CM8001

This is because acetone dissolves the polymer, allowing the gas of the foaming agent to escape. Since the gas is removed, the structure of the polymer is changed and the structure of the polymer becomes more dense.

(a) This is because LDPE does not have the required strength.

(b) Molecules of HDPE must line up in a way that gives the polymer strength. Moreover, using a thin linear HDPE allows sufficient flexibility.

3. No. This is because unlike plastic, paper is made of cellulose molecules that are held rigidly in place and are not free to be aligned. Hence, it will break when pulled. In contrast, in plastic, molecules can be aligned. This is because weak but extensive dispersion forces are present in plastic, allowing molecules to slip past one another.

(a) It has to be stable, durable, non-toxic and does not react with bodily fluids.

(b) Polymethyl methacrylate (PMMA) for rigid gas permeable lens and fluoro-silicone-acrylate/fluoro-silicones. The desirable properties would include being inexpensive, comfortable, non-toxic and oxygen permeable.

(c) As mentioned, hard contact lens are made of PMMA whereas soft lens are made of silicone. The difference lies in that silicone is flexible and allows oxygen to reach the eye and is hence more comfortable.