Dehydrocoupling amino acids and water with polymethylhydrosiloxanes and materials synthesized thereby

Abstract

Forming a crosslinked polymer includes combining one or more amino acids, water, or a combination thereof and one or more hydride-functionalized silicon-containing polymers in the presence of a catalyst to yield a mixture, and reacting the one or more amino acids, water, or combination thereof with the one or more hydride-functionalized silicon-containing polymers to yield a crosslinked polymer comprising Si-O and Si-N bonds.

Description

Attorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-cDEHYDROCOUPLING AMINO ACIDS AND WATER WITH POLYMETHYLHYDROSILOXANES AND MATERIALS SYNTHESIZED THEREBYCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Patent Application No. 63 / 698,677 filed on September 25, 2024, which is incorporated herein by reference in its entirety.STATEMENT OF GOVERNMENT SUPPORT

[0002] This invention was made with government support under 2154359 awarded by the National Science Foundation. The government has certain rights in the invention.TECHNICAL FIELD

[0003] This invention relates to dehydrocoupling amino acids and water with polymethylhydrosiloxanes and materials synthesized thereby.BACKGROUND

[0004] Polyurethanes have been shown to excel at acting as materials for cushioning, mattresses, insulation, packaging, and acoustic absorbers. This is due at least in part to their insulating, porous, and physical properties.

[0005] Traditional polyurethane is synthesized through the reaction of bifunctional isocyanates with bifunctional alcohols. To synthesize the polyols typically requires a catalyst, several of which contain antimony, fluorides, titanium, aluminum, and cyanides. Isocyanates can be synthesized using amine materials followed by the use of phosgene, which is extremely toxic. Additionally, isocyanates are toxic and release volatile organics. Alternative routes that substitute isocyanates for other chemicals typically require high pressure and the use of gas.

[0006] To create the polyurethane once the starting materials are obtained often requires a catalyst. While there are some organic options, several organometallic catalysts are used that contain antimony, tin, bismuth, lead, or mercury, which present toxicity concerns. In addition, polyurethane synthesis usually involves surfactants due to the poor solubility of polyols and isocyanates. This introduces more chemical waste. Synthesis also may require various stirring times, and additives for crosslinking or morphology purposes.Attorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-c

[0007] Blowing agents are usually also added to induce foaming. Usually, volatile organic compounds or hydrofluorocarbons are used, which are both highly concerning due to their contributions to the greenhouse gas effect. One alternative blowing agent that can be used is water, however, this reacts with isocyanate to produce CO2, which is a greenhouse gas. The addition of gases to polyurethanes creates pores. This typically involves the use of fluorocarbons, which form toxic compounds, accumulate in the environment, and are contributors to the greenhouse gas effect.

[0008] Current methods for recycling polyurethane foams involve either mechanical or chemical recycling. Mechanical recycling requires laborious grinding, milling process, and often high pressure and temperatures, wasting energy, resources, and requiring mechanical equipment. Additionally, in such methods polyurethane is not chemically broken down to be re-used, it can only be physically re-used for different purposes. Additionally, after contamination, postconsumer polyurethane waste is not suitable for mechanical recycling.

[0009] Chemical methods of recycling polyurethane involve hydroglycolysis, which requires glycols and high temperatures to obtain a partial mixture of starting material. Aminolysis is another option, but it often requires chlorinated solvents, mechanical grinding, high temperatures, inert gas, and a catalyst. Phosphorolysis is another option, but requires the addition of phosphoric acids or phosphoric esters, which is chemically wasteful. Other methods include gasification or pyrolysis which can only be used on scraps to produce syngas or oil and gas mixtures, respectively, not the original starting materials.

[0010] While hydrolysis is an option for polyurethane recycling, it requires an anaerobic environment and high temperature and high pressure, which is economically and environmentally costly. For this reason, hydrolysis of polyurethane is not commercial. The resulting products can only be used as additives for polyurethane production (they do not recover the starting materials).

[0011] Landfilling is the most used disposal method for polyurethane. This is both environmentally challenging and land consuming. Once polyurethane is left in the environment or landfill, its degradation is complicated. Research on polyurethane degradation is limited and often involves the addition of microorganisms. Polyurethanes are known to be resistant to biodegradation. Specific conditions and bacteria, fungi, or enzymes are needed to break down the polyurethane chemically.Attorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-cSUMMARY

[0012] This disclosure describes dehydrocoupling of polymethylhydrosiloxanes, amino acids, and water in varying ratios and materials synthesized thereby. Depending on the amino acid used, the reaction conditions, the loading of each component or mixture of components in the formulation (including PMHS or PMHS-PDMS copolymers, water, adventitious humidity, and catalyst) the materials range from porous foams to hard or soft gel-like materials. With the use of bio-based amino acids and biodegradable polymethylhydrosiloxanes, these materials are green alternatives to polyurethanes. These materials are also of interest in medical applications since the reagents used are non-toxic. In addition to their greener synthesis and nature, they offer potential for chemical recyclability upon prolonged exposure to water in order to cleave the Si-N and silyl ester bonds and regenerate the amino acid and a siloxane material that may be reused. Siloxane materials are known to break down in the environment to form sand due at least in part to the favorable formation of Si-0 bonds.

[0013] Although the disclosed inventive concepts include those defined in the attached claims, it should be understood that the inventive concepts can also be defined in accordance with the following embodiments.

[0014] Embodiment 1 is method of forming a crosslinked polymer, the method comprising: combining one or more amino acids, water, or a combination thereof and one or more hydride-functionalized silicon-containing polymers in the presence of a catalyst to yield a mixture; and reacting the one or more amino acids, water, or combination thereof with the one or more hydride-functionalized silicon-containing polymers in the mixture to yield a crosslinked polymer comprising Si-0 and Si-N bonds.

[0015] Embodiment 2 is the method of embodiment 1, wherein the one or more amino acids comprise L-lysine, L-serine, or a combination thereof.

[0016] Embodiment 3 is the method of embodiment 1 or 2, wherein the one or more hydride- functionalized silicon-containing polymers comprise PMHS, PMHS-PDMS co-polymers, or a combination thereof.

[0017] Embodiment 4 is the method of any one of embodiments 1-3, wherein the catalyst comprises NaH.Attorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-c

[0018] Embodiment 5 is the method of any one of embodiments 1-4, wherein the reacting occurs at room temperature and pressure.

[0019] Embodiment 6 is the method of any one of embodiments 1-5, wherein the crosslinked polymer is in the form of a foam or a gel.

[0020] Embodiment 7 is the method of embodiment 6, wherein the crosslinked polymer is in the form of a porous foam.

[0021] Embodiment 8 is the method of embodiment 7, wherein the porous foam defines pores having an average diameter in a range of 500 pm to 1000 pm, as determined by SEM analysis.

[0022] Embodiment 9 is the method of any one of embodiments 1-8, further comprising contacting the crosslinked polymer with an excess of water to yield the one or more amino acids and a siloxane material.

[0023] Embodiment 10 is the method of any one of embodiments 1-9, wherein the reacting further yields hydrogen gas.

[0024] Embodiment 11 is the method of any one of embodiments 1-10, wherein the reacting comprises dehydrocoupling.

[0025] Embodiment 12 is the method of any one of embodiments 1-11, wherein the reacting occurs in the absence of a solvent.

[0026] Embodiment 13 is the method of any one of embodiments 1-12, wherein the reacting occurs in air or under nitrogen.

[0027] Embodiment 14 is the method of any one of embodiments 1-13, wherein the mixture comprises 50 wt% to 99.999 wt% of the one or more hydride-functionalized silicon-containing polymers.

[0028] Embodiment 15 is the method of any one of embodiments 1-14, wherein the mixture comprises up to 50 wt% of the one or more amino acids and up to 10 wt% water, wherein the total amount of the one or more amino acids and the water is at least 0.001 wt%.

[0029] Embodiment 16 is the method of any one of embodiments 1-15, wherein the mixture comprises up to 5 wt% of the catalyst.

[0030] Embodiment 17 is the method of any one of embodiments 1-16, wherein, when the mixture comprises one or more amino acids, the reacting comprises dehydrocoupling between Si-H groups of one of the one or more hydride-functionalized silicon-containing polymers andAttorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-c one of the one or more amino acids to yield hydrogen gas and an intermediate in which an oxygen of the one or more amino acids is covalently bonded to a silicon of one of the one or more silicon-containing polymers.

[0031] Embodiment 18 is the method of embodiment 17, wherein the reacting further comprises dehydrocoupling between Si-H in a first additional chain of one of the one or more hydride-functionalized silicon-containing polymers and a first amine group of the one of the one or more amino acids, thereby crosslinking the chain and the first additional chain.

[0032] Embodiment 19 is the method of embodiment 18, wherein the reacting further comprises dehydrocoupling between a second amine group of the one of the one or more amino acids and Si-H in a second additional chain of one of the one or more hydride-functionalized silicon-containing polymers, thereby further crosslinking the chain and the second additional chain.

[0033] Embodiment 20 is the crosslinked polymer formed by the method of any one of embodiments 1-19.

[0034] Materials described herein offer advantages over polyurethane. One advantage includes the incorporation of Si into the structure. It has been shown that Si-containing polyurethanes are resistant to electrical currents, corrosive materials, and heat. Another advantage includes the use of amino acids, and their potential to release amino acids and nontoxic siloxanes upon degradation over time in water (either in the environment, or at a dedicated recycling facility). Since amino acids are abundant in the body, this could allow the products to be used as bio-delivery materials.

[0035] The details of one or more embodiments of the subject matter of this disclosure are set forth in the accompanying drawings and the description. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.BRIEF DESCRIPTION OF DRAWINGS

[0036] FIG. 1 is an SEM image of L-lysine foam.

[0037] FIG. 2 shows TGA and DSC plots of L-lysine foam.

[0038] FIG. 3 shows TGA and DSC plots of L-lysine foam.

[0039] FIG. 4 is an IR spectrum of L-lysine foam.Attorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-c

[0040] FIG. 5 is an IR spectrum of L-serine foam.DETAILED DESCRIPTION

[0041] This disclosure describes dehydrocoupling of polymethylhydrosil oxanes, amino acids, and water in varying ratios and conditions and the materials synthesized thereby. Depending on the amino acid used, the reaction conditions, the loading of each component or mixture of components in the formulation (including PMHS, PMHS-PDMS copolymers, water, adventitious humidity, and catalyst) the materials range from porous foams to hard or soft gellike materials. These materials are believed to be chemically recyclable upon prolonged exposure to water in order to cleave the Si-N and silyl ester bonds and regenerate the amino acid and a siloxane material that can be reused. Siloxane materials are known to break down in the environment to form sand due at least in part to the favorable formation of Si-0 bonds.Choice of materials

[0042] When selecting the reagents, amino acids were chosen as they are bio-based, environmentally friendly, and non-toxic building blocks. Additionally, since amino acids can be bio-based rather than petroleum-based, they stem from a renewable feedstock. Polymethylhydrosiloxane, referred to as PMHS, is also considered to be non-hazardous according to safety data specifications. PMHS is used in this reaction. Suitable alternatives include co-polymers of polydimethylsiloxane (PDMS) and PMHS. Many catalysts for Si-N and Si-0 dehydrocoupling can be used, and sodium hydride represents one example of a suitable catalyst. This was chosen in place of more complex dehydrocoupling catalysts that require laborious synthetic steps, purification methods, and often harsh reducing agents to synthesize. Several examples are shown to work with 5 mol% NaH, which is considered an acceptable amount even for highly engineered catalysts. The use of low loadings without the need for designing a highly complex catalyst makes this process not only more environmentally friendly and efficient, but also more industrially relevant. Although NaH is used as a catalyst in examples described herein, other catalysts that perform Si-N and Si-0 dehydrocoupling are also suitable. Some variations involve the purposeful addition of water or the dehydrocoupling of water present in the atmosphere.Attorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-c

[0043] The desired materials can be prepared from a combination of the following reagents: PMHS or PMHS-PDMS copolymers (50-99.999 wt%), amino acid (0-50 wt%), water (0-10 wt%, either added on purpose or through exposure to atmospheric humidity), and catalyst (0.00001-5 wt%), where the total amount of amino acid and water is at least 0.001 wt%. One or more amino acids, water, or any combination thereof, reacts with PMHS, PMHS-PDMS copolymer or a combination thereof, in the presence of a catalyst to yield products described herein.Recyclability

[0044] Since the mechanism to create the materials may involve Si-N and Si-0 dehydrocoupling, it is believed that the Si-H, Si-N, and Si-0 bonds can be hydrolyzed using water or another oxidizing agent to regenerate the amino acid starting materials and siloxane. Not only is this a relatively benign and efficient process, but degradation would also provide non-toxic products (amino acid and a siloxane material) that are biodegradable and can be used again. This material is thought to have similar properties to polyurethane.Biodegradation

[0045] The synthesized materials are thought to be readily biodegradable in prolonged exposure to water present in the environment. Water will slowly hydrolyze the material. The resulting products are amino acids and a siloxane, which are both considered non-hazardous materials for human and environmental health and are biodegradable. They also can be collected and used as chemical reagents.Synthesis

[0046] Amino acids were used as a carboxylic acid and amine source. The amino acids used included the L isomer of all 20 amino acids, although all isomers and mixtures of isomers of each amino acid are believed to be suitable. The Si source used was polymethylhydrosiloxane, with an average of 38 repeating SiMeH units. It is referred to from here on as PMHS or PMHS (n = 38). It is believed that any chain lengths of PMHS can be used to obtain similar materials, although average chain lengths from 4 to 38 are commercially available as a mixture. It is also believed this reaction can be carried out using co-polymers of PMHS and PDMS with theAttorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-c structure (PMHS)w(PDMS)qwhere w and q can be any number, but preferably with w ranging from 2 to 38 and q ranging from 4 to 290. These polymers, like PMHS, are trimethyl silyl - terminated. Examples provided herein use L-lysine, also referred to as lysine.

[0047] The reactions were carried out under five conditions. Condition 1 was performed in a N2 glovebox, to prevent the influence of humidity. Condition 2 was performed in a laboratory “benchtop” environment in the presence of 5-17% ambient humidity at room temperature. Higher or lower levels of ambient humidity (between 0-90%) and temperature (between 0-180 degrees Celsius) are expected to be suitable. Additionally, due to their hygroscopic nature, amino acids may absorb some water and are used in each condition from reagent bottles without further drying. Condition 3 was performed in the same environment as condition 2, but water was also intentionally added to the reaction. Condition 4 was carried out with the same conditions as condition 2, but with no amino acid and with water added. Condition 5 was carried out with the same conditions as condition 2 but with no amino acid added and no water added (only adventitious water from the atmosphere was admitted). The following detailed procedures were performed using NaH as a representative catalyst.

[0048] Condition 1, Sodium hydride, 60% dispersion in mineral oil, was washed with pentanes over a frit filter in a N2 atmosphere glovebox until completely dry. The NaH (0.0082 g, 0.34 mmol) was weighed into an oven dried vial in the glovebox. L-lysine was placed under vacuum in the glovebox antechamber and brought into the glovebox. L-lysine (1 g, 6.84 mmol) was then weighed on weigh paper and transferred to the vial of NaH. PMHS (n = 38) was placed into an oven-dried bomb with sieves, then O2 was removed using a Schlenk line. It was then brought into the glovebox and stored in vials over sieves. To the amino acid and NaH vial, PMHS (n = 38, 2.09 g, 0.86 mmol) was added using a syringe. An oven dried stir bar was added to the vial, then the vial was capped and set on a stir plate to stir. The reaction was carried out at room temperature in the N2 glovebox under solvent free conditions. The initial reaction was a yellow liquid. After 25 minutes, the resulting product was a yellow, porous foam that took the shape of the vial. The foam was easily broken with a spatula and resulting portions could crumble and could become powdery if continuously broken up. The reaction was complete (formed a foam) once the stir bar could no longer move.

[0049] Condition 2, Sodium hydride, 60% dispersion in mineral oil, was washed with pentanes over a frit fdter under a nitrogen atmosphere until completely dry. NaH (0.0082 g, 0.34Attorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-c mmol) was weighed into an oven dried vial in the glovebox and was capped, taped, and taken outside the glovebox. L-lysine (1 g, 6.84 mmol) was weighed on weigh paper and was transferred to the vial of NaH. PMHS (n = 38, 2.09 g, 0.86 mmol), stored in a reagent bottle over sieves, was syringed into the vial. An oven dried stir bar was added, and the vial was capped and set on a stir plate to stir. The reaction was carried out at room temperature under air, in the absence of solvent. The initial reaction was a yellow liquid. After 50 minutes, the resulting product was a yellow, porous foam that took the shape of the vial. The foam was easily broken with a spatula and resulting portions could crumble and could become powdery if continuously broken up. The reaction was complete (formed a foam) once the stir bar could no longer move.

[0050] Condition 3, Sodium hydride, 60% dispersion in mineral oil, was washed with pentanes over a frit fdter under a nitrogen atmosphere until completely dry. NaH (0.0082 g, 0.34 mmol) was weighed into an oven dried vial in the glovebox and was capped, taped, and taken outside the glovebox. L-lysine (1 g, 6.84 mmol) was weighed on weigh paper and was transferred to the vial of NaH. PMHS (n = 38, 2.09 g, 0.86 mmol), stored in a reagent bottle with sieves, was syringed into the vial. An oven dried stir bar was added. Deionized water (0.0308 g, 1.7 mmol) was added via a syringe. The vial was capped and set on a stir plate to stir. The reaction was carried out at room temperature in benchtop lab conditions, in the absence of solvent. The initial reaction was a yellow liquid. After 90 minutes, the resulting product was a yellow, slightly porous foam that took the shape of the vial. The foam was easily broken with a spatula and resulting portions could crumble and could become powdery if continuously broken up. The reaction was complete (formed a foam) once the stir bar could no longer move.

[0051] Condition 4, Sodium hydride, 60% dispersion in mineral oil, was washed with pentanes over a frit fdter under a nitrogen atmosphere until completely dry. NaH (0.0082 g, 0.34 mmol) was weighed into an oven dried vial in the glovebox and was capped, taped, and taken outside the glovebox. PMHS (n = 38, 2.09 g, 0.86 mmol), stored in a reagent bottle with sieves, was syringed into the vial containing NaH. An oven dried stir bar was added. Deionized water (0.0308 g, 1.7 mmol) was added via a syringe. The vial was capped and set on a stir plate to stir. The reaction was carried out at room temperature in benchtop lab conditions, in the absence of solvent. The initial reaction contained colorless liquids. The resulting product was a white to colorless porous gel-like foam that took the shape of the vial. The reaction was complete once the stir bar stopped moving.Attorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-c

[0052] Condition 5, Sodium hydride, 60% dispersion in mineral oil, was washed with pentanes over a frit fdter under a nitrogen atmosphere until completely dry. NaH (0.0082 g, 0.34 mmol) was weighed into an oven dried vial in the glovebox and was capped, taped, and taken outside the glovebox. PMHS (n = 38, 2.09 g, 0.86 mmol), stored in a reagent bottle with sieves, was syringed into the vial containing NaH. An oven dried stir bar was added. The vial was capped and set on a stir plate to stir. The reaction was carried out at room temperature in benchtop lab conditions, in the absence of solvent. The initial reaction contained colorless liquid. The resulting product was a colorless to white soft or hard gel, depending on the humidity, that took the shape of the vial. The reaction was complete once the stir bar stopped moving.

[0053] The following yields and percent conversions were obtained for the L-lysine foams synthesized under several conditions following workup. To carry out the workup, the foams were rinsed with either DMF or water to extract any unreacted amino acid from the product. The DMF or water rinse was then pipetted into a tared vial and the solvent was evaporated off using a rotary evaporator. The residual amino acid was weighed to obtain the percent conversion. The foam, after the rinse, was dried via rotary evaporator, and was weighed in a tared vial. The weight of the foam was used to calculate the yield. To obtain the yield after finding the weight of the foam the theoretical yield for the foams was calculated. The theoretical weight of the foam synthesized without the presence of added water (Conditions 1 and 2) is 3.029 g. This was calculated assuming the two amine groups and the one OH group on lysine dehydrocouple with 3 Si-H bonds within a PMHS chain. Assuming the 8: 1 amino acid to PMHS ratio, this would mean that within the PMHS chain, 24 Si-H bonds have reacted and 14 Si-H bonds remain. This would give a structure with stoichiometry resembling the one shown below (the true structure is expected to feature bonding between the amino acid functionalities and non-consecutive siloxane units within the chain and across chains, affording considerable crosslink density):

[0054] For the foam synthesized with amino acid and water (Condition 3) the theoretical yield for the foams is 3.080 g. This was calculated assuming the two amine groups and the oneAttorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-cOH group on lysine dehydrocouple with 3 Si-H bonds within a PMHS chain. Then, since 2 equivalents of water were added for every 1 PMHS chain, it can be approximated that 4 Si-H bonds are converted to Si-0 bonds through dehydrocoupling. This would result in 10 remaining Si-H bonds and a structure with stoichiometry resembling the one shown below, where R is H or another siloxane (the true structure is expected to feature bonding between the amino acid functionalities and non-consecutive siloxane units within the chain and across chains, affording considerable crosslink density):

[0055] While DMF and water can be used for the workup method described, water, after the synthesis when being used as a wash, has the potential to hydrolyze the foam, which may impact the weight of the product. However, water rinses were done quickly and there were no visible signs of bubbling or the material breaking down, so the water workup was considered to be a reasonable method for assessing percent conversion. For some applications, a workup may not be required.For DMF Workup:Attorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-cF or Water W orkup :Mechanism

[0056] The reaction is expected to proceed by the following mechanism, which may include a combination of one, some, or all of the listed potential steps in any order. L-lysine is used as the amino acid in this description. However, any isomer of any amino acid, or combination of amino acids, may be used as well as any of the formulations specified herein. PMHS with an average of 38 SiH units per chain is also used for this mechanistic description. However, any Si- H shown could represent any Si-H on any PMHS or (PMHS)w(PDMS)qco-polymer (the Si-H units towards the end of the chain are used for simplicity).

[0057] In the first step, dehydrocoupling is expected between a Si-H and O-H group on the amino acid, resulting in the loss of one equivalent of H2 gas and the following intermediate:Attorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-c

[0058] In the second step, dehydrocoupling is expected between the Si-H in a different chain (equivalent) of PMHS and an amine group of the amino acid. The reaction of an amino acid with several different chains is referred to as crosslinking and would result in the loss of an equivalent of H2 and the following intermediate:

[0059] In the third step, dehydrocoupling is expected between the remaining amine group of the amino acid and a Si-H on another chain of PMHS. This would result in the loss of another equivalent of H2 gas and further crosslinking.

[0060] Alternatively or concurrently, one or all of the amines could be converted into a tertiary amine group by Si-H and N-H dehydrocoupling, as shown below. In the example below, the side-chain amine is shown as forming the tertiary amine (the NH2 bond reacts twice), but any NH2 could react 0-2 times and any NH could react 0-1 times with any Si-H bond.Attorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-c

[0061] It is believed that the carboxylic acid on the amino acid can be reduced by an Si-H on the same or another equivalent of PMHS. This could induce more crosslinking as shown below:

[0062] These reactions can be carried out in the absence of water, or in varying degrees, in the presence of water, as described in the formulation description. If water is present in the reaction (either through its presence in the atmosphere or purposeful addition), there is the possibility of further crosslinking within the material, which can be favorable for creating a more heat-resistant material. In the presence of water, unreacted Si-H bonds within different chains of PMHS may dehydrocouple to produce Si-O-Si bonds between chains or within a chain, releasing 2 equivalents of H2 gas per 1 equivalent of water, and creating crosslinking as in the following:Attorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-c

[0063] It is believed that any of the reaction schemes shown above can be carried out within a single chain of PMHS rather than with an additional equivalent of PMHS. That is, the reaction can result in cyclization as opposed to crosslinking, as shown below:

[0064] For simplicity, the amino acid is shown reacting with four subsequent Si-H units at the end of the PMHS chain, however the amino acid does not have to react with subsequent Si-H bonds. Each OH group, carbonyl, NH2, or NH group on an amino acid can react with any Si-H bond at any point in the same or different PMHS or (PMHS)w(PDMS)qchains.

[0065] For all the schemes shown above, the terminal Si-H of each PMHS chain is shown to react with the amine group. However, it should be noted that any of the Si-H groups in the entire chain of PMHS or (PMHS)w(PDMS)qcan react. Each PMHS or (PMHS)w(PDMS)qchain can react from 0 to n times, where n is the number of Si-H groups present in the structure. The product can result in various degrees of crosslinking and cyclization between any of the following groups: Si-H and N-H groups, Si-H and NH2 groups, Si-H and Si-H groups (reacting with water to form Si-O-Si), Si-H and OH groups, Si-H and carbonyl groups, Si-H and Si-OH groups. An example structure is shown below to illustrate several features that could be expected in the product. Any given product could contain various degrees of any or all of the features shown below. The structures may include, but are not limited to the features shown below, where R = H or any SiMe(OSilox)2 group on any PMHS polymer within a single chain, or any SiMe(OSilox)2 group on a different PMHS chain, or any SiMe(OSilox)2 group on anyAttorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-c(PMHS)w(PDMS)qpolymer within a single chain or on different chains of any (PMHS)w(PDMS)q. Although the structure is shown with PMHS chains, any length of PMHS or PDMS and PMHS copolymer can be used. The structure is also shown with lysine, although any amino acid or combinations of amino acids can be used. In the structure, m represents the number of remaining Si-H units in the chain and can be any number, but most likely ranging from 0-38 for PMHS or 0-290 for PDMS-PMHS copolymers.

[0066] Several notable features include the bonding of lysine in a cyclic fashion to PMHS, and the presence of unreacted carbonyl groups on the amino acid, as well as reacted carbonyl groups. The structure also features Si-O-Si bonds formed between chains in a cyclic fashion. Also present are Si-N bonds between lysine and consecutive and / or nonconsecutive Si-H groups.Reaction Conditions

[0067] Considering the proposed mechanism, L-lysine, has four potential reaction sites.Given that the PMHS used contained an average of 38 repeating Si-H units, it was calculated that for every Si-H bond to react, 9.5 equivalents of lysine could be used for every PMHS equivalent. However, it was predicted that having excess PMHS was favorable due to the unlikelihood thatAttorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-c each amino acid could physically “reach” four Si-H bonds. For this reason, 8 equivalents of amino acid were reacted with 1 equivalent of PMHS. The reaction was also shown to work with a 4 to 1 and 6 to 1 ratio, however, 8 to 1 was shown to give the most desirable product. The ratios can also be adjusted for amino acids that have more than four potential reaction sites, for example for arginine, which has an additional NH2 on its side chain. The amino acid to Si-H ratio can be tailored beyond the ratios mentioned, in order to tune the material to the desired texture and properties. Additionally, various ratios of different formulation components are possible and are described herein.

[0068] As described, the reactions can be carried out in air or under nitrogen with varying degrees of water present (whether added to the reaction, in the reaction from undried reagents, or from the atmosphere). The reactions can be carried out in solvent free conditions at room temperature and pressure, which are desired conditions for green synthesis. While reactions have been shown to proceed using THF and Et O (dried over sieves), the products produced were mechanically less durable and seemed to degrade more easily in solvents such as DMF and water. In addition, carrying out the reactions at 60 degrees Celsius, has been shown to increase the rate of the reactions in some cases. It was found that, while foams from L-asparagine, L- arginine, and L-histidine could not be reproducibly synthesized at room temperature in a reasonable time (7 days), the L-arginine and L-asparagine foams could be synthesized in less than 19 hours and the L-histidine foam in less than 72 hours when carried out at 60 degrees Celsius.Scope

[0069] Alternatively, PMHS was reacted with NaH in the presence of no amino acid but with added water (condition 4) which yielded a porous gel-like foam. The reaction was repeated with no added water (condition 5) which yielded a hard or soft gel-like material depending on humidity. It was hypothesized that gel formation versus foam formation (product texture) may be correlated with variation in amino acid loading, water or humidity loading, reaction conditions, or a combination thereof. When condition 5 is repeated under inert atmosphere, no gel or foam is observed, justifying the formulations described herein.

[0070] To confirm the necessity of an Si-N dehydrocoupling catalyst, preferably NaH, L- serine was reacted with PMHS in the absence of NaH and remained a liquid. When the reactionAttorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-c was repeated with 5 mol% NaH the foam formed in less than 24 hours. Under benchtop conditions, lysine was reacted with PMHS in the presence of no NaH catalyst. The result was a dense solid, whereas when this was repeated with 5 mol% NaH, the result was a porous foam, implying that when controlled water and amino acid loadings are used, variations in texture and gel versus foam formation may be correlated with variations in catalyst loading.

[0071] To confirm the mechanism of Si-N dehydrocoupling, L-methionine, L-phenylalanine, and L-leucine, which do not contain side chains with NH2 groups, were reacted with PMHS under benchtop conditions with 5 mol% NaH and were left to stir at 60 degrees Celsius. The reactions did not produce foams and remained liquids for 7 days. It is believed that these did not create foams due at least in part to the lack of side chain crosslinking, but foam or gel formation may be accessible if higher water loadings are used.Description of Products

[0072] Several examples are shown below of the products that could be created, as well as a brief description of their visible properties. Included are two reactions that did not visibly produce foams or gels, which may be attributed to the limited abundance of NH2 groups present on the amino acid, or may indicate the need for the adjustment of water, humidity, or reaction conditions for foam or gel formation. The examples shown below depict the case where one Si-H on each PMHS chain reacts with one OH, NH, or NH2 group on one amino acid. However, the functionalization shown is for illustrative purposes, and the product could contain various degrees of crosslinking and cyclization between any of the following groups: Si-H and N-H groups, Si-H and NH2 groups, Si-H and Si-H groups (reacting with water to form Si-O-Si), Si-H and OH groups, Si-H and carbonyl groups, Si-H and Si-OH groups.L-lysine„ „ SivDehydrocoupled Siloxane Dehydrocoupled Siloxane— O 1 O0= / \NHSi-'Q--- Dehydrocoupled SiloxaneH !KT 50D I ehydrocoupled SiloxaneDehydrocoupled Siloxane^ g(Dehydrocoupled SiloxaneAttorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-c

[0073] Description: Carried out under Condition 2. The material is a yellow foam that is uniformly porous. The foam can be pierced and cut. The foam takes the shape of the reaction vial and “rises” when forming.L-serine ocoupled Siloxane Dehydrocoupled Siloxane Dehydrocoupled SiloxaneDehydrocoupled Siloxane. \ O hydrocoupled SiloxaneDehydrocoupled Siloxane

[0074] Description: Carried out under Condition 2. The material is a white, gel-like foam. It is hard and silicone-like. It has a stiff texture, is slightly waxy, and can be pierced and separated with a spatula. It takes the shape of the reaction vial. When carried out at 60 degrees Celsius, uniform pores are formed.L-asparagine coupled SiloxaneDehydrocoupled SilDehydrocoupled Siloxane ydrocoupled SiloxaneDehydrocoupled SiloxaneDehydrocoupled Siloxane

[0075] Description: Carried out under Condition 2 at 60 degrees Celsius. The material is a white, silicone-like foam that can be pierced into pieces. It has no pores and takes the shape of the reaction vial.Attorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-cL-arginine coupled SiloxaneDehydrocoupled SiloxaDehydrocoupled Siloxane ydrocoupled SiloxaneDehydrocoupled SiloxaneDehydrocoupled Siloxane

[0076] Description: The reaction followed Condition 2 with the addition of heat (60 degrees Celsius). The material is hard and smooth; silicone-like with no pores. It is difficult to pierce due to its hard nature. It takes the shape of the reaction vial.L-histidine^.Si^ Dehydrocoupled Siloxane Dehydrocoupled Siloxane — O | OO Dehydrocoupled Siloxanedrocoupled SiloxaneDehydrocoupled Siloxane-.o^Si^o,Dehydrocoup|ed si|0Xane

[0077] Description: The reaction was carried out under Condition 2 with the addition of heat (60 degrees Celsius). The material is white with some pores present. It is squishy and soft and can be pierced. It is a silicone-like material that can be cut and it jiggles when pressed. It takes the shape of the vial but can hold its shape if cut.L-methionineAttorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-c

[0078] Description: Light-colored liquid.L-phenylalanine

[0079] Description: Light-colored liquid.No Amino AcidDehydrocoupled Siloxane Dehydrocoupled SiloxaneDehydrocoupled Siloxane XL S Ii6.Dehydrocoupled Siloxane

[0080] Description: The reaction was carried out under Condition 4. The material is a colorless to white porous, bouncy gel-like foam.Applications

[0081] Possible applications involve those that polyurethane or silicone-like materials are currently used for, or in fields where the potential use of polyurethane, silicone-like materials, or similar materials have been researched, including but not limited to solvent absorption, oil absorption, cushioning (low density, high thermal insulation, and mechanical ability), mattress foam, insulation material, medical device storage material (non-toxic PU replacement), packing, drug delivery, insulating (thermal stability), acoustic absorbers, tissue growth, fdtration materials, flame retardant materials, absorption of porous volatile organic compounds, gas sensors, and wound healing materials.Designed to be Green

[0082] The reaction described herein was designed to follow principles of green chemistry. The following points indicate how the synthesis of these materials is green, and comparisons to traditional polyurethane synthesis are offered.Attorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-c1 . Prevention of waste: No side products are produced except H2, which can be collected and utilized.2. Atom economy: All atoms in the reactants end up in the product, except H2 which can be collected and used.3. Less hazardous chemical synthesis: In contrast to polyurethane synthesis, this production requires no additional heat, pressure, toxic gases, or dangerous metals.4. Design safer chemicals: The materials produced are meant to be safe when synthesized, used, and degraded. Unlike polyurethanes they do not require toxic isocyanates or phosgene (which is used for isocyanate production).5. Safer solvents and auxiliaries: The reactions are performed in solvent-free conditions.6. Design for energy efficiency: Stirring is required but can be minimized with mild heating.7. Use renewable feedstocks: Amino acids are renewable feedstocks since they are biobased and can be obtained from biomass.8. Reduce derivatives: This is a one-step synthesis.9. Catalysis: NaH has been used as the catalyst at 5 mol%, and lower loadings can be used.10. Design for degradation: The products were designed so that they can be degraded with prolonged exposure to water, which will produce the original non-hazardous starting material and a siloxane that can in turn be recycled or repurposed.11. Real-time analysis for pollution prevention: Unlike polyurethane production, this process does not require monitoring of polluting blowing agents, such as hydrofluorocarbons or volatile organics.12. Inherently safer chemistry for accident prevention: The synthesis (and potentially the recycling process) is thought to require little to no heat, ambient pressure, and no physical grinding equipment or harsh reagents.Solvent Absorption

[0083] The products have been observed visibly absorbing solvents, including DMF. When exposed to solvent, the materials required vacuum and heating to 50 degrees for several hours to reach complete dryness.Attorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-cPore size

[0084] Pores are desirable for foam materials as they provide the mechanical properties necessary. Pores influence physical strength, cushioning, sound absorption, oil and solvent absorption, stress absorption, and insulating properties. As an example, a pore size of <950 micrometers is desirable for oil absorption efficiency. Additionally, when testing insulating materials, smaller pore sizes are better, and such materials have been tested with pore sizes up to 1000 micrometers.

[0085] Materials described herein are synthesized using Si-N dehydrocoupling, which releases H2 gas, creating pores as a result of the reaction. This requires no additional steps, waste gases, toxic fluorocarbons, or special equipment. Additionally, since the H2 gas produced separates from the product, it could be collected and used as a commodity chemical.

[0086] The different amino acid and water reactions yield foams with different physical properties, some more porous and some more gel-like with few or no pores. However, porous foam production has been observed with L-lysine. The pore size for the lysine foam synthesized under Condition 2 is approximately 500-750 micrometers. This is within the range of desirable pore size for oil absorption and insulation. According to the SEM image shown in FIG. 1, the pores are relatively uniform in size and dispersement. The L-serine foam was also shown to contain several pores, though less uniformly dispersed.Thermal stability

[0087] FIG. 2 shows TGA and DSC plots of the L-lysine foam. After sitting in the vacuum oven at 100 degrees Celsius for 24 hours, the foam loses 5% of its weight upon heating to 184 degrees Celsius. FIG. 3 shows TGA and DSC plots of the L-serine foam. After sitting in the vacuum oven at 100 degrees Celsius for 31 hours, the foam loses 5% of its weight upon heating to 218 degrees Celsius. Both foams demonstrate thermal stability within temperatures considered reasonable for insulating materials.Infrared Spectroscopy

[0088] FIGS. 4 and 5 show IR spectroscopic data collected from L-lysine and L-serine foams, respectively.Attorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-c

[0089] Although this disclosure contains many specific embodiment details, these should not be construed as limitations on the scope of the subject matter or on the scope of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in this disclosure in the context of separate embodiments can also be implemented, in combination, in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments, separately, or in any suitable sub-combination. Moreover, although previously described features may be described as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can, in some cases, be excised from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination.

[0090] Particular embodiments of the subject matter have been described. Other embodiments, alterations, and permutations of the described embodiments are within the scope of the following claims as will be apparent to those skilled in the art. While operations are depicted in the drawings or claims in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed (some operations may be considered optional), to achieve desirable results.

[0091] Accordingly, the previously described example embodiments do not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure.

Claims

1. Attorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-cWHAT IS CLAIMED IS:

1. A method of forming a crosslinked polymer, the method comprising: combining one or more amino acids, water, or a combination thereof and one or more hydride-functionalized silicon-containing polymers in the presence of a catalyst to yield a mixture; and reacting the one or more amino acids, water, or combination thereof with the one or more hydride-functionalized silicon-containing polymers to yield a crosslinked polymer comprising Si-0 and Si-N bonds.

2. The method of claim 1, wherein the one or more amino acids comprise L-lysine, L- serine, or a combination thereof.

3. The method of claim 1, wherein the one or more hydride-functionalized silicon- containing polymers comprise PMHS, PMHS-PDMS co-polymers, or a combination thereof.

4. The method of claim 1, wherein the catalyst comprises NaH.

5. The method of claim 1, wherein the reacting occurs at room temperature and pressure.

6. The method of claim 1, wherein the crosslinked polymer is in the form of a foam or a gel.

7. The method of claim 6, wherein the crosslinked polymer is in the form of a porous foam.

8. The method of claim 7, wherein the porous foam defines pores having an average diameter in a range of 500 pm to 1000 pm, as determined by SEM analysis.

9. The method of claim 1, further comprising contacting the crosslinked polymer with an excess of water to yield the one or more amino acids and a siloxane material.

10. The method of claim 1, wherein the reacting further yields hydrogen gas.Attorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-c11. The method of claim 1, wherein the reacting comprises dehydrocoupling.

12. The method of claim 1, wherein the reacting occurs in the absence of a solvent.

13. The method of claim 1, wherein the reacting occurs in air or under nitrogen.

14. The method of claim 1, wherein the mixture comprises 50 wt% to 99.999 wt% of the one or more hydride-functionalized silicon-containing polymers.

15. The method of claim 1, wherein the mixture comprises up to 50 wt% of the one or more amino acids and up to 10 wt% water, wherein the total amount of the one or more amino acids and the water is at least 0.001 wt%.

16. The method of claim 1, wherein the mixture comprises up to 5 wt% of the catalyst.

17. The method of claim 1, wherein, when the mixture comprises one or more amino acids, the reacting comprises dehydrocoupling between Si-H groups of one of the one or more hydride- functionalized silicon-containing polymers and one of the one or more amino acids to yield hydrogen gas and an intermediate in which an oxygen of the one or more amino acids is covalently bonded to a silicon of one of the one or more silicon-containing polymers.

18. The method of claim 17, wherein the reacting further comprises dehydrocoupling between Si-H in a first additional chain of one of the one or more hydride-functionalized silicon- containing polymers and a first amine group of the one of the one or more amino acids, thereby crosslinking the chain and the first additional chain.

19. The method of claim 18, wherein the reacting further comprises dehydrocoupling between a second amine group of the one of the one or more amino acids and Si-H in a second additional chain of one of the one or more hydride-functionalized silicon-containing polymers, thereby further crosslinking the chain and the second additional chain.Attorney Docket No.: 22193-0394WO1 / M25-032PA-WOl-c20. The crosslinked polymer formed by the method of claim 1.

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