Synthesis and Properties of Bio-Based Long Carbon Chain Nylon 5X
The synthesis of three bio-based long-chain polyamides,namely Nylon 510,Nylon 512,and Nylon 513(PA5X),was accomplished through a two-step process involving the salt formation and melt polycondensation reactions of hexamethylenediamine with sebacic acid,dodecanedioic acid,and tridecanedioic acid,respectively.Gel permeation chromatography(GPC)analyses of the irreversible reaction kinetics indicate an increase in the relative molecular weight of the products with prolonged reaction time,accompanied by a gradual reduction in molecular weight distribution.PA5X10,PA512,and PA513 exhibit third-order kinetics,with polymerization rate constants of 19.79,25.80,and 23.19,respectively.Fourier-transform infrared spectroscopy(FT-IR)and nuclear magnetic resonance(NMR)analyses reveal that all small-molecule PA5X salts undergo polymerization into high-molecular-weight PA5X after melt polycondensation,with no other structural byproducts formed.Differential scanning calorimetry(DSC)and thermogravimetric(TG)analyses demonstrate that the melting points of PA5X decrease gradually with an increase in the length of repeating unit chain,reaching 214℃,209℃,and 204℃,respectively,while the decomposition temperatures are all above 400℃.Mechanical property results indicate that the tensile strength of PA5X ranges from 54 MPa to 60 MPa,with fracture elongation exceeding 200%.The bending strength and impact resistance exhibit a slight decrease with an increase in the chain length of dicarboxylic acid.
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