Preparation And Thermal Stability Of Heat-Resistant Copolyamide PA4T/46

Semi-aromatic polyamide is an important engineering plastics,which has the characteristics of high melting temperature,high heat resistance,excellent dimensional stability and mechanical strength.The copolyamide PA4T/46,which combined the characteristics of poly(p-benzoylbutylamine)(PA4T)and polybutylene adipate(PA46),is a promising new heat-resistant nylon.The thermal stability of PA4T/46 limits its processing and application,and there were few related reports.Relationship between the structure and thermal performance of PA4T/46 had been carried out as follows:The copolyamide PA4T/46 was prepared from monomers of terephthaloyl chloride,hexanoyl chloride and butanediamine in solvent of N,N-dimethylacetamide/calcium chloride(NMP/CaCl2)through low temperature solution polycondensation.The structure of product was characterized by FTIR and 1H-NMR,and optimal reaction conditions were obtained:the reaction temperature 0～5℃,the monomer mole ratio of-COCl over-NH2 1.008～1.012,the monomer concentration 0.25 mol/L,the acid scavenger 0.95～1 of amino mole amount,the reaction time 30～60 min.The effects of molecular weight,aromatic content,end-group type and sequence structure on the thermal stability of PA4T/46 were investigated by thermogravimetric analysis.The results showed that thermal stability of PA4T/46 increased with polymerization degree and the decomposition temperature effectively increased when benzene structure content increased.The PA4T/46 with amino terminal group was decomposed more easily than carboxyl terminal group.The thermal stability of random PA4T/46 was better than block,and their thermal degradation behaviors were different.Compared with the thermal degradation of PA4T/46 in the atmosphere of nitrogen,the decomposition temperature was significantly reduced in air atmosphere,meaning the mechanism of degradation reaction was changed by oxygen.The apparent activation energy of thermal degradation of PA4T/46 was calculated by KAS,F WO and Coats-Redfern methods,and the thermal degradation mechanism was determined as phase boundary reaction(R2 type).The pathway and mechanism of thermal degradation of PA4T/46 in inert atmosphere were investigated by Py-GC/MS,TG-MS and TG-FTIR.The results showed that main degradation of PA4T/46 was mainly caused by the scission of amide bond and its vicinal bond,which leads to main products including olefin,ketone,five-membered nitrogen heterocycle,nitrile,aromatic compounds and low molecular compounds such as NH3,HaO,CO,CO2 and so on.