Effect of Ligand Spacer on Silica Gel Supported Atom Transfer Radical Polymerization of Methyl Methacrylate

Silica gels grafted with tetraethyldiethylenetriamine (TEDETA) and di(2-picolyl)amine (DiPA) via poly(ethylene glycol) (PEG) spacers of different chain lengths were synthesized and used as CuBr support for the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). The spacer length strongly affected the polymerization rate and polymer molecular weight control. Catalyzed by CuBr immobilized on the silica gel, the MMA polymerization rate increased with spacer length in the order of PEG1 < PEG10 < PEG3 (the subscript is the number of the EG units). Copper bromide supported via three-unit PEG (SG-PEG3-TEDETA and SG-PEG3-DiPA) controlled the MMA polymerization best, producing PMMA with controlled molecular weights (initiator efficiency ca. 75%) and low polydispersities (M w/M n ∼ 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-(N,N-dimethylamino)ethyl methacrylate) with well-controlled molecular weight and low polydispersity was also synthesized by this support system.