Two excellent resources:
Our publication IS-220, Polyphosphoric Acid Modification of Asphalt. You can order off our website.
A workshop on Polyphosphoric Acid Modification of Asphalt Binders was conducted in Minneapolis, MN on April 7-8, 2009. This workshop was jointly sponsored by the Transportation Research Board (TRB), Federal Highway Administration, Minnesota Department of Transportation, TERRA, Association of Modified Asphalt Producers, Innophos, ICL Performance Products, and the Asphalt Institute. All the speaker presentations (both slides and videos) are now available for public viewing at the following link. https://engineering.purdue.edu/NCSC/PPA%20Workshop/2009/index.html