Chain-growth polymerisation consists of initiation, propagation, and termination steps. Which material below is NOT manufactured by a chain-growth mechanism (choose the best single answer after recovery/normalisation of options)?

Introduction / Context:
Two broad synthesis routes dominate polymer chemistry: chain-growth (addition) and step-growth (condensation). Recognising which materials come from which route is critical for predicting molecular weight development and processing behaviour.

Given Data / Assumptions:

• Vinyl polymers (PVC, PS, PE, PP) are classic chain-growth products.
• Polyamides such as nylon-6 and nylon-66 are step-growth (condensation or ring-opening) polymers.
• Some silicone elastomers are produced by condensation or addition curing of oligomers; nevertheless, the canonical non-chain-growth example among the list is polyamides.

Concept / Approach:
Chain-growth polymerisation builds chains via active centres adding unsaturated monomers (vinyl/olefinic). Step-growth polymerisation relies on reactions between functional groups (e.g., amine and acid) and requires very high conversion for high molecular weight. Polyamides (nylons) therefore do not arise from chain-growth routes.

Step-by-Step Solution:
Identify chain-growth exemplars: vinyl polymers, PE, PP.Identify step-growth exemplars: nylons (polyamides).Choose “Polyamides (nylons)” as not manufactured by chain-growth.

Verification / Alternative check:
Mechanistic schemes for nylon-66 (diamine + diacid) and nylon-6 (lactam ring-opening) confirm step-growth/ring-opening, not chain-growth radical addition.

Why Other Options Are Wrong:
Vinyl polymers / polyethylene / polypropylene: textbook chain-growth systems.Siloxane elastomers: may cure via condensation or hydrosilylation; included as a distractor—polyamides remain the clear non-chain-growth choice among commodity classes.

Common Pitfalls:
Assuming any crosslinked material must be step-growth; crosslinking can occur in chain-growth systems too.

Final Answer:
Polyamides (nylons)