Anionic polymerization of ε-caprolactam in the presence of symmetrically substituted ureas

N,N'-diphenylurea (DPU), N-butyl-N'-phenylurea (BPU), and N,N'-dibutylurea (DBU) were added to the anionic polymerization of epsilon-caprolactam (CL) initiated with sodium salt of CL either as individual activators (150-170 degrees C) or as an additional activator to iv-acetyl-E-caprolactam (AcCL) (at 150 degrees C). The activation effect of individual ureas was proved, but it unexpectedly increases in the sequence of their increasing N-acidity, i.e. DBU < BPU < DPU. The ureas produced during polymerization had practically the same number of polyamide chains (similar to 1.3 chains per molecule) irrespective of their structure and polymerization temperature. From the rates of urea consumption, the different polymerization rates can be explained in terms of the different rates of the primary initiation and first propagation step. The accelerating effect of ureas added to AcCL activator does not correlate with their N-acidities. They act primarily as basicity regulators reducing the side condensation reaction of AcCL and growth centres and produce additional polymer chains by transacylation cleavage and,or formation of new growth centres. (C) 1998 Elsevier Science Ltd. All rights reserved.