Question

Polypropylene is used in making polymer banknotes and textiles.

1. Give the structure of polypropylene.
2. Is this an addition polymer or a condensation polymer?
3. What conditions (cationic, anionic, free-radical) would be the most appropriate for polymerization of propylene? Explain your answer.

Short answer

(b) Polypropylene is an addition polymer since, no molecule is lost in the formation of polypropylene.

(c) Cationic polymerization would be the most appropriate for polymerization of propylene.

Step-by-step solution

Step-1. Explanation of part (a):

Polypropylene is formed from propylene monomer, and it is a type of polyolefin which is harder than polyethylene. It has low density and high heat resistance. It is a tough, rigid, and crystalline thermoplastic produced from propylene monomer. It is second most widely produced volume plastic after polyethylene.

Structure of polypropylene

Step-2. Explanation of part (b):

Addition polymers are produced from addition polymerization and no by-products are formed in the process. Molecular weight of the resulting polymer is an integral multiple of monomer’s molecular weight. Reaction results in high molecular weight polymers at once. Polypropylene is an addition polymer since during the polymerization process, no molecule is lost.

Step-3. Explanation of part (c):

Cationic polymerization would be most appropriate for the polymerization of propylene. During the polymerization process, tertiary carbocation forms which is stable and is the driving force for the mechanism and thus, cationic polymerization is the pathway which is followed. Propylene is a monomer in this mechanism and adds onto the growing chain of polymer to generate polypropylene. No molecule is lost in this mechanism and high molecular weight polymer results.