Active kinetic chain length: Guide for control in atom transfer radical polymerization

•Active Kinetic Chain Length (AKCL) is a general guideline for well-controlled ATRP.•The smaller AKCL can decrease polydispersity and diminish the radical termination.•The fraction of terminated chains (FTC) depends on the ratio kact[Cu(I)]/kde[Cu(II)]•Comparing the parameter effect in ATRP by equation, MC simulation and experiment.•This AKCL criterion could be extended to other controlled/living polymerizations. Since atom transfer radical polymerization (ATRP) was developed, various strategies have been adopted to design well-controlled ATRP procedures. However, there is no single criterion that could be used for various ATRP reaction conditions (e.g., different monomers, different targeted degrees of polymerization, conversions, etc.). In this work, we introduce a new factor - Active Kinetic Chain Length (AKCL) as a parameter that can guide the design of well-controlled ATRPs. Under a certain reaction system with a specific monomer type (kp), monomer concentration ([M]0), and targeted degrees of polymerization, the smaller value of AKCL, i.e., a smaller initial number of monomer units added to a growing chain during a chain active period, can decrease polymer dispersity and also diminish the radical termination. The effects of AKCL were compared with other parameters affecting dispersity and livingness in ATRPs, which clearly demonstrates the design principle of AKCL. The model examples of deactivation-enhanced ATRP (DE-ATRP) have further shown the effectiveness of this criterion.