Reversible-Addition Fragmentation Chain Transfer Step-Growth Polymerization

Abstract

Reversible-addition fragmentation chain transfer (RAFT) polymerization has been widely explored since its discovery due to its structural precision, versatility, and efficiency. However, the lack of tunability of the polymer backbone limits some applications. Herein, we synergistically combine RAFT and step-growth polymerization mechanisms, by employing a highly selective insertion process of a single monomer with a RAFT agent, to achieve RAFT step-growth polymerization. A unique feature of the RAFT step-growth polymers is that each backbone repeat unit bears a pendant RAFT agent, which can subsequently graft side chains in a second polymerization step and afford molecular brush polymers. Enabled by cleavable backbone functionality, we demonstrate transformation of the resulting brushlike polymers into linear chains of uniform size upon a stimulus.

Reversible addition–fragmentation chain transfer step-growth polymerization with commercially available inexpensive bis-maleimides

“…1A). As seen in our original report, 7 the formation of oligomeric cyclic species significantly lowers the M n and results in higher dispersity ( Đ = M w / M n ) (Fig. S2 and Table S1†).…”

“…37,38 It's important to emphasize, our modular nature of the step-growth backbone offers facile synthetic route for biological clearance. 7,39 In summary, we demonstrated RAFT step-growth polymerization using commercially available and cheap N-substituted bismaleimide monomers. In all cases (four examples), the evolution of molecular weight averages with conversion and intrinsic viscosity as function of molecular weight were both consistent with linear step-growth polymerization.…”

“…In our initial report, 7 we found trithiocarbonate-based CTA bearing carbonyl ester stabilized tertiary radical fragmentable R-group and N-alkyl maleimidic monomer functionality to successfully allow RAFT step-growth polymerization. 7 It is noteworthy, in addition to our initial report, Zhu et al have recently demonstrated successful RAFT step-growth using xanthate-based CTA bearing carbonyl ester stabilized secondary radical fragmentable R-group and vinyl ether. 18 The main draw-back of our original approach was the difficulty in preparing maleimidic monomer, which requires multiple synthetic steps (Scheme 1C).…”

“…In the preceding literature, Moad, 9–11 Zard 12 and Xu 13–17 have exploited various pairing of monomers and CTAs for selective insertion process of a single monomer to CTA. In our initial report, 7 we found trithiocarbonate-based CTA bearing carbonyl ester stabilized tertiary radical fragmentable R-group and N -alkyl maleimidic monomer functionality to successfully allow RAFT step-growth polymerization. 7 It is noteworthy, in addition to our initial report, Zhu et al have recently demonstrated successful RAFT step-growth using xanthate-based CTA bearing carbonyl ester stabilized secondary radical fragmentable R-group and vinyl ether.…”

“…4 On the other hand, Reversible Addition–Fragmentation Chain-Transfer (RAFT) polymerization 5 has been widely adopted due to its adaptability and user-friendly nature to design polymers with controlled architecture; 6 however, the scope of the polymer backbone is typically limited to inert C–C bonds from vinyl monomers. To overcome these limitations, we have recently reported a RAFT step-growth polymerization, 7 which combines user-friendly nature of RAFT polymerization and versatility of polymer backbone.…”