Carbomer, also known as carbopol, carboxyrinyl polymer, is a white fluffy powder with a characteristic slight odor. Carbomer is a high molecular polymer which is cross-linked by acrylic acid and allyl sucrose. Its chemical name is Carboxypolymethylene. Carbomer was first produced by Goodrich Company in the United States and has been included in the United States Pharmacopeia, British Pharmacopoeia, Chinese Pharmacopoeia, etc. Carbomer is a multi-purpose polymer material and pharmaceutical auxiliary material. Due to its good adhesion, gelation, emulsification, thickening, suspending, and film-forming properties, it is widely used in the pharmaceutical industry, Daily chemical industry, and other related industrial fields.

According to the different structures of polymer monomers, it can be divided into Carbomer 900 series and the Carbomer 1300 series. Carbomer 900 series is obtained by cross-linking acrylic acid monomer with allyl sucrose or allyl pentaerythritol. Carbomer 1300 series is a cross-linked polymer of acrylic acid-alkyl isobutylenic acid copolymer and allyl pentaerythritol. By controlling the relative molecular weight and cross-linking degree of the polymer, different carbomer specification can be obtained. The commonly used products are Carbomer 910,934,934P, 940, 941,971P, 974P, and 1342 (P indicates that it can be used as excipients for oral preparations). Carbomer can produce high-efficiency thickening at a very low dosage (0.25%-0.5%), thereby it can preparing gel formulations with a wide viscosity range and different rheological properties.

Carbomer is soluble in water, glycerin, and ethanol. The commonly used concentration is 0.1% ~ 3%. Because its molecular structure contains 52% ~ 68% acidic groups, so it has a certain acidity.
The pH value of 1% of the aqueous solution is 2.5 ~ 3. 0. When neutralized with alkali, as the macromolecules gradually dissolve, the viscosity gradually rises, forming a clear solution at low concentrations, and forming a translucent gel at higher concentrations. The gel pH has the maximum viscosity from 6 to 12. When pH < 3 or pH > 12, the viscosity decreases. The commonly used neutralizers are triethanolamine, ethylenediamine, laurylamine, sodium bicarbonate, sodium hydroxide, and so on. Both strong electrolyte and sunlight can reduce the viscosity of the gel, and the temperature also has a certain effect on the viscosity, but it does not change much. The gel is best stored in the dark.

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