The acetone dissolves the styrofoam. the gas that was initially trapped in the polymer chain escaped. Hence, a denser polymer is formed.

a. LDPE is not strong enough to resist being cut.
b. Linear HDPE offers the required flexibility while maintaining its strength compared to the normal HDPE.

The same thing will not happen when you pull a piece of paper. Paper is made from cellulose which has more crystalline-like properties compared to plastic which is amorphous. When plastic is stretched, the polymer chain aligns with each other in the direction of the force. Crystalline structure would break due to its rigid structure more easily.

The benefits for polymers intended for use in the body should far outweigh any risks. The two main properties are
(1) stable over time of intended use
(2) non-toxic
(3) inert (not reactive, not soluble)
(4) does not cause allergy to human body

b. Several different types of contact lenses are on the market and each uses a different type of polymer. Polymethyl methacrylate (PMMA), one of the earliest polymers used for rigid gas permeable lenses, is structurally similar to Lucite and plexiglas. Silicone-acrylate materials now are more commonly used under trade names such as Kolfocon. Newer rigid gas permeable (RGP) polymers contain fluorine: fluoro-silicone-acrylate polymers and fluoro-silicones. Polymacon (38% water) is typical of the polymers used for soft lenses and is a polymer of 2-hydroxyethyl methacrylate (HEMA). Other methacrylates include hioxifilcon (48% water) and methafilcon (55% water) or even lidofilcon (70% water). Manufacturers’ websites are good sources of information. Desirable properties include being nontoxic, permeable to oxygen, comfortable to wear, and inexpensive. Also desirable is the ability to conform to the shape of the eye and to be easily cleaned (if not disposable).

c. As mentioned in the previous part, hard contact lenses are typically made of PMMA, a rigid non-gas permeable plastic. The soft contact lenses that replaced them 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.