Free-radical initiation in polymer manufacture: benzoyl peroxide is commonly used as an initiator for which of the following—and notably NOT for which one?

Introduction / Context:
Benzoyl peroxide (BPO) is a classic free-radical initiator for chain-growth polymerisations such as styrene, vinyl acetate, and related vinyl monomers. Polypropylene, however, is manufactured via coordination catalysis (e.g., Ziegler–Natta or metallocenes), not via BPO-initiated free radicals.

Given Data / Assumptions:

• BPO decomposes thermally to produce radicals that initiate vinyl polymerisation.
• Vinyl monomers such as styrene, vinyl acetate, and vinyl chloride copolymers are amenable to radical routes.
• Propylene polymerisation uses coordination catalysts to control stereoregularity and high activity.

Concept / Approach:
Match initiator type to polymerisation mechanism. Radical initiation suits vinyl addition polymerisations with head-to-tail growth. Propylene requires specific active sites for isotactic/syndiotactic control, incompatible with simple radical initiation for commodity PP.

Step-by-Step Solution:
Identify polymers typically made by free-radical routes (PS, PVAc, VC/VAc).Exclude polypropylene, produced by coordination catalysis.Therefore, BPO is not used for polypropylene manufacture.

Verification / Alternative check:
Industrial PP plants employ Ziegler–Natta/metallocene catalysts in slurry, bulk, or gas-phase processes.

Why Other Options Are Wrong:
PS, PVAc, and VC/VAc copolymers are standard free-radical systems where BPO or AIBN are common initiators.

Common Pitfalls:
Confusing “benzoyl chloride” with “benzoyl peroxide.” The active initiator is benzoyl peroxide.

Final Answer:
Polypropylene