Alkyd resins: identify the polymer class most accurately describing these coating binders.

Introduction / Context:
Alkyd resins are ubiquitous in paints, varnishes, and enamels. Recognising their chemical family helps predict curing behavior, compatibility, and performance in coatings technology.

Given Data / Assumptions:

• Alkyds are produced from polyhydric alcohols and polybasic acids/anhydrides.
• They may be oil-modified (fatty acid chains attached).
• Used predominantly as film-forming binders.

Concept / Approach:
Chemically, alkyds are polyesters formed via condensation of polyols (e.g., glycerol, pentaerythritol) with dibasic acids/anhydrides (e.g., phthalic anhydride). Oil or fatty acid modification tailors flexibility, drying, and gloss. They are not polyamides or polyolefins, and their formation is by condensation (step-growth), not chain-growth addition.

Step-by-Step Solution:
Check synthesis route: condensation of polyol + dibasic acid → polyester.Relate properties: good film formation, oxidative crosslinking when oil-modified.Choose “Polyester.”

Verification / Alternative check:
Standard coating texts classify alkyds as oil-modified polyesters; drying occurs via oxidative crosslinking of unsaturated fatty acid side chains.

Why Other Options Are Wrong:
Polyamide: e.g., nylons; different chemistry.Polyolefin: chain-growth polymers like PE/PP.Addition polymer: incorrect mechanism for alkyd formation.Acrylic copolymer: distinct family (e.g., PMMA, styrene–acrylic).

Common Pitfalls:
Confusing curing mechanism (oxidative drying) with polymerisation route; assuming “alkyd” implies amide linkages due to sound-alike with “amide.”

Final Answer:
Polyester