The Modification Of Poly (Para-Phenylene Terephthalamide) By Copolycondensation

Poly (Para-Phenylene Terephthalamide) is a high performance polymer, but difficult to process because of its poor solubility. Copolycondensation by adding 4, 4'-Diaminodiphenyl ether (ODA) into the polymerization system is one of effective methods to improve the solubility of PPTA. In this paper, the copolyamides were prepared by low temperature solution copolycondensation using p-phenylenediamine, terephthaloyl chloride and ODA in the solvent system of N-methyl-2-pyrrolidone /calcium (NMP/CaCl2). The chemical structures of copolyamides were calculated semi quantitatively by FTIR. The optimum synthesis conditions were investigated, and high molecular weight copolyamides were obtained. The thermal behavior, thermal degradation kinetics, the rheological properties, the crystalline degree of the series copolyamides were studied by using thermo gravimetric analysis (TGA), rheology instrument and Wide angle X-ray diffraction. The solubility and coagulation phase separation of the copolymer solution of the copolyamides were also discussed.The conditions such as the reaction time, the reaction temperature, the amount of CaCl₂, the monomer concentration, the initial ratio of ODA /TPCl on the molecular weight of PPTA copolyamides were studied. Two series of high weight copolyamides (inherent viscosity 2.05-3.37dL/g) were prepared, including a different ODA content series which were synthesized by random copolymerization ,and a different initial ratio of ODA /TPCl series(25mol%ODA) which were synthesized by control the feed order. The optimal conditions were: monomer concentration of 0.35⁰.45mol/L, the final reaction temperature 80-85 ℃, the ratio of CaCl₂/diamine 0.375, and polymerization time 30-40 minutes. It was indicated that the content of - O-in the copolymers increased with the increase of the ODA content by FTIR.The TGA curves of the copolyamides indicated the copolymers had good thermal stability. 5% weight loss were in the ranges of 361-401 ℃.Most of the synthesized copolyamides were soluble in NMP/CaCl2 system, butwhen the ODA content was less than 15mol% in the different ODA content series, and the initial ratio of ODA/TPC1 was less than 1.9 in different initial ratio of ODA/TPC1 series(25mol%ODA), the copolyamides were insoluble. The solubility behavior is consistent with the result of x-ray diffraction studies. The X-ray diffraction pattens indicated when the ODA content less than 15mol% the crystallinity was about 40%, when the ODA content more than 15mol% the crystalline was rapidly decreased.Non-Newton exponent, viscous activation energy, structural viscosity index were obtained by studies of rheology properties of the dopes for the subsequent spinning process.The dependences of coagulation value and critical concentration of the solvent (NMP) on coagulant, coagulant concentration, temperature, concentration of CaCl₂ were investigated. It is shown that water was a kind of strong coagulant for its low coagulation value and that the coagulation value increased with the increase of coagulation concentration, CaCl₂ concentration and temperature.The shift life studies show most of the copolyamides spinning dopes was stable at room temperature and spinning temperature (70℃), whereas the PPTA concentrated sulfic acid spinning dope degraded quickly after 24 hour.