Preparation of a P(THF-co-PO)-b-PB-b-P(THF-co-PO) triblock copolymer via cationic ring-opening polymerization and its use as a thermoset polymer

The triblock copolymer poly(tetrahydrofuran-co-propylene oxide)-b-polybutadiene-b-poly(tetrahydrofuran-co-propylene oxide) [P(THF-co-PO)-b-PB-b-P(THF-co-PO)] was synthesized via the cationic ring-opening copolymerization of tetrahydrofuran (THF) and propylene oxide (PO) in the presence of hydroxyl-terminated polybutadiene (HTPB). The copolymerization mechanism was studied using Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), and size-exclusion chromatography coupled with multi-angle laser light scattering (SEC-MALLS). The results showed both active chain end (ACE) and activated monomer (AM) mechanisms contribute to the chain propagation process to different extents, and the copolyether segments in the triblock copolymer had a gradient microstructure accordingly. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and viscosity testing results showed that the triblock copolymer had lower T_g than HTPB, low crystallization tendency and viscosity, and excellent thermal stability. To explore its potential applications, the triblock copolymer was used to prepare elastomer by the thermosetting process. Dynamic thermomechanical analysis (DMA) and tensile test results indicated that the triblock copolymer based elastomer had lower T_g, as well as dramatically higher tan δ value and elongation at break, than HTPB based elastomer because of the introduction of copolyether segments.