Bulk anionic copolymerization of ε‐caprolactam in the presence of macroactivators derived from polypropylene glycol

Bulk anionic copolymerization of ε‐caprolactam (CPL) was conducted, under four different conditions by changing temperature (110 or 125°C) and [NCO]/[NaH] ratio (1, 2, or 3), in the presence of NCO‐terminated polypropylene glycol (P1) and its CPL‐blocked prepolymer (P2). Under the same conditions and reaction time, the conversion of CPL and reduced viscosity of the P2 system were higher than those of the P1 system. However, at the same conversion the P1 system showed higher viscosity for reactions at 125°C with [NCO]/[NaH] = 3 and at 110°C with [NCO]/[NaH] = 2. These results were attributed to cyclotrimerization of NCO groups of P1 (formation of isocyanurate) at the initial stage, which not only consumed the effective concentration of NCO but also increased the viscosity of the P1 system. Comparing IR spectra of the reaction products of model compounds, phenyl isocyanate and CPL‐blocked phenyl isocyanate, with NaH/CPL also supported this conclusion. The crystalline melting temperature (T_m = 198–208°C) and melting enthalpy of the final products depended on the conversion of CPL and the types of macroactivators. © 1993 John Wiley & Sons, Inc.