Unraveling Polymer Structures with RAFT Polymerization and Diels–Alder Chemistry

Abstract

Using Diels–Alders (DA) chemistry as a dynamic-covalent linkage, we explored the kinetic growth mechanism of polymer structures including starlike materials and nanogels. The use of reversible addition–fragmentation chain transfer (RAFT) polymerization allows for precise control of DA linkages within the polymer backbone. Controlling the competition between intra- and intermolecular cross-linking reactions allows for the preparation of polymer structures that can expand their volume after cleavage of the DA linkages as determined by dynamic light scattering (DLS). Macroscopically, this would be analogous to untying a rope ball knot, commonly termed a “monkey’s fist”.

Exploring polymer solubility with thermally‐responsive Diels‐Alder monomers: Revisiting the monkey's fist

“…In previous studies, polymer topology was altered by the cleavage of Diels‐Alder (DA) linkages within the main chain of the polymer 36–43 . Employing a mixture of DA reactions allowed materials to experience metamorphic changes 39,44 .…”

“…Other approaches utilized the DA linkages as a means to deconstruct branched materials to quantify their kinetic growth, which displayed controlled polymerization kinetics in the preparation of hyperbranched materials 40 . Using a difunctional monomer that contained a reversible DA linkage resulted in nanogel/starlike (NG/SL) structures 36 . In that work, a primary goal was to cleave DA linkages of the material through thermal treatment to observe the unraveled structures.…”

“…Instead of seeing purely linear structures after cyclo‐reversion of the DA adduct as hypothesized, a diverse range of molecular topologies were present. This was attributed to crosslinking within the polymers and underscored the complex interplay between inter‐ and intramolecular forces that dictate molecular folding trends 36 . Cloud point data of these samples were unpublished due to a lack of identifiable trends, which was correlated to complex topologies and variation in composition.…”

“…These polymers were synthesized via reversible addition‐fragmentation chain‐transfer (RAFT) polymerization, allowing for control of molecular weight and molecular weight distribution. A gradient composition was selected for this study to decrease synthetic burden, and to mimic the synthetic methodology employed in the preparation of NG/SL structures 36 . The polymer chain length and the comonomer feed ratio were systematically varied to evaluate their impact on the cloud point.…”

A Novel Approach for the Synthesis of Thermo‐Responsive Co‐Polyesters Incorporating Reversible Diels–Alder Adducts

“…The versatility of the DA chemistry allowed the creation of new monomers and the consequent constitution of sophisticated macromolecular thermo‐responsive architectures . An elegant example sees the DA chemistry as a dynamic covalent bond in association with RAFT polymerization to synthesize nanogels able to expand their volume after selective DA cleavage . Despite the proven synthetic potential of the DA reaction in polymer science and the fabrication of materials presenting peculiar thermal properties, the constitution of DA co‐polymers remains uncharted territory.…”