Gel formation in atom transfer radical polymerization of 2-(N,N-dimethylamino)ethyl methacrylate and ethylene glycol dimethacrylate

Copolymers of 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA) and ethylene glycol dimethacrylate (EGDMA) were synthesized via atom transfer radical polymerization using ethyl 2-bromoisobutyrate as the initiator, Cu(I)Br as the catalyst, and 1,1,4,7,10,10-hexamethyltriethylene tetramine as the ligand. At low crosslinker levels, the polymerizations followed the first-order kinetics. However, when the crosslinker level was above 10 mol %, the ln([M](0)/[M]) versus time curves showed deceleration at medium conversions because of the higher reactivity of EGDMA than that of DMAEMA. An acceleration at high conversions was also observed and probably caused by the diffusion limitations of catalyst/ligand complex in the polymer network. The hydrogels were characterized by swelling experiments, and the Sol polymers were characterized by the size exclusion chromatographic technique to determine the number-average molecular weight and polydispersity. The gel data were analyzed and, via a comparison to Flory's gelation theory, found to be more homogeneous than similar hydrogels prepared by conventional free-radical polymerization methods. (C) 2001 John Wiley & Sons, Inc.