Final answer:
Polymer flexibility is determined by the structure and type of monomers present. Synthetic polymers, containing fewer monomer varieties, can be engineered for attributes such as flexibility, and branching in a polymer strongly influences its elasticity and density.
Step-by-step explanation:
Polymers are large molecules comprised of repeating subunits called monomers. The properties of these polymers, such as flexibility, are largely determined by their structure and the type of monomers used. For instance, synthetic polymers, which usually contain only a few different monomers, can be designed for specific qualities like flexibility or rigidity.
In contrast, biological polymers have a broader variety of monomers, such as amino acids, which can be arranged in numerous configurations, influencing their properties in complex ways. An example is how the structure of a polymer such as polyethylene affects its density and flexibility. A highly branched version of polyethylene, known as low-density polyethylene (LDPE), is more flexible and used to make objects that require elasticity, like beach balls. Conversely, high-density polyethylene (HDPE), which has a more linear structure with fewer branches, is more rigid and used to produce sturdy objects like plastic bottles.