1. When Styrofoam packing peanuts are immersed in acetone (the primary component in some nail-polish removers), they dissolve. If the acetone is allowed to evaporate, a solid remains. The solid still consists of Styrofoam, but now it is solid and much denser. Explain. Hint: Remember that Styrofoam is made with foaming agents.
Styrofoam is made from random orientation addition polymers. When immersed in acetone, the polymers are rearranged into a crystalline structure with H to T arrangement so it is denser.
2. Consider Spectra, Allied- Signal Corporation’s HDPE fiber, used as liners for surgical gloves. Although the Spectra liner has a very high resistance to being cut, the polymer allows a surgeon to maintain a delicate sense of touch. The interesting thing is that Spectra is linear HDPE, which is usually associated with being rigid and not very flexible.
a. Suggest a reason why branched LDPE cannot be used in this application.
Not enough effective inter-molecular bonding due to less surface area, material not as strong and may be cut through.
b. Offer a molecular level reason for why linear HDPE is successful in this application.
HDPE is more spread out, has more surface area for london dispersion forces to attract each other polymer more strongly, and it is thus more resistant to being cut – Stronger inter-molecular forces.
3. When you try to stretch a piece of plastic bag, the length of the piece of plastic being pulled increases dramatically and the thickness decreases. Does the same thing happen when you pull on a piece of paper? Why or why not? Explain on a molecular level.
No. Atoms in paper are unable to slide over one another and stretch when a force is applied, due to the type of inter-molecular forces – covalent bonding restriction. It cannot stretch and will break immediately after a great force is applied.
4. A Teflon ear bone, a Fallopian tube, or heart valve? A Gore-Tex implant for the face or to repair a hernia? Some polymers are bio-compatible and now used to replace or repair body parts.
a. List four properties that would be desirable for polymers used within the human body.
2) Non-Toxic
4) Fast & Flexible
b. Other polymers may be used outside your body, but in close contact with it. For example, no surgeon is needed for you to use your contact lenses- you insert, remove, clean and restore them yourself. From which polymers are contact lenses made? What properties are desirable in these materials? Either a call to an optometrist or a search on the Web may provide some answers.
The properties of an ideal polymer for contact lenses include:
Water absorbing that has water current to transmit oxygen to eye through lens.
The difference in material depends on the type of polymer being used. The polymers are different because it contains nitrogen atoms in its structure unlike PMMA which does not contain nitrogen. Polyacrylamide is similar to the polymers used to make acrylic fibres for fabrics. When the polyacrylamide chains are cross-linked, the material absorbs water. Substances such as this are called hydrophilic.
The differences in properties can keep the lens soft and flexible. However, the high water content also makes the lens more fragile and reduces clarity of vision.