We have synthesized single-chain polymeric nanoparticles through the intramolecular formation of copper phthalocyanines from polystyrene-co-poly[4-((4-vinylbenzyl)oxy)phthalonitrile] under diluted conditions. Linear copolymer precursors carrying phthalonitrile pendant groups were prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization followed by intramolecular macrocyclization reactions to form Cu-metallated phthalocyanines, which concurrently enabled single chain nanoparticle formation. The preparation of copper phthalocyanines within a single chain nanoparticle was confirmed using FT-IR and UV/Vis spectroscopy. The intramolecular chain collapse was characterized by SEC and AFM.