Linear Gradient Quality of ATRP Copolymers

Abstract

The linear gradient quality and the control over chain length and endgroup 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.

Exploring the Full Potential of Reversible Deactivation Radical Polymerization Using Pareto-Optimal Fronts

“…It has been indicated that the outcome of the ARGET ATRP is very sensitive to the initial concentrations. In particular, the amount of reducing agent has to be selected carefully, taking into account a trade-off between polymerization rate and livingness [29][30][31][32]. Moreover, by switching to continuous operation, a more industrial attractive process can be obtained [33,34].…”

Fed-Batch Control and Visualization of Monomer Sequences of Individual ICAR ATRP Gradient Copolymer Chains

“…However, in these kinetic studies, in which no explicit calculation of the copolymer composition is included, the fed/semi-batch addition of comonomer is accompanied by a low polymerization rate, a rather high dispersity and a relatively low livingness. As indicated in a recent kMC study of Van Steenberge et al [26] low dipersities are required for controlled linear gradient synthesis and it can therefore be expected that under the reported literature conditions still relatively high <GD> values are obtained, despite the linear relation between F 1,inst and x overall .…”

“…Except for reactions involving conventional radical initiator fragments, these intrinsic parameters are taken from a previous kinetic study on the related "normal" ATRP system [26]. For simplicity, a constant conventional radical initiator efficiency of 0.70 [22] is used and the activation/deactivation kinetic parameters related to the conventional radical initiator are taken equal to those of the secondary species.…”

“…Importantly, the sample size is sufficiently high to ensure an accurate simulation of the ICAR ATRP kinetics, i.e., convergence testing is performed. To assess the gradient quality of the obtained polymers, the recently introduced <GD> (GD: gradient deviation) polymer property, as introduced by Van Steenberge et al [26], is calculated in silico, in case the number average chain length is sufficiently high (>10), as for low average chain lengths ( ≤ 10) no true gradient behavior can be mimicked. In this <GD> calculation, first for each copolymer chain in a representative kinetic Monte Carlo sample, the individual monomer sequences are compared with those of the corresponding "perfect" linear gradient chain possessing the same chain length.…”

“…Furthermore, in the present work, the <GD> value is calculated without accounting for possible losses of low-quality oligomeric chains upon polymer isolation. For more details on the mathematical aspects of the applied kMC modeling approach, the reader is referred to Van Steenberge et al [26,32,34].…”