Polyacrylic acid

• Carbomer ( generic name )
• CARBOMER (INCI)
• Carbopol ( trademark)
• Polypropensäure
• Poly (1- carboxyethylene )
• Acidum polyacrylicum
• Carboxyvinylpolymer
• Polyacrylic acid (PAA ) (English)

Fixed

1.4 g · cm -3

100-105 ° C.

At 25 ° C in g · 100 ml -1

• Dioxane, dimethyl formamide, glycerol, ethanol, methanol, > 1
• Insoluble in acetone, Cylclohexan, benzene, diethyl ether

In part:

Risk

Carbopol 934

• Rat: 4.3 g · kg -1 ( oral)
• Mouse: 4.6 g · kg -1 ( oral)
• Guinea pigs: 2.5 g · kg -1 ( oral)
• Dog: > 8 g · kg -1 ( oral) Template: Infobox Polymer/LD50 not empty

Polyacrylic acid is a chemical compound, and a synthetic high molecular weight polymer of acrylic acid. Polyacrylic acid is usually considered hygroscopic, white powder and is either odorless or has a faint sour odor.

Polyacrylic acid is able to form with absorption of water in the pH - neutral to weakly basic range gels and is therefore used as a thickening agent, such as in pharmaceutical and cosmetic preparations, but also in paints, lubricants, and other products used industrially.

Polyacrylic acid occurs in various degrees of polymerization.

• 2.1 Start reaction
• 2.2 Growth response
• 2.3 termination reaction

• 3.1 Pharmaceutical and medical use
• 3.2 Other Applications

Properties

Polyacrylic acid - as a powder - is white, hygroscopic, either no perceptible odor or slightly sour smelling. The polymer is little cross-linked and contains 56% to 68 % carboxyl groups. The pKa value is 6.0 ± 0.5 (Carbopol 934). The information on the bulk density may vary between about 0.2 g · cm -3, and 2.08 g · cm - 3, at a particle size of 2-6 microns. Polyacrylsäuregranulate have grain sizes of about 180-425 microns.

1% aqueous Polyacrylsäuresuspensionen have a pH value of 2.5 to 3.2 to. Only after addition of a proton (eg, tromethamine ( Tris), ammonium hydroxide (ammonia water) or sodium hydroxide ( caustic soda) ) sets the gel formation: the carboxyl groups are deprotonated and repel each other, previously coiled polymer chains stretch and form a linear colloid structure, in which the water is stored. The gel formation is pH-dependent. If a certain pH value is exceeded, breaks down the gel structure and the gel liquefies. Also to strong acids, multiply charged cations, and cationic polymers, the gel structures are sensitive. Even low cation concentrations (about Ca2 , Al3 ) can cause the gel to liquefaction or coagulation ( flocculation ). Stabilizing effect in such cases, the complexation of multivalent cations with for example sodium from.

Depending on the degree of polymerization ( molecular weight ) distinguishes different types, the gels differ in their viscosity.

Pharmaceutically types used

The U.S. Pharmacopeia (United States Pharmacopoeia, USP) differentiated homopolymer polyacrylic acid ( carbomer ) into types A, B and C, the gels are characterized by different pharmaceutically relevant viscosities. These correspond to the so-called viscosity-average molecular mass Mv ( Viscosity Average Molecular Weight ) which is approximately determined by the viscosity and is also used for distinguishing the types.

Pharmaceutical Carbomerqualitäten which comply with the European Pharmacopoeia, have a 0.5% gels viscosities from 300 to up to 115,000 mPa · s.

The pre-existing limitation of use of polyacrylic acids on the outer use, founded on the presence of residues of toxic solvents ( benzene ) from the synthesis process, is no longer significant. Pharmaceutical grades are manufactured benzene-free today and are very pure (maximum benzene content 2 ppm). The proportion of monomeric acrylic acid is limited to 0.25%.

Technically and budgetary terms used Carbomers however, usually contain residual benzene.

Carbomers are useful as viscosity enhancer for aqueous- alcoholic and alcoholic preparations.

Polyacrylic acid is generally well tolerated by the skin and also applicable to mucous membranes; only at higher concentrations it is irritating.

Hazard (hazardous materials labeling Legal )

Polyacrylic acid is non-toxic and it will go no subject to declaration dangers according to EC - directives. Types that are included in the manufacturing process resulting admixture of substances of concern in labeling pflichter amount to be marked accordingly. Benzene -containing types are about as GHS08 and as toxic ( T) - classified - according to the EC Directives. They carry the R phrases: 45 - 46 and S: 53 - 45, or H: 340-350 and P: 201-308 313. Benzene -free types do not have hazardous material identification.

All types can form explosive dust-air mixture.

Synthesis

Polyacrylic acid is synthesized by free radical polymerization in the presence of peroxides, azo compounds or with other radical forming substances as polymerization initiators.

Start reaction

To the start of the chain breaks the radical 1, the C = C double bond of the acrylic acid (2) and produces the viable radical 3:

Growth response

In a growth response attach themselves to the radical of three monomers. That is, in the radical 3, another molecule of the acrylic acid (2 ) is mounted on. Through this repeated addition of the acrylic acid is formed again a new radical, so that the chain is getting longer. Here, n is a natural number that describes the number of the repeated deposits of acrylic acid:

Termination reaction

In the following illustrations, m and n are natural numbers describing the number of previous repeated deposits of acrylic acid in the growth reaction. It may be different m and n. The growth of the chain can be terminated by a radical disproportionation:

Alternatively, a Kettenabruch take place by recombination of two radicals, eg by the recombination of two radicals with a high molecular mass:

A specific example looks like: Acrylic acid is added with small amounts of allyl pentaerythritol, an organic peroxide and a mixture of the solvents, cyclohexane and ethyl acetate in a polymerization reactor. Then mixed, polymerized, dried, and crushed.

To prepare the Carbomers according to the European Pharmacopoeia is cross-linked with Polyalkenethern of sugars or polyalcohols in small quantities. The U.S. Pharmacopoeia ( USP) leads under the monograph carbomer homopolymer also a cross-linking with allyl ethers of polyhydric alcohols (eg, pentaerythritol ) to.

Also possible is the preparation through hydrolysis of the corresponding polyacrylonitrile precursors or by oxidative polymerization of acrolein and hydrogen peroxide.

Use

Pharmaceutical and medical use

• As gelling agent in the manufacturing of dosage forms for application to skin and mucous membranes. Carbomers are also suitable for the production of Haftgelen. To the carbomer is incorporated in high concentration in liquid paraffin to form a semi-solid preparation is produced. After application to the mucous membranes caused by moisture absorption of water, the gel having a high adhesiveness.
• As viscosity -enhancing adjuvant in liquid medicines to prevent sedimentation / creaming in disperse systems or improve feed.
• As Pseudoemulgatoren Carbomers stabilize oil-in- water emulsions. For neutralization, long-chain aliphatic amines such as Stearylamine used.
• As a binder in tablets.
• As a component in artificial tears. By the effect of moisture binding, the mucous membranes of the eye to be kept moist.

Other areas of application

In emulsion-based lubricants, in printer ink, in polishes and waxes, in ink or paint, in water - or oil- resistant coatings, beauty products, " industry specialties ," says polyacrylic another application.