Polypropylene molecular chain scission problem
Thread Content
In current polypropylene production, hydrogen is generally used as a chain transfer agent for polypropylene molecules. I would like to ask: since there is no hydrogen in the gas-phase reactor, how are the polypropylene molecular chains broken apart?
I’m not sure, but I know that thermal pyrolysis can break the polymer chains. In the process of reproducing chlorinated polypropylene, carbon tetrachloride was used as a solvent in the past; however, its use is no longer allowed now, and trichloromethane has been used instead. But trichloromethane does not have sufficient solvating power for polypropylene, so the purchased polypropylene is processed using a twin-screw extruder, with the temperature increased, to enable further extrusion. By reducing the molecular weight of polypropylene and increasing its melt index, it can be dissolved by trichloromethane.
When producing polypropylene, we also add additives containing peroxides at the extruder stage to break the polymer chains and increase the melt index
When a reaction occurs, a molecular chain is formed, which is known as chain transfer; hydrogen gas also needs to be added to the gas-phase reactor. If not added, it can be transferred to catalysts, monomers, and other substances, causing chain termination and the formation of molecular chains.
What peroxide should be added? Benzoyl peroxide?
Chain termination mainly includes: automatic termination, termination by transfer to monomer, termination by transfer to hydrogen, and termination by transfer to aluminum alkyls