Final answer:
Isotactic polypropylene is the form where methyl groups are oriented on the same side of the polymer chain, resulting in a material with greater crystallinity and strength compared to other polypropylene configurations.
Step-by-step explanation:
The polymer of polypropylene where the methyl groups are on the same side is known as isotactic polypropylene. In this configuration, all the methyl groups (CH3) are oriented on the same side of the polymer chain backbone, which allows for greater crystallinity and density. This structured regularity gives isotactic polypropylene different physical properties compared to other forms of polypropylene, such as enhanced strength and resistance to solvents.
In contrast, atactic polypropylene has a random placement of the methyl groups, leading to a material that is less rigid and more pliable. Syndiotactic polypropylene has methyl groups arranged in a regular alternating pattern, which also confers distinct properties. Finally, copolypropylene refers to polypropylene which is copolymerized with other monomer units, such as ethylene, which alters the properties of the resulting plastic.