1. As acetone dissolves the polymer, the gas of the foaming agent can therefore escape. This leads to the collapse of the polymer on itself, making it more dense due to the removal of the gas.

2.

a. It does not have the strength required to be used.

b. HDPE molecules need to be lined up in a way that produces the amount of strength required. Sufficient flexibility can be obtained by using a thinner linear HDPE.

3. No, it does not happen to the piece of paper. When pulling force is applied to a piece of paper, the paper tears. This is due to cellulose molecules in paper being held more rigidly in place as compared to in plastic. Therefore, in comparison, when a piece of plastic is stretched, its molecules are free to align themselves parallel to each other and in the direction of the pull. However, once the plastic has been pulled to alteration, the structure is no longer reversible.

4.

a. 1) Stable, 2) non-toxic, 3) lack of reactivity in body fluids, and 4) does not dissolve in body fluids.

b. There are different types of contact lenses which each use different types of polymers. One of the earliest polymers used for lenses is Polymethyl methacrylate (PMMA). It was used for its rigid gas permeable (RGP) property to make lenses.
Nowadays, silicone-acrylate materials are used (more commonly known by its trade name, Kolfocon). These RGP polymers contain fluorine, thus altering the structures slightly to form fluoro-silicone-acrylate polymers and fluoro-silicones.
As for soft lenses, Polymacon is usually used. Polymacon is a polymer of 2-hydroxyethyl methacrylate (HEMA). Other such methacrylates include hioxifilcon and methafilcon.

The properties that are desirable from these materials include their being non-toxic, inexpensive, comfortable to wear and their permeability to oxygen. Furthermore, their ability to be flexibly shaped to the shape of one’s eye as well as to be cleaned easily is desirable.

c. As mentioned above, hard contact lenses are typically made of PMMA, an RGP plastic. The soft contact lenses in comparison are made of silicone, which is flexible and allows oxygen to reach the eye. Because of these properties, the soft lenses tend to be more comfortable.