Synthesis of surface initiated diblock copolymer brushes from flat silicon substrates utilizing the RAFT polymerization technique

The synthesis of a variety of well-defined diblock copolymer brushes, including poly(methyl methacrylate) (PMMA)-b-poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA), PMMA-b-poly(styrene) (PSty), and PSty-b-poly(methyl acrylate), was achieved via surface immobilized reversible addition-fragmentation chain transfer (RAFT) polymerization. Initially, silicon surfaces were modified with RAFT chain transfer agents (CTAs) by utilizing a modified atom transfer addition reaction involving a silicon wafer modified with (11-(2-bromo-2-methyl)propionyloxy)undecyltrichlorosilane and dithiobenzoyl disulfide. Diblock copolymer brushes were then prepared via sequential surface initiated RAFT polymerization from the immobilized CTA. Various characterization techniques including ellipsometry, contact angle measurements, grazing angle attenuated total reflectance-Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the immobilization of CTAs on the silicon wafer and the subsequent polymer formation. The addition of free CTA was required for the formation of well-defined diblock copolymer brushes, which subsequently resulted in the presence of free polymer chains in solution. The free polymer chains were isolated and used to estimate the molecular weights and polydispersity index of chains attached to the surface.