Which statement about branched polymers is true?

• A. Branches can reduce density and increase stiffness and toughness
• B. Branches always lower stiffness
• C. Branches do not affect density
• D. Branches only affect color

Answer: (C)

Branching changes how polymer chains pack and how they move, which directly influences density and mechanical behavior. When branches interrupt ordered packing, crystalline regions shrink and free volume increases, so density typically decreases compared with a linear polymer of the same chemistry. Stiffness, or the modulus, usually drops with branching because the chains can’t align as well and crystallinity is reduced; however, the extra entanglements from branching can enhance toughness by dissipating more energy during deformation. Color is not a direct effect of branching, since pigment content and molecular conjugation govern color.

So, the idea that branches do not affect density isn’t accurate—branching does influence density (as well as stiffness and toughness), and color isn’t a direct consequence of branching.