Which property is NOT associated with polypropylene?

Polypropylene is a thermoplastic polymer known for its versatility and desirable mechanical properties. The option regarding brittleness under stress is not characteristic of polypropylene. Instead, polypropylene exhibits good flexibility and toughness, allowing it to endure stress without breaking.

It is solid and flexible, which means it can return to its original shape after being deformed. Its lightweight nature makes it an attractive choice for various applications, such as packaging, automotive parts, and textiles. The material can also be easily formed into various shapes using techniques like injection molding, extrusion, and thermoforming, contributing to its extensive use in manufacturing.

Thus, the property of being brittle under stress does not align with the qualities of polypropylene, making this the correct choice for the question.