Linear Gradient Quality of ATRP Copolymers

The linear gradient quality and the control over chain length and end-group functionality in the copolymerization of acrylates, methacrylates, and styrenes via atom transfer radical polymerization (ATRP) are evaluated by detailed kinetic Monte Carlo simulations with explicit tracking of macromolecules. In all simulations, diffusional limitations on termination are taken into account. The linear gradient quality is characterized by a linear gradient deviation ⟨GD⟩ ranging between 0 and 1. For a ⟨GD⟩ value of 0.06 or lower, the linear gradient quality is defined as excellent, whereas for ⟨GD⟩ values higher than 0.25 gradient copolymers of poor quality are formed (targeted chain length (TCL) = 100). Under batch ATRP conditions, using a catalytic system consistent with Cu(I)Br/PMDETA (PMDETA = N, N, N ′, N ″, N ″-pentamethyldiethylenetriamine), an excellent control over chain length and end-group functionality is possible, and copolymers with a good linear gradient quality at final conversion can be prepared. Moreover, for sufficiently high conversions and depending on the monomer reactivity ratios, a strong correlation exists between ⟨GD⟩ and the polydispersity index (PDI), allowing an approximate assessment of the linear gradient quality based on PDI. For higher targeted chain lengths, this correlation shifts toward lower ⟨GD⟩ values under controlled ATRP conditions.