfonic acid groups, ionic crosslinking networks forms that resulted in polymer membranes with good dimensional stability in water even at high temperature (e.g., 100 °C). The ion exchange capacity (IEC) of the polymer membranes was investigated through a new simple pH‐determination method. A comparison between the experimental IEC values with the calculated ones based on the polymer structures indicated that each BIP unit interacted with one sulfonic acid group. Thus, by controlling the relative content of BIP units and sulfonate groups in the polymers, the intra‐ and intermolecular acid–base interactions could be readily optimized so as to achieve polymers with high IEC values, high proton conductivities as well as low swelling ratios, demonstrating good potential for proton exchange membrane applications. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1920–1929, 2009     

Thermostable poly(p-phenylene sulfide sulfonic acid) as ion exchangers

Poly(p-phenylene sulfide sulfonic acid) was thermally crosslinked for use as a cation exchange polymer with high thermal stability. The decomposition temperature (T_d) of the polymer increases with an increase in the crosslinking temperature. The crosslinking reaction at 300°C in air resulted in the formation of a strongly acidic cation exchange polymer with a T = 467°C and having an SO₂ bond, whose crosslinked structure was investigated using IR spectroscopy.     

The Polymerization of 1,3-Dioxolane Catalyzed by Ion Exchange Resin (Polystyrene Sulfonic Acid)

Polystyrene sulfonic acid resin (Amberlyst 15) was found to initiate the cationic polymerization of 1,3-dioxolane easily in bulk at 0 to 50° C, and polymers with a reduced viscosity of 0.1 were obtained. However, this resin showed only low initiator activity for the polymerizations of 2-methyl-1, 3-dioxolane and trioxane.     

Halogenated polymeric humidity sensors

The limitations of known organic polymer humidity sensors in humidity-sensing applications may be overcome through the use of halogenated organic polymers having pendant groups of both a relatively strong acidic type and a relatively weak acidic type. The combined advantages of halogen in the polymer and the presence of two pendant functional groups provides for a longer sensor life and stability.Thin membrane films of hygroscopic, fluorinated organic polymer having pendant functional groups of sulfonic acid and of carboxylic acid have been investigated for their electrical and thermodynamic characteristics for humidity sensing at high levels of relative humidity and elevated temperatures. Based on the measured conductance data, values of differential thermodynamic functions of enthalpy and entropy are found to be significantly larger than those previously obtained for a sensor system at relative humidities and temperatures above 70% and 50 °C respectively.     

Influence of heat treatment conditions on the porosity changes of sulfonated styrene/divinylbenzene copolymers

Sulfonic cation exchangers with two ion exchange group concentrations (0.5 and 2.4 mmol/g, samples A and B, respectively) were obtained by sulfonation of a porous styrene (S) and divinylbenzene (DVB) copolymer with chlorosulfonic acid. Strong thermal decomposition of the sulfonated copolymer A, accompanied by significant changes in its porous structure, starts at ca. 400°C. The char has no sulfonic groups. After heat treatment at 400°C in steam, a sorbent was obtained (yield 65%) that shows higher phenol sorption than the untreated sample when related to the bed volume. The chlorosulfonic derivatives of the initial copolymer were less thermally resistant than the sulfonic ones obtained by hydrolysis. Pyrolysis of the cation exchanger B, in its H+ and Ca²⁺ forms, was carried out at 900°C (yield of both chars close to 30%). By subsequent steam activation at 800°C to a 50% burn-off of the char, sorbents with well-developed, but distinctly different, porous structures were obtained. The activated char from the sulfonated copolymer in its hydrogen form was highly microporous and indicated an effective surface area of 1180 m²/g. However, because of a low contribution of mesopores, its ability to adsorb phenol from the liquid phase was not very high. The activated char from the calcium-doped copolymer, indicating a smaller surface area (580 m²/g) but characterized by a well-developed mesoporosity, was a better sorbent for phenol. © 1994 John Wiley & Sons, Inc.     

Thermal decomposition of polymer mixtures of PVC,PET and ABS containing brominated flame retardant: Formation of chlorinated and brominated organic compounds

The thermal decomposition of various mixtures of acrylonitrile butadiene styrene copolymer (ABS), ABS containing brominated epoxy resin flame retardant and Sb₂O₃, poly(ethylene terephthalate) (PET) and poly(vinyl chloride) (PVC) has been studied in order to clarify the reactions between the components of mixed polymers. More than 40 halogen-containing molecules have been identified among the pyrolysis products of mixed samples. Brominated and chlorinated aromatic esters were detected from the mixtures containing PET and halogen-containing polymers. A series of chlorinated, brominated and mixed chlorinated and brominated phenols and bisphenol A molecules have been identified among the pyrolysis products of polymer mixtures containing flame retarded ABS and PVC. It was established that the decomposition rate curves (DTG) of the mixtures were not simple superpositions of the individual components indicating interactions between the decomposition reactions of the polymer components. The maximal rate of thermal decomposition of both ABS and PET decreases significantly if the mixture contains brominated epoxy flame retardant and Sb₂O₃ synergist. The dehydrochlorination rate of PVC is enhanced in the presence of ABS or PET.     

Thermal degradation and evolved gas analysis of thiourea-formaldehyde resin (TFR) during pyrolysis and combustion

Thiourea formaldehyde resin (TFR) has been synthesized by condensation of thiourea and formaldehyde in acidic medium and its thermal degradation has been investigated using TG-FTIR-MS technique during pyrolysis and combustion. The results revealed that the thermal decomposition of TFR occurs in three steps assigned to drying of the sample, fast thermal decomposition of polymers, and further cracking. The similar TG and DTG characteristics were found for the first two stages during pyrolysis and combustion. The combustion process was almost finished at 680?°C, while during pyrolysis a total mass loss of 93 wt% is found at 950?°C. The release of volatile products during pyrolysis are NH₃, CS₂, CO, HCN, HNCS, and NH₂CN. The main products in the second stage are NH₃ CO₂, CS₂, SO₂, and H₂O during combustion. In the next stage, the combustion products mentioned above keep on increasing, but some new volatiles such as HCN, COS etc., are identified. Among the above volatiles, CO₂ is the dominant gaseous product in the whole combustion process. It is found that the thermal degradation during pyrolysis of TFR produced more hazardous gases like HCN, NH₃, and CO when compared with combustion in similar conditions.     

Study on thermal decomposition processes of polysiloxane polymers—From polymer to nanosized silicon carbide

The objective of this study is to determine experimentally the usefulness of different polysiloxanes as precursors for bulk ceramic products. Such resins are an alternative for currently commercially used polycarbosilanes. Four types of polysiloxanes were used. The polymers differed in C/Si molar ratio. Thermogravimetric measurements of polymers were made to determine curing and heat treatment conditions. Ceramic yield (Y_c) after heat treatment over the temperature range from 20 to 1700 °C was determined. Structure, microstructure and phase composition of ceramic products obtained from the polymers were investigated. It was found that during thermal decomposition of polymers in the temperature range from 20 to 1000 °C amorphous inorganic Si–C–O ceramics were formed. When the temperature exceeded 1500 °C nanosized 3C and 2H types of silicon carbide crystallized from the resin precursors with C/Si molar ratio higher than 1. On the contrary, heat treatment of polymer with C/Si molar ratio close to 1 did not lead to the formation of nanocrystalline silicon carbide.     

Novel sepiolite reinforced emerging composite polymer electrolyte membranes for high-performance direct methanol fuel cells

Methanol permeation is the main issue of Nafion membranes when they are used as a polymer electrolyte membrane (PEM) in direct methanol fuel cells (DMFCs). In the current study, novel nanocomposite polymer membranes are prepared by the integration of surface-modified sepiolite (MS) in polyvinylidene fluoride grafted polystyrene (PVDF-g-PS) copolymer as PEM in DMFCs. Sepiolite (SP) surface is chemically modified using vinyltriethoxysilane and analyzed by Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Nanocomposite PVDF-g-PS/MS membranes are prepared by phase inversion technique and subsequently treated with chlorosulfonic acid to induce sulfonic acid (SO₃H) active sites at the membrane surface. The prepared nanocomposite membranes (S-PPMS) are analyzed for their physicochemical characteristics in terms of water uptake percentage, cation exchange capacity, proton conductivity (σ), and methanol permeability. MS dispersion in the copolymer matrix is proved through morphological SEM examination. The S-PPMS membranes exhibit increased proton conductivity due to the presence of well-dispersed MS and surface functional –SO₃H groups. A peak power density of 210 mWcm^?2 is recorded for S-PPMS10 at 110 °C, which is higher than the output obtained from Nafion-117. These promising results indicate the potential utilization of prepared nanocomposite PEMs for DMFC application.     

Poly(N-acylethylenimine) copolymers containing pendant pentamethyldisiloxanyl groups. III. Surface properties and abhesion

The surface properties and abhesion of both N/Si and U/Si series of random copolymers were studied by contact angle and peel strength measurements. When these copolymers are coated on clean glass slides, the contact angles of water on the polymer films are over 105° for copolymers with less than 50 mol % of Si , and 98-104° for those with more than 50 mol % of Si. All the polymers have similar critical surface energies, 21 dyn/cm (from hydrocarbon probes) and 20 dyn/cm (from EtOH/H₂O probes), within the experimental error. This demonstrates that the amide groups in the polymer backbones are buried and all the polymers have methyl surfaces. The copolymers with less than 50 mol % Si (for N/Si copolymers) or 20 mol % (for U/Si copolymers) are stable and show good abhesive properties toward Scotch magic tape at or below 50°C. The peel strengths of Scotch magic tape with the copolymer coated slides rise dramatically as the annealing temperatures approach to the melting points of the polymers.     

Chlorinated products of plastic pyrolysis

The formation of various chlorinated products in pyrolysis of polymers and plastics additives was studied. Formation of chlorobenzenes (in addition to the monomers) from poly(chlorostyrene) and poly(vinylbenzyl chloride) was observed. Hydrogen chloride is only produced from these polymers at above 600 °C when the chlorine atoms are cleaved off and abstract hydrogen. A similar process takes place in aromatic chlorine-containing dyes, in which the strong aromatic molecular structure prevents the thermal cleavage of chloroaromatic volatile products. We have observed that cupric and ferric chlorides chlorinate phenolic thermal decomposition products of plastic materials which originate either from the polymer or from the stabilizer. The highest yields of chlorophenols are obtained in pyrolysis at around 700 °C.     

Superacid polymers from sulfonated poly(styrene-divinylbenzene): Preparation and characterization

Superacid polymers were prepared by bringing metal halides (AlCl₃, SnCl₄, TiCl₄, BF₃, or SbF₅) in contact with macroporous sulfonic acid resins [sulfonated, crosslinked poly(styrene-divinylbenzene)]. The resulting solids were characterized by chemical analysis, temperature-programmed desorption, transmission electron microscopy, and X-ray photoelectron spectroscopy. They were also tested as catalysts for n-butane isomerization at 0.5 bar and 60 to 120°C. The polymers consist of supported metal oxyhalide particles, complexes of metal oxyhalides and sulfonate groups, and the remaining unreacted sulfonic acid groups. In the presence of HCl, these polymers were highly active catalysts for the butane isomerization reaction, the activity being a consequence of a high proton-donor strength inferred to be associated with H₂Cl⁺ groups stabilized on the polymer surface by negative charge delocalization over sulfonate–metal oxyhalide sulfonate groups.     

Facile synthesis and characterization of the copolymers and their pure nanoparticles from aniline with 4‐sulfonic diphenylamine

Copolymer nanoparticles from aniline (AN) and 4‐sulfonic diphenylamine (SDP) were simply synthesized for the first time by an oxidative precipitation polymerization with inorganic oxidants in an acidic aqueous medium without any external emulsifier or stabilizer. The polymerization yield, intrinsic viscosity, solubility, solvatochromism, electrical conductivity, and thermal stability of the copolymers were systematically studied through changes in the AN/SDP ratio, polymerization temperature, oxidant species, monomer/oxidant ratio, and acidic medium. The molecular structure of the copolymers was characterized with elemental analysis, IR, and ultraviolet–visible spectra. The polymers exhibited very good solubility in polar solvents, water, and NH₄OH, and this was mainly attributable to the presence of sulfonic acid side groups. The electrical conductivity of the copolymers increased greatly, from 6.00 × 10^?4 to 2.55 × 10^?1 S/cm, with increasing AN content. The size of the copolymer particles, determined by laser particle analysis and atomic force microscopy (AFM), strongly depended on the polymer state and oxidant/monomer ratio. Pure dedoped particles of the AN/SDP (50/50) copolymer at an oxidant/monomer ratio of 1/2 exhibited minimum length/diameter ratios of 62/44 and 45/30 nm by AFM and transmission electron microscopy, respectively. The copolymers showed typical four‐step weight‐loss behavior in nitrogen and air and higher thermostability in nitrogen. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3380–3394, 2004     

Film‐formation property of vinylidene chloride‐methyl methacrylate copolymer latex. II. Effect of latex storage temperature

Changes in the minimum film‐formation temperature (MFFT) of 91:9 wt % vinylidene chloride (VDC)‐methyl methacrylate (MMA) latex prepared by the seeded batch process during storage at 5, 20, and 40 °C were investigated. MFFT of the latex rose the fastest at 20 °C. Infrared absorption of fresh and stored latexes and wide‐angle X‐ray diffraction of powder polymers obtained by lyophilization of fresh and stored latexes indicated a much greater increase in polymer crystallinity during latex storage at 20 °C than at 5 and 40 °C. Observed increases in MFFT during latex storage correlated with increases in polymer crystallinity. Infrared absorption of polymer stored at 5–60 °C in the dry state, such as lyophilized polymer and coating film, indicated that a polymer crystallinity increase was greater during storage at higher temperatures. These results showed that crystallization behavior of 91:9 wt% VDC‐MMA copolymer latex differed from that of VDC‐MMA copolymer in the dry state. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 948–953, 2002     

Sulfonic and Phosphonic Acid and Bifunctional Organic–Inorganic Hybrid Membranes and Their Proton Conduction Properties

Hybrid organic–inorganic approaches are used for the synthesis of bifunctional proton exchange membrane fuel cell (PEMFC) membranes owing to their ability to combine the properties of a functionalized inorganic network and an organic thermostable polymer. We report the synthesis of both sulfonic and phosphonic acid functionalized mesostructured silica networks into a poly(vinylidenefluoride‐co‐hexafluoropropylene) (poly(VDF‐co‐HFP) copolymer. These membranes, containing different amounts of phosphonic acid and sulfonic acid groups, have been characterized using FTIR and NMR spectroscopy, SA‐XRD, SAXS, and electrochemical techniques. The proton conductivity of the bifunctional hybrid membranes depends strongly on hydration, increasing by two orders of magnitude over the relative humidity (RH) range of 20 to 100 %, up to a maximum of 0.031 S cm⁻¹ at 60 °C and 100 % RH. This value is interesting as only half of the membrane conducts protons. This approach allows the synthesis of a porous SiO₂ network with two different functions, having  SO₃H and  PO₃H₂ embedded in a thermostable polymer matrix.     

Matched ring diblock and linear triblock copolymers in dilute solution

A unique diblock copolymer ring and its linear triblock copolymer precursor composed of polystyrene and polydimethylsiloxane have been characterized by static and dynamic light scattering in dilute solution. The measurements were carried out with cyclohexane as the solvent over a temperature range of 12–35°C. Cyclohexane has the useful property that it is nearly isorefractive with the PDMS so that the PDMS block segments are invisible to the light-scattering technique and it is a theta solvent for polystyrene at 34.5°C. The block polymers in this work contain 35.1 wt % of styrene as determined by proton NMR. In the linear triblock polymer, the polystyrene is the center block with PDMS blocks on each side. Static light scattering measurements give 4.31 × 10⁴ for the average molecular weight of the whole polymer. Light scattering also shows that the apparent theta temperature for the linear triblock is shifted by 15°C to a value of 20°C at which point the second virial coefficient drops sharply and phase separation begins to induce aggregation. The diblock ring, however, shows a strongly positive second virial coefficient and no aggregation even at 12°C which is the limit of these experiments. The diffusion coefficients of cyclic diblock (D_c) and linear triblock copolymer (D₁) are measured by dynamic light scattering. The ratio of diffusion coefficients of cyclic and linear copolymers at 14.9°C and 30°C are D_c/D_l = 1.13 and 1.107 respectively. These compare well with prediction of 1.18 for this ratio from consideration of the hydrodynamics of matched linear and cyclic polymer chains. Dynamic light scattering quantitatively confirms that the linear copolymer experiences a solvent quality change near 20°C but the cyclic polymer remains in good solvent over the entire experimental temperature range. © 1993 John Wiley & Sons, Inc.