Deactivation of catalytic species

Surprisingly, the initially fast cationic polymerization of caprolactam slows down before reaching the monomei -polymer equilibrium [176, 182—184,188, 192, 193] and after a certain period the rate of polymerization again increases (Fig. 22). This peculiar course of polymerization indicates that the catalytic species are deactivated in some side reaction and that other active species are formed in a slow reaction. 

Amine hydrochlorides are known to react at elevated temperature with diacylamines and amides with the formation of amidines [201] 

There is an increasing amount of evidence that the amidine groups are present in the semicyclic form resulting either from intramolecular cyclization of the terminal amine hydrochloride [202, 204, 206, 210], viz. 

So far, no kinetic data are available for the estimation of k i, 52 and ks3- The decay of the strongly acidic amide hydrochloride follows the equation [184] 

The preferential formation of semicyclic amidine groups was supported by the fact that amidine groups were not found in cationic polymers of capryl- and laurinlactam [203, 206], where formation of the corresponding unstable cycles is very improbable. Detailed studies revealed that, under certain conditions, cationic capryllactam polymers contain semicyclic and non-cyclic amidine groups [252]. 

---