**5. Conclusion and outlook**

Polypropylene-based polyolefins are undoubtedly one of the most robust material fields in polymer production and consumption worldwide. The remarkable progress in olefin polymerization catalyst and PP process technology contributes to the development of various PP-based polyolefins and helps to meet the continuous growing demand of the global market. Today, HY/HS Ziegler-Natta catalysts and RGT technology will continue to play a significant role in production of HPP, RPP, and impact PP especially via bulk, gas-phase polymerization process, or combination of the two processes with the newest developed process technology. With RGT technology which provides virtual nanoreactors within the catalyst and the polyolefin particles, it is possible to design more high performance micro-reactor catalysts. The molecular catalysis of single-site metallocene and post-metallocene catalysts enables precise control of the molecule structure and properties via homogeneous solution polymerization, and high-throughput screening technology provides more robust single-site catalysts with a molecular architecture approach. This allows materials scientists and engineers to design products with a broadening range of properties with advanced catalysts and polymerization process. Despite high activities, a little nontoxic catalyst residue could still be left in the polyolefin; therefore, research and development of greener and cleaner PP products with special highperformance are still way ahead.
