Study On The Preparation Of PA6 Via An Active Anionic Ring-open Polymerization And Its Properties

Nylon 6(PA6)is one of the most important engineering plastics,widely used in daily life and industrial production fields.At present,commercial PA6 is usually prepared by hydrolysis ring-opening polymerization with caprolactam as raw material.The monomer conversion is less than 90%since this reaction is an equilibrium reaction,and many monomers and oligomers in the polymerization products must be removed later,which takes time and requires a lot of energy.In contrast,living anion polymerization has the advantages of solvent-free,fast reaction rate,high conversion,and high product molecular weight.Therefore,developing anionic ring-opening polymerization of caprolactam to prepare high performance PA6 is of great significance in the application of engineering plastics.This paper focuses on the preparation of PA6 engineering plastics by anionic ring opening polymerization of caprolactam.Firstly,the rules of initiator species and their effects on the polymerization process and product characteristics were examined to prepare PA6 with different molecular weights,and the effect of molecular weight of PA6 on its properties was investigated;then examined the reproducible processability and thermal degradability of anionic ring opening polymerization to prepare PA6 and investigated the effect of antioxidant modification on its properties;Finally,anionic polymerization was applied to prepare PA6 reinforced with glass fibers to study its application in 3D printing.The paper achieved the following research results:(1)Initiators with different numbers of active sites have an important effect on the polymerization of caprolactam anions,When employing diisocyanates with dual active sites as initiators,the polymerization reaction rate of caprolactam anion is very fast and cross-linking will occur,resulting in a poorly soluble product,while using a single active site initiator,n-acetylcaprolactam(AcCL),will avoid the occurrence of crosslinking reaction and the molecular weight of polymerization product PA6 can be well regulated by changing its dosage.As the molecular weight increases,the crystallinity of PA6 gradually decreases;The tensile and bending properties first increase and then decrease,while the impact properties continue to increase.When the average molecular weight of PA6 reaches 38.6 kg/mol,the impact strength of PA6 reaches 26 kJ/m2.In addition,under the same molecular weight,the mechanical properties of PA6 prepared by anionic polymerization are basically the same as those of commercial materials prepared by hydrolysis ring opening polymerization.(2)The stability of PA6 was investigated through repeated injection molding and extrusion melting processing.The results showed that the molecular weight of PA6 was significantly reduced during the first processing,and remained stable during both secondary and multiple processing,similar to the commercial PA6 prepared by hydrolysis ring opening polymerization;As the number of melt processing increases,the tensile and bending properties increase,because an increase in processing times will increase the crystallinity of PA6.The heat resistance of PA6 was investigated by thermogravimetric analysis.The results showed that the heat resistance of PA6 prepared by anionic polymerization was not as good as that of commercial materials prepared by hydrolytic ring opening polymerization,mainly because there were residual caprolactam monomers and oligomers in PA6 prepared by anionic polymerization.Adding antioxidants through in-situ polymerization and melt blending can improve its heat resistance performance.(3)Preparation of PA6/glass fiber composite by melt blending extrusion processing and investigation of its properties,The results indicate that the addition of glass fibers can significantly improve the tensile and bending properties of PA6,as well as improve its heat resistance.The higher the molecular weight and melt viscosity of PA6 matrix,the more stable the size of the 3D printing wire prepared after composite with glass fiber.Moreover,when printing 3D models,the stronger the interlayer bonding strength and lower the shrinkage rate,demonstrating excellent 3D printing effects.