Investigation of the End Group Fidelity at High Conversion during Nitroxide-Mediated Acrylate Polymerizations

The impact of formation of midchain radicals-and more specifically the follow up reactions of beta-scission and macromonomer addition to propagating macroradicals stemming from this process-on the nitroxide-mediated polymerization of acrylates have been studied via kinetic modeling with the software package Predici on the example of butyl acrylate polymerization at 120 degrees C. Only small influences of the midchain radical formation on the livingness of the process is observed, however, large effects must be envisaged by the (reverse) scission reaction at high monomer-to-polymer conversions. A significant loss of livingness, depending on the temperature, monomer and initiator concentration must be expected at elevated stages of polymerizations. For a polymerization at 120 degrees C and a target chain length of 100, less than 75% livingness of the polymer product can be expected at 80% conversion. From this point of polymerization on, significant broadening of the overall polymer product is predicted in accordance to literature data and eventually the chain-length-conversion relation is lost at the end of reaction.