Sweet Composites, 6211 Ridge Drive, Bethesda, MD 20816-2641 USA
301-229-2201  –  9:00 a.m. to 5:00 p.m. Eastern, Mon.-Fri.

Last Update: 13 February 2010

Methyl Ethyl Ketone Peroxide

Please be advised that we no longer sell methyl ethyl ketone peroxide [MEKP]. We maintain this page because it provides a generalized “user-friendly” MSDS for MEKP, along with some basic guidelines for its use with polyester and vinylester resins and NPG gelcoat. Please refer to the manufacturer’s official MSDS for complete technical information on whatever brand of MEKP you are using.

MEKP is a colorless solution of methyl ethyl ketone peroxide in dimethyl phthalate, with 9% active oxygen. Hazard classification: Organic peroxide, Type D, class 5.2. ID No.: UN-3105. A maximum of 4 oz. may be shipped by UPS as an ORM-D (No HazMat fee). A maximum of four pints may be shipped by UPS as a Hazardous Material, requiring special shipping papers and payment of a HazMat fee. Gallon jugs of MEKP may be shipped only via common-carrier truck.

Transportation Emergency: Phone CHEMTREC 800-424-9300 Day or Night.

IngredientCAS number
methyl ethyl ketone peroxide1338-23-4
dimethyl phthalate  131-11-3
methyl ethyl ketone    78-93-3
hydrogen peroxide7722-84-1

MEKP should be stored in the original closed container in a cool place away from all sources of heat, sparks, or flames, and out of direct sunlight. Exposure to high temperatures or contamination with foreign materials may result in explosive decomposition. Do not store in unvented glass containers. Do not store in the vicinity of cobalt naphthenate, dimethyl aniline, or other promoters, accelerators, acids, bases, or strong reducing agents. Do not store in the vicinity of food or drink. Do not reuse the container. Maximum storage temperature 38°C (100°F). Decomposition temperature 68°C (155°F).

MEKP is a strong irritant. Avoid swallowing and all contact with eyes and skin. Ingestion can be fatal! Discard contaminated clothing. Wash contaminated skin thoroughly with soap and water. If swallowed, take large quantities of milk or water and immediately call a physician. MEKP in the eye may result in irreversible blindness, even if flushed out with water! Flush the eyes immediately with water. SECONDS COUNT! Continue flushing for at least 30 minutes, and call a physician. Do not take chances with this chemical. Wear goggles, gloves, protective clothing, and a respirator, and be careful. We sell an Eyewash Bottle and recommend keeping one anywhere MEKP is used to provide instant first aid while one gets to a sink with running water.

Be sure all promoters and accelerators are thoroughly mixed into the resin before adding MEKP. These agents should never be mixed directly with MEKP. Violent decomposition and fire could result from such mixing or contamination. Stir MEKP into the resin slowly and carefully to avoid splashing.

Spilled material should be absorbed in inert materials such as vermiculite or sand and then wet with water. All such contaminated material should be placed in double polyethylene bags and kept out of doors and away from combustibles until it can be removed by qualified hazardous waste personnel. In case of FIRE, spray with water [preferably with a fog nozzle], or with CO2 or foam from a safe distance. Dry chemical or other extinguishers may be effective against a very small fire.

Guidelines for use of MEKP with Dion 9800 vinylester resin containing 0.4% of 6% CoN:
Minimum for a slow cure, or for very thick sections, or for high temperatures0.75%
Normal for boat layups at moderate temperatures (20° to 25°C)1.5 to 2.0%
Hot batch for single layers or small patches or for low-temperature use3.0 to 4.0%

Vinylester from other manufacturers, or the same resin with a different amount of promoter, may require more or less MEKP. The amount of MEKP listed above should be reduced by about 20% for comparable gel times with typical polyester resins. Do not exceed 2% with NPG gelcoats to prevent premature gelation. These must be taken as guidelines only. You are advised to carry out your own tests before starting large-scale work. You must consider the desired gel time, as well as the temperature and other conditions in your shop, whenever mixing resin.

The above information is accurate to the best of our knowledge. However, since data, safety standards, and government regulations are subject to change, and since the conditions of handling and use or misuse are beyond our control, we make NO WARRANTY, either expressed or implied, with respect to the COMPLETENESS or CONTINUING ACCURACY OF THE INFORMATION CONTAINED HEREIN, AND DISCLAIM ALL LIABILITY FOR RELIANCE THEREON. The user should satisfy himself that he has all current data relevant to his particular use.