Synthesis and properties of multiblock copolymers based on polydimethylsiloxane and piperazine‐aromatic polyamides

Polydimethylsiloxane (PDMS)–polyamide multiblock copolymers were synthesized by three different methods, i.e., two‐step low‐temperature solution polycondensation, one‐step solution polycondensation, and interfacial polycondensation. In the two‐step method, α,ω‐diacid chlorideterminated polyamide oligomers were prepared from trans ‐2,5‐dimethylpiperazine (DMP) and terepthaloyl chloride (TPC) or isophthaloyl chloride (IPC) in chloroform in the presence of triethylamine, which in turn were subjected to reaction with α,ω‐bis (3‐aminopropyl) polydimethylsiloxane (PDMS–diamine) in the same solvent to from multiblock copolymers. In the one‐step method, the reaction components, DMP, TPC (or IPC), and PDMS–diamine, were reacted altogether in chloroform in the presence of triethylamine. In the interfacial method, the reaction components were also reacted altogether in an aqueous sodium hydroxide–chloroform two‐phase system. These polycondensations afforded the multiblock copolymers having inherent viscosities of 0.1–1.3 dL g −1 in m ‐cresol. The PDMS–polyamide multiblock copolymers dissolved in formic acid and 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFIP), and transparent, ductile, and elastomeric films were obtained by casting from the HFIP solutions. The films of the multiblock copolymers prepared by three different methods exhibited similar properties by means of thermal analysis and tensile measurements. In the multiblock copolymers, the tensile strength and modulus of the films decreased with increasing the PDMS content, whereas the elongation at break increased.