In the polymerization of caprolactam, the stoichiometry of carboxyl groups and amine groups in the process of melt polycondensation needs to be balanced, which greatly limits the copolymerization modification of polyamide 6. In this paper, by combining the characteristics of the polyester polymerization process, a simple and flexible synthetic route is proposed. A polyamide 6-based polymer can be prepared by combining caprolactam hydrolysis polymerization with transesterification. First, a carboxyl-terminated polyamide 6-based prepolymer is obtained by a caprolactam hydrolysis polymerization process using a dibasic acid as a blocking agent. Subsequently, ethylene glycol is added for esterification to form a glycol-terminated polyamide 6-based prepolymer. Finally, a transesterification reaction is carried out to prepare a polyamide 6-based polymer. In this paper, a series of polyamide 6-based polymers with different molecular weight blocks were prepared by adjusting the amount and type of dibasic acid added, and the effects of different control methods on the structural properties of the final product are analyzed. The results showed that compared with the traditional polymerization method of polyamide 6, the novel synthetic strategy developed in this paper can flexibly design prepolymers with different molecular weights and end groups to meet different application requirements. In addition, the polyamide 6-based polymer maintains excellent mechanical and hygroscopic properties. Furthermore, the molecular weight increase in the polyamide 6 polymer is no longer dependent on the metering balance of the end groups, providing a new synthetic route for the copolymerization of polyamide 6 copolymer.
Keywords: melt polymerization; polyamide 6; polyamide 6 (PA6)-based polymer; polyesteramide; synthetic methodology; transesterification.