RAFT Step-Growth Polymerization of Diacrylates

Abstract

RAFT step-growth polymerization was previously demonstrated with monomers that bear low rate of homopropagation to favor the chain transfer process; by contrast, acrylates are known to be fast homopropagating monomers, thereby posing serious challenges for RAFT step-growth. Here, we identified a chain transfer agent (CTA) that rapidly yields single unit monomer inserted (SUMI) CTA adducts with a model acrylate monomer. Using a bifunctional reagent of this CTA, we successfully demonstrated RAFT step-growth polymerization with diacrylates, yielding linear polymer backbones. Furthermore, we achieved inclusion of functionality (i.e., disulfide) into RAFT step-growth polymer via a disulfide incorporated bifunctional CTA. Grafting from this backbone resulted in molecular brush polymers with cleavable functionality in each repeat unit of the backbone, allowing selective degradation to afford well-defined unimolecular species of two polymeric side chains. Given the wide selection of commercially available diacrylates, RAFT step-growth polymerization of diacrylates will further enable facile synthesis of complex architectures with modular backbones.

Step-growth polymerization by the RAFT process

“…29 To expand RAFT step-growth polymerization to acrylic monomers, Archer et al screened a selection of CTAs with butyl acrylate (BA) as the model monomer. 21 In their study, 4-cyano-4-(((dodecylthio)carbonothioyl)thio) pentanoic acid (CTA 1F ), bearing similar cyano-stabilized tertiary radical (R˙), only showed a limited rate of product formation (Fig. 3A).…”

“…These two criteria can be fulfilled by screening a selection of CTAs for a given monomer, which has been demonstrated with maleimides and acrylic monomers as detailed below. 16,21…”

Photoinduced RAFT Step‐Growth Polymerization toward Degradable Living Polymer Networks

“…[ 31‐41 ] Wei and coworkers have explored the RAFT step‐growth polymerization using various N ‐substituted maleimide monomers and further extended to acrylates recently. [ 42‐43 ] Our group has studied the polymerization of xanthate and vinyl ethers. To further expand the monomer scope, a series of unconjugated diene monomers were screened (Scheme 1A).…”

RAFT step-growth polymerization of bis-acrylamides and their facile degradation

“…Recently, You et al disclosed the successful thermal RAFT step-growth polymerization of bis-acrylates utilizing the same bifunctional trithiocarbonate CTA 2 . 31 This was significant because maleimides and vinyl ethers do not homopolymerize rapidly, whereas acrylates undergo rapid homopolymerization with trithiocarbonate based CTA, thus an extremely efficient SUMI must be achieved to ensure a successful RAFT step-growth polymerization free of acrylate homopropagation which will lead to branching and/or crosslinking. Highlighting the utility of this technique to prepare degradable bottle-brush polymers, the successful incorporation of degradable disulfide bonds was achieved using a custom CTA.…”