Nucleophilic
Polymers and Gels in Hydrolytic Degradation of Chemical Warfare Agents
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Abstract
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