Which product is NOT made by addition polymerisation?

Introduction / Context:
Commodity vinyl and olefin polymers are typically formed via addition mechanisms, while many engineering polymers form via condensation. Correctly classifying the mechanism helps anticipate by-products and processing methods.

Given Data / Assumptions:

• LDPE, PVC, PS, PP are vinyl/olefinic classes.
• Nylon-66 is a polyamide produced from a diamine and diacid.

Concept / Approach:
LDPE, PVC, PS, and PP are classic chain-growth addition polymers derived from unsaturated monomers. Nylon-66 (polyhexamethylene adipamide) is a step-growth condensation polymer produced by reacting hexamethylenediamine with adipic acid to form amide links and release small molecules (e.g., water).

Step-by-Step Solution:
Identify vinyl/olefin monomers → addition route.Recognise nylon-66 chemistry → condensation route.Select nylon-66 as the exception.

Verification / Alternative check:
Industrial processes: Ziegler–Natta/metallocene or radical routes for addition polymers; nylon salt polymerisation (condensation) for nylon-66.

Why Other Options Are Wrong:
LDPE, PVC, PS, PP are all produced by addition polymerisation.

Common Pitfalls:
Assuming “engineering polymer” implies addition; confusing nylon-6 (ring-opening of caprolactam) with addition (it is also step-growth via ring opening, effectively condensation-like).

Final Answer:
Polyhexamethylene adipamide (nylon-66)