Design of composite films and ultrathin membranes of interpolymer complexes

The formation of stoichiometric interpolymer complexes (IPCs) between the poly(vinyl ether) of ethyleneglycol and the copolymer of acrylic acid–butyl vinyl ether, between copolymers of vinyl ether of ethyleneglycol–butyl vinyl ether, and the copolymer of acrylic acid–vinylbutyl ether is demonstrated by conductimetric, potentiometric, viscometric and spectroturbidimetric methods in aqueous solution. The swelling/deswelling behavior of composite films derived from the IPC has been studied in water, alcohol and water–alcohol mixtures, depending on various factors. The formation of polyelectrolyte complexes (PECs) between the copolymer of acrylic acid–vinyl butyl ether and poly(vinyl ether of monoethanolamine) on a dimeric interface of water–butanol has been studied by the potentiometric method. The kinetics of PEC formation on a dimeric interface was measured and the activation energy of this process was calculated. Copyright © 2000 John Wiley & Sons, Ltd.     

Designing aromatic polyamides and polyimides for gas separation membranes

Aromatic polyamides and polyimides with improved gas permselectivity, can be designed and prepared by systematically changing structural elements that affect these properties. Indeed, a conscientious choosing of the chemical changes may still provide a promising approach to get better and better polymers for selective filtration of gases. The results of this work, in which novel monomers have been used, have confirmed that gas permeability through aromatic polyamides and polyimides much higher than that of conventional polyamides and polyimides can be achieved. It has been done by introducing bulky side groups, using non-planar monomers, and combining these elements on both monomers: diamines and dianhydrides or diamines and diacids. A theoretical study has also been made to explain the behaviour of some individual polymers, comparing experimental and calculated values of density and free volume.     

Helical polymers based on intramolecularly hydrogen-bonded aromatic polyamides

Inspired by arylamide-based oligomeric foldermers that are stabilized by intramolecular hydrogen bonding, a series of polyamides with intramolecular hydrogen-bonding motifs were synthesized via polycondensation reactions. These polymers can fold into helical conformation different from their linear control. The chirality of helical conformation can further be tuned via acid-base complexation using chiral residues.     

Preparation and characterization of aromatic polyamides based on ether-sulfone-dicarboxylic acids

Two ether-sulfone-dicarboxylic acids, 4,4′-[sulfonylbis(2,6-dimethyl-1,4-phenylene)dioxy]dibenzoic acid (Me- III ) and 4,4′-[sulfonylbis(1,4-phenylene)dioxy]-dibenzoic acid ( III ), were prepared by the fluorodisplacement of 4,4′-sulfonylbis(2,6-dimethylphenol) and 4,4′-sulfonyldiphenol with p-fluorobenzonitrile, and subsequent alkaline hydrolysis of intermediate dinitriles. Using triphenyl phosphite (TPP) and pyridine as condensing agents, aromatic polyamides containing ether and sulfone links were prepared by the direct polycondensation of the dicarboxylic acids with various aromatic diamines in the N-methyl-2-pyrrolidone (NMP) solution containing dissolved calcium chloride. The inherent viscosities of the resulting polymers were above 0.4 dL/g and up to 1.01 dL/g. Most of the polyamides were readily soluble in polar solvents such as NMP, N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO), and afforded tough and transparent films by solution-casting. Most of the polymers showed distinct glass transition on their differential scanning calorimetry (DSC) curves, and their glass transition temperatures (T_g) were recorded between 212–272°C. The methyl-substituted polyamides showed slightly higher T_gs than the corresponding unsubstituted ones. The results of the thermogravimetry analysis (TGA) revealed that all the polyamides showed no significant weight loss before 400°C, and the methyl-substituted polymers showed lower initial decomposition temperatures than the unsubstituted ones. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2421–2429, 1997     

A new class of pressure-sensitive adhesives based on interpolymer and polymer-oligomer complexes

On the basis of previous concepts concerning the molecular nature of pressure-sensitive adhesion, a simple method of preparing new adhesives with the desired mechanical and adhesive behavior and water-absorbability via mixing of nonadhesive polymers has been developed. Pressure-sensitive adhesion is related to the combination of a high energy of cohesion and a large free volume, which leads to a high molecular mobility. This method is based on the formation of interpolymer or polymer-oligomer complexes during mixing of macromolecules capable of hydrogen, electrostatic, or ionic bonding. In interpolymer complexes, a high cohesion results from the formation of bonds between macromolecules carrying complementary groups in main chains, whereas free volume is related to defectiveness of the resulting network and formation of loops. In complexes formed by a high-molecular-mass polymer and an oligomer carrying complementary reactive groups at ends of short chains, a high energy of cohesion is related to their interaction with mainchain functional groups of the polymer, whereas a relatively large free volume is associated with the length and flexibility of intermacromolecular crosslinks via oligomer chains. The adhesive and viscoelastic properties of adhesives and their water absorbability are regulated by changes in the composition of mixtures of a film-forming polymer with a polymer or oligomer crosslinker and a plasticizer. In this case, an increase in cohesive strength is achieved owing to an increase in the crosslinker concentration, while the enhancement of free volume is ensured by the increasing plasticizer content in the blend. Adhesive materials capable of adherence to wet substrates, hydroactivated adhesives, and adhesion moisture sorbents have been prepared for the first time.     

Conformational energies of aromatic polyamides

PCILO conformational calculations have been made on several model compounds of aromatic polyamides. The calculated structures can be compared with the X-Ray crystallographic analyses and related to the physical properties of these polymers. Poly-p-phenylene terephthalamide appears as a more flexible polymer than poly-p-benzamide.     

Broad-line NMR of aromatic polyamides

Broad-line NMR spectra have been obtained at 90 MHz in the temperature region 140–530°K for four aromatic polyamides: poly(1,3-phenylene isophthalamide), poly(1,4-phenylene terephthalamide), poly(4,4,-diphenylene terephthalamide), and poly(4,4,-diphenylene isophthalamide). For the latter three materials, a broad-line narrowing process occurs in the 210–370°K region. At temperatures above 340°K a complex line shape is observed for all samples. Possible causes of these processes are discussed, and comparison made with dynamic mechanical results.     

Solution behavior of sulfonate ionomer interpolymer complexes

The interaction of metal sulfonate ionomers with polymers containing low levels of amines has been investigated in solution. For example, zinc sulfo EPDM and a styrene/vinyl pyridine copolymer form such complexes over broad concentration ranges. The resultant solutions offer enhanced viscosities at dilute polymer concentrations. At high polymer levels solutions based on these complexes are lower in viscosity than the ionomer alone. These interpolymer complexes have been shown to exhibit an improved property/rheology balance in bulk systems. In solution, polymer complexes provide control of hydrocarbon solution viscosity not available with conventional polymers. Reduced viscosity-concentration studies suggest that these polymer complexes are a result of the amine-containing polymer interacting with intramolecular-associated ionomer coils, which at higher concentrations form a pseudonetwork.     

High-temperature proton-exchange membranes based on polymer-acid complexes

The published data on proton-exchange membranes designed for solid-polymer fuel cells with operating temperatures of up to 200°C are surveyed. Complexes of basic polymers with strong acids are the most attractive materials for these membranes. Particular attention is paid to complexes of polybenzimidazoles with phosphoric acid. The basic characteristics of membranes, such as proton conductivity and thermal stability, are covered in detail. The testing of the title membranes under high-temperature fuel-cell performance conditions is examined. Alterative systems containing heteropolyacids and acid-doped systems based on polybenzimidazole blends with several sulfonated polyheteroarylenes are mentioned. As an alternative for polybenzimidazoles, other aromatic condensation polymers containing basic nitrogen atoms are considered.     

Thermal properties of wholly aromatic polyamides

Various wholly aromatic polyamides based on m-and p-phenylene diamines and isophthaloyl and terephthaloyl chloride have been synthesized and their thermal properties and oxygen index values have been studied. The effect of different substituents on the aromatic ring of the diamine have been explored by comparing their differential thermal analysis (DTA) and thermogravimetric analysis (TGA) behavior, their relative char yields at 700°C, and their oxygen indices. The ? Cl, ? NO₂, and ? OH substituted polyamides have been found to produce the highest char yields. The high char yields are probably associated with crosslinking occurring at high temperatures. Attempts at correlating char yield with oxygen index indicated enhancement for the chlorosubstituted aramids.     

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     

Ternary interpolymer complex based on aniline

On the basis of aniline, poly(acrylic acid), and sodium polyphosphate, a ternary interpolymer complex with a monobasic amine comprising an aromatic ring without any substituents and two polyacids has been prepared. The composition, structure, and behavior of the complex in aqueous solutions containing a low-molecular-mass salt have been investigated.     

Study on wholly aromatic polyamides containing methyl-substituted phenylene linkage

In order to study the influence of chemical modification on properties of polyamides, wholly aromatic polyamides have been synthesized from p-phenylenediamine, its 2,5-dimethyl and 2-methyl derivatives, m-phenylenediamine, its 2-methyl and 4-methyl derivatives, and terephthaloyl and isophthaloyl dichlorides by solution polycondensation at low temperature. The thermal stability and solubility of the methyl-substituted polyamides were compared with those of unsubstituted ones. The introduction of methyl groups in a polymeric chain led to a decrease in their thermal stability to different degrees depending on the positions of methyl groups, accompanied by an increase in their solubility. The unsymmetrical introduction of methyl groups in benzene rings had a greater effect on the increase in solubility of polyamide than did symmetrical methyl groups.     

Synthesis and properties of aromatic polyamides based on a benzonorbornane bis(ether carboxylic acid)

A set of new aromatic polyamides containing ether and benzonorbornane units were synthesized by the direct phosphorylation polycondensation of 3,6‐bis(4‐carboxyphenoxy)benzonorbornane with various aromatic diamines. The polymers were produced in high yields and moderate to high inherent viscosities (0.64–1.70 dL/g). The polyamides derived from rigid diamines such as p‐phenylenediamine and benzidine were semicrystalline and insoluble in organic solvents. The other polyamides were amorphous and organosoluble and afforded flexible and tough films via solution casting. These films exhibited good mechanical properties, with tensile strengths of 95–101 MPa, elongations at break of 13–25%, and initial moduli of 1.97–2.33 GPa. The amorphous polyamides showed glass‐transition temperatures between 176 and 212 °C (by differential scanning calorimetry) and softening temperatures between 194 and 213 °C (by thermomechanical analysis). Most of the polymers did not show significant weight loss before 450 °C in nitrogen or in air. Some properties of these polyamides were also compared with those of homologous counterparts without the pendent norbornane groups. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 947–957, 2002     

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.     

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     

New approach to synthesis of aromatic N-phenyl-substituted polyamides

It is shown that polyimidates obtained by polycondensation of bisphenols with imidoyl chlorides may be transformed into N-phenylsubstituted aromatic polyamides. The rearrangement occurs as a result of heating at 260–340°C, and, in a diphenyl ether solution, at 240°C. The resulting polymers are soluble in organic solvents and demonstrate high thermooxidative stability.     

Synthesis of aromatic polyamides by 1-hydroxybenzotriazole-catalyzed polycondensation of active aromatic diesters with aromatic diamines

Catalytic actions of various additives were studied in the polycondensation of di(4-nitrophenyl) isophthalate with bis(4-aminophenyl) ether in N-methyl-2-pyrrolidone, and 1-hydroxybenzotriazole (HOBt) was found to be a highly effective catalyst that yielded high-molecular-weight polyamide. In addition to the polycondensation of the 4-nitrophenyl ester, the polymerization of negatively substituted phenyl esters like di(2,4,5-trichlorophenyl) isophthalate was also accelerated by HOBt. For the HOBt-catalyzed aminolysis of esters a bifunctional concerted mechanism that involves an eight-membered transition state was proposed.     

Effects of linking groups in fluorinated aromatic polyamides

Based on dynamic thermogravimetric analysis (TGA) of fluorinated aromatic polyamides, we found that substituting terephthaloyl units for isophthaloyl units usually increased the thermal stability of the polymers. In contrast, the first steps of thermal degradation of poly(5,5′-sulfonyl-2,2′-difluoro-diphenyl terephthalamide) (2,2′-DIF-PSDPT) and poly(5,5′-sulfonyl-2,2′-difluorodphenyl isophthalamide)(2,2′-DIF-PSDPI) followed almost the same curve. This was attributed to the relative flexibility of the ? SO₂? group, and also to the activating effect on the dehydrofluorination reaction, which was believed to be the first step of the degradation of the ortho-fluorinated aromatic polyamides, , resulting in the formation of benzoxazole groups, , on the polymer backbone. With fluorinated aromatic polyamides having ortho fluorine to the amide nitrogen, the electron releasing ? CH₂? group deactivated the nucleophilic substitution of the dehydrofluorination reaction and the electron withdrawing group ? SO₂? activated the reaction, so that the onset degradation temperatures of the fluorinated aromatic units R in followed the order: