Kinetic modeling of the chain-end functionality in atom transfer radical polymerization

The evolution of chain-end functionality of polymers synthesized by atom transfer radical polymerization (ATRP) was modeled. By comparing various kinetic models, the effect of specific side reactions was estimated. The slow elimination of hydrobromic acid from the polymer end-groups as well as the thermal self-initiation of the monomer may affect the chain-end functionality. Although the polymerization possesses several characters of a living process (i.e. linear increase of molecular weight versus conversion, low polydispersity index), the final polymer may have a limited functionality. However, polymers with enhanced functionality can be prepared through adjusting certain experimental parameters such as conversion of the monomer or initial concentration of the reactants. Plots of the percentage of chain-end functionality versus [XMtm+1(L)z]0 for the bulk polymerization of styrene at 110 °C: [M]0 = 8.74 mol L−1, [RX]0 = 0.0874 mol L−1, [Mtm(L)z]0 = 0.0874 mol L−1. Simulation plots: ideal model (▪), CLD model (▵), thermal-initiation model (⧫), elimination model (○). The inset shows an expansion of the region 90 to 100% of the y-axis.