An integrated synthetic biology and fermentation platform enables rapid production of diverse sesquiterpenes for testing in advanced fuel, polymer, and optical material applications.

Boron nitride nanotubes (BNNTs) have great potential as reinforcing agents in polymer composites due to their robust mechanical and thermal properties. BNNT-Polyacrylonitrile (PAN) electrospun composite nanofibers were fabricated with BNNT loadings ranging from 5 to 20 weight percent (wt

Ammonium perchlorate (AP) is commonly used in propulsion technology. Recent studies have demonstrated that two-dimensional (2D) nanomaterials such as graphene (Gr) and hexagonal boron nitride (hBN) dispersed with nitrocellulose (NC) can conformally coat the surface of AP particles and enhance the reactivity of AP. In this work, the effectiveness of ethyl cellulose (EC) as an alternative to NC was studied. Using a similar encapsulation procedure as in recent work, Gr and hBN dispersed with EC were used to synthesize the composite materials Gr-EC-AP and hBN-EC-AP. Additionally, EC was used because the polymer can be used to disperse other 2D nanomaterials, specifically molybdenum disulfide (MoS2), which has semiconducting properties. While Gr and hBN dispersed in EC had a minimal effect on the reactivity of AP, MoS2 dispersed in EC significantly enhanced the decomposition behavior of AP compared to the control and other 2D nanomaterials, as evidenced by a pronounced low-temperature decomposition event (LTD) centered at 300 °C and then complete high-temperature decomposition (HTD) below 400 °C. Moreover, thermogravimetric analysis (TGA) showed a 5% mass loss temperature (Td5%) of 291 °C for the MoS2-coated AP, which was 17 °C lower than the AP control. The kinetic parameters for the three encapsulated AP samples were calculated using the Kissinger equation and confirmed a lower activation energy pathway for the MoS2 (86 kJ/mol) composite compared to pure AP (137 kJ/mol). This unique behavior of MoS2 is likely due to enhanced oxidation-reduction of AP during the initial stages of the reaction via a transition metal-catalyzed pathway. Density functional theory (DFT) calculations showed that the interactions between AP and MoS2 were stronger than AP on the Gr or hBN surfaces. Overall, this study complements previous work on NC-wrapped AP composites and demonstrates the unique roles of the disperagent and 2D nanomaterial in tuning the thermal decomposition of AP.

Apopinene was synthesized from myrtenal by catalytic decarbonylation followed by either hydrogenation to generate dihydroapopinene or Simmons-Smith cyclopropanation to generate exo-(1R,2R)-7,7-dimethyltricyclo [4.1.1.02,4]octane (cyclopropanated apopinene, CPA). Key fuel properties of apopinene and the two derivative fuels were evaluated including density, heat of combustion, and low temperature viscosity. CPA exhibited a density of 0.918 g mL-1 and a volumetric net heat of combustion (NHOC) 20 % higher than the lower limit for conventional jet fuel. This exceptional NHOC is a result of the high density of the tricyclic compound and the ring strain of the bridging cyclobutane and fused cyclopropane groups. Dihydroapopinene exhibited a high freezing point that will limit its applications as a jet fuel blendstock. In contrast, no freezing point down to-80 & DEG;C was observed for CPA via differential scanning calorimetry (DSC). In addition, CPA exhibited a moderate kinematic viscosity of 10.11 mm2 s-1 at-20 & DEG;C and 22.76 mm2 s-1 at-40 & DEG;C. This work demonstrates that fuels with both high energy densities and excellent low temperature properties can be generated from bio-based substrates through cyclopropanation reactions.

Three propargyl ether thermosetting resins were prepared from biosynthetic trans-resveratrol (1), cis-resveratrol (2), and dihydroresveratrol (3). The cure chemistry of the monomers as well as the thermal stability and mechanical properties of cross linked networks were then characterized by techniques including differential scanning calorimetry, thermal gravimetric analysis, and dynamic mechanical analysis. The monomers were highly processable, existing as low melting solids (1, Tm = 81 degrees C; 3, supercooled liquid with an ultimate Tm = 40 degrees C), or a permanent room-temperature liquid (2). All three resins exhibited broad processing windows and high degrees of cure ranging from 97-99%. The glass transition temperatures (Tg) of 1 and 2 were 389 and 384 degrees C (loss modulus), respectively, while 3 did not exhibit a well-defined Tg. All three of the networks exhibited outstanding thermal stability with char yields of 66, 64, and 54% at 1000 degrees C (under N2) for 1, 2, and 3, respectively. Heat release capacities of 1, 2, and 3 were 53, 41, and 114 J g-1K-1, respectively, consistent with self-extinguishing (3) or non-ignitable (1, 2) polymers. The networks also exhibited low water uptakes ranging from 3.64 to 1.59 wt %. The thermal stability, fire-resistance, and mechanical properties of the resveratrol-based resins represent significant improvements over monomers derived from conventional petroleum-based bisphenols (e.g., bisphenol A). This work demonstrates that the unique morphology afforded by bio-based monomers allows for the preparation of polymer networks with enhanced properties. The resveratrol networks have potential applications as components of high-temperature and fire-resistant composite materials for aerospace applications.

A cyanate ester derived from bio-based cardanol was cross-linked at room temperatureviasynergistic thiol–ene chemistry catalyzed by UV irradiation.

Poly(2,5-bis[N-methyl-N-hexylamino] phenylene vinylene) (BAM-PPV) has been studied for several decades as an anti-corrosion coating. Although the polymer is readily synthesized via base-promoted radical chain polymerization, BAM-PPV exhibits poor solubility at high-molecular weights (M-w > 100 kDa), which limits its applications. In this work, the molecular weight of BAM-PPV was modulated with nitrobenzene. At nitrobenzene loading as low as 0.9 mol%, the polymerization reaction produced low-molecular weight BAM-PPV (M-w = 5-46 kDa). The polymerization of BAM-PPV was systematically studied via size-exclusion chromatography (SEC), liquid chromatography-mass spectrometry (LC-MS), and H-1 NMR spectroscopy, which revealed suppression of the dimer intermediate before chain polymerization. Collectively, this work could expand the practical applications of BAM-PPV for use in optoelectronic devices or corrosion inhibition coatings.

Several bio-based bisphenols were found to be non-estrogenic through in vitro studies. Polycarbonates derived from these compounds exhibited glass transition temperatures and thermal stability comparable to petroleum-derived thermoplastics.

Seven different high-performance fuels were synthesized from bio-based monoterpenes (3-carene, sabinene, alpha-pinene, beta-pinene, limonene, 1,6-dimethyl-1,5-cyclooctadiene, and myrcene) by Simmons-Smith cyclopropanation. Key fuel properties of the resulting multicyclic fuel mixtures were measured including, density, net heat of combustion (NHOC), and low-temperature viscosity. The mixtures exhibited densities 10-16% higher and volumetric NHOCs 12-16% higher than conventional jet fuel, while maintaining low temperature (-20 degrees C) viscosities either below or close to the specification limit. To evaluate the fuels as potential rocket propellants, heats of formation were calculated using the G4 composite method. These values were then used to calculate specific impulse (Isp) and density-specific impulse (d-Isp) for each fuel mixture. The cyclopropanated monoterpenes exhibited sea level Isp values up to 1.2% higher than conventional rocket propellant (RP-1) and d-Isp values up to 4.1% higher than RP-1. The results of this study suggest that cyclopropanated monoterpenes may have utility as high-performance jet fuel blendstocks or specialized rocket propellants, offering the ability to increase the payload capacity and enhance the mission capability of space-delivery systems. This work further highlights the potential of biosynthetic fuels for high-performance applications.

Ammonium perchlorate (AP) is an oxidizer material that is widely employed in applications ranging from rocketry to airbags. Previous research has suggested that efficient electron transfer plays a critical role in determining the kinetics of catalyzed AP decomposition reactions. Consequently, intimate contact between AP crystals and electron acceptors has the potential to accelerate decomposition kinetics, which motivates the development of conformal coatings with suitably tailored electronic structures. Here, we demonstrate a scalable method for conformally coating AP crystals with two atomically well-defined 2D materials with orthogonal electronic properties-namely, pristine graphene, which is a zero-band gap semiconductor that has been shown to be an effective electron acceptor in diverse heterojunctions and hexagonal boron nitride (hBN), which is a wide-band gap electrical insulator. Consistent with an electron transfer mechanism, graphene-coated AP undergoes accelerated decomposition kinetics compared to uncoated (neat) or hBN-coated AP. Through extensive structural characterization including electron microscopy and X-ray diffraction, the effects of AP crystal size and crystallinity are examined. In addition, the accelerated decomposition kinetics of graphene-coated AP are quantified through thermogravimetric analysis, gas chromatography mass spectrometry, and kinetic modeling. Overall, this work establishes pristine graphene as an effective coating for promoting accelerated decomposition of AP, which enhances its utility in various applications.

Resveratrol is a sustainable and versatile bio-derived phenolic compound that has shown promise as a high glass-transition temperature (T-g), flame-resistant building block for thermoset networks. In this study, three components of epoxy thermoset resins were synthesized from resveratrol: trans-resveratrol trisepoxy (1), dihydroresveratrol trisepoxy (2), and a trifunctional amine, 4,4'-((5-(4-(4-aminophenoxy)phenethyl)-1,3-phenylene)bis(oxy))dianiline (4). The epoxy monomers were low melting solids (mp < 80 degrees C) or thick oils consisting of primarily monomeric trisepoxides. Toxicity testing of 4 revealed that it was not mutagenic and had a low LD50 of 560 mg/kg, an aquatic toxicity of >2000 mg/L, and no cytotoxicity up to its solubility limit. The epoxy monomers were cured with 4,4'-methylenedianiline (3) and 4 to produce four epoxy-amine networks (A-D). Networks C and D, prepared with the resveratrol-derived aniline, contained up to 52.6% bio-based material. The moisture uptake, thermal stability, and dry/wet thermomechanical properties of the networks were measured. The networks had T-g's as high as 285 degrees C, approximately 110 degrees C higher than networks based on petroleum-derived bisphenol A (BPA). In addition, the resveratrol networks had char yields as high as 51 and 46% in nitrogen and air, respectively, compared to ca. 15 and 5%, respectively, for BPA-based networks. Overall, this study shows the advantages of resveratrol-based epoxy and amine monomers as components of sustainable, low-toxicity, high-temperature resin systems.

Ortho-substitution with hydrophobic aliphatic groups has shown reduced moisture uptake in a variety of thermoset networks. In this study, the number and size of ortho-substituents were systematically varied on the epoxy monomers and aniline curing agents to determine network structure-property relationships. Networks were formed from combinations of four epoxies cured with seven aniline curing agents. The cured epoxy-amine networks were exposed to boiling water for 96 h to determine network moisture uptake, as well as wet thermomechanical properties. Ortho-substitution on both the epoxy and aniline monomers showed a reduced moisture uptake of up to 62% over an unsubstituted network. Also, the substituted networks had smaller wet T-G knockdowns compared to the unsubstituted network, and networks derived from 2,2'-(((butane-1,1-diylbis(2-(tert-butyl)-5-methyl4,1-phenyiene))bis(oxy)bis(methylene))bis(oxirane) (t-Bu Bisepoxy) had the smallest wet T-G knockdowns of only 5 degrees C or less. These results show the unique advantages of ortho-substituents on epoxy-amine networks in terms of network hydrophobicity and wet thermomechanical behavior. Applications of the ortho-substituted monomers and networks include use in marine environments as composite materials, hydrophobic coatings, or adhesives.

cis-ResCy is a relatively low melting cyanate ester monomer (<80 °C) derived from the renewable phenol, resveratrol. Thermal cross-linking of this material generates a high Tg polycyanurate network with a char yield >73% in air (600 °C). However, the monomer still presents processing challenges because it is a solid at room temperature and readily recrystallizes upon cooling below the melting point. In this study, cis-ResCy was blended with commercial cyanate ester resins (Primaset LeCy, PT15, and PT30) at loadings between 0 and 80% (by mass) to improve the processability of cis-ResCy and evaluate the structure-property relationships of the blends and corresponding networks. Blends with LeCy were low melting solids, while the PT15 and PT30 blends remained liquid after mixing. The cure chemistry of the blends was evaluated and the thermomechanical properties, thermal stability, moisture uptake, and hot/wet properties of the corresponding networks were studied. In general, the char yields of the blended networks increased with higher cis-ResCy loading. This result was most pronounced for the LeCy networks, which yielded much higher char yields (>70% in air) at ≥ 40% cis-ResCy loading compared to pure LeCy (<40% in air). The Tgs of the networks increased with increasing cis-ResCy content and reached temperatures as high as 391 °C after in-situ cure. Overall, the combination of cis-ResCy with various commercial cyanate esters allowed for the development of processable resins with higher Tgs, improved thermal stability, and lower moisture uptake than the monomer components.

Boron nitride nanotubes (BNNTs) have unique thermomechanical properties that make them excellent candidates for use in structural heat resistant composites, but their usage has been limited in the past due to difficulties associated with dispersing the material into a usable configuration. Techniques to facilitate dispersion into solution, such as functionalization and surface activation of the BNNTs, alter and degrade desirable properties of the material, and high surface energies of BNNT make it difficult to obtain sufficient concentrations to take advantage of those properties by using conventional mixing techniques. This research demonstrates homogeneously dispersed electrospinning sol-gel solutions of up to 20 wt % unfunctionalized boron nitride nanoparticles (BNPs) and BNNTs in polyacrylonitrile (PAN) by using a novel high g-load mixing technique. It confirms that the BNPs and BNNTs influenced bulk PAN properties such as glass transition temperature (T-g) and tensile strength. It also indicates that the BNNTs were loaded beyond the percolation threshold, and the load-bearing structure of the electrospun composite transitioned to a stable core of interconnected nanofiller due to increasing levels of boron nitride present. This was evident by the increase in tensile strength of the composite and in the creation of a stable mat of interconnected BNNTs after PAN pyrolysis. The research highlights the advantages of utilizing unfunctionalized material and points to the success of high g-loading as a viable mixing technique for high weight percentage of unfunctionalized BNNTs.

A heptacyclo[6.6.0.0(2,6).0(3,13).0(4,11).0(5,9).0(10,14)]-tetradecane (HCTD) complex with terminal allylidene groups at the 7- and 12-positions (HCTD-7,12-diallylidene, 2) was generated at the multigram scale from norbornadiene via an efficient six-step synthesis. Thermal polymerization of 2 at temperatures ranging from 160 to 240 degrees C yielded a robust cross-linked material with thermal stability up to 488 degrees C in air, a glass transition temperature of 377 degrees C, and a char yield (600 degrees C) of 56% in air. This degree of thermal stability is remarkable for a nonaromatic hydrocarbon polymer and is likely due to the rigid multicyclic cages that make up the bulk of the material. To elucidate the polymerization mechanism, a model compound, 7-allylidenenorbornane (4), was synthesized and thermally cured. This resulted in the formation of polymeric material, suggesting that the cross-linking reaction of 2 proceeds via a free-radical reaction and not through Diels-Alder cycloaddition. Addition of dibutylhydroxytoluene (BHT) to compound 2 delayed the onset of cure, providing further support for a radical mechanism. On the basis of these results, it can be concluded that exocyclic allylidene groups represent a new class of thermosetting end-cap capable of generating highly cross-linked materials with thermal stabilities that rival those of high temperature polyimides. Applications include heat resistant composites utilized in the aerospace, electronic, automotive, and textile industries.

ABSTRACTThree cyanate esters containing phosphorus are synthesized in good overall yields starting from bromoanisoles. Di‐ and tricyanates with meta configuration are most stable while para is less so. The para dicyanate ester isomer is particularly affected by water from the atmosphere. The meta dicyanate ester 2 has good thermal properties with glass transition at 268 °C and char yield of 65% in air at 600 °C. All three phosphorus‐containing cyanate esters are low flammability in an open flame. They make highly combustible cyanate esters resins less flammable simply by blending. Mixing 10 wt% dicyanate ester 2 into bisphenol A or E dicyanate esters makes them rate V‐0. Published 2018.† J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1100–1110