4 research outputs found
Nucleophilic Polymers and Gels in Hydrolytic Degradation of Chemical Warfare Agents
Water- and solvent-soluble
polymeric materials based on polyalkylamines modified with nucleophilic
groups are introduced as catalysts of chemical warfare agent (CWA)
hydrolysis. A comparative study conducted at constant pH and based
on the criteria of the synthetic route simplicity, aqueous solubility,
and rate of hydrolysis of CWA mimic, diisopropylfluorophosphate (DFP),
indicated that 4-aminopyridine-substituted polyallylamine (PAAm-APy)
and polyvinylamine substituted with 4-aminopyridine (PVAm-APy) were
advantageous over 4-pyridinealdoxime-modified PVAm and PAAm, poly(butadiene-<i>co</i>-pyrrolidinopyridine), and PAAm modified with bipyridine
and its complex with Cu(II). The synthesis of PVAm-APy and PAAm-APy
involved generation of a betaine derivative of acrylamide and its
covalent attachment onto the polyalkylamine chain followed by basic
hydrolysis. Hydrogel particles of PAAm-APy and PVAm-APy cross-linked
by epichlorohydrin exhibited pH-dependent swelling and ionization
patterns that affected the rate constants of DFP nucleophilic hydrolysis.
Deprotonation of the aminopyridine and amine groups increased the
rates of the nucleophilic hydrolysis. The second-order rate of nucleophilic
hydrolysis was 5.5- to 10-fold higher with the nucleophile-modified
gels compared to those obtained by cross-linking of unmodified PAAm,
throughout the pH range. Testing of VX and soman (GD) was conducted
in 2.5–3.7 wt % PVAm-APy suspensions or gels swollen in water
or DMSO/water mixtures. The half-lives of GD in aqueous PVAm-APy were
12 and 770 min at pH 8.5 and 5, respectively. Addition of VX into
3.5–3.7 wt % suspensions of PVAm-APy in DMSO-<i>d</i><sub>6</sub> and D<sub>2</sub>O at initial VX concentration of 0.2
vol % resulted in 100% VX degradation in less than 20 min. The unmodified
PVAm and PAAm were 2 orders of magnitude less active than PVAm-APy
and PAAm-APy, with VX half-lives in the range of 24 h. Furthermore,
the PVAm-APy and PAAm-APy gels facilitated the dehydrochlorination
reaction of sulfur mustard (HD) and its analogue 2-chloroethyl ethylsulfide
(CEES). The ability of the reported aminopyridine-modified polyalkylamine
materials to degrade the most persistent of CWAs, coupled with aqueous
solubility, and the presence of numerous amino groups that provide
convenient “handles” for covalent attachment on polymeric
and inorganic supports yields promise for applications such as protective
fabric and textile treatment and components of decontaminating materials
Alkylaminopyridine-Modified Aluminum Aminoterephthalate Metal-Organic Frameworks As Components of Reactive Self-Detoxifying Materials
Aluminum aminoterephthalate MOF particulate materials
(NH<sub>2</sub>-MIL-101(Al) and NH<sub>2</sub>-MIL-53(Al)), studied
here as components of self-detoxifying surfaces, retained their reactivity
following their covalent attachment to protective surfaces utilizing
a newly developed strategy in which the MOF particles were deposited
on a reactive adhesive composed of polyisobutylene/toluene diisocyanate
(PIB/TDI) blends. Following MOF attachment and curing, the MOF primary
amino groups were functionalized with highly nucleophilic 4-methylaminopyridine
(4-MAP) by disuccinimidyl suberate-activated conjugation. The resulting
MOF-4-MAP modified PIB/TDI elastomeric films were mechanically flexible
and capable of degrading diisopropyl fluorophosphate (DFP), a chemical
threat simulant
Thermoelectric Enhancement by Compositing Carbon Nanotubes into Iodine-Doped Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]
Free-standing
iodine-doped composite samples of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]
(MEH-PPV) with carbon nanotubes (NTs) showed thermoelectric (TE) power
factors (PFs) up to 33 μW·m<sup>–1</sup>·K<sup>–2</sup> after optimizing multiple factors, including: (1)
sample fabrication solvent, (2) doping time, (3) average MEH-PPV molecular
weight, (4) NT fraction in the composite, and (5) use of single-wall
versus multi-wall nanotubes (SWNT and MWNT, respectively). Composite
fabrication from halogenated solvents gave the best TE performance
after iodine doping times of 2–4 h; performance drops substantially
in ∼20 h doped samples. TE performance dropped after at least
24 h of removal from iodine vapor but was fully restored upon re-exposure
to the dopant. Longer-chain MEH-PPV gave not only mechanically stronger
films but also higher PFs in doped SWNT composites. MWNT composites
gave low PFs, attributed to poor NT dispersion. Scanning electron
microscopy showed increasingly extensive network formation as NT fraction
increased in the composites; this phase separation provides charge
transport pathways that improve thermoelectric PFs. The results support
a strategy of producing phase-separated materials having both electrical
conduction enhanced regions and Seebeck thermopower retaining regions
to maximize organic TE response
All-Organic, Stimuli-Responsive Polymer Composites with Electrospun Fiber Fillers
Stimuli-responsive materials are desired for a wide range
of applications.
Here, we report the design and fabrication of all-organic, stimuli-responsive
polymer composites using electrospun nanofibers as the filler. The
incorporation of 4 wt % of filler into the polymer matrix increased
the tensile storage modulus by 2 orders of magnitude. Upon exposure
to water, the filler fibers plasticize and no longer provide mechanical
reinforcement. The tensile storage modulus subsequently diminishes
2 orders of magnitude to the value of the neat matrix polymer