Die kationische Caprolactam-Polymerisation

5. Internationales Makromolekulares Symposium

Abstract

The lactam polymerizations initiated by proton acids, Lewis acids, and ammonium salts, resp., as well as the hydrolytic polymerization are summarized as “cationic polymerizations”. Initiation and propagation reactions are due to the high acylating properties of the lactam cation which reacts with the strongest nucleophihc compound in the polymerization mixture. 

In the polymerization initiated by anhydrous acids the free lactam is acylated with the formation of an ω-aminoacyllactam, in the amine salt initiated polymerization the corresponding amine is converted to the amide of the ω-amino acid, and in the hydrolytic polymerization the acylation of water yields the ω-amino acid. All amino compounds are formed as the ammonium salts. 

During the propagation reaction a proton transfer occurs first leading from the amine salt formed in the initiation reaction to the lactam (or acyllactam) to give lactam and acyllactam cations, resp., which now acylate the free amine formed with the regeneration of an ammonium group. 

In addition, large amounts of amidine (and acylamidine) groups are formed from the tetrahedral intermediate originated from the initiation products. The water eliminated in this reaction subsequently hydrolyses acyllactams, acylamidin eand lactam salts yielding carboxylic groups in high concentrations. The amidinium groups initiate the polymerization of lactams much less effectively than ammonium groups. Therefore, their formation leads to a high decrease of the polymerization rate.