Synthesis of methacrylate macromonomers using silica gel supported atom transfer radical polymerization

A silica gel supported CuBr-hexamethyl-triethylenetetramine (HMTETA) (SG-Cu Br/HMTETA) catalyst system was developed for the synthesis of poly-(methyl methacrylate) (PMMA) and poly(dimethylaminoethyl methacrylate) (polyDMAEMA) macromonomers with terminal vinyl or allyl group by atom transfer radical (ATRP). Catalyzed by SG-CuBr/HMTETA and with vinyloxyethyl 2-bromoisobutyra te (VBIB) or allyl 2-bromoisobutyrate (ABIB) as initiator, the MMA polymeri zation showed first order kinetics up to a 60% monomer conversion. The poly merization rate slowed down at higher conversions due to a reduction in rad ical concentration. Gel permeation chromatography (GPC) results showed that the decrease in radical concentration was caused by the reaction of radica ls with the initiator's vinyl or allyl group moieties. In contrast, the DMA EMA polymerization was first order kinetics throughout the polymerization. The molecular weights of the resulting PMMA and polyDMAEMA increased linear ly with conversion with low polydispersities, After the first run polymeriz ation, the catalysts were recycled for second and third runs. The recycled catalysts still mediated a living polymerization of MMA or DMAEMA, producin g polymers with controlled molecular weight and narrow polydispersity, but their catalytic activities decreased significantly. The reactivity reductio n of the recycled catalyst was due to radical side reactions that yielded a n extra amount of CuBr2 as well as the catalyst loss during recycling.