Synthesis and characterization of three-arm polyamide 6-polyurethane block copolymer by monomer casting process

Three-arm polyamide 6-polyurethane (PA 6-PU) block copolymers were synthesized using ε-caprolactam as a monomer, caprolactam sodium as a catalyst, and a three-arm carbamyl caprolactam terminated polyurethane (PU) prepolymer as macroactivator. The three-arm PU prepolymer was formed from polyether glycerol (PPG) and diphenyl methane-4,4′ diisocyanate (MDI). The block copolymers were obtained using the monomer casting process (MC) of ε-caprolactam at different content of three-arm PU prepolymer (5–20%). In increasing the content of the soft phase, in Fourier transform infrared (FTIR), a displacement was observed in the band at 1637 cm−1, which is assigned to the amide I of polyamide 6 (PA 6) shifted to a higher wavenumber. This suggested an interaction between the amide group of the PA 6 and the urethane group of the PU. The effects of the PU prepolymer content on the mechanical properties of the block copolymers were investigated. The results showed that the impact strength of the block copolymers at 25 °C and −50 °C temperature could be significantly improved. The crystallization and melting behaviors, structure and thermal properties and morphological characteristic of the block copolymers were studied using the different techniques such as differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMTA) and scanning electronic microscopy (SEM).