Polyurethane elastomers based on amphiphilic poly(caprolactone)-b-poly(butadiene)-b-poly(caprolactone) triblockcopolyols

Hydroxyl-terminated poly(butadiene) (HTPB; M_n = 2100 g mol⁻¹) was capped with 30 and 60 wt % of ɛ-caprolactone to reach amphiphilic triblock copolymers in form of capped poly(butadiene) CPB. The former (CPB30; M_n = 3300 g/mol) is amorphous with a glass temperature of −56 °C. CPB60 (M_n = 4000 g mol⁻¹) is semi-crystalline with a melting point of 50 °C and a glass transition at −47 °C. The CPBs, HTPB and polycaprolactone diol (M_n = 2000 g mol⁻¹) were used as soft segment components in the preparation of polyurethane elastomers (PUE), using a 1/1 mixture of an MDI prepolymer and uretonimine modified MDI, and hard phase components in form of 1,3-propane diol, 1,4-butane diol, and 1,5-pentane diol. CPB-based elastomers with 1,4 butane diol (8 wt %) show hard domains as fringed aggregates with a better connection to the continuous phase than the HTPB-based PUE. The soft segment glass transition temperature (T_g) is at −28 °C for HTPB-based PUE and at −43 °C for those of CPB. The tensile strength of the CPB30&60-based PUE is found between 20 and 30 MPa at an elongation at break of 400% and 550%, respectively.