Selective Grafting of Block Copolymers. 2. Multimetalated (Co)polymers as Initiators for Grafting Process. Model Metalation Studies

Metalation of polystyrene, poly(4-methylstyrene), and their block copolymers is described using either superbases (made of organolithium compounds and potassium tert-pentoxide) or sec-butyllithium complexed with N, N,N ‘ ,N ‘-tetramethylethylenediamine as metalating agents. Depending on the type and concentration of the metalating agent, different sites in the above polymers were metalated. Generally, only the most acidic and the most accessible hydrogen atoms in polystyrene (aromatic protons) and poly(4-methylstyrene) (methyl group protons) were selectively metalated using the above metalating agents at metalation ratios lower than unity. At higher metalation ratios, nonselective metalation occurred, and also other positions in the polymers (backbone, aromatic protons in poly(4-methylstyrene)) were metalated. To distinguish positions of metalation, functionalization of metalated polymers with chlorotrimethylsilane and subsequent 29Si NMR analysis of polymer-bonded trimethylsilyl groups were applied.