Bioinspired cross-linking of preceramic polymers via metal ion coordination bonding

Posey

et al. 2023

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Processable preceramic materials are critically important to a range of applications, especially with regard to biomedical coatings and filling interstitial spaces in preform materials to produce ceramic matrix composites useful for aerospace propulsion. Preceramic polymers (PCPs) with added nanoparticle (NP) components are an attractive way to influence the final ceramic composition and reduce the changes in density and volume during PCP conversion to inorganic material. Cross-linking a polymer to an NP surface is one potential route to mitigating phase separation and potentially improving char yields for the combined materials. In this report, two pyridine-functionalized PCPs were studied by linking the polymers to pyridine-terminated SiO2 nanoparticle (NP) surfaces via a zirconium metal center. The polymer–metal–nanoparticle (PMN) system was studied in an assembled, polymeric form during pyrolysis (i.e., via thermogravimetric analysis) and post-conversion (at 1600 °C) by X-ray diffraction, Raman spectroscopy, scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM) with EDS. A dramatic 57% increase in char yield of the PMN relative to the summed char yields of the individual components is observed, showing a significant synergistic effect and yielding a SiO2–ZrO2 nanocomposite.

Section: ■ Results and Discussionmentioning

confidence: 99%

“…PyMPS has been previously reported . SMP-877 was purchased from Starfire Systems with an average molecular mass of ∼1000 Da as determined by GPC.…”

Section: Methodsmentioning

confidence: 99%

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Preceramic Polymers Grafted to SiO₂ Nanoparticles via Metal Coordination Pyrolyzing with High Ceramic Yields: Implications for Aerospace Propulsion and Biomedical Coatings

Delcamp

Posey

et al. 2023

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“…Preceramic polymers (PCPs) offer advantages in ceramics production, including the production of high-performance ceramic fibers and composites as well as the generation of compositional diverse ceramics (e.g., SiC, Si 3 N 4 , and SiCN). − PCPs have been investigated for several decades, revealing synthetic procedures for unique structures and a deeper understanding of processing science and pyrolysis chemistry. − For example, it is accepted that network forming through high cross-link densities is more important than achieving high polymer molecular weights (MWs) for improving char yield. − Moreover, emphasis on the role of weight loss during pyrolysis as it relates to volume shrinkage of the derived ceramic is being better understood …”

Section: Introductionmentioning

confidence: 99%

Influence of Thermal Treatment on Preceramic Polymer Grafted Nanoparticle Network Formation: Implications for Thermal Protection Systems and Aerospace Propulsion Components

Clarkson

Thompson

et al. 2022

Preceramic polymer grafted nanoparticles (PCP GNPs) offer potential advantages in the production of polymerderived ceramic composites compared to neat preceramic polymers (PCPs), such as reduced thermal shrinkage and increased char yield. In comparison to traditional composites (particles + free polymer), PCPs avoid issues of compatibility, agglomeration, and phase separation during processing and provide routes to control nanoparticle arrangement. Prior literature has established that the conversion efficiency of PCPs and PCP GNPs to ceramics and ceramic composites is linked to the thermal pretreatment of these precursor polymers (e.g., curing). Herein, we investigate the material transformations that occur when exposing PCP GNPs to a low-temperature thermal treatment (≤250 °C) prior to pyrolysis. The PCP GNPs explored in this study possessed silica nanoparticle cores but were distinct in their PCP coronas, having poly(1,1-dimethylpropylsilane) (allyl-GNP)-or poly(1,1-dimethylbenzylethylsilane) (styryl-GNP)-grafted polymers. After undergoing low-temperature thermal treatment, these PCP GNPs exhibited increased char yield at 800 °C; however, unlike commercial PCPs (e.g., allylhydridopolycarbosilane (SMP-10)), obvious cross-linkable sites are not present in the PCP corona structure. Differential scanning calorimetry, oscillatory rheology, and X-ray photon correlation spectroscopy were utilized to elucidate the thermally induced material changes in the allyl-and styryl-GNPs. Thermally induced changes to the structure and behavior of the PCP GNPs were determined to be linked to the chemical structure of the grafted polycarbosilane chains. Styryl-GNPs experienced a curing event between 180 and 250 °C, effecting the formation of a network, which contributed to char yield improvement (at 800 °C). The nanoscale dynamics of this material also shows a transition from diffuse behavior to ballistic behavior because of the cross-linking event. Conversely, the allyl-GNPs did not exhibit a curing event under heat treatment but did show an increase in thermally induced physical cross-linking. The allyl-GNP physical network is stronger after the first cycle of thermal treatment, and it is considered that this contributed to the improvement in char yield post thermal treatment. The advancements in the understanding of the cross-linking behavior of these hybrid materials are expected to advance the application of these materials to turbine engine, advanced friction, and heat-shielding components.

“…The polymers utilized to produce the CMC matrix in the PIP process are preceramic polymers (PCPs), which are specialty materials that yield ceramics on heat treatment. , PCPs can be synthesized through straightforward chemistries like hydrosilylation, Grignard reactions, ring-opening polymerization, radical polymerization, and sol–gel methods to produce synthetically diverse PCPs with varying molecular weight, polydispersity, and viscosity. − Such synthetic tunability produces materials that not only can be processed through several techniques (i.e., additive manufacturing and fiber spinning) but can also give unique ceramic compositions. For example, polysilazanes convert to SiCN, a composition that is unobtainable using powder processing .…”

Section: Introductionmentioning

confidence: 99%

Impact of the Backbone Structure on the Rheological and Thermal Properties of Preceramic Polymer-Grafted Nanoparticles and Derived Ceramics

Street

Thompson

et al. 2021

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Here, we demonstrate the synthesis of two novel preceramic grafted nanoparticles (GNPs) and compare their physical properties and derived ceramics to previously reported GNPs. Three variations of preceramic polymer GNPs are synthesized using hydrosilylation grafting-from chemistry, with brushes comprising poly(1,1dimethylpropylsilane) (allyl-GNP), poly(1,1-dimethylethylbenzylsilane) (styryl-GNP), and poly(1,1-dimethylethylsilane) (vinyl-GNP) on silica nanoparticles (10−15 nm in diameter). The brush structure is confirmed using FTIR, 1 H NMR, and dynamic light scattering (DLS). The rheological properties of the GNPs change depending on the brush composition, with the allyl-GNP displaying the formation of a strong interparticle network and the styryl-GNP exhibiting a weaker interparticle network. Thermal gravimetric analysis shows that after thermal treatment, the ceramic yield of all three GNPs increases at 800 °C, with the allyl-GNP and vinyl-GNP showing a significant improvement in yield as compared to the styryl-GNP. Finally, the three GNPs are pyrolyzed to 1400 °C giving ceramic composites with compositions dependent upon the precursor brush, as determined through X-ray diffraction (XRD) and Raman spectroscopy. This study demonstrates that hydrosilylation grafting-from is a robust method of anchoring ceramic precursor polymers to nanoparticles and can be employed to produce preceramic GNPs that subsequently convert to brush-dependent ceramic composites.