R-RAFT or Z-RAFT? Well-Defined Star Block Copolymer Nano-Objects Prepared by RAFT-Mediated Polymerization-Induced Self-Assembly

Abstract

Reversible addition-fragmentation chain transfer (RAFT)-mediated polymerization-induced self-assembly (PISA) has served as a versatile platform for the large-scale preparation of block copolymer nano-objects with a diverse set of morphologies. However, almost all PISA formulations are focused on the syntheses of linear block copolymers rather than star block copolymers. Owing to the asymmetrical structure of the RAFT agent, herein, we report a direct comparison between Z-RAFT (the nonfragmenting group attached to the core) and R-RAFT (the fragmenting group attached to the core) strategies for preparing well-defined star block copolymer nano-objects via RAFTmediated PISA. We showed that the Z-RAFT strategy is a more suitable strategy for the preparation of star block copolymer nano-objects without compromising the control over the molecular weight and morphology. A binary mixture of Z-type and R-type tetrafunctional macro-RAFT agents was used to control the morphologies of star block copolymer assemblies. The effect of numbers of the RAFT group on polymerization kinetics and morphologies of block copolymer nano-objects was also investigated in detail. Finally, (ABC) 4 four-arm star triblock copolymer vesicles were prepared by seeded RAFT dispersion polymerization of solvophobic and solvophilic monomers using (AB) 4 four-arm star diblock copolymer vesicles as seeds. This research not only expands the scope for preparing well-defined star block copolymer nano-objects but also provides important insights into the effect of the polymer architecture on RAFT-mediated PISA.

Type I Photoinitiator-Functionalized Block Copolymer Nanoparticles Prepared by RAFT-Mediated Polymerization-Induced Self-Assembly

“…Typical self-assembled morphologies such as spheres, worms, vesicles, and large compound vesicles (LCVs) could be readily prepared by changing reaction conditions. Similar to other PISA formulations, increasing the monomer concentration and the DP of the core-forming block facilitated the formation of higher-order morphologies. − TPO-PPEGMA n -PHPMA m -CDPA block copolymer nanoparticles with various morphologies can also be prepared by redox-initiated RAFT-mediated PISA at room temperature (Figure S3).…”

Expanding the Scope of Polymerization‐Induced Self‐Assembly: Recent Advances and New Horizons

“…This can be attributed to the reason that R-type macro-RAFT agents are employed in these cases and all solvophobic blocks grow in the periphery of star block copolymers, which would enhance the bridging between particles. Very recently, Zeng et al [163] reported a direct comparison of alcoholic RAFT-mediated dispersion polymerization of styrene by using either R-type multifunctional macro-RAFT agents (the leaving group (R-group) is attached to the core) or Z-type multifunctional macro-RAFT agents (the nonfragmenting group (Z-group) is attached to the core), as shown in Figure 2. They found that using Z-type multifunctional macro-RAFT agents could lead to the formation of welldefined star block copolymers with narrow molar mass distributions (M w /M n < 1.30) and a variety of morphologies including spheres, worms, and vesicles.…”

“…Reproduced with permission. [163] Copyright 2020, American Chemical Society. can be attributed to the significant influence of chain ends, reduced hydrodynamic volume, and decreased chain-chain entanglement.…”

Polymerizations by RAFT: Developments of the Technique and Its Application in the Synthesis of Tailored (Co)polymers

“…Better control over the morphology of the nanoparticles could be achieved by using a binary mixture of the two RAFT agents. [ 100 ] Branching has also been used as a strategy to form star shaped nanoparticles. Initially linear poly( N ‐isopropyl acrylamide)‐ b ‐polystyrene (PNIPAM‐ b ‐PS) block copolymer was synthesized under dispersion PISA conditions forming spherical nanoparticles.…”