Effect of water sorption on oxygen‐barrier properties of aromatic polyamides

Aromatic polyamides based on poly(m‐xylylene adipamide) (MXD‐based polyamides) and poly(hexamethylene isophthalamide) (HMD‐based polyamides) were examined. Insight into the excellent gas‐barrier properties was obtained by the characterization of the effect of water sorption on the thermal transitions, density, refractive index, free‐volume hole size, and oxygen‐transport properties. Reversing the carbonyl position with respect to the amide nitrogen substantially lowered the oxygen permeability of MXD‐based polyamides in comparison with that of HMD‐based polyamides by facilitating hydrogen‐bond formation. The resulting restriction of conformational changes and segmental motions reduced diffusivity. The primary effect of water sorption was a decrease in the glass‐transition temperature (T_g) attributed to plasticization by bound water. No evidence was found to support the idea that sorbed water filled holes of free volume. When the polymer was in the glassy state, the drop in T_g accounted for hydration‐dependent changes in the density, refractive index, and free‐volume hole size. The correlation of the oxygen solubility with T_g and density confirmed the concept of oxygen sorption as filling holes of excess free volume. In some cases, water sorption produced a glass‐to‐rubber transition. The onset of rubbery behavior was associated with a minimum in the oxygen permeability. The glass‐to‐rubber transition also facilitated the crystallization of MXD‐based polymers, which complicated the interpretation of oxygen‐transport behavior at higher relative humidity. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1365–1381, 2005     

Water vapor sorption by fibers of aromatic polyamides

Isotherms of water vapor sorption by fibers of aromatic polyamides of several types have been obtained in a wide range of relative pressures (p/p _s from 0 to 0.8–0.9). It has been shown that different values of moisture sorption determined from sorption isotherms correlate with molecular and structural characteristics, such as the thermodynamic rigidity of macromolecules, the integral specific surface area with respect to an inactive sorbate (krypton), the average off-orientation angle, and the phase state of the structure. It has been speculated that a difference in the moisture sorption of the test fibers is primarily related to their phase structure, particularly, to the prevalence of either a mesophase or crystalline order.     

Water vapor sorption in naphthalenic sulfonated polyimide membranes

The water vapor uptake of sulfonated polyimides (SP) was investigated by electronic microbalance (IGA, Hiden) from 15 to 55°C. The sigmoïdal isotherms obtained (BET II type) are considered as dual sorption (concave part) plus clustering (convex part) and are fitted with good agreement by Park’s equation. Zimm–Lundberg’s method is used to study the clustering process of water molecules: limit clustering activity, a^*, and the number of molecules per cluster are estimated.

To obtain a better understanding of polymer structure and isotherm analysis, H⁺ (counter-ions of sulfonic groups) were replaced by ions with a smaller hydration shell (Cs⁺ and EDAH⁺). Comparison of the three isotherms shows no significant difference in the water affinity of the cations. This is attributed to a partial control of the sorption by microcavities existing in the membrane.     

Dendritic aromatic polyamides and polyimides

The syntheses and properties of dendritic and hyperbranched aromatic polyamides and polyimides are reviewed. In addition to conventional stepwise reactions for dendrimer synthesis, an orthogonal/double‐stage convergent approach and dendrimer syntheses with unprotected building blocks are described as new synthetic strategies for dendritic polyamides. Hyperbranched polyamides and polyimides composed of various repeating units are presented. Besides the self‐polycondensation of AB₂‐type monomers, new polymerization systems with AB₄, AB₈, A₂ + B₃, and A₂ + BB′₂ monomers have been developed for hyperbranched polyamides and polyimides. The copolymerization of AB₂ and AB monomers is discussed separately with respect to the effects of branching units on the properties. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1293–1309, 2004     

Dielectric relaxation studies of aromatic polyamides

Dielectric relaxation spectroscopy (DRS) is presented for a family of four aromatic polyamides trying to relate the structure of the lateral groups to the molecular mobility. A prominent sub-T_g absorption is always seen followed in some cases by remanent dielectric activity at room temperature and a subsequent increase of the loss permittivity. The low temperature relaxation is analyzed in terms of a Fuoss–Kirkwood equation to obtain the broadness and the strength of these relaxations as well as the activation energy (ranging from 10 to 11 Kcal/mol). The low frequency conductive peak shows in each case a half-width higher (1.30) than those corresponding to a single relaxation time peak (1.144). These values of the half-width are an indication of the complex character of these phenomena. A final discussion of the rotational barriers of the lateral chains rules out that such motions are the only molecular origin for the gamma relaxation. Instead, some kind of motion involving the main chain and where the interchain interactions play a significant role should be considered as responsible for that relaxation. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 919–927, 1997     

Water sorption and diffusion coefficients of protons and water in PVDF-g-PSSA polymer electrolyte membranes

Water sorption properties, proton NMR spectra, and diffusion of water and protons in poly(vinylidene fluoride)-graft-polystyrene sulfonic acid (PVDF-g-PSSA) polymer electrolyte membranes were studied. Sorption curves for the membranes with different degrees of grafting in protonated and Na⁺ form were measured by equilibrating the membranes over saturated salt solutions. The membrane water content was found to be sensitive to changes in relative humidity (RH). The water/sulfonic acid ratio λ for the protonated samples was around 2 at 20% RH and increased to λ ∼ 30 at 100%. Proton NMR, pulsed field gradient proton NMR (PFG-NMR), and impedance measurements were made on membranes with different λ. In the proton NMR spectra only one peak was found, originating from the water in the membrane. The chemical shift of the peak was found to be dependent on the counterion and the water content. The water self-diffusion coefficients D_H2O, measured by PFG-NMR, increased with degree of grafting and water content of the membranes. The proton conductivity and the calculated proton mobility decreased more steeply than the D_H2O with decreasing water content. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2893–2900, 1999     

Water sorption and permeation in chitosan films: Relation between gas permeability and relative humidity

The water sorption of chitosan has been studied at 20 °C. Water transport is governed by a Fickian process for relative humidities lower than 0.4, and in that range of partial pressures, the diffusion coefficient is concentration‐dependent. At a higher activity, anomalous diffusion is observed. The sorption isotherm is well described by the Guggenheim‐Anderson‐de Boer (GAB) model, and the clustering phenomenon observed at high relative pressures can be studied with the parameters of this model. The water permeability coefficient greatly increases with the relative pressure, and the water plasticization effect leads to a loss of the gas barrier properties under wet conditions. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 3114–3127, 2001     

Sorption and diffusion of water vapor in polyimide films

Sorption and diffusion of water vapor are investigated gravimetrically for polyimide films. The activity dependence of the solubility and diffusion coefficients, S and D, respectively, is classified under four types: (1) constant S and D type, (2) dual-mode sorption and transport type, (3) dual-mode type followed by a deviation due to a plasticization effect at high vapor activity, and (4) constant S and D type followed by a deviation due to water cluster formation at high activity. For the dual-mode type, the Henry's law component is much larger than the Langmuir component except at low activity, and therefore deviation in behavior from the first type is small. S is larger for polyimides with higher content of polar groups such as carbonyl, carboxyl, and sulfonyl. D is larger for polyimides with a higher fraction of free space, with some exceptions. The polyimide from 3,3′,4,4′-biphenyltetracarboxylic dianhydride and dimethyl-3,7-diaminodibenzothiophene-5, 5-dioxide belongs to the third type and displays both large S and large D. The polyimide from 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride and 4,4′-oxydianiline belongs to the fourth type, and has the largest D but rather small S because of the hydrophobic C(CF₃)₂ groups. © 1992 John Wiley & Sons, Inc.     

Synthesis and characterization of new soluble aromatic polyamides from diaminotetraphenylimidazolin-2-one and various aromatic dicarboxylic acid chlorides

Novel aromatic polyamides, having inherent viscosities of 0.76-2.31 dL/g, were synthesized by the low temperature solution polycondensation of a new highly phenylated diamine monomer having an imidazolinone group, 1,3-bis(4-aminophenyl)-4,5-diphenylimidazoline-2-one (TPIDA), with various aromatic diacid chlorides. All the polymers were amorphous, and most of the polyamides were readily soluble in organic solvents such as N-methyl–2-pyrrolidone, N,N-dimethylacetamide (DMAc), and m-cresol. Flexible and tough films could be prepared from the DMAc solutions of these soluble aromatic polyamides. The glass transition temperatures and 10% weight loss temperatures under nitrogen of the polyamides were in the range of 275–315°C and 430–505°C, respectively. © 1995 John Wiley & Sons, Inc.     

Proton magnetic relaxation in aromatic polyamides during water vapor sorption

The state of the components in the aromatic polyamide-water system was studied by NMR and sorption. A comparative analysis of spin-lattice and spin-spin relaxation in aromatic para-polyamide (para-aramid) technical fibers Rusar, Kevlar, and Technora was performed depending on the sorption value. The NMR results correlated with the supramolecular structure of polymers and quasi-chemical equation parameters for water vapor sorption. Original Russian Text ? T.V. Smotrina, Yu.S. Chulkova, D.V. Karasev, N.P. Lebedeva, K.E. Perepelkin, S.F. Grebennikov, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 7, pp. 1346–1351.     

Preparation and properties of aromatic polyamides from 1,4-bis(p-carboxyphenoxy)naphthyl and aromatic diamines

A new aromatic dicarboxylic acid, 1,4-bis (p-carboxyphenoxy)naphthyl ( 3 ), was synthesized by the reaction of p-fluorobenzonitrile with 1,4-naphthalenediol, followed by hydrolysis. Aromatic polyamides having inherent viscosities of 1.27–2.22 dL/g were prepared by the triphenyl phosphite activated polycondensation of diacid 3 with various aromatic diamines. Most of the resulting polymers showed an amorphous nature and were readily soluble in a variety of organic solvents including N,N-dimethyl-acetamide (DMAc), N-methyl-2-pyrrolidone (NMP), and m-cresol. Transparent, tough, and flexible films of these polymers could be cast from the DMAc or NMP solutions. The cast films had tensile strengths ranging from 64–104 MPa, elongations-at-break from 6 to 10%, and initial moduli from 1.52 to 2.14 GPa. These polyamides had glass transition temperatures in the range of 195 to 240°C. Almost all polymers were thermally stable up to 400°C, with 10% weight loss being recorded above 480°C in air and nitrogen atmospheres. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2273–2280, 1997     

Rigid aromatic fractal polyamides

The preparation of rigid aromatic, highly branched polyamides is described. Owing to the method of preparation and the chosen ratio of difunctional to trifunctional monomers, these entities are highly porous and not dendrimeric in nature. They better conform with the fractal model and are therefore called fractal polyamides (FPs). The effects of variations in the polymerization procedure, in total monomer concentration, in the ratio of amine to carboxyl groups and in the duration of the polycondensation reaction are investigated. Some characterization was performed and the results are presented and briefly discussed.     

Water sorption and diffusion studies in an epoxy resin system

The kinetics of water absorption in epoxide materials was studied by the aid of a diglycidyl ether of bisphenol‐A–triethylenetetramine (DGEBA–TETA) epoxy–resin system containing various amounts of the plasticizer THIOCOL (0–40 phr). The presence of plasticizer permits the formation of products with different crosslinking densities and hydrophilic characters. Dynamic water absorption experiments were carried out at 15, 40, and 70°C. For the fitting of the experimental results, a new model was used, based on a model proposed earlier by Jacobs and Jones. This model considers epoxide product as a two‐phase system consisting of a master phase (where the major part of the water is absorbed), which is homogeneous and nonpolar (phase 1), and of a second phase with different density and/or hydrophilic character (phase 2). By making the assumption that water diffusion can take place independently in the different phases of the material in accordance with Fick's second law, we can calculate the diffusion coefficient D and the water content at saturation M_∞ for each phase separately. Equilibrium water sorption measurements were performed at 40°C, and the data were analyzed and discussed based on the Guggenheim–Anderson–de Boer (GAB) equation, the results being in support of the two‐phase model used in the analysis of absorption kinetics. The linear expansion coefficient and the glass transition temperature of the materials, employed in the discussion of the results, were measured by thermomechanical analysis. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1165–1182, 1999     

High-resolution solid-state 19F-NMR spectroscopy of the sorption and diffusion of fluorine-containing aromatic molecules in polymeric media

High-resolution ¹⁹F solid-state NMR spectroscopy was employed to study the sorption properties of hexafluorobenzene (HFB) and 3,5-bis (trifluoromethyl) aniline (TFMA) in polystyrene (PS) and butyl rubber (BR). The NMR spectra indicate that the penetrants undergo dual-mode sorption in the glassy polymer (PS), but are highly mobile in the rubbery polymer (BR). In addition, the NMR method was utilized in the experimental determination of diffusion coefficients for the HFB/PS, TFMA/PS, and HFB/BR systems through desorption studies. The diffusion results for the TFMA/PS case agree very well with those previously obtained via resonance nuclear reaction analysis. © 1993 John Wiley & Sons, Inc.     

Mobility-sensitive fluorescence probes for quantitative monitoring of water sorption and diffusion in polymer coatings

The fluorescent molecular rotor probes 4-tricyanovinyl-[N-(2-hydroxyethyl)-N-ethyl]-aniline, tricyano-4-(dimethylamino) benzylidene, and tricyanovinyljulolidene have been used as extrinsic fluorescence probes for quantitative monitoring of water uptake in polymeric coatings. The presence of water causes plasticization of the polymer, which results in increased local mobility within the film. The nonradiative decay pathways of the rotor probes are increased as local mobility increases, and the resulting decrease in fluorescence intensity of the probes is directly proportional to the amount of water sorbed. Beyond allowing for the characterization of sorbent content, this fluorescence technique can be used to determine the diffusion coefficient of water in a polymer film. The relative change in fluorescence fits well to a Fickian diffusion model, yielding a diffusion coefficient for water of 3 × 10^-8 cm²/s in poly(vinyl acetate), and a value of 6 × 10^-9 cm²/s in a room-temperature cured epoxypolyamide, in excellent agreement with diffusion coefficient values determined from gravimetric analysis. Preliminary studies also demonstrate the utility of molecular rotor probes to monitor water uptake in individual layers of multilayered polymer systems. © 1995 John Wiley & Sons, Inc.     

Aromatic polyamides with pendant urea moieties

This work describes six novel aromatic polyamides with bulky pendant groups, each having a polyisophthalamide backbone substituted with different urea groups in ring position 5 of the diacid or the diamine residue. Thus, one of the nitrogen atoms of the urea is chemically anchored to the main rigid polyamide chain, while the other nitrogen atom is substituted by phenyl, nitrophenyl, naphthyl, and phenylureidophenyl groups. The polyamides are amorphous and soluble in polar aprotic solvents. They demonstrate a film‐forming capability with outstanding mechanical properties, and exhibit moderate thermal resistance in nitrogen and oxygen atmospheres. The urea group imparts hydrophilicity to the polymers, and facilitates the future preparation of specialty polymers through the easy chemical modification of this group. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4026–4036, 2007     

Synthesis and properties of aromatic polyamides based on non-, methyl-, and phenyl-substituted 4,4′-bis(1,4-phenylenedioxy)dibenzoic acids

4,4′-(1,4-Phenylenedioxy)dibenzoic acid (3), 4,4′-(2,5-tolylenedioxy)dibenzoic acid (Me-3), and 4,4′-(2,5-biphenylenedioxy)dibenzoic acid (Ph-3) were prepared by the nucleophilic substitution reaction of p-fluorobenzonitrile with hydroquinone, methylhydroquinone, and phenylhydroquinone, respectively, followed by alkaline hydrolysis. Several aromatic polyamides having inherent viscosities of 0.66–1.34 dL/g were directly prepared by a Yamazaki phosphorylation polyamidation technique from dicarboxylic acids 3, Me-3, and Ph-3, respectively, with aromatic diamines using triphenyl phosphite and pyridine as condensing agents. The solubility of methyl- or phenyl-substituted polyamides was remarkably enhanced when compared to that of nonsubstituted analogues. Most of the substituted polyamides revealed an amorphous nature and were readily soluble in a variety of organic solvents including N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide, dimethyl sulfoxide, and m-cresol. Transparent, flexible, and tough films of these polymers could be cast from the DMAc or NMP solutions. These films had tensile strength of 60–100 MPa, elongation to break of 6–11%, and tensile modulus of 1.68–2.25 GPa. The glass transition temperatures (T_g) of most polyamides could be determined by differential scanning calorimetry (DSC) and were in the range of 200–232°C. Thermogravimetric analyses established that these polymers were fairly stable up to 450°C, and the 10% weight loss temperatures were recorded in the range of 458–535°C in nitrogen and 468–528°C in air atmosphere. In general, the phenyl-substituted polyamides exhibited relatively higher T_g, thermal stability, and solubility. © 1996 John Wiley & Sons, Inc.     

Water vapor sorption and diffusion in glassy polymers

By establishing relationships between polymer structure and gas permeation behavior, significant advances have been made in designing materials for membrane separation of gas mixtures. However, the situation is not so well understood when water vapor is one of the components since water molecules may interact with the polymer (plasticization) or each other (clustering) in ways that complicate the structure-property relationships. In addition, accurate measurement of water sorption, diffusion, and permeation is more complicated than for gases because of the unique hydrogen bonding capability of water, e.g., its tendency to strongly adsorb on high-energy surfaces and high heat of vaporization. A progress report on a broad program to understand water sorption and diffusion in glassy polymers that may be of interest for membrane applications is outlined; specific strategies include studies of structurally related polymers and miscible blends of hydrophobic/hydrophilic polymer pairs.     

Synthesis of aromatic polyesters and polyamides by alternating copolymerizations of 1,4-dicarbonyl-1,4-dihydronaphthalene with bezoquinones and benzoquinone diimines

1,4-Dicarbonyl-1,4-dihydronaphthalene ( 1 ) was synthesized by the dehydrochlorination reaction of 1,4-dihydronaphthalene-1,4-dicarbonyl chloride with triethylamine and obtained as its very dilute solution, but it easily polymerized in the concentration as high as 0.1 mol/L to give its polymer. 1 generated in situ by the dehydrochlorination reaction of 1,4-dihydronaphthalene-1,4-dicarbonyl chloride in a deoxygenated toluene polymerized alternatingly with benzoquinones such as 2-dodecylthio-p-benzoquinone, 2,5-di(tert-butyl)-p-benzoquinone, p-benzoquinone, and 2,3-dichloro-5,6-dicyano-p-benzoquinone, and with benzoquinone diimines such as N,N′-diethoxycarbonyl-p-benzoquinone diimine, N,N′-dibenzoyl-p-benzoquinone diimine, and N,N′-diphenyl-p-benzoquinone diimine to give aromatic polyesters and polyamides, respectively. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1929–1936, 1998     

Chapman rearrangement in the synthesis of aromatic polyamides

It is established that N‐phenylsubstituted aromatic polyamides can be obtained via Chapman rearrangement of polybenzanyliminoesters synthesized by an interaction of bisphenols with imidoylchlorides. The rearrangements in melt or in film occur as a result of heating at 260–340 °C, and in a diphenyl ether solution rearrangement occurs at 240 °C. The resulting polymers are soluble in organic solvents and demonstrate high thermooxidative stability. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4656–4660, 2007