Benzoyl Peroxide (BPO, CAS 94-36-0) is one of the most widely used diacyl organic peroxides — a workhorse for unsaturated polyester (UP) resin curing, styrene/acrylate polymerization initiation, and silicone rubber crosslinking. This guide summarises its key properties, half-life, form selection, applications and safety.
Identity
- Chemical name: Dibenzoyl peroxide / benzoyl peroxide
- CAS: 94-36-0; Formula: C₁₄H₁₀O₄; MW: 242.23
- Theoretical active oxygen: ~6.6%
- Common forms: 100% powder/granule, 75% in water (BPO-75W), 50% in phthalate paste (BPO-50), 70% etc.
Half-life & decomposition temperature
BPO is a medium-temperature initiator. Typical literature values (vary with medium — always confirm against the SDS/TDS):
- 10-hour half-life temperature: ~72–73 °C
- 1-hour half-life temperature: ~90–92 °C
BPO therefore suits 60–90 °C curing/polymerisation; ambient curing normally requires an amine promoter (e.g. DMPT) or a cobalt system.
Applications
- UP / vinyl ester resin curing: medium-temperature moulding, pultrusion and casting, with a promoter for a wider cure window.
- Polymerisation initiator: suspension/bulk polymerisation of styrene, acrylates.
- Silicone rubber crosslinking: high-temperature vulcanisation (HCR) systems.
Forms & selection
Dry powder is highly active but friction/shock sensitive; industry mostly uses phlegmatised granules or water/plasticiser pastes (75W, 50 paste) for better dispersion, lower dust and safer handling. 100% granules suit applications needing high active-oxygen content. Common equivalents include Enox BPO-75W, Luperox A75 and Perkadox L-50.
Safety & storage
- Organic peroxide: strongly oxidising and combustible; the dry solid is friction/shock sensitive. Avoid contact with reducing agents, promoters, metal powders and strong acids/bases.
- Store cool and ventilated (typically 5–25 °C), away from heat and sunlight; follow the SDS SADT (self-accelerating decomposition temperature) and stack-size limits.
- Never store/mix with cobalt or amine promoters; meter and add separately.
Versus other initiators
BPO decomposes at lower temperature than high-temperature initiators such as TBPB, TBPEH and DCP, but above ambient MEKP + cobalt systems. For a 60–90 °C cure window with good cost-efficiency, BPO is usually first choice; above ~120 °C use TBPB/TBPEH/DCP. See the organic peroxide half-life chart.
Note: half-life and property values are typical industry figures; they vary by supplier and form — confirm with the current TDS/SDS before selection.