Properties and Classifications of Organic Peroxides

Properties of organic peroxides

Physical properties

Most organic peroxides are colorless to pale yellow liquids or white powder or crystals. They generally have weak acidity, are insoluble in water, and are easily soluble in organic solvents such as phthalic acid and dimethyl ester. They are a class of unstable and flammable compounds.

Chemical properties

The structural features of the peroxide functional group in organic peroxides determine the following chemical properties: Strong oxidizing properties, natural decomposition properties, decreased active oxygen at temperatures above 40°C, promotion of decomposition by acid or basic substances, violent decomposition caused by the hydroxides of strong acids and alkali metals or alkaline earth metals (solid or high concentration aqueous solutions), promotion of decomposition by iron, cobalt, manganese organic peroxides, and redox system compounds, promotion of decomposition by strong reducing amine compounds and other reducing agents, promotion of decomposition by materials such as rubber, local temperature rise caused by friction, vibration, or impact on storage containers, and promotion of decomposition.

Classification of organic peroxides

The main varieties of organic peroxides are hydrogen peroxides (ROOH), diacyl peroxides (RCOOOOCR'), polycarboxylic esters (RCOOOR'), peroxy carbonate esters (ROCOOOOCOR'), and ketone peroxide [R2C(OOH)2]. They have different application characteristics. For example, dibenzoyl peroxide powder (BPO) is usually used as an initiator for free radical polymerization and a curing agent for unsaturated polyesters. Dicumyl peroxide (DCP) can be used as a crosslinker and initiator for melt grafting. Generally, the active oxygen content, activation energy, half-life, and decomposition temperature are four indicators used as the basic criteria for selection.

The decomposition temperature of organic peroxides at an effective rate largely determines their use. Other important factors include cost, solubility, safety, efficiency, type of generated free radicals, necessity of freezing and storage, compatibility with the production system, potential impact on the product, and ability to be activated. Organic peroxides can decompose at a controlled rate at high or room temperature to generate reactive free radicals.

The commonly used quantitative determination method for the reactivity of organic peroxides is to measure the half-life, which is the time required for a certain amount of peroxide to decompose to half of its initial amount at a specific temperature. Nowadays, the data on the half-life of commercial organic peroxides can be obtained on computer disks. Using a computer menu program, an appropriate peroxide can be selected for a certain polymerization or process condition.