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APP is atactic polypropylene, a byproduct generated during polypropylene production. Starting in the 1970s and 1980s, both domestically and internationally, researchers began exploring ways to comprehensively utilize this byproduct. Over time, significant breakthroughs were achieved in areas such as asphalt modification, adhesives, rubber–plastic modification, and coating formulations, establishing APP as a highly regarded specialty chemical. As production processes evolved, the amount of APP generated as a byproduct declined, prompting several companies in Europe and North America to adopt dedicated manufacturing technologies for its targeted production, now reaching scales of tens of thousands of tons per year. However, nomenclature varies across regions, with terms such as APP (atactic polypropylene), APAO (amorphous α‑olefin copolymer), and APOs (“amorphous polyolefins”) all referring to products of the same class.