Multifunctional Block Copolymer: Where Polymetallic and Polyelectrolyte Blocks Meet

Sequential reversible addition–fragmentation transfer (RAFT) polymerization of a mixed sandwich cobaltocene monomer (η⁵-cyclopentadienyl-cobalt-η⁴-cyclobutadiene (CpCoCb)) and a phosphonium salt functionalized styrene monomer resulted in the first example of a unique multifunctional block copolymer consisting of a metallopolymer block and a polyelectrolyte block. The polyelectrolyte block was decorated with a gold anion (AuCl₄^–) via salt metathesis, resulting in a heterobimetallic block copolymer with distinct gold and cobalt sections. Solution self-assembly behavior of this unique metallopolymer-b-polyelectrolyte copolymer before and after salt metathesis was studied. Heterobimetallic micelles with a gold containing core and a cobalt-containing corona were obtained, and then the core was reduced to form gold nanoparticles (AuNPs). Studies on the solid-state self-assembly of this unique block copolymer showed that it phase separated into hexagonally packed cylinders. Salt metathesis of the phase-separated block copolymers was utilized as the first example of a nonstandard selective staining method to exclusively stain the polyelectrolyte domains with the AuCl₄^– anion. Staining the metallopolymer domain by RuO₄ provided the complementary pattern. Pyrolysis of the self-assembled block copolymers resulted in magnetic cobalt-phosphate nanoparticles with 17% char yield.