Reactivity ratios of bio-based itaconates and acrylates in radical copolymerizations

Replacing petrochemically-based monomers by bio-based building blocks is an important topic in polymer chemistry. Recently, itaconic acid and its derivatives are investigated as potential alternatives. Free-radical polymerizations of these monomers are associated with a very low propagation rate. Moreover, the propagation reaction becomes reversible already at temperatures of 60 °C, which limits the accessible monomer conversion. To overcome these issues, copolymerizations with acrylates are attractive due to not being prone to depropagation at typical polymerization temperatures and fast propagation rates. Due to the presence of acrylate units in the copolymer higher monomer conversions are accessible compared to homopolymerizations. Since copolymer properties are strongly depending on the copolymer composition, their prediction via reactivity ratios (r values) is important. Here, r values determined via Monte Carlo simulations with consideration of depropagation are reported for several copolymerizations of three itaconates and four acrylates with non-functional ester groups. Polymer characterization is based on SEC elution curves and ¹H NMR spectra recorded with an 80 MHz benchtop NMR spectrometer. A common pair of reactivity ratios is obtained, with 1.50 and 0.54 for the itaconate and acrylate comonomer, respectively. It is shown that these r values can be transferred to other non-functional comonomer pairs.