Effect of ligand spacer on silica gel supported atom transfer radical polymerization of methyl methacrylate

Silica gels grafted with tetraethyldiethylenetriamine (TEDETA) and di(2-pic olyl)amine (DiPA) via poly(ethylene glycol) (PEG) spacers of different chai n lengths were synthesized and used as CuBr support for the atom transfer r adical polymerization (ATRP) of methyl methacrylate (MMA). The spacer lengt h strongly affected the polymerization rate and polymer molecular weight co ntrol. Catalyzed by CuBr immobilized on the silica gel, the MMA polymerizat ion rate increased with spacer length in the order of PEG(1) < PEG(10) < PE G(3) (the subscript is the number of the EG units). Copper bromide supporte d via three-unit PEG (SG-PEG(3)-TEDETA and SG-PEG(3)-DiPA) controlled the M MA polymerization best, producing PMMA with controlled molecular weights (i nitiator efficiency ca. 75%) and low polydispersities (M-w/M-n similar to 1 .2-1.4). The recycled catalysts had activities similar to the fresh ones at the late stage of polymerization with improved initiator efficiencies. The PMMA-block-poly(2-(NN-dimethylamino)ethyl methacrylate) with well-controll ed molecular weight and low polydispersity was also synthesized by this sup port system.