2-Acrylamido-2-methylpropane sulfonic acid

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2-Acrylamido-2-methylpropane sulfonic acid (AMPS) is a water-loving, sulfonic-acid-containing acrylic monomer. It was sold as a Lubrizol trademark and is used to modify a wide range of polymers to make them more hydrophilic and anionic.

What it is
- AMPS adds a sulfonic acid group to an acrylic structure, giving polymers strong water absorption, increased salt tolerance, and a negative charge over a wide pH range.

How it is made
- AMPS is produced by a Ritter reaction between acrylonitrile and isobutylene in the presence of sulfuric acid and water. This can yield high-purity AMPS, and newer processes can improve yield by using liquid isobutene in the reaction mixture.

Key properties
- Stability: The molecule’s bulky groups provide hydrolytic and thermal stability to AMPS-containing polymers.
- Polarity and hydrophilicity: The sulfonate group makes AMPS highly polar and water-absorbing, contributing to water transport in polymers.
- Solubility: AMPS dissolves well in water and in DMF; solubility in many other polar solvents is limited.
- Salt handling: AMPS-containing polymers strongly resist precipitation of divalent salts (like calcium and magnesium), which helps maintain performance in hard-water environments.

Applications
- Fibers and coatings: Improves dye uptake, moisture absorption, static resistance, and adhesive properties; helps reduce surfactant loss in paints.
- Detergents and personal care: Enhances cleaning performance and provides lubricating properties in high-malability formulations.
- Hydrogels and medical devices: Used in hydrogels for medical applications, including ECG electrodes, wound dressings, and other biocompatible devices.
- Oil field and water treatment: Acts as a scale inhibitor, friction reducer, and water-control polymer; helps in dispersing and controlling minerals in water treatment.
- Membranes and construction: Improves water flow and fouling resistance in membranes; used in cement and concrete formulations to improve workability and durability.
- Pesticide formulations: Helps increase bioavailability of some crop protection products.

History and availability
- AMPS has a long history in research and industry, with many patents and publications since the 1970s for uses in fibers, coatings, hydrogels, and more.
- Production by Lubrizol was discontinued in 2017 due to competitive pressures from copycat producers.

Quick facts
- Common abbreviations: AMPS
- Also known as: 2-Acrylamido-2-methylpropane sulfonic acid
- See also: PolyAMPS, Hydrogels

In short, AMPS is a versatile, salt-tolerant, water-loving monomer used to make polymers that perform well in wet, salty, and hydrogel-rich environments.