Curing compositions having low-free amounts of methylenedianiline

1. A curing composition comprising:

an inert liquid carrier comprising a plasticizer selected from the group consisting of esters of polycarboxylic acids and monohydric alcohols or phenols, and esters of polyols and monocarboxylic acids;

from 30 to 70 wt % based on the total weight of the curing composition of a coordination complex of 4,4′-methylenedianiline and an alkali metal salt selected from the group consisting of sodium chloride, sodium bromide, sodium iodide, lithium chloride, lithium bromide, lithium iodide;

from 0.1 to 5 wt % based on the total weight of the curing composition of one or more surfactants selected from the group consisting of lecithin, polyoxypropylated quaternary ammonium halides, phosphated glycerides; and

less than 500 wppm of free methylenedianiline,

wherein the curing composition has a Brookfield viscosity of less than 2,500 cP at 30° C. using a #21 spindle wherein said curing composition is obtained by a process comprising,

A) adding an initial methylenedianiline to a mixture comprising the alkali metal salt and one or more inert liquid carrier, one or more surfactant and brine or water to form the coordination complex,

B) removing water from the mixture comprising the coordination complex to form a dry stage intermediate,

C) adding an isocyanate compound to the dry stage intermediate to react with residual methylenedianiline,

wherein 99.1% or more of the initial methylenedianiline consists of 4,4′-methylenedianiline and from 0.9% to 0.01% of the initial methylenedianiline is one or more of 2,2′-methylenedianiline, 2,4′-methylenedianiline and N-methyl-4,4′-methylenedianiline,

wherein, in the process by which the curing composition is obtained, the initial methylenedianiline in A) is added to a mixture comprising

i) an alkali metal salt selected from the group consisting of sodium chloride, sodium bromide, sodium iodide, lithium chloride, lithium bromide, lithium iodide;

ii) one or more inert liquid carrier comprising a plasticizer selected from the group consisting of esters of polycarboxylic acids and monohydric alcohols or phenols, and esters of polyols and monocarboxylic acids;

iii) one or more surfactant selected from the group consisting of lecithin, polyoxypropylated quaternary ammonium halides, and phosphated glycerides:

and

iv) brine or water,

wherein, in the process by which the curing composition is obtained, no surfactant is added during or after addition of an isocyanate compound to the dry stage intermediate.

2. The curing composition of claim 1 , wherein the process by which the curing composition is obtained further comprises adding additional plasticizer selected from the group consisting of esters of polycarboxylic acids and monohydric alcohols or phenols, and esters of polyols and monocarboxylic acids to the dry stage intermediate obtained in B).

3. The curing composition of claim 1 , wherein the plasticizer is selected from the group consisting of di(2-ethylhexyl)phthalate, diisodecyl phthalate, di(2-ethylhexyl) adipate, diisodecyl adipate and mixtures thereof.

4. The curing composition of claim 1 , wherein the isocyanate compound added to the dry stage intermediate is selected from the group consisting of phenyl isocyanate, p-tolyl isocyanate, cyclohexyl isocyanate, butyl isocyanate, tolylene-2,4-diisocyanate, mixtures of tolylene-2,4-diisocyanate with tolylene-2,6-diisocyanate, 4,4′-methylenebis(phenyl isocyanate), 2,4,4′-triisocyanato-diphenyl ether, phenylene-1,4-diisocyanate, 4,4′-methylenebis(cyclohexyl isocyanate), para-phenylene diisocyanate, 1,6-hexane diisocyanate, isophorone diisocyanate, 3,3′-bitoluene diisocyanate, 1,4-cyclohexyl diisocyanate, and naphthalene-1,5-diisocyanate.