Assessment of end-group functionality in atom transfer radical polymerization of N-isopropylacrylamide

The “one-pot” “two-step” synthesis of well-defined poly(ethylene oxide-b-N-isopropylacrylamide-b-acrylamido-2-methyl-1-propane sodium sulfonate) (P[EO-b-NIPAm-b-AMPSNa]) triblock copolymers is reported in aqueous medium using atom transfer radical polymerization (ATRP) with Cu(I)Cl.Me6TREN (Me6TREN: tris[(2-dimethylamino)ethyl]amine) as catalyst and N,N-dimethylformamide (DMF) as cosolvent. Polymerization conditions leading to a high end-group functionality (EGF) during the first synthesis step, i.e. the formation of the P(EO-b-NIPAM) diblock copolymer, are selected based on kinetic modeling insights for the corresponding NIPAm ATRP homopolymerization. For these conditions, the significant influence of viscosity effects on the NIPAm ATRP kinetics is illustrated based on dynamic viscosity measurements of the saturated monomer solution and William-Landel-Ferry parameters for the polymer. The importance of cyclization and termination reactions for the loss of EGF is shown to be limited. Only at very high conversions, cyclization reactions can lead to a decrease of EGF to a minimal value of ca. 80%.