Thomas J. Groshens

Synthesis, Characterization, and Cure Chemistry of Renewable Bis(cyanate) Esters Derived from 2-Methoxy-4-Methylphenol

A series of renewable bis(cyanate) esters have been prepared from bisphenols synthesized by condensation of 2-methoxy-4-methylphenol (creosol) with formaldehyde, acetaldehyde, and propionaldehyde. The cyanate esters have been fully characterized by infrared spectroscopy, (1)H and (13)C NMR spectroscopy, and single crystal X-ray diffraction. These compounds melt from 88 to 143 °C, while cured resins have glass transition temperatures from 219 to 248 °C, water uptake (96 h, 85 °C immersion) in the range of 2.05-3.21%, and wet glass transition temperatures from 174 to 193 °C. These properties suggest that creosol-derived cyanate esters may be useful for a wide variety of military and commercial applications. The cure chemistry of the cyanate esters has been studied with FTIR spectroscopy and differential scanning calorimetry. The results show that cyanate esters with more sterically demanding bridging groups cure more slowly, but also more completely than those with a bridging methylene group. In addition to the structural differences, the purity of the cyanate esters has a significant effect on both the cure chemistry and final Tg of the materials. In some cases, post-cure of the resins at 350 °C resulted in significant decomposition and off-gassing, but cure protocols that terminated at 250-300 °C generated void-free resin pucks without degradation. Thermogravimetric analysis revealed that cured resins were stable up to 400 °C and then rapidly degraded. TGA/FTIR and mass spectrometry results showed that the resins decomposed to phenols, isocyanic acid, and secondary decomposition products, including CO2. Char yields of cured resins under N2 ranged from 27 to 35%, while char yields in air ranged from 8 to 11%. These data suggest that resins of this type may potentially be recycled to parent phenols, creosol, and other alkylated creosols by pyrolysis in the presence of excess water vapor. The ability to synthesize these high temperature resins from a phenol (creosol) that can be derived from lignin, coupled with the potential to recycle the composites, provides a possible route to the production of sustainable, high-performance, thermosetting resins with reduced environmental impact.

Renewable thermosetting resins and thermoplastics from vanillin

Two cyanate ester resins and a polycarbonate thermoplastic have been synthesized from vanillin. The bisphenol precursors were prepared by both an electrochemical route as well as by a McMurry coupling reaction. 1,2-Bis(4-cyanato-3-methoxyphenyl)ethene (6) had a high melting point of 237 °C and did not cure completely under a standard cure protocol. In contrast, the reduced version, 1,2-bis(4-cyanato-3-methoxyphenyl)ethane (7) melted at 190 °C and underwent complete cure to form a thermoset material with Tg = 202 °C. 7 showed thermal stability up to 335 °C and decomposed via formation of phenolics and isocyanic acid. A polycarbonate was then synthesized from the reduced bisphenol by a transesterification reaction with diphenylcarbonate. The polymer had Mn = 3588, Mw/Mn = 1.9, and a Tg of 86 °C. TGA/FTIR data suggested that the polycarbonate decomposed via formation of benzodioxolones with concomitant elimination of methane. The results show that vanillin is a useful precursor to both thermosetting resins and thermoplastics without significant modification.

Synthesis of Renewable Bisphenols from Creosol

A series of renewable bisphenols has been synthesized from creosol (2-methoxy-4-methylphenol) through stoichiometric condensation with short-chain aldehydes. Creosol can be readily produced from lignin, potentially allowing for the large scale synthesis of bisphenol A replacements from abundant waste biomass. The renewable bisphenols were isolated in good yields and purities without resorting to solvent-intense purification methods. Zinc acetate was shown to be a selective catalyst for the ortho-coupling of formaldehyde, but was unreactive when more sterically demanding aldehydes were used. Dilute HCl and HBr solutions were shown to be effective catalysts for the selective coupling of aldehydes in the position meta to the hydroxyl group. The acid solutions could be recycled and reused multiple times without decrease in activity or yield.

High Tg thermosetting resins from resveratrol

The tricyanate esters of the natural product resveratrol (1) and dihydroresveratrol (2) were synthesized and subjected to thermal curing which gave polycyanurate network polymers which exhibited glass transition temperatures of >340 °C and 334 °C, respectively. Thermal decomposition temperatures of 412 °C and 403 °C for polycyanurates of 1 and 2, respectively, were typical of this class. However, char yields (600 °C) of 71% and 66% for 1 and 2, respectively, were more than double that from the polycyanurate of bisphenol A dicyanate (25%).

Characterization of Nanometer- to Micron-Sized Aluminum Powders: Size Distribution from Thermogravimetric Analysis

Thermogravimetric analysis was used to study the reactivity of aluminum powders in air, oxygen, and nitrogen. In addition, the data were used to characterize active Al content, Al oxide content, volatile impurity content, particle size, and particle size distribution. Weight gains from complete oxidation of the Al were used to calculate average particle sizes in the range of 30 to 500 nm. These particle sizes correlated well with particle sizes derived from surface area measurement. Particle size was also examined by scanning electron microscopy, and compared with crystallite size determined by x-ray diffraction. Particle size distributions were derived from thermogravimetric analysis data based on a model of uniform oxidation of Al from the exterior to the interior of the particle. The method is well suited for analyzing samples with broad particle size distributions, and in particular, for monitoring the presence of 500-5000 nm particles within nominally nanosized samples. Quantitative information was not obtained for particles around 100 nm or smaller, due to large variations in oxidation behavior below 700° C. Nitridation of Al powders was studied for extended times at 600° C. Surprisingly, 2 μm powder was nearly completely nitrided in 1 h, indicating that the nitride product has little inhibiting effect on the reaction.

Sustainable hydrophobic thermosetting resins and polycarbonates from turpentine

Carvacrol is a renewable phenol that can be derived from abundant components of pine resin. To demonstrate the utility of carvacrol for polymer applications, a bisphenol was synthesized from carvacrol and converted to both a cyanate ester resin (CarvCy) and polycarbonate. A cured resin disk prepared from CarvCy exhibited a Tg of 224 °C and a water uptake of only 0.7% after being immersed in 85 °C water for four days. The wet Tg of the material was only 3 °C lower than the dry Tg showing that the cured resin was virtually unaffected by exposure to hot water. Despite the presence of aliphatic groups on the aromatic rings, the cured resin exhibited good thermal stability with only 5% weight loss at 390 °C. The polycarbonate prepared from carvacrol had Mn = 10 200, Mw/Mn = 1.60, Tg = 119 °C, and even better thermal stability than the cyanate ester with 5% weight loss observed at 421 °C. The results provide compelling evidence that the sustainable phenol carvacrol can be used as a platform molecule for the generation of high performance polymers with exceptional properties.

Synthesis, characterization, and coordination chemistry of the dihydrobis(5-aminotetrazol-1-yl)borate anion

The new anionic dihydrobis(5-aminotetrazol-1-yl)borate ligand was synthesized in high yield and structurally characterized. Electron donating effects of the amino substituent on the tetrazole ring are discussed comparing the basicity and coordination chemistry to the previously reported unsubstituted dihydrobistetrazol-1-ylborate anion. Both mono- and diprotonated ligand species were isolated and structurally characterized. Increased σ-electron donating strength of the aminotetrazole compound provides more than one tetrazolyl nitrogen position capable of metal coordination. One-dimensional coordination polymers of {H2B(H2NCN4)2}2Cu(NH3)2 and {H2B(H2NCN4)2}Zn(NH3)Cl are structurally characterized demonstrating both a symmetrically bridging and a new unsymmetrically bridging motif involving more than one of the tetrazolyl ring positions of the ligand.

Synthesis and characterization of compounds with a group 12-arsenic bond. The crystal structure of [tBuZnAs(tBu)2]2

Abstract The series of compounds [RMAs( t Bu) 2 ] n (R  Me, t Bu; M  Zn, Cd, Hg), with an arsenic-Group 12 bond was investigated.

Mineralization of RDX-Derived Nitrogen to N2 via Denitrification in Coastal Marine Sediments

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a common constituent of military explosives. Despite RDX contamination at numerous U.S. military facilities and its mobility to aquatic systems, the fate of RDX in marine systems remains largely unknown. Here, we provide RDX mineralization pathways and rates in seawater and sediments, highlighting for the first time the importance of the denitrification pathway in determining the fate of RDX-derived N. (15)N nitro group labeled RDX ((15)N-[RDX], 50 atom %) was spiked into a mesocosm simulating shallow marine conditions of coastal Long Island Sound, and the (15)N enrichment of N2 (δ(15)N2) was monitored via gas bench isotope ratio mass spectrometry (GB-IRMS) for 21 days. The (15)N tracer data were used to model RDX mineralization within the context of the broader coastal marine N cycle using a multicompartment time-stepping model. Estimates of RDX mineralization rates based on the production and gas transfer of (15)N2O and (15)N2 ranged from 0.8 to 10.3 μmol d(-1). After 22 days, 11% of the added RDX had undergone mineralization, and 29% of the total removed RDX-N was identified as N2. These results demonstrate the important consideration of sediment microbial communities in management strategies addressing cleanup of contaminated coastal sites by military explosives.

Synthesis of p-Quinquephenyl from E,E-1,4-Bis(4-bromophenyl)-1,3-butadiene

p-Quinquephenyl was synthesized in five steps from E,E-1,4-bis(4-bromophenyl)-1,3-butadiene in 34% overall yield. The butadiene was prepared in six steps from 4-bromobenzaldehyde in 35% overall yield.