Polyamide (PA) is a widely used engineering plastic with high mechanical strength, heat resistance, abrasion resistance and chemical resistance. In the field of raw materials for chemical production, there are two main manufacturing methods for polyamides: polycondensation and ring-opening polymerization. This article will introduce these two manufacturing methods in detail.
I. Polycondensation
The polycondensation method is a method of preparing polyamides by polycondensation reaction between dibasic acid and dibasic amine. In this process, the dibasic acid and diamine react to produce a polymer and water molecules. Usually used dibasic acids include adipic acid, terephthalic acid, etc., and diamines include hexanediamine and ethylenediamine.
1. Continuous polycondensation method
Continuous polycondensation method is to add dibasic acid and dibasic amine monomers continuously in a certain proportion into the reactor, control the reaction temperature and pressure, and carry out the polycondensation reaction. The water molecules generated by the reaction need to be removed in time to keep the reaction proceeding in the direction of polyamide generation. At the end of the reaction, the polymer is extruded, cooled and pelletized to obtain the polyamide product.
2. Intermittent Polymerization
Intermittent polymerization is a method in which the polycondensation reaction is carried out in an intermittent reactor. Dibasic acid and dibasic amine monomer are added to the reactor in a certain proportion, heated to a certain temperature, and the polycondensation reaction is carried out. The water molecules generated by the reaction need to be removed in time to maintain the reaction equilibrium. At the end of the reaction, the polymer is removed and post-treated to obtain the polyamide product.
II. Ring-opening polymerization method
Ring-opening polymerization method is a method of preparing polyamide by ring-opening polymerization of cyclic monomers. Commonly used cyclic monomers are ε-caprolactone, δ-valerolactone and so on.
1. Anionic ring-opening polymerization
Anionic ring-opening polymerization is a method of initiating ring-opening polymerization of cyclic monomers using an alkali metal compound as an initiator. In this process, the initiator reacts with the cyclic monomers to generate reactive anions, which continuously react with the cyclic monomers to open the monomers and attach them to the polymer chain. At the end of the reaction, the polymer is removed and post-treated to obtain the polyamide product.
2. Cationic ring-opening polymerization
Cationic ring-opening polymerization is a method of initiating ring-opening polymerization of cyclic monomers using protonic or Lewis acid as an initiator. In this process, the initiator reacts with the cyclic monomers to generate reactive cations, and the reactive cations continue to react with the cyclic monomers, causing the monomers to open the ring and attach to the polymer chain. At the end of the reaction, the polymer is removed and post-treated to obtain the polyamide product.
In general, both the polycondensation method and the ring-opening polymerization method can be used to prepare polyamides, but the two methods are different in terms of raw materials, processes, equipment and so on. In actual production, you can choose the appropriate manufacturing method according to the product performance requirements, production costs and other factors. At the same time, in order to ensure the quality and performance stability of polyamide products, it is also necessary to strictly control the temperature, pressure, material ratio and other parameters in the production process to ensure the smooth progress of the reaction and the purity of the product.
