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New Class of Stable Ambient Temperature Liquid Salts with Possible Anti-static, EMI Shielding and Lithographic Applications

IP.com Disclosure Number: IPCOM000107436D
Original Publication Date: 1992-Feb-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 3 page(s) / 160K

Publishing Venue

IBM

Related People

Angelopoulos, M: AUTHOR [+3]

Abstract

Disclosed is a class of highly conductive, low volatility room- temperature molten salts that can be used effectively as antistats in low humidity or vacuum. With thermal stability higher than common anti-static agents, blending into advanced polymers becomes possible. Blends with polymers may also be applicable to EMI shielding and lithographic charging problems.

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New Class of Stable Ambient Temperature Liquid Salts with Possible Anti-static, EMI Shielding and Lithographic Applications

       Disclosed is a class of highly conductive, low volatility
room- temperature molten salts that can be used effectively as
antistats in low humidity or vacuum.  With thermal stability higher
than common anti-static agents, blending into advanced polymers
becomes possible.  Blends with polymers may also be applicable to EMI
shielding and lithographic charging problems.

      The new compounds are organic salts.  The anion is a
short-chain alkyl or perfluoroalkyl sulfonate, such as
methanesulfonate (CH3SO3(-), "mesylate") or trifluoromethanesulfonate
(CF3SO3(-), "triflate").  The cation is an aromatic 5- or 6-member
ring heterocycle in which at least one of the heteroatoms is
alkylated and carries a positive charge, e.g.,
1-ethyl-3-methylimidazolium, 3-ethylthiazolium (other suitable
heterocyclic systems include but are not limited to pyridinium,
pyrimidinium and pyrazinium).  Thus, some of the new salts resemble
those studied in [*], except that the stable sulfonate anions here
replace the hydrolytically unstable AlCl4(-) and Al2Cl7(-) anions in
(*).

      Although there is no general way to ensure that a new compound
will have a low melting point, it is found that lower molecular
symmetry is helpful.  Cation symmetry can be lowered by proper choice
of the alkyl substituents and their positions on the ring, as well as
by chosing parent heterocycles of intrinsically lower symmetry (e.g.,
thiazole, pyrimidine).  The alkyl substituents can be normal or
branched, but not very large if conductivity is to be kept high;
also, very long alkyl chains may promote formation of mesophases,
consequently pushing the melting point up.

      The new salts can be prepared from commercially available
compounds in several ways.  The most direct method is the one-step
reaction of the heterocycle, e.g., 1-methylimidazole, with an alkyl
ester of the sulfonic acid, e.g., ethyl triflate, in a volatile,
non-acid, non-basic solvent, such as toluene, at or slightly above
room temperature (triflate esters react energetically and require
dropwise addition with cooling; mesylate esters react slower).  After
reaction completion the solvent is vacuum-evaporated, yielding the
liquid salt which are further purified by extraction with a non-polar
solvent. (Caution:alkyl sulfonates, especially triflates, are highly
reactive and hygroscopic and - as strong alkylating agents - probably
highly toxic.)

      The sample compound, 1-ethyl-3-methylimidazolium
trifluoromethanesulfonate ("e.m.i. triflate", C6H10N2(+) CF3SO3(-)),
is a nearly colorless liquid with a melting point of about -10~C (cf.
e.m.i.  tetrachloroaluminate, +7~C (*)).  It is very stable
thermally, losing less than 1% weight in 30 min at 350~C in nitrogen
and only 1.3% under the same conditions in air.  By comparison,
organic nitrogen halide salts are sta...