Latent Acid Catalysts

A way to circumvent the problems encountered by adding acid catalysts to the polymerization feed (i.e. cationic polymerization and interaction with Mayo 

Reaction conditions Polymer color Residual styrene (ppm) A/w A/n PD 

---

Pyrovatex CP coreacts on cellulose with an amino resin in the presence of a latent acid catalyst, to produce finishes durable to laundering (125,126). A higher assay version, Pyrovatex (CP New, has also been introduced. 

An important aspect of this procedure is the use of latent acid catalysts, such as phenyl hydrogen maleate, phenyl trifluoracetate, and butadiene sulfone. These catalysts reduce the peak exotherm from over 200°C to 130—160°C. The resin catalyst mixture has a working life of up to several days at RT. The elevated temperature of mol ding these latent catalysts generates the corresponding acids, namely, maleic, trifluoracetic, and phenolsulfonic, which cataly2e the resole reaction. Typically, a cycle time of 1—2 min is requited for a mold temperature of - 150° C. 

In order to obtain a sufficient rate of cure at moulding temperatures it is usual to add about 0.2-2.0% of a hardener (accelerator). This functions by decomposing at moulding temperatures to give an acidic body that will accelerate the cure rate. A very large number of such latent acid catalysts have been described in the literature, of which some of the more prominent are ammonium sulphamate, ammonium phenoxyacetate, ethylene sulphite and trimethyl phosphate. 

Urea-formaldehyde powders have a limited shelf-life but some improvement is made by incorporating a stabiliser such as hexamine into the moulding power. In some formulations the cure rate and the related time for flow are controlled by keeping the latent acid catalyst fixed and adjusting the stabiliser. 

There are reactive softeners, some of which are N-methylol derivatives of long-chain fatty amides (10.241) while others are triazinyl compounds (10.242). The N-methylol compounds require baking with a latent acid catalyst to effect reaction, whereas dichloro-triazines require mildly alkaline fixation conditions. The N-methylol compounds are sometimes useful for combination with crease-resist, durable-press, soil-release and water-repellent finishes. In this context, the feasibility of using silane monomers such as methyltri-ethoxysilane (10.243), vinyltriethoxysilane (10.244), vinyl triace tylsilane (10.245) and epoxypropyltrimethoxysilane (10.246) in crosslinking reactions to give crease-resist properties and softness simultaneously has been investigated [492]. 

A more soluble derivative of compound 11.17, the tetrasulphonated analogue 11.18, has been recommended for application to cotton in combination with a resin finish. Unlike DAST-type FBAs under these conditions, compound 11.18 is compatible with resin formulations containing zinc nitrate as latent acid catalyst. The brightness achieved is not high, however. 

Latchup mode, 22 252 Latent acid catalysts, in liquid-injection molding, 18 795... 

They are made to react with the cellulose in the presence of latently acid catalysts under the influence of heat within a few minutes (dry crosslinking) or in the presence of potentially acid catalysts at room temperature and with longer treating time (moist crosslinking, wet crosslinking). 

The product is fixed to cellulose in the presence of latently acid catalysts at 130-140C, and even without the addition of an N-methylol compound, the finish is wash resistant. The product has hardly any Influence on the handle. 

INTEX BINDER 18 is also suggested as a nonwoven binder, particularly where a soft hand is desired. Addition of 1.5 to 2.0% of a latent acid catalyst, such as ammonium chloride, is also recommended to promote cross-linking of the polymer. 

USE See Gluconolactone. Ammonium salt used as latent acid catalyst in textile printing. 

To obtain a sufficiently high rate of cure at molding temperatures, it is usual to add about 0.2-2.0% of an accelerator (hardener)—a latent acid catalyst which decomposes at molding temperatures to yield an acidic body that will accelerate the rate of cure. Many such materials have been described, the most prominent of them being ammonium sulfamate, ammonium phenoxyacetate, trimethyl phosphate, and ethylene sulfite. A stabilizer such as hexamine is often incorporated into the molding powder to improve its shelf life. 

For different applications, there are different U/F ratios and B-stage oligomers. They can be stabilized by hexamethylene tetramine to keep them alkaline, or they can be reversibly etherifled with methanol or butanol to make them stable and soluble in organic solvents (Fig. 3.10). They may be compounded and processed in water or organic solution or as solid powders for different applications. For final cnre, they are compounded with latent acid catalysts such as ammonium sulfamate, ammonium phenoxyacetate, ethylene sulfite, and trimethyl phosphate and generally heated to accelerate the cross-hnking reaction. 

The catalysts required by plastics may be classified as (1) strong add catalysts (e.g., sulfuric acid, hydrochloric acid, and phosphoric acid alone or in combination with modifiers), (2) latent acid catalysts (e.g., ammonium salts of strong acids such as ammonium chloride generally useful in accelerating the setting of urea or melamine resins), (3) aldehydic catalysts (e.g., catalysts peculiar to phenol-formaldehyde and urea-formaldehyde resins such as paraformaldehyde and hexamethylenetetramine often used in urea and resorcinol adhesives), and (4) peroxide catalysts (e.g., benzoyl peroxide and dicumyl peroxide promote polymerization of polyesters through a free radical mechanism). 

Some resoles contain latent acid catalysts, which on heating generate moderately strong acids. Examples inclnde aryl phosphites such as diphenyl hydrogen phosphite and ammonium sulfate (48,49). The use of latent acid catalysis broadens the range of applications of phenolic resins to include areas such as liquid composite molding and pultrusion. Also resoles, which can contain so-called free formaldehyde, can be formulated with formaldehyde scavengers in form of amines such as melamine. 

Synonyms include Furyl Carbinol, 2-Hydroxy Methyl Furan, 2-Furan Methanol, Furfuryl alcohol resin. Furan resin, FA resin, Poly(furfuryl alcohol). Prepolymers of FA. It is a raw material for organic synthesis, producing levulic acid, resin of various furane kinds in different properties, furfuryl alcohol urea formal resin and phenolic resin. It is a fine solvent for furane resin and oil varnish and pigment as well as used in rocket fuel. It is also used in the production of synthetic fibers, rubber, agricultural chemicals and foundry products. Furfuryl alcohol resins are derivatives of agricultural waste products and complex polymers that are formed in a condensation reaction that occurs when the furfuryl alcohol is acidified. The resins have low viscosity with an odor of furfuryl alcohol. The resin systems are highly reactive and can be catalyzed using a variety of active and latent acidic catalysts. When thermoset, the resins produce polymers that are heat resistant and extremely corrosion resistant to acids, bases and solvents. 

---