Synthesis of thermosetting poly(amide-ether) block copolymers and their shape memory properties

Abstract

Crosslinkable polyether-b-amides (XPEBA) were successfully prepared by combining three-armed acyl azo-functionalized N-methylbenzamide pentamers with a trimesic acid core (TMA-3MAB5N3) as the hard segment and NH2-terminated poly(ethylene oxide) (PEO; Mn = 8.0 kDa)/poly(propylene oxide) (PPO; Mn = 4.0 kDa) as soft segments in o-dichlorobenzene. TMA-3MAB5N3 was first prepared by reacting TMA-3MAB5 with diphenylphosphoryl azide (DPPA) in N-methyl-2-pyrrolidone (NMP) in the presence of triethyl amine at 20 °C for 12 h at 92.2% yield. Transparent to opaque crosslinked XPEBA films were successfully prepared from all samples via thermal polyaddition by the Curtius rearrangement, and the gel fraction was determined to be 68.3%–84.6%. The crystallization degree χc of the PEO segment in the crosslinked XPEBA films was estimated to be 52% to 58% by differential scanning calorimetry. The mechanical properties of the cured XPEBA films were controlled by changing the PEO/PPO ratio in the XPEBA formulation, where the tensile strength, elongation at break, and elastic modulus were in the range of 2.7 to 12.4 MPa, 328%–863%, and 0.13 to 3.6 GPa, respectively. The good shape memory properties of crosslinked XPEBA were confirmed by deformation at 80 °C, shape retention (memory) at room temperature, and shape recovery by reheating.