Sugar‐Based Polymers from d‐Xylose: Living Cascade Polymerization, Tunable Degradation, and Small Molecule Release

Abstract

Enyne monomers derived from D‐xylose underwent living cascade polymerizations to prepare new polymers with a ring‐opened sugar and degradable linkage incorporated into every repeat unit of the backbone. Polymerizations were well‐controlled and had living character, which enabled the preparation of high molecular weight polymers with narrow molecular weight dispersity values and a block copolymer. By tuning the type of acid‐sensitive linkage (hemi‐aminal ether, acetal, or ether functional groups), we could change the degradation profile of the polymer and the identity of the resulting degradation products. For instance, the large difference in degradation rates between hemi‐aminal ether and ether‐based polymers enabled the sequential degradation of a block copolymer. Furthermore, we exploited the generation of furan‐based degradation products, from an acetal‐based polymer, to achieve the release of covalently bound reporter molecules upon degradation.

Controlled Living Cascade Polymerization of Polycyclic Enyne Monomers: Leveraging Complete Degradability for a Stereochemical and Structural Investigation

“…Previously, we demonstrated that our sugar-based polymers with acetal or hemi-aminal ether linkages (contained in every repeat unit) could be fully degraded under mild acidic conditions to well-defined small molecules. 13,14 As complete repeat units in P1 and P2 also contain 2,5-dihydrofuran moieties, they could be cleaved under dilute HCl conditions to generate furan moieties (Figure 4), which provided easily identifiable downfield signals in the 1 H NMR spectrum. On the other hand, the interrupted repeat unit linkages were stable under the degradation conditions.…”

“…10−12 Recently, we successfully polymerized new enyne monomers (2) derived from sugars (glucose, galactose, or xylose). 13,14 Substituents on the dihydro-2H-pyran core of the monomers, and their stereochemistry, had an appreciable influence on the cascade polymerization performance. For instance, having an anti-relationship between the substituents on the ring enabled faster and better controlled polymerization.…”

“…For instance, having an anti-relationship between the substituents on the ring enabled faster and better controlled polymerization. 13 To date, the cascade polymerization of enyne monomers has been used to prepare a diverse range of polymers, including dendronized, 12 sequenced-controlled, 15,16 degradable, 13,14,17 and cargo-releasing polymers. 14 In order to further expand the scope of polymer structures, we set out to develop new monomers (e.g., 4) which undergo extended cascade sequences.…”

“…13 To date, the cascade polymerization of enyne monomers has been used to prepare a diverse range of polymers, including dendronized, 12 sequenced-controlled, 15,16 degradable, 13,14,17 and cargo-releasing polymers. 14 In order to further expand the scope of polymer structures, we set out to develop new monomers (e.g., 4) which undergo extended cascade sequences. We recently applied the concept of extended cascade sequences to the metathesis and metallotropy (M&M) polymerization 18,19 by increasing the number of alkyne moieties in a monomer to promote multiple RC and metallotropic shift reactions and thus increasing the number of rings in the repeat unit.…”