Structural Remodeling of Polymeric Material via Diffusion Controlled Polymerization and Chain Scission

Abstract

Here we show a synthetic system that uses reaction and diffusion to both grow new material via polymerization and remove material through polymer chain breakagemimicking the process of bone remodeling in a synthetic system. Researchers have explored the use of reaction/diffusion systems to pattern microstructures with success, but very little work focuses on using these processes to shape microstructures in a dynamic manner. This report provides an example of a dynamic system that can reshape itself using diffusion gradients. Mimicking this dynamic process could enable the development of materials that strengthen in response to repeated application of stress and are able to undergo remodeling after initial fabrication.

Integrated Extrinsic and Intrinsic Self‐Healing of Polysiloxane Materials by Cleavable Molecular Cages Encapsulating Fluoride Ions

“…First, the germoxane cages cleave upon hydrolysis of the Ge–O–Ge bonds to release F − . Second, the following two types of cleavage of the siloxane bonds in PDMS occur: i) the coordination of F − to silicon [ 10 , 20 ] promotes nucleophilic attack by H 2 O, resulting in the formation of Si–OH end groups (Figure 3a ), and ii) the nucleophilic attack of F − on the silicon atoms directly forms Si–O − and Si–F end groups (Figure 3b ). Si–OH groups can be subsequently formed by the attack of the Si–O − groups on H 2 O (Figure 3b ).…”

“…The next step is the reformation of the siloxane bonds. The nucleophilic attack of the Si–OH groups on the F − ‐coordinated silicon atoms in other PDMS chains [ 10 , 20 ] results in the exchange of Si–O–Si bonds (Figure 3c ). The Si–O − groups can also contribute to the exchange reactions (Figure 3d ).…”

“…[ 8 , 21 , 22 ] In addition, condensation between two Si–OH groups (Figure 3e ) and Si–OH and Si–O − groups (Figure 3f ) occur. [ 10a ]…”

“…We focus on molecular capsules of fluoride ion (F − ) for controlling the timing of the rearrangement of the Si–O–Si bonds. It is known that F − catalyzes the rearrangement of the Si–O–Si bonds [ 10 ] and that double‐four‐ring (D4R)‐type siloxane [ 11 ] and germoxane (Ge–O–Ge) [ 12 ] cage compounds can encapsulate F − . By incorporation of the molecular capsules of F − into siloxane networks, the rearrangement of the Si–O–Si bonds for self‐healing can be triggered by external stimuli to release F − .…”

Self-Amplified HF Release and Polymer Deconstruction Cascades Triggered by Mechanical Force

“…While HF is widely used in the synthesis of fluorine-containing compounds, such as fluoropolymers and pharmaceutical intermediates, we were drawn to its use as a versatile reagent for material remodeling. In particular, fluoride sources react readily with silica-containing materials, and this efficient characteristic has been applied in self-immolative polymers, remodeled siloxane elastomers, , vitrimer alteration, and degradable polymers. ,, The corrosiveness and toxicity of HF, however, present a safety concern for its handling and storage . We therefore set out to develop a latent source of HF that resides within a polymer until it is released in response to a mechanical signal, at which point it could be converted in situ to a fluoride salt for the uses described above.…”