High-density polyethylene (HDPE) is known for its rigidity and strength, while low-density polyethylene (LDPE) is soft and flexible. This difference in properties is primarily due to:
Correct: D
The distinct properties of HDPE and LDPE stem from their molecular structures and resulting degrees of crystallinity. LDPE is produced under high pressure and high temperature via free-radical polymerization, leading to a highly branched polymer structure. These branches prevent efficient packing of polymer chains, resulting in lower density, lower crystallinity, and thus greater flexibility and softness. HDPE, on the other hand, is produced using Ziegler-Natta catalysts or Phillips catalysts under low pressure and low temperature, which yields a predominantly linear polymer structure with very few branches. This linear structure allows for close packing of chains, leading to high density, high crystallinity, and consequently, greater rigidity, strength, and a higher melting point. Therefore, option D correctly describes the structural differences leading to property variations.