Termination of Surface Radicals and Kinetic Analysis of Surface‐Initiated RAFT Polymerization on Flat Surfaces

Abstract

si‐RAFT polymerization is widely used for surface modification. However, how the surface radicals terminate requires further elucidation. A kinetic model is developed for si‐RAFT via the R group approach. The model describes the molecular weight of grafted polymers as well as polymer layer thickness and various chain concentrations. It is shown that surface/surface radical termination plays an important role. The termination is facilitated by the migration of surface radicals through “hopping” and “rolling” mechanisms. “Hopping” occurs through activation/deactivation cycles between surface and solution chains, dependent on the RAFT concentration in solution. “Rolling” occurs through transfers between surface/surface chains, dependent on the grafting density at surface.

Factors Affecting Grafting Density in Surface‐Initiated ATRP: A Simulation Study

“…On the other hand, the termination theory justifies the deceleration through decreased active chain ends due to surface radical termination, which is assisted by radical migration through the reversible activation–deactivation reactions involved in ATRP. These two theories have also been used to offer explanation under which conditions the solution and surface chains possess similar or different properties in a simultaneous solution and surface polymerization . This helps to evaluate whether the properties of free polymer chains formed in solution can be used as an estimate for those of the grafted poly­mer brush on surface for calculation of grafting density, as often assumed in experimental studies.…”

The Kinetics of Surface‐Initiated RAFT Polymerization of Butyl acrylate Mediated by Trithiocarbonates

“…The polymerization was conducted in a system consisting of PTPT‐functionalized SiNPs, BA, toluene, AIBN, and free PTPT. The latter was added because doing so, a better control of the RAFT polymerization should be obtained . Employing TGA and SEC measurements (see Figure b,c in the Supporting Information) for the analysis of the obtained grafted polymeric material, the successful synthesis of a surface‐attached RAFT agent with a macromolecular polyBA‐leaving group ( R2 , Figure ) could be proven.…”

“…The worse control became apparent either by a constant molar mass of the polymer with increasing consumption of monomer or by high dispersity ( Ð ≥ 1.5) . The control could be improved by adding an additional free RAFT agent . These facts indicate that the kinetics of the RAFT equilibrium is significantly influenced by the surface anchorage of the RAFT agent.…”

Shielding Effects in Polymer‐Polymer Reactions, 6

“…It should be noted that for the R‐RAFT approach contact between free ends is relevant, however, predominant with the other end segments of both chains attached to the surface, which is beyond the scope of this study. Thus, we aim at the Z‐RAFT approach as a specific example although the R‐RAFT approach is more efficient in experiment, see, e.g., ref . for a recent discuss of the advantages and disadvantages of these methods.…”