Which statement best describes the relationship between the density of a polymer and its percent crystallinity?

• A. Percent crystallinity has no effect on the density of a polymer.
• B. As percent crystallinity increases, the density of the polymer generally increases.
• C. Density and percent crystallinity are inversely proportional in polymers.
• D. As percent crystallinity increases, the density of the polymer generally decreases.

Answer: (B)

Verified step by step guidance

1. Understand that polymers can have regions that are crystalline (ordered) and amorphous (disordered). Percent crystallinity refers to the fraction of the polymer that is in the crystalline state.
2. Recognize that crystalline regions are packed more tightly than amorphous regions, meaning the molecules are closer together in crystalline areas.
3. Recall that density is defined as mass per unit volume, \(\rho = \frac{m}{V}\), so if molecules are packed more tightly (less volume for the same mass), density increases.
4. Therefore, as the percent crystallinity increases, the polymer has more tightly packed regions, which generally leads to an increase in overall density.
5. Conclude that the correct relationship is: as percent crystallinity increases, the density of the polymer generally increases.