Acrylic Acid
Properties
| State | Liquid |
| Color | Colorless |
| Solubility | Miscible with water, ethanol, and diethyl ether |
| Melting Point | 14°C |
| Boiling Point | 141°C |
About Acrylic Acid
Acrylic acid is the simplest unsaturated carboxylic acid — a vinyl group directly attached to a carboxyl, three carbons total — and the combination of those two functional groups is what makes it one of the highest-volume monomer feedstocks in industrial chemistry. The carboxyl gives a pKa near 4.25, comparable to other small acids; the vinyl group is what does the real work, polymerizing under radical initiation into polyacrylic acid and a long list of acrylate copolymers. Annual production is around 6 million tonnes, almost all of it routed into one of three downstream products. The largest is sodium polyacrylate, the cross-linked superabsorbent polymer in disposable diapers and adult incontinence products — a single SAP particle can absorb 200–300 times its weight in water by osmotically pulling fluid into a hydrogel network. Next is the family of acrylate esters (methyl, ethyl, butyl, 2-ethylhexyl) that go into acrylic paints, pressure-sensitive adhesives, and elastomeric coatings, where the vinyl polymerization gives long chains and the ester pendant group tunes the glass-transition temperature. Detergent dispersants and scale inhibitors round out the third major use. Because the vinyl group polymerizes spontaneously when warm or exposed to free radicals, every commercial bottle of acrylic acid contains a small amount of MEHQ (monomethyl ether of hydroquinone) as inhibitor — and the storage temperature is kept below 25 °C to keep the inhibitor effective.
Where you'll encounter it
If you've handled a disposable diaper, a contact-lens packaging blister, or a Post-it note, you've handled acrylic-acid-derived polymer — the SAP in the diaper, the acrylate adhesive on the note. In the lab, acrylic acid itself is mostly an avoid-handling reagent because of the polymerization risk; chemists use the more stable acrylate esters when they actually need to do conjugate-addition chemistry on the bench. Where acrylic acid does still show up directly is in scale-inhibitor formulations for boilers and cooling-tower water, where the carboxyl groups on the polymer chelate Ca2+ and Mg2+ before they can deposit as scale.
Common Uses
- Sodium polyacrylate superabsorbent polymer for hygiene products
- Acrylate-ester monomers for paints, adhesives, and elastomers
- Scale-inhibitor and dispersant polymers for water treatment
- Textile-and-leather finishing copolymers
- Specialty hydrogels for biomedical and agricultural applications
Safety Information
Corrosive to skin and eyes — concentrated acrylic acid causes severe burns and permanent eye damage on contact. Flammable (flash point 50 °C). The major safety concern beyond corrosivity is uncontrolled polymerization: warming inhibitor-depleted bottles or contaminating with iron oxides or peroxides triggers a runaway exotherm capable of bursting containers. Always store below 25 °C with intact MEHQ inhibitor and an air headspace (acrylic acid polymerization is inhibited by oxygen, so a nitrogen blanket is actively unsafe).
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.