PET-RAFT Enables Efficient and Automated Multiblock Star Synthesis

Abstract

We show that photoinitiated electron/energy transfer–reversible addition–fragmentation chain transfer (PET-RAFT) enables vastly superior control over the polymerization of multiblock star copolymers compared to conventional techniques. Monomodal distributions with dispersities <1.3 could be achieved after the 10th block despite pushing the polymerization to >95% conversion in each block extension. The improvement in control is likely due to the reabsorption of the free radical at the propagating chain end by the excited catalyst, which would otherwise lead to a termination product. Simple modeling shows the dramatic effect that this has in the case of star polymerizations. Because PET-RAFT is also tolerant to oxygen, we were able to automate the synthesis of up to heptablock stars at short block lengths, providing a useful technique for screening the effect of polymer composition on the solution structure.

PET-RAFT Increases Uniformity in Polymer Networks

“…Further, a recent study has reported the differences between photochemical and the traditional thermal RAFT polymerization using block polymers, indicating superior livingness for the photochemical approach. In 2022, Foster et al showed a similar conclusion, demonstrating the superior control of PET-RAFT compared to conventional RAFT using multiblock star polymers …”

“…In 2022, Foster et al showed a similar conclusion, demonstrating the superior control of PET-RAFT compared to conventional RAFT using multiblock star polymers. 12 Initially, photochemically driven RAFT polymerization has been achieved through the UV-based photolysis of CTAs through the photoiniferter process. 13−16 However, due to the harsh conditions and potential degradation of the CTA, highenergy UV light-irradiated systems can be challenging to implement.…”

Photocontrolled RAFT polymerization: past, present, and future

“…279 Finally, Chapman and coworkers analyzed the effects of the type of monomers (hydrophobic, hydrophilic, and charged) and their order of arrangements on the sizes and assemblies of multiblock star polymers in solution. 277 It is noted that the core of star polymers can be linked to either the R or Z group of the CTA (Scheme 23). In the Z-group approach, the polymers grow from the fragmented R group liberated from the core, whereas in the R-group approach, the polymers grow from the core.…”

“…279 Finally, Chapman and coworkers analyzed the effects of the type of monomers (hydrophobic, hydrophilic, and charged) and their order of arrangements on the sizes and assemblies of multiblock star polymers in solution. 277…”

“…For example, star or multi-arm polymers have been synthesized from multi-arm CTAs. 265,[276][277][278][279] Multi-arm TTCs were prepared from thiols, carbon disulfide, and scaffold molecules with multiple bromines which underwent substitution reactions, whereas multi-arm xanthates were prepared using xanthogenate instead of thiol and carbon disulfide. Multi-arm polymers have been examined for various applications.…”