The most efficient and cost-effective method to synthesize polypropylene from propylene monomer is through the process of Ziegler-Natta polymerization. This method uses a catalyst system, typically composed of a transition metal compound such as titanium tetrachloride and an organoaluminum compound such as triethylaluminum , to initiate the polymerization of propylene monomer.The Ziegler-Natta polymerization process has several advantages:1. High catalytic activity: The catalyst system used in this process is highly active, allowing for high production rates and lower catalyst consumption.2. Stereospecificity: The Ziegler-Natta catalyst system can control the stereochemistry of the polymer, producing isotactic or syndiotactic polypropylene, which have desirable properties such as high crystallinity and improved mechanical properties.3. Cost-effectiveness: The raw materials for the catalyst system are relatively inexpensive, and the process can be carried out at relatively low temperatures and pressures, reducing energy costs.4. Scalability: The Ziegler-Natta polymerization process can be easily scaled up for industrial production, making it suitable for large-scale manufacturing of polypropylene.In summary, the Ziegler-Natta polymerization process is the most efficient and cost-effective method for synthesizing polypropylene from propylene monomer due to its high catalytic activity, stereospecificity, cost-effectiveness, and scalability.