Evidence for chain transfer in the atom transfer radical polymerization of butyl acrylate

Poly(butyl acrylate (PBuA) of high molecular weight was synthesized by atom transfer radical polymerization (ATRP) in ethyl acetate. Whereas for low molecular weight polymers, a linear increase of the number-average molecular weight, (M) over bar(n), versus conversion and narrow molecular weight distributions indicate the suppression of side reactions, a downward curvature in the plot of (M) over bar(n) versus conversion was observed for high molecular weights ((M) over bar(n) > 50 000). This effect is explained by chain transfer reactions, leading to branched polymers. GPC measurements with a viscosity detector give evidence for the branched structure of high molecular weight polymers obtained in ATRP. In addition, transfer to solvent or monomer is likely to occur.