Meta-phenylene Units Research Articles

Ferromagnetic spins interaction in networked triarylamine polymers

Two hyperbranched polymers containing star-shaped conjugated triarylamine units altered with meta-phenylene units were synthesized. The polymers can be oxidized on chemically or electrochemically to radical cations which are the sources of electronic spins. The presence of meta-phenylenes in the polymers chemical structures allows for the ferromagnetic coupling of electronic spins which leads to the formation of high spin states. Quantitative magnetization measurements show that the doped polymers exhibit mainly S=3/2 or S=1 spin states, depending on the triarylamine couplers. The ferromagnetic exchange coupling constant J=+1meV was estimated for the polymer 2, assuming a Heisenberg-type exchange.

Novel Self-Dyed Wholly Aromatic Polyamide-Hydrazides Covalently Bonded with Azo Groups in Their Main Chains: 1. Structure-Property Relationships

Twelve novel intrinsically colored wholly aromatic azopolyamide-hydrazides containing various proportions of para- and meta-phenylene units were successfully synthesized by a low temperature (−10 °C) solution polycondensation reaction of either 4-amino-3-hydroxybenzhydrazide (4A3HBH) or 3-amino-4-hydroxybenzhydrazide (3A4HBH) with an equimolar amount of either 4,4′-azodibenzoyl chloride (4,4′ADBC), 3,3′-azodibenzoyl chloride (3,3′ADBC), or mixtures of various molar ratios of 4,4′ADBC and 3,3′ADBC in anhydrous N,N-dimethyl acetamide (DMAc) containing 3% (wt/v) LiCl as a solvent. The structures of the polymers were proven by elemental analysis, FTIR, 1H- and 13C-NMR spectroscopy. The polymers’ properties were strongly affected by their various structures. The intrinsic viscosities of the polymers were ranged from 0.7 to 4.75 dL g−1 and increased with the para-phenylene units content. The polymers are partially soluble in DMAc, dimethyl formamide (DMF) and N-methyl-2-pyrrolidone (NMP). Their solubility increases with the introduction of meta-phenylene moieties into the polymer chains. The polymers exhibit a great affinity for water sorption. Their hydrophilicity increases as a function of the content of meta-phenylene rings incorporated into the polymer. Mechanical properties of the polymer films are improved markedly by substitution of para-phenylene units for meta-phenylene units. The completely para-oriented type polymer has the best thermal and thermo-oxidative stability relative to those of the other polymers.

Synthesis and photophysical properties of poly(aryleneethynylene)s bearing dialkylsilyl side substituents

A series of poly(aryleneethynylene)s bearing dialkylsilyl (–SiR 2H) side substituents has been synthesized by Sonogashira cross-coupling reactions of 1,4-diethynyl-2,5-bis(dialkylsilyl)benzene and diiodoarylene compounds. Their photophysical properties in solution have been studied. All of the polymers showed intense fluorescence with high quantum yield. Compared with their analogues containing para-phenylene units, the polymers with meta-phenylene units in the main chain showed absorption and emission maxima at shorter wavelengths, whereas the polymers having thiophenylene units in their backbones showed bathochromically shifted spectra. For polymers having the same conjugated parent backbone, silyl substituents have been found to exert negligible effect on their photophysical properties.

Structure–property relationships for novel wholly aromatic polyamide–hydrazides containing various proportions of para-phenylene and meta-phenylene units—V: Evaluation of the electrical surface conductivity of several metallized plastic films

Electrical conductivities of several metallized polyamide–hydrazide films have been investigated. These metallized plastic films were prepared by reduction of the corresponding polyamide–hydrazide-transition metal complex films using sodium boron hydride (NaBH 4). The metals incorporated into the polymeric chains include silver, copper, and cobalt. The effect of NaBH 4 concentration, temperature and time of exposure on the conductivity of the polyamide–hydrazide–metal complex films has been studied. The optimum effect was attained using 4–6 wt% of NaBH 4 aqueous solution for about 2–3 min exposure at 60–80 °C. The electrical resistivities are in the range of 10 −6–10 3 Ω cm −2, and are influenced by the type of metal incorporated into the polymeric chains. They decrease in the following order: Co>Cu>Ag. For a particular metal, the surface resistivity of the films decreases with increasing metal content. The metallic layer generated on the surfaces of the films upon reduction was believed to be responsible for their electrical conductivity. Moreover, the surface resistivity is also affected by polymer structural variations and is decreased by increasing para-oriented phenylene ring content of the polymer. The metallized films showed good environmental stability.

Synthesis and characterization of novel wholly aromatic azopolyamide-hydrazides

The influence of controlled structural variations upon the physical, thermal and mechanical properties of a series of novel wholly aromatic azopolyamide-hydrazides has been investigated. The polymers were prepared by a low temperature solution polycondensation reaction of p-aminosalicylic acid hydrazide (PASH) and an equimolar amount of either 4,4′-azodibenzoyl chloride (4,4′ADBC), 3,3′-azodibenzoyl chloride (3,3′ADBC), or their appropriate combinations in anhydrous N, N-dimethyl acetamide (DMAc) as solvent at −10 °C. The content of para-/ meta-phenylene units was varied within this series between 50/50 and 100/0. Polymer structures were characterized by elemental analysis and infrared spectrometry. Polymer properties were evaluated by intrinsic viscosity, solubility, moisture regain, thermal and thermo-oxidative stability, mechanical properties and X-ray diffraction. The results obtained during the preparation of these polymers, their subsequent structural characterization and their property evaluations are discussed. All the polymers have the same structural formula except the way of linking phenylene units inside the polymer chain. The polymers intrinsic viscosities were ranged from 1.5 to 4.3 dl g −1 in DMAc/3% LiCl at 25 ± 0.1 °C and increased with the increase of para-phenylene units content. The polymers are found to be partially soluble in polar aprotic solvents like DMAc, dimethyl formamide [DMF], and N-methyl pyrrolidone (NMP) at room temperature. Their solubilities in these solvents were found to be enhanced remarkably by adding LiCl and their solutions could be cast into flexible films. All the polymers dissolved freely in concentrated sulphuric acid but with degradation. The polymers having para-linkages in this series are less soluble than the polymers having meta-linkages. The prepared polymers exhibit a great affinity to water sorption. The hydrophilic character increases as a function of meta-phenylene rings content incorporated into the polymer. Thermogravimetric measurements indicated that the perfectly p-oriented type of polymer has better thermal and thermo-oxidative stabilities relative to that of the other polymers. Mechanical properties of the polymers films are improved markedly with introduction of para-phenylene nuclei into the polymers. All these polymers were found to be amorphous as confirmed by X-ray diffraction.

Structure–property relationships for novel wholly aromatic polyamide-hydrazides containing various proportions of para-phenylene and meta-phenylene units : IV Preparation and characterization of metallized plastic films through transition metal complexation

A series of metallized plastic films based on several polyamide-hydrazides has been synthesized. Metallization process was achieved via complexation of the polymers with various transition metal salts, followed by surface modification of the resulting complex films by a chemical reduction. The complexation reaction was simply carried out by stirring the mixed N, N-dimethylacetamide [DMAc] solutions of the polymer and the metal salt at room temperature overnight. The metals incorporated into the polymeric chains include silver, copper and cobalt. The complex solutions appeared clear, highly viscous, colored and could readily be cast into films. The complex films were further modified by a chemical treatment using an aqueous sodium boro hydride solution. The complexes were investigated by elemental analyses, infrared spectra and ultraviolet-visible spectrophotometry. The results revealed that metal ions were complexed with polymer repeating unit by a ratio of 1:1. These complexes showed a good solubility in several common organic solvents. Scanning electron microscopy and X-ray diffraction were employed to characterize the surfaces of the complex films before and after modification. Upon treatment with a reducing agent, all the complex films showed a significant change in their colors to a shiny metallic appearance. Their surfaces changed from smooth to very rough appearance as observed by scanning electron microscope. This can be attributed to the abundant aggregation of metal particles on the surfaces of the complex films which develop to form a metallic surface layer. This result is strongly evidenced by X-ray diffraction. All the metal complexes showed better thermal and thermooxidative stability relative to those of the corresponding polymers in terms of initial degradation temperatures as well as residual weight (%) at a particular temperature. The data also demonstrate how the thermal and thermooxidative stability of these complexes are significantly affected both by the type of the metal incorporated and by the nature of the polymer. Further, the metallized films maintain good mechanical properties.

Structure–property relationships for novel wholly aromatic polyamide–hydrazides containing various proportions of para-phenylene and meta-phenylene units III. Preparation and properties of semi-permeable membranes for water desalination by reverse osmosis separation performance

Abstract Flat sheet asymmetric reverse osmosis membranes were successfully prepared from N , N -dimethylacetamide (DMAc) solutions of a series of novel wholly aromatic polyamide–hydrazides that contained different amounts of para - and meta -phenylene rings. These polyamide–hydrazides were synthesized by a low temperature solution polycondensation reactions of either 4-amino-3-hydroxybenzhydrazide or 3-amino-4-hydroxybenzhydrazide with an equimolar amount of either terephthaloyl dichloride [TCl], isophthaloyl dichloride [ICl] or mixtures of various molar ratios of TCl and ICl in anhydrous DMAc as a solvent. All the polymers have the same structural formula except of the way of linking phenylene units inside the polymer chains. The content of para - to meta -phenylene moieties was varied within these polymers so that the changes in the latter were 10 mol% from polymer to polymer, starting from an overall content of 0–100 mol%. All the membranes were characterized for their salt rejection (%) and water permeability (cm 3 cm −2 day −1 ) of 0.5 N aqueous sodium chloride feed solution at 3924 kPa operating pressure. The effects of polymers structural variations together with several processing parameters to achieve the best combination of high selectivity and permeability were studied. Effects of various processing parameters of the membranes on their transport properties were investigated by varying the temperature and period of the solvent evaporation of the cast membranes, coagulation temperature of the thermally treated membranes, annealing of the coagulated membranes, casting solution composition, membrane thickness and the operating pressure. During the thermal treatment step, the asymmetric structure of the membranes with a thin dense skin surface layer supported on a more porous layer was established. The former layer seems to be responsible for the separation performance. The results obtained showed that membrane performance was very much influenced by all of the examined processing variables and that membranes with considerably different properties could be obtained from the same polymer sample by using different processing parameters. Thus, the use of higher temperatures and longer exposure times in the protomembrane forming thermal treatment step would result in a membrane of lower solvent content and with a thicker skin layer and consequently led to higher salt rejection at lower water permeability. Most significantly, the membrane properties clearly depended on the polymer structure. Under identical processing condition, substitution para -phenylene rings for meta -phenylene ones within the polymer series resulted in an increase in salt rejection capability of the membranes. This may be attributed to an increase in their chain symmetry associated with increased molecular packing and rigidity through enhanced intermolecular hydrogen bonding. This produces a barrier with much smaller pores that would efficiently prevent the solute particles from penetration. Coagulation temperature controls the structure (porosity) of the membrane particularly its supported layer and consequently its water permeability. Moreover, annealing of the prepared membranes in deionized water at 100 °C was found essential for useful properties in the single-stage separation applications, which required optimum membrane selectivity. Upon annealing, the membrane shrinks resulting in reducing its pore size particularly in the skin layer and consequently improving the salt rejection. Addition of lithium chloride to the casting solution produced a membrane with increased porosity and improved water permeability. Salt rejection capability of the membranes is clearly affected by the applied pressure, reaching its maximum at nearly 4000 kPa. Furthermore, the water permeability is inversely proportional to the membrane thickness, while the salt rejection is not substantially influenced.

Structure–property relationships for novel wholly aromatic polyamide–hydrazides containing various proportions of para-phenylene and meta-phenylene units: I. Synthesis and characterization

A series of novel wholly aromatic polyamide–hydrazides was synthesized by a low temperature solution polycondensation reaction of either 4-amino-3-hydroxybenzhydrazide or 3-amino-4-hydroxybenzhydrazide with an equimolar amount of either terephthaloyl chloride (TCl), isophthaloyl chloride (ICl), or mixtures of various molar ratios of TCl and ICl in anhydrous N, N-dimethylacetamide (DMAc) as a solvent. Polymer structures were identified by elemental analysis and infrared spectroscopy. All the polymers have the same structural formula except the way of linking phenylene units inside the polymer chain. The content of para- and meta-phenylene moieties was varied within this series so that the changes in the latter were 10 mol % from polymer to polymer, starting from an overall content of 0–100 mol %. The prepared polymers were characterized for their properties in order to acquire clear understanding of the influence exerted by controlled structural variations in these polymers upon some of important properties, such as solubility, intrinsic viscosity, moisture regain, mechanical properties and thermal as well as thermo-oxidative stability. The polymers were readily soluble in several organic polar solvents such as DMAc, N, N-dimethylformamide, dimethyl sulphoxide, N-methyl-2-pyrrolidone and hexamethyl phosphoramide and could be cast into flexible films. Their solubilities were found to increase remarkably with introduction of meta-phenylene moieties into the polymer chains. Their intrinsic viscosities ranged from 0.73 to 4.83 dl g −1 in DMAc at 30 °C and increased with the increase of para-phenylene units content. Mechanical properties of the films produced from these polymers are improved markedly by substitution of para-phenylene units for meta-phenylene units. Thermogravimetric studies revealed that the completely para-oriented type of polymer has better thermal and thermo-oxidative stability relative to that of the other polymers. Moreover, the results reveal that the prepared polymers have a great affinity to water sorption. The hydrophilic character increases as a function of meta-oriented phenylene rings incorporated into the polymer chains.

Crystallization, melting, and relaxation of modified poly(phenylene sulfide). II. Dynamic relaxation characteristics

Abstract The relaxation characteristics of a series of random PPS copolymers based on sodium hydrosulfide (NaSH) and 1,4- and 1,3-dichlorobenzene monomers have been investigated via dielectric and dynamic mechanical methods. Comparison of dielectric and dynamic mechanical glass-rubber (α) relaxation temperatures measured for the crystallized copolymers with their amorphous analogues indicated that the presence of meta-phenylene defects led to a progressive reduction in the degree of constraint imposed by the crystallites on the relaxing amorphous chains. Estimation of the mobile amorphous phase fraction in the crystallized samples based on dielectric relaxation intensity revealed complete mobilization of the rigid amorphous phase above Tg for those copolymers containing 8% and 10% meta-phenylene units. Examination of the subglass (β) relaxation in the amorphous samples showed that the introduction of meta segments in the polymer chain backbone produced a positive offset in relaxation temperatures and a co...

Crystallization, melting, and relaxation of modified poly(phenylene sulfide). I. Calorimetric studies

Abstract The crystallization, melting, and glass-rubber relaxation characteristics of a series of random poly(phenylene sulfide) (PPS) copolymers based on sodium hydrosulfide (NaSH) and 1,4- and 1,3-dichlorobenzene monomers have been investigated; sample compositions included the PPS homopolymer, and copolymers incorporating 5%, 8%, and 10% meta-phenylene linkages. The introduction of increasing levels of meta-phenylene units led to a modest decrease in amorphous glass transition temperature (from 86°C [0%] to 74°C [10%]) and a strong decrease in equilibrium melting temperature as determined by Hoffman-Weeks extrapolation(from 331°C[0%] to 273°C [10%]). Wide-angle x-ray scattering (WAXS) studies indicated that the meta units were excluded as defects from the bulk crystal structure, with no variation in unit cell parameters. Measurements of glass transition temperature for the crystallized polymers revealed a significant positive offset in Tg with the presence of crystallinity owing to the constraints impo...

Wholly aromatic polyamide‐hydrazides. IV. Structure–property relationships for polymers containing p‐phenylene and m‐phenylene units

AbstractA series of wholly aromatic polyamide‐hydrazides was investigated in order to acquire clear understanding of the influence exerted by controlled structural variations in these polymers upon some of important properties, such as chain flexibility, membrane permselectivity, and thermal as well as thermo‐oxidative stability. For that reason, the content of para and meta phenylene units was varied within this series so that the changes in the latter were 12.5 mol % from polymer to polymer, starting from an overall content of 0–50 mol %. The polymers were prepared by a low‐temperature solution polycondensation reactin of p‐aminobenzhydrazide (ABH) and terephthaloyl chloride (TCI), isophthaloyl chloride (ICI), and their appropriate combinations in N,N‐dimethylacetamide (DMA) as solvent and all of these preparations were monitored viscometrically in order to prepare the products with as similar as possible average molecular weights. Polymer structures were characterized by elemental analysis, infrared spectrometry, and 13C NMR spectroscopy, while their molecular weights were determined by light scattering and dilute‐solution viscometry. Polymer properties were evaluated by solution viscometry, reverse osmosis tests, and thermal gravimetric analysis. The results obtained during the preparation of these materials, their subsequent structural characterization, and their property evaluations are discussed. They clearly indicate that substitution of m‐phenylene units for p‐phenylene ones within this polymer series led to an increase in polymer chain flexibility (from what is usually referred to as semiflexible or semirigid to typically flexible macromolecules), disrupted selectivity of the asymmetric thin membranes under reverse osmosis conditions and decreased stability at elevated temperatures in inert as well as in oxidative atmospheres.