Studies On Preparation Of Nylon-46 In Supercritical Carbon Dioxide

Supercritical carbon dioxide (SC-CO2), known as "green solvent", is widely used in polymerization since the 1970's because of its special property. Polyamide-46, named "Super Nylon", is an aliphatic polyamide with high crystallinity and high melting point, which is mainly used in automobile manufacturing and electronics industries, as its excellent overall property.In this paper, nylon-46 salt is prepared by 1,4-diamine and 1,6-adipic acid as raw materials to synthesis nylon-46 in SC-CO2 medium. Several different polymerization methods were studied to obtain high molecular weight of nylon-46 samples. Chemical structure, properties and molecular weight of nylon-46 samples were characterized by Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TG), Infrared Spectrum (IR) and viscosity average molecular weight test method. The conclusions are followed:polycondenseDuring one-step polymerization, influence of polymerization conditions on the molecular weight of nylon-46 samples was studied in a closed system of SC-CO2. Suitable polymerization conditions of nylon-46 samples are of 180℃and 1h for pre-polymerization; 280℃and 3.5 h for after-condensation. And the molecular weight and melting point of nylon-46 samples is 1.81×104 and 306.3℃, respectively. A linear relationship between pressure and molecular weight of products was found. In two-step polymerization, nylon-46 samples were re-polymerized after the prepolymer was breaked into pieces. The molecular weight of nylon-46 increased from 1.81×104 to 2.2×104. Based on the above summary, effects of excess molar of 1,4- diamine and water content in nylon-46 salt on the molecular weight of nylon-46 were further studied. The results showed the high molecular weight of nylon-46 can be obtained, when excess diamine of 5% molar and water content of 70% were used in nylon-46 salt. the polymerization. The highest molecular weight and melting point of nylon-46 were 2.87×104 and 310.8℃, respectively, when the pre-condensation was carried out at 200℃for 2 h by above method.In order to move the condensation polymerization balance and enhance the molecular weight of nylon-46, a precursor of nano-particles, tetraethyl orthosilicate (TEOS), and nylon-46 salt were simultaneously polymerized in the closed system of SC-CO2. The results showed that SiO2 particles and nylon-46 can be obtained at the same time and the molecular weight of nylon-46 could also be increased. The structure of SiO2 particles was characterized by IR, DSC, X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM).The size of SiO2 particles was in the range from namometer to micrometer, and the SiO2 particles had regular spherical shape and smooth surface in the way of an equable dispersion.The non-isothermal crystallization kinetics of nylon-46 was analyzed by using modified method of Avrami equation of Jeziorny, Ozawa and Mo Zhishen. The nonisothermal kinetic parameters could be obtained. The results showed that the nucleation mechanism and growth patterns of nylon-46 during the non-isothermal crystallization process were not single.