PDMA-g-PMMA (poly(N,N-dimethylacrylamide)-graft-poly(methyl methacrylate)) graft copolymers were synthesized by radical copolymerization of DMA (N,N-dimethylacrylamide) and vinyl-PMMA macromonomers with AIBN (2,2'-azobis(isobutyronitrile)) as an initiator. The association behavior of high molecular weight graft copolymers of PDMA-g-PMMA with low graft density in methanol-TBE (tris(hydroxymethyl)aminomethane-boric acid-EDTA) buffer solvent mixtures has been investigated by laser light scattering. With changing solvent quality, the PMMA side chains could be associated. The association points acted as cross-linking points which effectively increased the molecular weight of the associated graft copolymers and also prevented the entangled backbone chains from sliding away against one another. This association behavior could be used to improve the quasi-network formation of such copolymers as better separation media in DNA capillary electrophoresis. pBR322/Hae III digest was successfully separated within 10 min in a 10 cm long capillary with one base pair (bp) resolution (123/124 bp). The methanol component in the solvent mixture affected not only the polymer conformation in solution but also the DNA conformation. The average hydrodynamic radius of DNA decreased from 76.2 nm in 1 x TBE buffer to 43.7 nm in 30% methanol + 70% 1 x TBE (volume fraction) mixed solvent, resulting in a corresponding change in electrophoretic mobility.