Catalyst-Free, Visible-Light-Induced Step-Growth Polymerization by a Photo-RAFT Single-Unit Monomer Insertion Reaction

Abstract

Photoinduced polymerization is an attractive technique with the advantages of easy operation, mild conditions, and excellent temporospatial controllability. However, the application of this technique in step-growth polymerization is highly challenging. Here, we present a catalyst-free, visible-light-induced stepgrowth polymerization method utilizing a photo-RAFT single-unit monomer insertion reaction between the xanthate and vinyl ether groups. Benefitting from this reaction, a pendant cationic RAFT agent can be generated in each repeating unit of the polymer backbone. Both cationic and radical side chain extensions were successfully realized, providing a facile approach for the postpolymerization of step-growth polymers for the development of various functional polymeric materials.

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

“…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). Fortunately, we found a series of commercially available and affordable N-aromatic bismaleimides (Scheme 1D).…”

“…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…”

RAFT Step-Growth Polymerization of Diacrylates

“…This important insight was first investigated by McLeary and Klumperman, − and independently confirmed by Chen and Ghiggino with stoichiometric ratio of monomer to CTA. , Taking advantage of the RAFT-SUMI cycle, we recently reported RAFT step-growth polymerization by using bifunctional reagents bearing CTA and monomer functionalities that yield high SUMI-CTA adducts . RAFT step-growth polymerization synergistically combines the desirable features of both RAFT (functional group tolerance and user-friendly nature) and step-growth (functional backbone). , Shortly after, Li and Zhu independently reported a catalyst-free, photomediated RAFT step-growth …”

“…14,15 Shortly after, Li and Zhu independently reported a catalyst-free, photomediated RAFT step-growth. 16 Figure 1A outlines the proposed mechanism of RAFT stepgrowth polymerization. Specifically, the R • (fragmented CTA end group species) adds to the monomer end group (M) to generate the R-M • (k i ), which can react with R-group bearing CTA species (k add ) to form the chain transfer intermediate adduct.…”

“…However, branching would occur if R-M • reacts with additional monomer species, which is dictated by the homopolymerization rate of the monomer ( k p ). To limit this occurrence, monomers with low k p were chosen (maleimides and vinyl ether) in previous reports to promote chain transfer cycle. − To date, more reactive monomers such as acrylates that bear high k p have never been explored for RAFT step-growth polymerization.…”