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.

Graphical Abstract

Keywords:

• Heck coupling
• palladium-catalyzed polymerization
• polycinnamamide
• bidentate phosphine palladium complex
• heterogeneous catalysis

Additional information

Funding

We thank the National Natural Science Foundation of China (Project 21664008), the Natural Science Foundation of Jiangxi Province of China (Project 20172BAB203015) and Key Laboratory of Functional Small Organic Molecule, Ministry of Education (No. KLFS-KF-201704) for financial support.