Hydroxypropyl Methacrylate (HPMA, CAS No. 27813-02-1) is a specialized functional methacrylate monomer produced through the reaction of methacrylic acid with propylene oxide. It consists of an isomeric mixture of 2-hydroxypropyl methacrylate (major isomer, ~75–80%) and 1-methyl-2-hydroxyethyl methacrylate (minor isomer, ~20–25%).
HPMA features both a methacrylate double bond and a secondary hydroxyl group. With a homopolymer glass transition temperature (Tg) of approximately +26°C to +30°C, HPMA provides the ideal middle ground between the high hardness of HEMA (+55°C) and the softness of acrylate monomers, making it a premier choice for balanced toughness, chemical resistance, and weatherability.
Technical Specifications & Property Profile
| Specification Item | Standard Value | Analytical Standard |
|---|---|---|
| Chemical Name | Hydroxypropyl Methacrylate (HPMA) | IUPAC Standard |
| CAS Number | 27813-02-1 | Chemical Abstracts Service |
| Assay (Total Isomers by GC) | ≥ 98.0% (high purity ≥ 98.5%) | Gas Chromatography |
| Molecular Weight | 144.17 g/mol | Calculated |
| Appearance | Clear, colorless transparent liquid | Visual |
| Water Content (Karl Fischer) | ≤ 0.10 wt% (special grade ≤ 0.05%) | ASTM E203 |
| Acid Value (as MAA) | ≤ 0.50 wt% | Titration |
| MEHQ Inhibitor | 150–250 ppm | Colorimetric / HPLC |
Key Industrial Applications of HPMA
1. Automotive OEM and Refinish Clearcoats
HPMA-based acrylic polyols deliver exceptional leveling, high DOI (Distinctness of Image), superior resistance to environmental etch, and outstanding chemical resistance against fuels and solvents.
2. Anaerobic Adhesives & Threadlockers
HPMA is a primary monomer in anaerobic structural adhesives, threadlockers, and pipe sealants. In the presence of metal ions and the absence of oxygen, HPMA polymerizes rapidly into a tough, heat-resistant, and vibration-proof crosslinked network.
3. Marine & Protective Industrial Coatings
Due to the sterically protected ester bond on the methacrylate backbone, HPMA-based resins exhibit superior resistance to alkaline and saline environments, making them ideal for heavy-duty marine primers and offshore steel coatings.
4. Dental Biomaterials & Acrylic Cements
Specialty high-purity HPMA grades serve as reactive diluents and crosslinkers in dental restoratives and bone cements, where low shrinkage and biocompatibility are paramount.
How to Select the Right HPMA Grade: Buyer Checklist
- Low Moisture Grade: required for moisture-cured polyurethane or isocyanate-terminated prepolymers (H2O ≤ 0.05%).
- Low Diester Grade: essential for linear acrylic resin synthesis to avoid batch thickening and gel particle formation (PGDMA ≤ 0.10%).
- Logistics Reliability: DECHEM provides standard 200 kg drums, 1,000 kg IBCs, and ISO tank shipments worldwide with complete COA, TDS, SDS, and REACH documentation.