Impact of polymer particle purification on the structural and catalytic properties of in situ generated gold nanoparticles

This report describes the influence of polymer particle purification on the in situ generation of gold nanoparticles (AuNPs) and their catalytic properties. The use of purified polymer particles after radical polymerization solely yields the generation of smaller and more uniform AuNPs (average diameter from ~ 5 nm to ~ 14 nm), despite controlling the gold ions and reducing agent ratios. However, unpurified polymer particles allow for the formation of relatively larger and slightly polydisperse AuNPs (average diameter from ~ 14 to ~ 29 nm) with an elongated shape. Although the interactions between the AuNPs and polymer matrices are known to be very weak, the presence of additional hydrophilic small molecular species, including oligomers and unreacted monomers, readily disturbs the growth of AuNPs. Regardless of the purification, highly stable AuNPs are successfully incorporated across the polymer particles where the representative composite particles are tested as catalysts in the aerobic homocoupling of arylboronic acid. Although the experimental activation energy was examined to be very similar (56–57 kJ/mol), the turnover frequency was detectably different (~ 46/h and ~ 69/h for the composite particles possessing elongated AuNPs and ~ 58/h and ~ 81/h for the composite particles possessing uniform AuNPs). However, the composite particles possessing the uniform AuNPs have shown a greater catalytic reactivity (e.g., 30% higher yields) toward base-free homocoupling reactions. The influence of polymer particle purification is evident in the generation of AuNPs in situ, as well as their catalytic properties in the chemical reaction, which offers an interesting insight for designing various metal-polymer composite particles.