Polymerization of n-butyl acrylate with high concentration of a chain transfer agent (CBr4): detailed characterization and impact on branching

Abstract

Poly(n-butyl acrylate) (polyn-BA) polymers synthesized by radical bulk polymerization in the presence and absence of a high concentration (0.4 mol L⁻¹) of carbon tetrabromide (CBr₄) as a chain transfer agent at nominal temperatures of 60, 100 and 140 °C were fully characterized by 1D and 2D NMR, SEC/MALS and MALDI-TOF mass spectrometry. The structures generated by chain transfer to CBr₄ in secondary chain-end radicals and reinitiation of polymer chains by CBr₃ radicals formed by chain transfer to CBr₄ reactions were identified by MALDI-TOF and NMR analysis. The potential structures that might have been created by chain-transfer to tertiary radicals (quaternary carbons with a Br unit) formed by backbiting or intermolecular chain transfer to polymer could not be detected and hence their abundance was not important. The branching density (BD) of the polymers synthesized in the presence and absence of CBr₄ was also determined. The BD increases with temperature in both cases, and for each temperature the branching density considerably reduced when CBr₄ was employed in the polymerization as found for other transfer agents and controlled radical mediated polymerizations. However, the explanation that patching on the tertiary radicals was the cause of reduction of the branching in the polyn-BA was discarded in this case because the resulting structures could not be identified.