Polyamide 4(PA4)-polyurethane(PU)-PA4 triblock copolymers performing property of thermoplastic elastomers were synthesized by isocyanate(NCO)-terminated polyurethane as an initiator and potassium pyrrolidonate(P-py) as a catalyst for anionic ring opening polymerization of 2-pyrrolidone. The PU-prepolymer was obtained by reaction 4,4''-methylene diphenyl diisocyanate(MDI) and poly(tetramethylene glycol)(PTMG) having average molecular weight 2,000. The catalyst, P-py was generated by adding assigned molar % of potassium tert-butoxide to the total 2-pyrrolidone polymerized. In the triblock copolymers similar to the conventional thermoplastic elastomers, such as SBS, the PU and the PA4 block act as soft block and a hard block, respectively. The chemical structure of the synthesized production from each step was identified by using FT-IR and 1H NMR. In addition the integral ratio of the 1H NMR spectrum and the gel permeation chromatography(GPC) data were used to obtain the molecular weight of the prepolymer applied and each block in the copolymer. Thermal and mechanical properties of the copolymers were characterized by differential scanning calorimetry(DSC) and universal test machine(UTM).
Molecular architecture of copolymer was controlled to contain different or same molecular weight of PA4 hard block with same or different molecular weight of PU soft block in order to investigate the effects from those differences on various properties of triblock copolymers as thermoplastic elastomer. As the results the mechanical strength and melting point(Tm) of the copolymers increased with increasing in the molecular weight of PA4 block while the elongation at break increased with increasing in that of PU block. It is expected that the PA4-PU-PA4 triblock copolymers will be applied for a compatibilizer to modify the thermal and the mechanical properties of commercialized PAs or PUs as well as for a heat resistant thermoplastic elastomers using under a relatively high temperature.