I synthesized 4,4'-bis(bromomethyl)-2,2'-bipyridine by brominating 4,4'-bis(methyl)-2,2'-bipyridine. I confirmed the presence of the bis substituted product by  NMR, but there also exist the mono substituted (with the other substituent remaining the unreacted methyl). 

Literature stated they used a column with DCM:Acetone (98:2) to separate the two. However, I was having trouble getting much separation between the two and also the TLC showed a lot of streaking. I messed around the the ratios and found that making it more polar (increasing the amount of acetone) lead to a greater separation on TLC, but it didn't carryover to the column.

Does anyone have any suggestions for a possible solvent system that could give better separation?