Yes, polypropylene is a polymer, specifically a thermoplastic polymer, meaning it can be melted and reformed. It's part of the polyolefin group and is characterized by its lightweight, durable, and resistance to many chemical solvents, bases, and acids. Polypropylene is known for its versatility and is widely used in various applications including packaging, textiles (such as ropes, thermal underwear, and carpets), laboratory equipment, automotive components, and reusable containers due to its resilience to physical damage and chemical action. Its ability to adapt to different manufacturing techniques, such as injection molding and extrusion, makes it an industrial favorite. The material also has a high melting point, which makes it suitable for items that need to withstand heat.

Crystalline and amorphorous polymers differ significantly in their densities due to the difference in molecular arrangement. Crystalline polymers have a highly ordered structure, where molecules pack closely together, resulting in higher density. This orderly pattern maximizes the number of interactions (e.g., Van der Waals forces, hydrogen bonding) between chains, making them more dense. On the other hand, amorphous polymers lack this regular arrangement, leading to less efficient packing and, consequently, lower density. Molecules in amorphous polymers are arranged randomly, creating more free volume and resulting in a less dense material. The specific density of a polymer depends on the degree of crystallinity; many polymers are semi-crystalline, containing both amorphous and crystalline regions, so their densities will be intermediate, reflecting the proportion of each phase.

Steve Spangler's polymers, particularly famous ones like "Water Gel" or "Slime," are typically made of sodium polyacrylate or polyvinyl alcohol, respectively. Sodium polyacrylate, a superabsorbent polymer, can absorb hundreds of times its weight in water, making it ideal for experiments demonstrating water absorption and retention. Polyvinyl alcohol, on the other hand, interacts with borate ions (from solutions like borax) to form a gooey, stretchable slime, showcasing the properties of non-Newtonian fluids. These chemicals are examples of how simple chemical reactions can create substances with unique and educational properties, embodying Spangler's aim to make science exciting and accessible.