Introduction to Hydroxyethyl Methacrylate (HEMA)
2-Hydroxyethyl Methacrylate (HEMA, CAS No. 868-77-9) is arguably the most widely recognized and extensively utilized hydroxy-functional monomer in the global polymer industry. Featuring a methacrylate backbone combined with a terminal primary hydroxyl group, HEMA combines excellent mechanical rigidity, thermal resistance, optical clarity and chemical stability.
Unlike acrylate analogs, the alpha-methyl group (-CH3) on the methacrylate backbone sterically shields the polymer chain, imparting superior hydrolytic stability, a higher glass transition temperature (homopolymer Tg around +55°C) and outstanding weatherability in outdoor environments.
Technical Specifications & Key Quality Parameters
In industrial and specialty polymer manufacturing, slight variations in monomer purity can drastically alter polymer molecular weight, viscosity and optical clarity. DECHEM provides technical-grade and high-purity grades of HEMA meeting global standards:
| Key Parameter | Industrial Grade | High Purity / Optical Grade |
|---|---|---|
| Purity (Assay by GC) | ≥ 97.0% | ≥ 98.0% |
| CAS Number | 868-77-9 | 868-77-9 |
| Ethylene Glycol Dimethacrylate (EGDMA) | ≤ 0.15 wt% | ≤ 0.05 wt% (low crosslinker) |
| Diethylene Glycol Monomethacrylate (DEGMA) | ≤ 0.80 wt% | ≤ 0.30 wt% |
| Methacrylic Acid (MAA) | ≤ 0.50 wt% | ≤ 0.10 wt% |
| Water Content (KF) | ≤ 0.15 wt% | ≤ 0.05 wt% |
| Color (APHA / Pt-Co) | ≤ 15 | ≤ 10 (water-white) |
| Homopolymer Tg | +55°C | +55°C |
| Inhibitor (MEHQ) | 150-250 ppm | 50-100 ppm (or custom) |
★ Why EGDMA content is crucial for HEMA buyers
Ethylene Glycol Dimethacrylate (EGDMA, CAS 97-90-5) is a natural bifunctional by-product in HEMA synthesis. In linear polymer synthesis (solution acrylic resins or thermoplastic coatings), high EGDMA levels cause unintended crosslinking, micro-gels and cloudiness. DECHEM’s vacuum distillation technology maintains EGDMA below 0.05% for demanding applications.
Major Industrial & Specialty Applications of HEMA
1. High-Solid Thermosetting Acrylic Coatings — HEMA is the cornerstone monomer for hydroxylated acrylic resins used in two-component polyurethane (2K PU) and amino-baking systems. Its relatively high Tg (+55°C) contributes film hardness, mar resistance and solvent tolerance in automotive OEM, machinery and coil coatings.
2. Biomedical Hydrogels & Soft Contact Lenses — crosslinked poly-HEMA (pHEMA) forms an optically transparent, hydrophilic hydrogel with water absorption between 38% and 42%, making it a benchmark material for soft contact lenses and intraocular devices.
3. Dental Materials & UV-Curable Nail Gels — in dental composites and adhesive bonding agents, HEMA acts as a penetrating primer monomer on dentin collagen fibers. In the cosmetics industry, HEMA is the primary reactive component in professional UV/LED gel nail polishes due to its rapid curing and strong keratin adhesion.
4. Emulsion Polymers & Industrial Adhesives — HEMA is incorporated into waterborne acrylic emulsions (0.5% – 3.0% by weight) to enhance mechanical shear stability, freeze-thaw resistance and wet adhesion on polar surfaces.
Global B2B Buyer’s Sourcing Checklist for HEMA
- Purity and by-product profile: always verify the Certificate of Analysis (COA) for EGDMA and DEGMA limits tailored to your specific polymerization process.
- Inhibitor balance (MEHQ): ensure inhibitor concentrations align with your storage timeline without impeding your initiator system during polymerization.
- Packaging & sea freight logistics: HEMA should be shipped in coated steel drums (200 kg), IBC totes (1,000 kg) or temperature-controlled ISO tanks from experienced chemical export terminals.
FAQ
Q: What purity grades of HEMA are available from DECHEM?
A: DECHEM supplies HEMA-97 (≥ 97%) and HEMA-98 (≥ 98%) commercial grades, both inhibited with MEHQ and supplied with COA per lot.
Q: Is HEMA registered under REACH?
A: Yes. HEMA (CAS 868-77-9) is covered by a REACH registration held by DECHEM.