18 research outputs found
Development of habitat suitability criteria for Neotropical stream fishes and an assessment of their transferability to streams with different conservation status
Synthesis, Characterization, and Cure Chemistry of Renewable Bis(cyanate) Esters Derived from 2‑Methoxy-4-Methylphenol
A series of renewable bisÂ(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, <sup>1</sup>H and <sup>13</sup>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 <i>T</i><sub>g</sub> 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 CO<sub>2</sub>. Char yields
of cured resins under N<sub>2</sub> 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
Synthesis, Characterization, and Cure Chemistry of Renewable Bis(cyanate) Esters Derived from 2‑Methoxy-4-Methylphenol
A series of renewable bisÂ(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, <sup>1</sup>H and <sup>13</sup>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 <i>T</i><sub>g</sub> 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 CO<sub>2</sub>. Char yields
of cured resins under N<sub>2</sub> 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
Atomic Layer Deposition of Metal Tellurides and Selenides Using Alkylsilyl Compounds of Tellurium and Selenium
Low-pressure pyrolysis studies of a new phosphorus precursor: Tertiarybutylbis(dimethylamino)phosphine
Abiotic habitat assessment for arctic grayling in a portion of the big Manistee river, Michigan
© American Fisheries Society 2017. Arctic Grayling Thymallus arcticus were once the dominant salmonid in the Big Manistee River, Michigan, but were extirpated from the watershed around 1900 and from the state of Michigan by 1936, likely due to overfishing, biotic interactions with introduced fish species, and habitat loss occurring largely around the turn of the 20th century. An interest in reestablishing native species by the Little River Band of Ottawa Indians led to an assessment of environmental conditions in a portion of the watershed encompassing 21 km of the Big Manistee River to determine whether suitable Arctic Grayling habitat remains. During summer in 2011–2013, abiotic habitat metrics, including water characteristics, substrate composition, channel profile, channel geomorphic unit, and stream velocity, were assessed across eight tributaries within the watershed. To assess whether abiotic conditions in these tributaries might support Arctic Grayling, the environmental conditions were compared to literature values from rivers where current or historical Arctic Grayling populations have been reported. This comparison, in conjunction with an assessment using a habitat suitability index for Arctic Grayling, indicated that important abiotic conditions were within ranges consistent with those associated with current and past populations of Arctic Grayling in North America. The results of this study will guide potential future reintroductions and indicate that suitable Arctic Grayling habitat does exist in portions of the Big Manistee Rive