Copolymers of ε-caprolactam and polypropylene oxide via anionic polymerization: synthesis and properties

Copolymers with an elastic polypropylene oxide (PPO), middle block in the main chain of poly(ε-caprolactam) were synthesized via activated anionic ring opening polymerization of ε-caprolactam (CL) in the presence of a basic initiator sodium salt of CL (Na-CL) and effective bifunctional polymeric activators (PACs). By varyng the molecular weight, two types of PACs were synthesized based on carbamoyl derivatives of hydroxyl terminated PPO with isophorone diisocyanate and were blocked with CL. The formation of copolymers has been confirmed by proton nuclear magnetic resonance spectroscopy (1H–NMR) and Fourier transform infrared spectroscopy (FT-IR). The influence of the molecular weight of the PACs, the CL/PAC ratio and polymerization conditions on the conversion, intrinsic viscosity and polymerization kinetics, was investigated. The calorimetric, wide-angle X-ray diffraction (WAXD), thermogravimetric analysis (TGA), notched impact test and dynamic mechanical thermal analysis (DMTA) were performed to estimate the influence of the composition ratio and the type of PACs on the physical, thermal, and mechanical properties of the copolymers. The use of the synthesized PACs reduced the polymerization time to several minutes. The copolymers showed improved impact resistance up to more than two times higher than those of the polyamide 6 (PA-6) homopolymer, without significant changes in their high melting temperatures.