Synthesis of hyperbranched poly(ether nitrile)s as supporting polymers for palladium nanoparticles

A novel hyperbranched poly(ether nitrile) (HBPEN) and its copolymer were synthesized as supports for palladium nanoparticles (PdNPs). Soluble HBPEN and its copolymer were obtained by self-polycondensation of an AB2 monomer with or without an AB monomer. The study of the model reaction suggested the formation of HBPEN with a degree of branching (DB) of 0.37. Soluble linear poly(ether nitrile) (LPEN) was also synthesized from 2,2-bis(4-hydroxyphenyl)hexafluoropropane and 2,6-difluorobenzonitrile. The coordination of nitrile groups in the repeating unit with Pd2+ was confirmed by infrared measurements. The reduction of the coordinated complexes with NaBH4 resulted in the formation of HBPEN-, HBPEN copolymer- and LPEN-supported PdNPs. Both transmission electron microscopy images and X-ray diffraction patterns suggested that PdNPs supported by HBPEN (3.0±0.8 nm) were the smallest in size among these three polymers. A comparison of the three PdNPs suggested that the branched architecture in HBPEN can help prevent the aggregation of PdNPs generated in the early stages of reduction.