Synthesis And Characteristics Of Nylons Containing Aromatic Rings

The demand of polymers has been in large, and the performance requirement of polymers has been improved in military affairs, spaceflight, and civil industry with the rapid development of civil economy. As a class of engineering plastics having high performance, semi-aromatic polyamides have been paid more and more close attention to, for their excellent heat performance, easily machining, impact resistance, chemical resistance, and low water absorption etc. PA6T/66 is namely one typical polymer of the materials. However, these polymers mostly have been monopolized by several monopoly company overseas at present. Nylons containing aromatic rings were prepared by the following route in the thesis : forming salt followed by prepolymerizing, finally polymerizing. Especially stoichiometric ratio and influences on PA6T/66 polymer molecular weight (MW) , heat performance, melt and crystal behavior in Solid Phase Polycondensation (SPP) were investigated.Nylon 66 salt ( PA66 salt ) and nylon 6T salt were prepared from hexamethylendiamine, hexanedioic acid and terephthalic acid, sodium hypophosphite as catalyst, water as sovent at suitable temperature. The composition form, the structure form, the thermal stability and the solubility of PA66 salt, PA6T salt and "PA6T/66" salt were analyzed with FTIR, HLPC, NMR, elementary analysis, ultraviolet analysis, TGA and solubility analysis. The analysis results indicate that "PA6T/66"salt is not associated by PA6T66 salt and PA6T salt, but PA6T salt crystallized before PA66 salt because the solubility of the former is obviously smaller than the latter. The experiment on the solubility of PA6T salt, and the fitting result of the solubility(C_s=1124.07-7.72T+0.0135T²) provided theory reference for the feed stock in the prepolymerizing stage of PA6T/66 polymer. TGA results which show that thermal stability of PA6T salt provide temperature reference for prepolymerization.Nylon prepolymers containing aromatic rings were prepared from PA66 salt and PA6T salt, water as sovent at high temperature and high pressure,followed by polymers preparation in the gas SPP reactor. The thesis also investigated the structure, MW, thermal stability, melting and crystallizing behavior of PA6T/66 prepolymer and polymer with FTIR, NMR, intrinsic viscosity measurement, GPC, TGA and DSC. The results indicated that, because the reaction activity of PA66 was priority to PA6T, the polymerizing process was beginning with a great deal of PA66 and a small amount of PA6T, ending with forming PA6T/66 random copolymer. MW of prepolymers is influenced by temperature programming, water amount and air escape. The suitable preparation temperature of PA6T/66 copolymer improved with the increasing of the content of PA6T. 50%PA6T/66 prepolymer with relatively high MW could be prepared at 220℃, under the paddle rotation 300r/min, during 5hours. The analysis results show that there are double peaks during PA6T/66 prepolymers' melting process because the polymerizing degree is not complete and the segments are not regular. Intrinsic viscosity and GPC testing with acetylized copolymers indicated that MW of the nylons reduced with the increase in PA6T content at given condition. MW of nylons containing PA6T given content ( 50% ) increased with the improving of temperature to smaller and smaller amplitude, with the continuation of time to a stable position even to degradation, and with the augment of N₂ flow rate to equilibrium. Therefore, the suitable SPP technology condition of 50%PA6T/66 copolymer was developed: temperature: 230-250℃, time: 6-10h, N₂. flow rate: 40-60ml/min. DSC and TGA show that the SPP copolymer is a type of polymer having high crystallinity, good melting performance ( 290-305℃), and good thermal stability (the maximum decomposition temperature .above 450-500℃).