Recyclable heterogeneous palladium-catalyzed Heck coupling polycondensation of bis(acrylamide)s with aromatic diiodides towards polycinnamamides

Abstract

A new and practical method for the preparation of high molecular weight polycinnamamides has been developed through a heterogeneous palladium-catalyzed Heck coupling polycondensation of bis(acrylamide)s with aromatic diiodides. The polymerization proceeded smoothly in DMF at 100 °C in the presence of a magnetic nanoparticles-anchored bidentate phosphine-palladium(II) acetate complex [Fe3O4@SiO2-2P-Pd(OAc)2] and tributylamine, yielding a series of polycinnamamides with inherent viscosities up to 0.89 dL/g and a low level of palladium residue (below 10 ppm). The polycinnamamides obtained were quite soluble in dipolar aprotic solvents and had glass transition temperatures ranging from 221 to 269 °C and 10% weight loss temperatures ranging from 437 to 458 °C in nitrogen. These polymers could afford transparent and tough films by solution-casting with tensile strengths of 59.6–82.8 MPa, tensile moduli of 1.78–2.12 GPa, and elongations at break of 7.5–12.5%. The Fe3O4@SiO2-2P-Pd(OAc)2 catalyst can be conveniently separated from the polymer and recovered by simply using an external magnetic field, and recycled at least eight times without apparent decrease in catalytic efficiency.