Mechanistic Investigation of the Position of Reversible Addition–Fragmentation Chain Transfer (RAFT) Groups in Heterogeneous RAFT Polymerization

Abstract

Heterogeneous reversible addition–fragmentation chain transfer (RAFT) polymerization is of growing interest as an in situ route to well-defined block copolymers and block copolymer nanoparticles. Recent investigations on heterogeneous RAFT polymerization have demonstrated that the position of RAFT groups has a significant effect on the nature of heterogeneous RAFT polymerization as well as the final block copolymer nanoparticles. Herein, we investigated RAFT dispersion polymerization mediated by an R-type macromolecular RAFT (macro-RAFT) agent or a Z-type macro-RAFT agent. We found that well-controlled polymerization was achieved in the R-RAFT dispersion polymerization, while uncontrolled polymerization occurred in the Z-RAFT dispersion polymerization (i.e., low monomer conversion, broad molar mass distribution, and low blocking efficiency). This problem could be addressed by using a binary mixture of the R-type macro-RAFT agent and the Z-type macro-RAFT agent. Additionally, RAFT seeded dispersion polymerization was also employed to improve the RAFT controllability of the Z-RAFT dispersion polymerization. Well-controlled polymerization was observed in each case regardless of the position of RAFT groups. Finally, the spatial distribution of RAFT groups could significantly affect the morphologies of block copolymer nanoparticles. This study not only provides important insights into the mechanism of heterogeneous RAFT polymerization but also enables one to control the position of RAFT groups within block copolymer nanoparticles without compromising the RAFT controllability.

In Situ Synthesis of Branched Block Copolymer Assemblies via RAFT Dispersion Polymerization Using Branched Macro‐RAFT Agents†

“…Over the past thirteen years or so, polymerization‐induced self‐assembly (PISA) has become an efficient and versatile approach for the synthesis of various block copolymer assemblies at high polymer concentrations (10—50 wt%). [ 5‐43 ] PISA involves the growth of a second block from a soluble precursor block that forms a block copolymer. The second block becomes insoluble as increasing the molar mass, which drives in situ self‐assembly of the block copolymer during polymerization.…”

Multiblock copolymer synthesisviaRAFT emulsion polymerization

“…171 Additional advantages include easier surface functionalization and removal of both the RAFT moiety and the solvophilic block, if desired. 172,173 It thus may be of interest to use such macroRAFTs for the synthesis of multiblock copolymers; block copolymers have already been synthesized via PISA and dispersion polymerization in this manner. 171–174…”

“…172,173 It thus may be of interest to use such macroRAFTs for the synthesis of multiblock copolymers; block copolymers have already been synthesized via PISA and dispersion polymerization in this manner. 171–174…”

“…172,173 It thus may be of interest to use such macro-RAFTs for the synthesis of multiblock copolymers; block copolymers have already been synthesized via PISA and dispersion polymerization in this manner. [171][172][173][174] While previous systems exhibit relatively low molecular weights for multiblock copolymers, Clothier et al demonstrated that through prudent control over experimental parameters in conjunction with a judicious choice of the colloidal stabilizing macroRAFT, high molecular weight multiblock copolymers can be synthesized with low reaction times (30 min per block), low dispersities, and high conversions. 40 This was achieved even for low k p monomers (methacrylates), courtesy of the compartmentalization effect in emulsion polymerization.…”

Exploiting the Monomer-Feeding Mechanism of RAFT Emulsion Polymerization for Polymerization-Induced Self-Assembly of Asymmetric Divinyl Monomers

“…The Zhang group − prepared a series of highly cross-linked polymer microspheres for molecular imprinting through either atom transfer radical precipitation polymerization or RAFT precipitation polymerization. Recently, polymerization-induced self-assembly (PISA) via heterogeneous RAFT polymerization has emerged as an effective method for the preparation of block copolymer nanoparticles with diverse morphologies. − However, copolymerizing the core-forming monomer with divinyl monomers in PISA is always challenging, since the formation of highly cross-linked network during the early stage of PISA would restrict swelling and the subsequent chain reorganization . Therefore, it is difficult to induce the morphological transition of block copolymer nanoparticles in the presence of divinyl monomers.…”