Mercaptan hardener

The mercaptan hardener is one of a very few hardeners which can cure the resin at low temperature even below the freezing point in a few minutes using basic catalysts such as amines. There are only very few studies of the curing reaction mechanism and the physical properties of the cured resin available 42 45). 

Crosslinkers and Accelerators. Besides the polymers themselves, changes and improvements are taking place in curing agents, hardeners, catalysts, and polymer modifiers. For example, if epoxy adhesives with improved heat resistance are needed, the hardeners can be aromatic anhydrides and amines such as benzophenone tetracarboxylic dianhydride, py-romellitic dianhydride, diaminodiphenyl sul-fone. To enhance curing speed, epoxy systems utilize mercaptan hardeners, while acrylic monomer/polymer blends avail themselves of amine/aldehyde catalysts with benzosulfimide (saccharin) accelerators. Radiation-curing systems for today and tomorrow utilize both visible light and laser beams. 

The polysulfide base material contains 50—80% of the polyfunctional mercaptan, which is a clear, amber, sympy Hquid polymer with a viscosity at 25°C of 35, 000 Pa-s(= cP), an average mol wt of 4000, a pH range of 6—8, and a ntild, characteristic mercaptan odor. Fillers are added to extend, reinforce, harden, and color the base. They may iaclude siUca, calcium sulfate, ziac oxide, ziac sulfide [1314-98-3] alumina, titanium dioxide [13463-67-7] and calcium carbonate. The high shear strength of the Hquid polymer makes the compositions difficult to mix. The addition of limited amounts of diluents improves the mix without reduciag the set-mbber characteristics unduly, eg, dibutyl phthalate [84-74-2], tricresyl phosphate [1330-78-5], and tributyl citrate [77-94-1]. 

The polymercaptans can also be used to accelerate the curing of epoxy resins systems blended with polyamines, amidoamines, or amines. The other curatives serve as the base to accelerate mercaptans, and the mercaptans react rapidly, generating the heat to accelerate the cure with the other hardener. 

Organic phosphorus compounds are also produced in the interaction of wliite phosphorus with an epoxide or an episulfide and an alcohol or mercaptane in the presence of alkaline catalysts at 25 °C to 200 °C In order to remove P-H bonds the reaction mixture is treated witli formaldehyde and oxidized. The products are said to be useful as hardeners for epoxy resins or as antistatic agents and fire retardants. 

Another example is shown by the thiol-ene system in which two different reactants A and B photochemically react to form larger molecules with concomitant reduction in solubility. Thus, in the presence of sensitizers/initiators, the multiple functional mercaptan (IV) will react with the multiple unsaturated oligomer (V) to form hardened addition products useful in letterpress platemalong (Figure 7). 

Chem. Descrip. Uncatalyzed mercaptan polymer Uses Epoxy hardener, accelerator tor amides, amines, and amido-amines in conventional and high-solids applies., fast-set concrete adhesives, castings, potting, laminates Features Requires amine catalyst tor activation Properties Gardner 2 max. color sp.gr. 1.15 dens. 9.6 Ib/gal vise. 100-150 poise gel time 4.5-6.5 min (30-50 g) After 7 day 25 C cure tens, str. 5900 psi elong. 3.75% flex. str. 10,000 psi 100% solids Capcure 40 sec HV [Cognis/Coatings Inks]... 

Chem. Descrip. Mercaptan polymer precatalyzed, accelerated Uses Epoxy hardener, accelerator in concrete adhesives, grouts, mortars, and coatings co-curative improves bond to glass and metal Features Fast cure eliminates induction times of polyamides and amido-amines... 

Flexiblization. Aliphatic diepoxide reactive diluents enhance the flexibility or elongation by providing chain segments with greater free rotation between cross-links. Polyaminoamide hardeners, based on aliphatic polyamines and dimerized fatty acids, perform similarly. Liquid polysulfide polymers possessing terminal mercaptan functionality improve impact properties in conjimction with polyamine hardeners. 

Crosslinking through epoxy groups is done by means of hardeners polyamines, anhydrides of di- and polybasic acids, phenolic resins, polyphenols, poly-mercaptans, and carbon sulfur. 

Iwo-component adhesives that are used for household applications differ quite strongly as to their properties. For instance, there are epoxy resin adhesives that are very well suited for bonding glass, china, ceramics and metals. They set ss-clear, are dishwasher-safe, and therefore exceptionally well suited for repairing dishes or similar household articles. Usually, the two components resin (epoxy) and hardener (amine or mercaptan) are filled in aluminum tubes or plastic double syringes and are mixed before application according to the directions for use. Other two-component adhesives are based on meffiacrylate and contain a powder hardener (dibenzqyl peroxide in gypsum). These adhesives bond materials such as stone, plastics, ceramics, and metal ... 

Several types of hardeners are used in the curing Aliphatic amines Amidoamines Aromatic amines Cycloaliphatic amines Imidazoles Polyamides Anhydrides Polysulfides Mercaptans Dicyandiamide (DiCy)... 

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