Anionic polymerization of epsilon-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 d egrees C) or as an additional activator to iv-acetyl-E-caprolactam (AcCL) ( at 150 degrees C). The activation effect of individual ureas was proved, bu t it unexpectedly increases in the sequence of their increasing N-acidity, i.e. DBU < BPU < DPU. The ureas produced during polymerization had practica lly 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 explai ned in terms of the different rates of the primary initiation and first pro pagation step. The accelerating effect of ureas added to AcCL activator doe s not correlate with their N-acidities. They act primarily as basicity regu lators reducing the side condensation reaction of AcCL and growth centres a nd produce additional polymer chains by transacylation cleavage and,or form ation of new growth centres. (C) 1998 Elsevier Science Ltd. All rights rese rved.