AbstractLactams and lactam derivatives may be polymerized by various types of processes, but only the cationic mechanisms provide suitable pathways for the polymerization of all types of lactam monomers. Therefore, the cationic polymerization is predestinated for the synthesis of their copolymers. Random copolymers can be obtained even if the rates of homopolymerization of comonomers differ by several orders of magnitude, either by transacylation of block copolymers, or in a new process designated as polymerization with transient chemical activation. This process is operative e.g. in the copolymerization of an unsubstituted and an N‐acylated lactam. It implies N‐acylation of the unsubstituted lactam by the polymer of the N‐acylated one, followed by the incorporation of the activated monomer and subsequent deacylation of the incorporated monomer