Hi everyone, So I'm a chemical engineering grad student and oddly enough I have been tasked with doing chemistry (strange I know). I'm currently doing atom-transfer radical polymerization (ATRP) using a metal (CuCl or CuBr) and a ligand (dNbpy or PDMETA). My monomer is a methacrylate group with a tert-butyl dimethyl silyl tail on it. Currently, I'm having an issue with my polymerization and I think it's caused by catalyst (CuCl) poisoning, but I was hoping someone here might be able to shed some light on the situation. Current State: I have CuCl, lightish green so it's oxidized a little bit, but I assume it's no big deal. I place in roughly a 2:1 molar ratio of ligand (dNbpy) and metal (CuCl). I then proceed to put in my monomer and initiator (the initiator is a 1:1 molar ratio with the metal compound). The dNbpy is solid and so is the CuCl, the monomer and initiator being liquids. As soon as the liquids meet with the solids, I get a reddish color that will (over the course of about ten to twenty minutes) go from red, to brown, to green. I know that Cu(II)Cl2 is a green color, so I assume that once it becomes green, the majority of the metal is in its oxidized state. For ATRP, the key (as I understand it) is for propagation to be slow and initiation to be fast. Control is possible through the activation of a radical by the initiator (or halogen capped group) and the Cu(I)Cl reacting to form a radical and Cu(II)Cl2. This is a reversible reaction so assuming that activation and deactivation occur at roughly the same speeds, I'd expect the reaction to be red with all Cu(I)Cl present, brown with a mixture of Cu(I)Cl and Cu(II)Cl2 present, and green when pure Cu(II)Cl2 is present. So I figured my solution, during polymerization, should be brown...however...the solution is green! This makes worried, especially since the polymerization is going 7 times slower than it normally should. Today I attempted to "very quickly" add the monomer and initiator and then freeze-pump-thaw (I always do this before polymerization) three times before the solution turned green. After three freeze/pump/thaw cycles, I saw no bubbles in the solution and assumed all the oxygen was gone. The solution was still red, and I then placed it in a heated oil bath (75oC) for the polymerization. 15-20 minutes later I checked on the polymerization (it's a bulk polymerization by the way) and the solution was green. I run all my polymerizations under vacuum, rather than over nitrogen or argon. Can anyone tell me if the color of ATRP-type polymerizations with CuCl is suppose to red, brown, or green during the polymerization? Catalyst poisoning is the only criminal I can think of for my failed reactions.