Bisphenol A bis(diphenyl phosphate), universally known as BDP, is a high-performance, halogen-free, viscous liquid phosphate ester flame retardant. It is characterized by its high phosphorus content, exceptional thermal stability, and very low volatility. BDP is a premier flame retardant for engineering plastics, particularly in applications that demand superior thermal performance and UL 94 V-0 ratings.

Flame Retardant Mechanism

BDP is an extremely effective condensed-phase flame retardant, meaning its primary action occurs within the solid polymer material during combustion.

• Condensed Phase Action (Primary Mechanism): When exposed to the intense heat of a fire, BDP thermally decomposes to generate polyphosphoric acid. This acid acts as a powerful catalyst on the polymer’s surface, promoting a rapid dehydration and      cross-linking reaction. The high aromatic content from both the bisphenol A and diphenyl phosphate groups in the BDP molecule contributes to the formation of an exceptionally stable, dense, and glassy char layer. This insulating char acts as a robust physical barrier that:
  1. Shields the underlying polymer from external heat flux.
  2. Prevents oxygen from reaching the polymer surface.
  3. Traps flammable volatile compounds in the solid phase, drastically reducing the fuel supply to the flame.
• Superior Thermal Performance: As a high-molecular-weight oligomeric liquid, BDP exhibits extremely low volatility and outstanding thermal stability. This allows it to be processed at the high temperatures required for engineering plastics (e.g., >300°C) without significant degradation. This stability translates directly to the final part, resulting in a higher Heat Distortion Temperature (HDT) and better dimensional stability compared to many other liquid flame retardants.
• Gas Phase Action (Secondary Mechanism): While its primary action is in the condensed phase, a minor portion of the phosphorus-containing fragments can enter the gas phase. These fragments release phosphorus-based radicals (PO), which help to quench the flame by interrupting the free-radical chain reaction of combustion.

Key Application Areas

BDP’s unique combination of being a liquid (for ease of handling and dispersion) and providing high thermal performance makes it a top choice for demanding halogen-free applications.

• PC/ABS & PC/ASA Alloys: This is the primary market for BDP. It is used to achieve UL 94 V-0 ratings in housings for electronic devices (e.g., chargers, power tool casings, 5G infrastructure components) and durable automotive interior/exterior parts  where excellent heat resistance (HDT) is essential.
• PPO/HIPS Alloys (mPPO): A key flame retardant for modified Polyphenylene Oxide (PPO) alloys used in enclosures for business machines, telecommunications equipment, and electrical components.
• Epoxy Resins & Laminates: Used in high-performance, halogen-free epoxy systems for electronic applications, including laminates for servers and data storage equipment.
• Thermoplastic Polyurethanes (TPU): Can be used in specialty TPU applications requiring high flame retardancy and thermal stability.