SYNOPSISTwo reaction routes for the preparation of aromatic poly-1,3,4-oxadiazoles and poly-1,2,4-triazoles are studied and their influence on the physical properties, i.e., inherent viscosity, glass transition, degradation temperature, and film integrity of the final products are discussed. Aromatic poly-1,3,4-oxadiazoles are prepared by means of a polycondensation reaction of terephthaloyl chloride and isophthalic dihydrazide yielding a precursor polymer, poly (p,m-phenylene ) hydrazide, which is converted into the corresponding poly-1,3,4-0~-adiazole by means of a cyclodehydration reaction. Poly-1,3,4-oxadiazoles are also prepared by means of a polycondensation reaction between terephthalic and isophthalic acid and hydrazine yielding poly-1,3,4-oxadiazoles with higher inherent viscosities. Flexible poly-1,3,4-oxadiazole films are obtained only if the inherent viscosities of the polymers used are higher than 2.7 dL/g. The thermal stability is found to i n c r e a s with increasing content of p-phenylene groups in the polymer backbone. Aromatic poly-1,2,4-triazoles are prepared using polyhydrazides with alternating para-and meta-phenylene groups and poly-1,3,4-oxadiazoles with a random incorporation of para-and rneta-phenylene groups in the main chain as precursor polymers. The glass transition temperatures are found to increase with increasing content of p -phenylene groups in the main chain of these polymers. Cold crystallization is observed only for the alternating polymer. 0 1994 John Wiley & Sons, Inc. Keywords: poly-1,3,4-oxadiazoles polyhydrazide poly-l,2,4-triazoles cold crystallization I NTRO DU CTI ON Aromatic poly-1,3,4-oxadiazoles and poly-1,2,4-triazoles are chemically resistant and thermally stable polymers soluble only in strong acids and stable up to 45OOC.l We have studied these polymers as new membrane material^,^'^ with the aim to develop membranes that can be applied under severe operating conditions, such as elevated temperatures and acidic or basic environments. Such membranes also should be highly resistant towards organic solvents. A number of reaction routes are known for the preparation of these poly-l,3,4-oxadiazoles and poly-1,2,4-triazoles.~ We decided to study the preparation of aromatic poly-1,3,4-oxadiazoles by means of a solid state cy- To whom correspondence should be addressed.clodehydration reaction of an aromatic polyhydra~i d e ,~'~ the latter being used as a tractable precursor polymer. Since poly-1,3,4-oxadiazoles with inferior mechanical properties were obtained,' a second reaction route was also studied. This route directly yields aromatic poly-1,3,4-oxadiazoles from hydrazine sulphate, and terephthalic and isophthalic acid as m o n o m e r~.~ Aromatic poly-1,2,4-triazoles were prepared by a reaction of an aromatic polyhydrazide' and poly-1,3,4-oxadiazoles9 with aniline in polyphosphoric acid.The synthesis routes are represented in Figure 1. Polyhydrazides with alternating para-and metaphenylene groups in the main chain were prepared using terephthaloyl chloride and iso...

SYNOPSISNew aromatic poly-1,2,4-triazoles and poly-l,3,4-oxadiazoles are studied as thermally stable membrane materials. Various groups were introduced onto the pendant phenyl groups of poly-1,2,4-triazoles. Glass transition temperature, degradation temperature, and cold crystallization behavior were studied as a function of these groups. Cold crystallization appeared to be highly sensitive to macromolecular regularity. The solubility of poly-l,3,4-oxadiazoles was highly improved upon incorporation of 5-t-butylisophthalic, 1,1,3-trimethyl-3-phenylindane, 4,4'-( 2,2'-diphenyl) hexafluoro propane, and diphenyl ether groups into the polymeric main chain, whereas the high glass transition temperatures and degradation temperatures typical for aromatic poly-1,3,4-oxadiazoles were maintained. 0 1994 John Wiley & Sons, Inc.Keywords: poly-1,3,4-oxadiazoles polyhydrazide poly-1,2,4-triazoles cold crystallization I NTRODU CTl O N Aromatic poly-1,2,4-triazoles and poly-1,3,4-oxadiazoles are studied as new thermally stable membrane materials for gas separation applications, especially poly [ p -, n-phenylene-(4-phenyl) -1,2,4-triazole], which is known for its excellent gas separation properties.' The use of these polymers as membrane materials is hampered due to their poor solubility, which limits the number of possibilities of fabricating membranes with a desired morphology, like asymmetric structures. For example, poly ( p -, nphenylene ) -1,3,4-oxadiazole is soluble only in concentrated sulphuric acid, which is a very difficult solvent to handle in practice.In this article we wish to report the syntheses and physical properties of poly-1,3,4-oxadiazoles and poly-1,2,4-triazoles where various functional groups are incorporated into and onto the polymer backbone with the aim of increasing their solubility while maintaining their thermal stability. The relationship between the gas separation properties and these molecular structures was also studied and is reported elsewhere.2 The solubility of polymers is often increased when flexible bonds, large pendant groups, or polar substituents are incorporated in the polymer backbone. The introduction of large pendant bulky groups along the polymer backbone results in a less ordered polymer matrix increasing the solubility characteristics. This is nicely illustrated by the fact that poly ( p -, m-phenylene) -1,3,4-oxadiazoles are soluble only in concentrated sulphuric acid while poly [ p -, m-phenylene-(4-phenyl) -1,2,4-triazoles], having an extra pendant phenyl group, are also soluble in mcresol and formic acid.Solubility is also highly increased if, instead of aromatic groups, aliphatic groups are incorporated into the polymer backbone, but a significant reduction in thermal stability is also observed. Incorporation of aliphatic groups for that reason was avoided. ( Nonetheless, cyclohexane was incorporated as a comparison to the aromatic poly(p-, mphenylene-1,3,4-oxadiazoles. ) A number of authors have reported poly ( 1,3,4-oxadiazoles ) with increased solubility characteris-ti...

Synthetic gas separation membranes have developed tremendously since the first commercial system was introduced just 15 years ago. Factors affecting the permeabilities and selectivities of new “tailor‐made” membrane materials are discussed. For example, because the p‐isomer is more rod‐like than the m‐isomer chain shown in the figure, the resulting membranes have a higher permeability.

SYNOPSISConventional polymers are compared as gas separation membrane materials with "tailormade" polymers. The increased permeability of the latter are due to their higher free volume available for gas transport. The increased free volume is associated with the rigidity polymer backbone. Free volume is obtained by subtracting the occupied volume, calculated using group contributions from the polymer specific volume. Wide Angle X-ray techniques are used to obtain average d -spacings that are interpreted in terms of average intermolecular space, and that are related to permeability data. These highly permeable rigid polymer membranes have high glass transition temperatures. The physical parameters, that is, Tg and the jump in heat capacity ( AC,) , are obtained with Differential Scanning Calorimetry, and are used to obtain an estimation of free volume. A good correlation for a series of random copoly [p, rn-phenylene ( 4-phenyl) -1,2,4-triazoles] is obtained. A relationship between permeability and a free volume term, which can be estimated from thermodynamic properties, is equally valid for a wide variety of conventional polymers. In a previous article, we have reported on the gas transport and separation properties of poly-1,3,4-oxadiazoles and poly-1,2,4-triazole membranes.' An increase in permeability appeared to be a function B is a constant, depending on the penetrant, and Vj is the polymer specific free volume. Since S can practically be considered a constant, eq. ( 1) can be written as:( 2 ) P = A exp( -B / V f ) of the diffusivity, only because the latter increased linearly with permeability, whereas solubility remained almost constant.Permeability and diffusivity could be expressed as a function of the polymer-free volume, using a Doolittle-type equation, previously used by Fujita' and later successfully employed by Lee,3 who used this equation to correlate the carbon dioxide and oxygen permeability in various commercial polymers to the polymer specific free volume: in which the parameters A and B depend only on the type of gas. Free volume here is defined aswhere, V is the polymer specific volume and Vo is the volume occupied by the polymer chains at 0 K. This volume is assumed to be impermeable for diffusing gas molecules. Lee calculated Vo using the relation proposed by Bondi4:The Van der Waals volume (V,) is calculated using a group contribution method. We have used the tabulation of Askadskii5 to calculate V,,,. This simple free volume treatment allows a direct insight on the gas transport properties. The factor 1.3 is, however, arbitrary and may sometimes result in a faulty in- 2081in which P is the permeability, S is the solubility, ' To whom correspondence should be addressed. The free volume treatment is gaining interest, since various authors were able to correlate the permeability and diffusivity of various polymer classes to their free volume. For example, Maeda and Paul' used this equation to interpret the reduction in transport in polysulfone and polyphenylene oxide, containing low molec...

results in a polymer with a low permeability but an extremely high selectivity. While the permeabilities vary over four orders of magnitude, the solubility remains almost constant and, therefore, the increase in permeability is mainly due to an increase in diffusivity. The permeability is discussed in terms of the polymer free volume.