SynopsisPoly(l,3,4-oxadiazole-2,5-diylvinylene) and poly(1,4-phenylene-l,3,4-oxadiazole-2,5-diylvinylene) were prepared by polymerizing different quantities of terephthalic acid (T), maleic acid (MI, and hydrazine sulfate (HS) in the presence of fuming sulfuric acid. Homopolymers of M and T and various copolymers of M:T were prepared. The polymers were characterized by viscosity, IR, UV, and elemental analysis. Their solubility in different solvents was investigated. The relative thermal stability of the polymers was evaluated by TGA and DTA.

SynopsisFive 1,3,4-oxadiazole copolymers having p-phenylene and cis or trans vinylene groups in the backbone were prepared by reacting terephthalic acid, maleic acid, and fumaric acid with hydrazine sulfate in the presence of fuming sulfuric acid or polyphosphoric acid. The copolymers were characterized by IR spectra and intrinsic viscosity determinations. Thermal stability was investigated by dynamic thermogravimetry in nitrogen atmosphere. The anaerobic char yields of copolymers containing trans vinylene groups were higher than those of samples having cis vinylene groups. Wet spinning was used to spin fibers of these copolymers. An increase in jet stretch during spinning resulted in an improvement of tenacity and initial modulus of the fibers. Copolymers with symmetrical trans vinylene groups in the backbone gave fibers with better mechanical properties. Density of these fibers was higher compared to fibers having cis vinylene groups. X-ray diffraction photographs indicated poor orientation in the as-spun fibers. Surface flaws were revealed by scanning electron microscopy.

SynopsisPoly( 1,3,4-oxadiazole-2,5-diyl-1,2-ethendiyl) and poly( 1,4-phenylene-l,3,4-0xadiazole-2,5 diyl-1,a-ethenediyl) have been prepared by condensation polymerization using fuming sulfuric acid and different quantities of terephthalic acid (T), fumaric acid (F), and hydrazine sulfate (HS). Homopolymers of F and T and various copolymers of F T have been prepared. The polymer structure waa investigated by IR and visible-range spectra and elemental analysis. The existence of poly( 1,3,4-oxadiazole-diylphenylene) and poly(hydrazoterephthaloy1) structures waa revealed by these studies. These polymers were thermally stable, and most of them did not show a weight loss below 350OC. The relative thermal stabilities of the various polymers have been evaluated by "integral procedural decomposition temperature" and activation energy meaaurementa.

SynopsisThe phase diagrams of the ternary system poly(ethenyl-1,3,4-oxadiazole-2,5-diyl-l,4 phenylene), sulfuric acid, and water indicated that the increase of the ethenyl residue in the copolymers increased the solubility in the acid. The critical point of separation in sulfuric acid was determined, and it decreased from 74% to 60.5% as the ethenyl ratio of copolymers was increased. The electrical properties in the temperature range of 0-90°C at a fixed frequency of 1592 Hz were also investigated. The tan 6 values increased with increase in temperature and passed through a maximum. The temperature of this maximum varied with the nature of the copolymer. The observed increase in the dielectric constant with temperature may be due to increased segmental motion in the amorphous region of the polymers.

The effect of backbone flexibility on the thermal behaviour of the polyimides was investigated by synthesizing copolyimides based on pyromellitic dianhydride (PMDA) and benzidine (B), p-phenylene diamine (P), and p,p'-diamino diphenyl methane (D). Soluble polyamic acids were obtained by carrying the reaction in dimethyl formamide (DMF) at 0°C. The cyclodehydration of amic acid to polyimides was carried out by chemical means (acetic anhydride : pyridine). Several copolyimides were prepared by changing the molar ratios of diamines in initial monomer feed. These were characterized by evaluation of intrinsic viscosity of polyamic acid in DMF at 30 "C. The presence of amic acid and imide structures in the backbone was confirmed by IR spectra. Thermal behaviour of the polymers in air and nitrogen atmosphere was evaluated by dynamic thermogravimetry. The integral procedural decomposition temperature and activation energy of thermal degradation has been evaluated. ZUSAMMENFASSUNG:Es wurde der EinfluR der Kettenbeweglichkeit auf das thermische Verhalten der Polyimide untersucht. Die Copolyimide wurden aus Pyromellithdianhydrid (PMDA), Benzidin (B), p-Phenylendiamin (P) und p,p'-Diaminodiphenylmethan (D), hergestellt. Losliche Polyamidsaure wurde durch Ausfuhren der Reaktion in Dimethylformamid (DMF) bei 0 "C erhalten. Die cyclische Dehydrierung von Amidsauren zu Polyimiden wurde auf chemischem Wege ausgefuhrt (Acetanhydrid: Pyridin). Es wurden verschiedene Copolyimide durch Veranderung des Ausgangsmonomerenverhaltnisses hergestellt.Die Copolyimide wurden durch Bestimmen des Staudinger-Index der Polyamidsaure in DMF bei 30 " C charakterisiert. Die Anwesenheit von Amidsaure-und Imidstrukturen im Ruckgrat wurde durch IR-Spektren bestatigt. Mit Hilfe der dynamischen Thermogravimetrie wurde das thermische Verhalten der Polymeren in Luft und Stickstoff beurteilt; auRerdem sind die insgesamt ermittelte Zersetzungstemperatur und die Aktivierungsenergie des thermischen Abbaus gemessen worden.