Methyl ethyl ketone peroxide

CAS: 1338-23-4

Overview

Methyl ethyl ketone peroxide (CAS 1338-23-4 ), commonly known as MEKP, is an organic peroxide used as a free-radical initiator in polymer curing and crosslinking systems. Supplied as a solution rather than in pure form, it activates resin systems at room temperature without requiring elevated heat.

Formulators and compounders rely on it to control cure speed and crosslink density across a range of thermoset applications. MEKP is the standard initiator for curing unsaturated polyester and vinyl ester resins in fiberglass-reinforced composites.

This includes marine hulls, automotive panels, and construction laminates. In combination with cobalt-based accelerators, it enables ambient-temperature cure cycles that are critical for open-mold and hand lay-up fabrication.

Rubber compounders use it as a crosslinking agent to improve heat resistance and mechanical performance in elastomeric profiles and molded parts. It also initiates polymerization in gel coats and casting resins.

In these applications, cure uniformity directly affects surface quality and product yield. MEKP is supplied as a liquid solution, typically diluted in plasticizers or inert carriers to reduce reactivity hazards during handling and transport.

Standard commercial concentrations range from approximately 33% to 60% active oxygen content, with grades varying by reactivity profile to suit different resin systems and processing conditions.

Technical-grade material is the norm for most industrial uses. Buyers should confirm active oxygen percentage and dilution carrier with suppliers when qualifying for specific applications to ensure compatibility.

Physical Properties

Melting Point	<25 °C
Boiling Point	19 °C
Density	1.18 g/cm³
Flash Point	190 °F
Appearance	MEKP, an organic peroxide, is a colorless liquid.
Form	Liquid
Water Solubility	0.1-0.5 g/100 mL at 22 ºC
Vapor Pressure	0.644-73.6Pa at 25℃
Refractive Index	n 20/D 1.455
Log P	0.3 at 25℃

Safety & Handling

Danger GHS02 GHS05 GHS07 GHS01 GHS06 GHS08 Hazard Statements H227 Combustible liquid H241 Heating may cause a fire or explosion H242 Heating may cause a fire H302 Harmful if swallowed H312 Harmful in contact with skin H313 May be harmful in contact with skin H314 Causes severe skin burns and eye damage H315 Causes skin irritation H318 Causes serious eye damage H330 Fatal if inhaled H332 Harmful if inhaled H335 May cause respiratory irritation H336 May cause drowsiness or dizziness H341 Suspected of causing genetic defects H370 Causes damage to organs H373 May causes damage to organs through prolonged or repeated exposure H401 Toxic to aquatic life H302+H332 Harmful if swallowed or if inhaled Precautionary Statements P203 Obtain, consult and follow expert instructions for use. P210 Keep away from heat, hot surfaces, sparks, open flames and other ignition sources. No smoking. P234 Keep only in original packaging. P235 Keep cool. P240 Ground and bond container and receiving equipment. P260 Do not breathe dust/fume/gas/mist/vapours/spray. P261 Avoid breathing dust/fume/gas/mist/vapours/spray. P264 Wash … thoroughly after handling. P270 Do not eat, drink or smoke when using this product. P271 Use only outdoors or in a well-ventilated area. P273 Avoid release to the environment. P280 Wear protective gloves/protective clothing/eye protection/face protection. P284 In case of inadequate ventilation wear respiratory protection. P316 Get emergency medical help immediately. P317 Get emergency medical help. P318 IF exposed or concerned, get medical advice. P319 Get medical advice/attention if you feel unwell. P320 Specific treatment is urgent (see … on this label). P321 Specific treatment (see … on this label). P330 Rinse mouth. P363 Wash contaminated clothing before reuse. P378 Use … for extinction. P403 Store in a well-ventilated place. P405 Store locked up. P410 Protect from sunlight. P411 Store at temperatures not exceeding … °C/…°F. P420 Store away from other materials. P501 Dispose of contents/container in accordance with local regulations. P264+P265 Wash … thoroughly after handling. P301+P317 Get emergency medical help. P302+P317 Get emergency medical help. P302+P352 IF ON SKIN: Wash with plenty of water. P304+P340 IF INHALED: Remove person to fresh air and keep comfortable for breathing. P308+P316 Get emergency medical help immediately. P332+P317 Get emergency medical help. P362+P364 Take off contaminated clothing and wash it before reuse. P370+P378 Use … for extinction. P403+P233 Store in a well-ventilated place. Keep container tightly closed. P301+P330+P331 Rinse mouth. Do NOT induce vomiting. P302+P361+P354 IF ON SKIN: Take off immediately all contaminated clothing. Rinse skin with water/shower. P305+P354+P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing. P370+P380+P375 Evacuate area.

Trade & Regulatory

UN Number	3105
ADR Class	5.2
Storage Class	5.2 - Organic peroxides and self-reacting hazardous materials
WGK (Germany)	1

Other Names

Industries

Rubber & Tire Plastics & Polymers