Preparation And Properties Of Semi-aromatic High Temperature Resistant Nylon PA6T-66

With the increasingly high heat resistance requirements of communication equipment,storage module and heat dissipation components around automobile engine for materials,the market application prospect of high-temperature resistant nylon is very broad.Semi-aromatic high-temperature resistant nylon combines the flexibility of aliphatic nylon and the high heat resistance of all-aromatic nylon.PA6T has become a representative variety of high-temperature resistant nylon due to its low cost and excellent properties.However,the melting point of pure PA6T is higher than its thermal decomposition temperature,so the third monomer is generally added to the copolymerization to obtain the meltable high-temperature resistant PA6T copolymer.Among them,the PA6T-66 copolymer has become one of the hotspots of current research because of its excellent comprehensive properties.The research and development of high-temperature resistant nylon in foreign countries started early and has formed the patent and technology monopoly.Therefore,it is of great significance to strengthen the research on high properties and high-temperature resistant nylon resin for the development of the material industry.In this paper,the preparation of high-temperature resistant nylon PA6T-66 copolymer with good uniformity was taken as the goal.On the basis of optimizing the salt formation parameters of PA66 and PA6T,the PA6T-66 copolymer was prepared by the traditional high-temperature and high-pressure solution polycondensation method,with adipic acid,terephthalic acid and adipic diamine as the polymerization monomers,and the salt formation-polymerization continuous reaction was carried out in the polymerization kettle.Furthermore,the effects of monomer ratio,total amine acid ratio,pressure relief time and type of capping agent on the properties of the copolymer were explored.The main research contents are as follows:The effects of amine acid ratio and reaction temperature on the salt formation process of nylon66 salt and nylon 6 T salt were studied in a flask with water as solvent.The appropriate salt formation temperature was obtained,and the saturated water solubility of the two monomer salts was tested.The structure and purity of the synthesized monomer salts were confirmed by FTIR and ~1H NMR tests.The melting points and thermal stability of nylon salts and mixed salts were further characterized by DSC and TGA,and the melting points of 66 and 6T salts corresponding to a series of different 6T/66 mixed ratios were obtained,which had important guiding significance for the control and optimization of subsequent polymerization temperature.Based on the study of the salt-forming process in the flask,in order to improve the efficiency and reduce the energy consumption caused by the single salt-forming step,the high-temperature resistant nylon PA6T-66 copolymer was prepared by direct polycondensation after mixing salt reactions into polymerization equipment.The effects of monomer content,total amine acid ratio,pressure relief time and capping agent types on the properties of copolymers were investigated.The structure and sequence distribution of the copolymers was confirmed by FTIR,~1H NMR and ¹³C NMR,and the thermal properties of each sample were tested by DSC and TGA.The results showed that the content of 6T played a dominant role in the heat resistance of the copolymer.When the relative viscosity of PA6T-66(57.5-42.5)reached 2.63,the secondary heating melting point of the copolymer could reach 308.4?,which had excellent heat resistance and good machinability.The relative viscosity and melting point of PA6T-66 copolymer can be effectively controlled by total amine acid ratio and polymerization pressure relief time.Nonisothermal crystallization kinetics of two PA6T-66 copolymers with higher(55 mol%)and lower(45 mol%)6T content was analyzed.The study of the Avrami equation showed that the Avrami index n of PA6T-66 copolymer was 2.02-3.54,and its crystal growth mode was mainly two-dimensional flake.The crystallization behavior of PA6T-66 copolymer was analyzed by the Jeziorny and Mo methods,and the non-isothermal crystallization activation energy was calculated by the Kissinger and Takhor methods.The results showed that the samples with higher 6T content had lower half-crystallization time and crystallization activation energy,and the crystallization rate was faster.