US-20260125523-A1 - FLUXIONAL CARBON CAGE POLYMER NETWORKS

US20260125523A1US 20260125523 A1US20260125523 A1US 20260125523A1US-20260125523-A1

Abstract

Polymer networks including one or more polymers and a fluxional carbon cage are described. The fluxional carbon cage covalently crosslinks the one or more polymers to form the polymer network. Methods to synthesize the polymer network include preparing a fluxional carbon cage crosslinker, combining the fluxional carbon cage crosslinker with monomers and/or one or more polymers and a free radical initiator to form a mixture, and exposing the mixture to thermal energy and/or electromagnetic energy to form the polymer network.

Inventors

Matthew Golder
Peiguan Sun

Assignees

UNIVERSITY OF WASHINGTON

Dates

Publication Date: 20260507
Application Date: 20251106

Claims (20)

1 . A polymer network comprising: one or more polymers and a fluxional carbon cage, wherein the fluxional carbon cage covalently crosslinks the one or more polymers to form the polymer network.
2 . The polymer network of claim 1 , wherein the fluxional carbon cage has the structure: wherein carbons 1-10 of the fluxional carbon cage comprise a substituent selected from the group consisting of a hydrogen, a halogen, a hydroxyl group, an amino group, a carboxyl group, a carbonyl group, a nitro group, a thiol group, a cyano group, an alkyl group, and an aromatic group, and the fluxional carbon cage covalently crosslinked to the one or more polymers has the structure: wherein X 1 and X 2 independently comprise a hydrocarbon chain, an aromatic group, an amino group, a sulfur (S), or an oxygen (O), and R 1 comprises a first sidechain of the one or more polymers and R 2 comprises a second sidechain of the one or more polymers.
3 . The polymer network of claim 1 , wherein the fluxional carbon cage comprises a bullvalene, a barbaralyl cation, a barbaralyl radical, a barbaralane, a bullvalone, a barbaralone, or a semibullvalene.
4 . The polymer network of claim 1 , comprising the fluxional carbon cage in an amount of 1 mol % to 99 mol % of the polymer network.
5 . The polymer network of claim 1 , wherein the one or more polymers comprise at least one of an acrylate polymer, a polyester, a polysiloxane, a polyamide, a polyether, a polyolefin, a poly(vinyl ether), a polystyrene, a polyimide, a polysulfone, or a polyurethane.
6 . The polymer network of claim 5 , wherein the one or more polymers comprise alkyl polyacrylate, alkyl polymethacrylate, aryl polyacrylate, aryl polymethacrylate, or combinations thereof.
7 . The polymer network of claim 6 , wherein the one or more polymers comprise poly butyl acrylate or poly(methyl methacrylate).
8 . A method of synthesizing the polymer network of claim 1 , the method comprising: preparing a fluxional carbon cage crosslinker; combining the fluxional carbon cage crosslinker with monomers and/or one or more polymers and a free radical initiator to form a mixture; and exposing the mixture to thermal energy and/or electromagnetic energy to form the polymer network.
9 . The method of claim 8 , wherein the fluxional carbon cage crosslinker has the structure: wherein the Z 1 and Z 2 comprise an acrylate group or a methacrylate group.
10 . The method of claim 8 , wherein the monomers comprise at least one of: an acrylate monomer, an epoxy monomer, a methacrylate monomer, a styrene monomer, an acrylamide monomer, a diene monomer, a vinyl acetate monomer, or a acrylonitrile monomer.
11 . A composition comprising the polymer network of claim 1 .
12 . A thermosetting polymer comprising the polymer network of claim 1 .
13 . The thermosetting polymer of claim 12 , comprising an elastomer or a resin.
14 . A thermoplastic polymer comprising the polymer network of claim 1 .
15 . The thermoplastic polymer of claim 14 , comprising an elastomer or a resin.
16 . A force responsive material comprising: a polymer network comprising at least one polymer strand of one or more polymers covalently bound to a fluxional carbon cage, the at least one polymer strand configured to isomerize about the fluxional carbon cage by a sigmatropic rearrangement in response to a mechanical force acting upon the strand.
17 . The force responsive material of claim 16 , wherein an activation barrier of the fluxional carbon cage for the at least one polymer strand to isomerize about the fluxional carbon cage by a sigmatropic rearrangement in response to the mechanical force is in a range of 8 kcal/mol to 23 kcal/mol.
18 . The force responsive material of claim 16 , wherein, upon application of the mechanical force, the fluxional carbon cage isomerizes in the direction of a force vector of the mechanical force, thereby stiffening the force responsive material.
19 . The force responsive material of claim 16 , wherein the mechanical force comprises a compressive force, a shear force, or a tensile force and wherein the mechanical force comprises a static force, an oscillating force, a vibrational force, or an intermittent force.
20 . A kit comprising: a mixture of monomers, a fluxional carbon cage crosslinker, and a free radical initiator.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application claims priority to U.S. Provisional App. No. 63/717,100, which was filed on Nov. 6, 2024 and is incorporated by reference herein in its entirety. STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH This invention was made with government support under Grant No. W911NF2310106, awarded by the U.S. Army Research Office. The government has certain rights in the invention. FIELD OF THE DISCLOSURE The present disclosure relates to force responsive materials and polymer mechanochemistry. Particularly, improvements to polymer network structures within force responsive materials to provide energy absorption, improved strength, and lowered fragility are described. BACKGROUND Recent advances in polymer mechanochemistry have led to the development of force responsive materials. Force responsive materials include polymers that contain force-sensitive molecules (e.g., mechanophores) designed to undergo a chemical transformation when a mechanical force is applied to the material. Mechanophores are specific molecular units embedded within a polymer chain that are sensitive to tensile, shear, and compressive forces. For example, when a force responsive polymer material is stressed, the mechanical force is transmitted through the polymer chain(s) to the mechanophores. Incorporating force-responsive small molecules (e.g., mechanophores) into polymer networks can introduce properties such as cargo release, wherein a specific molecular cargo, such as a drug, catalyst, dye, etc., attached to the mechanophore is deliberately detached from the larger molecular structure when mechanical force is applied, or stress visualization, wherein embedded molecules act as sensors to produce a visual output, such as color change, fluorescence, luminescence, etc., that maps and quantifies mechanical forces within a material. Many force-responsive material systems are prized, however, for their “sacrificial bonds” that can dissipate exogenous force and enhance mechanical properties. Materials with such bonds can generally be separated into two categories-non-covalent (“low force” activation) (FIG. 1, panel A) and covalent (“high force” activation) (FIG. 1, panel B) depending on how the mechanically-active units are structured. Non-covalent systems take advantage of supramolecular interactions and/or mechanical bonds; specific examples include soft materials containing folded proteins, π-π aromatic stacking hydrogen-bonding, metal-organic motifs, rotaxanes, and catenanes. Adaptations in these systems are generally reversible with low activation barriers. On the other hand, systems bearing covalent mechanophores use higher energy barrier chemical transformations to adapt to applied mechanical force (e.g., pericyclic reaction). Specific examples include reversible retro-[4+2] Diels-Alder reactions for adaptable materials and non-reversible cycloreversions for tear resistance or toughening. SUMMARY OF DISCLOSURE This Summary is provided to introduce a selection of concepts in a simplified form that is further described below in the Detailed Description. This Summary is not intended to identify all key features or essential features of the claimed subject matter, nor is it intended to be used alone as an aid in determining the scope of the claimed subject matter. The present disclosure presents a novel class of “low force” activation materials mediated by covalent bonds (i.e., chemical reactions). The low force bonds of non-covalent interactions can provide reversible energy absorption and self-recovery, however they also introduce a trade-off between strength and recovery. Increasing the density of weak reversible bonds, for example, enhances toughness but can reduce stiffness and long-term strength of a material. Non-covalent interactions may require long times or specific conditions (heat, moisture) to re-form after deformation. Non-covalent bonds may also be susceptible to environmental sensitivity, for example, hydrogen bonding and metal-ligand coordination can be influenced by humidity, pH, or temperature, affecting performance consistency. Covalent, high-force bonds offer advantages over non-covalent bonds to deliver robust toughness and fracture resistance in force responsive materials as they are able to deform, absorb shocks, and recover from mechanical stress. Challenges remain, however, in achieving fully reversible, durable, and scalable molecular systems that use covalent bonds. Many covalent mechanochemical reactions are one-time events. After activation, they cannot reform, leading to fragility and permanent structural degradation over repeated cycles. Furthermore, synthetic complexity of force responsive materials, including the positioning of mechanophores and control of network architecture, has made it difficult and costly to achieve substantial advancements in these materials as well as production on an industrial scale. Polymer networks of the present disclosure can include o