Brief review of the chemistry of polyphosphoric acid (PPA) and bitumen

Bitumen finds great use in paving and roofing applications. To enhance or extend its performance, it is often modified with a polymer, including polyphosphoric acid (PPA). PPA is a reactive oligomer, a short-chain polymer, whose reaction with bitumen is poorly understood. In an effort to better understand their reaction, the chemical characteristics of PPA and bitumen are reviewed. It is concluded that PPA cannot dissociate and react with bitumen unless enclaves of high dielectric constant exist in bitumen.