Week 10 – Unit 7: Polymers Q&A

Q1) 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 initially with small spherical polystyrene beads made with foaming agents. Foaming agents are basically a material that facilitates the formation of foam. As such, the formation of styrofoam involves  polystyrene beads being heated with steam and left to cool down before heating it again within a mould. As such, styrofoam are made up of 98% air. Hence when it is dissolve in acetone, the air in the foam will get released, leaving behind the solid polystyrene which is more dense.


Q2) 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 a 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.

Branched HDPE may be too fragile and break under the high pressure exerted by surgical tools or the surgeon’s intricate hand manoeuvres. If the glove breaks, it can pose a great danger to the surgeon as the surgeon may be exposed to biohazardous material.

b. Offer a molecular level reason for why linear HDPE is successful in this application.

Linear polyethylene is normally produced using the monomer ethylene (C2H4), with molecular weights in the range of 200,000 to 500,000 or higher. While it is very flexible, it is still very tough. Its flexible nature makes it suitable for use as gloves for surgeons who need to make intricate hand movements very carefully, while its toughness protects the surgeon from contact with biohazardous material.


Q3) 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. 

Papers are made of long fibres of cellulose which has 2 main kinds of bonds, mainly strong intermolecular forces such as hydrogen bonding between microfibrils of cellulose and weak intermolecular forces such as van der wall forces.Cellulose are actually made up of many glucose monomers that let the chain stretch out, nice and straight. Since the cellulose is a long polymer chain consisting of many glucose molecules, it forms many strong hydrogen bonds .Thus, it is hard to separate the cellulose apart therefore it is not possible to pull on a piece of paper.
Plastics on the other hand, are made of polyethylene.(LDPE). Such polymers have long molecules that lie side by side.As such, these molecules can uncoil and slide past each other, making the material flexible since it does not have intermolecular hydrogen bonds, only weak inter molecular forces like van der wall forces which are easy to break apart.


Q4) A Teflon ear bone, fallopian tube, or heart valve? A Gore-Tex implant for the face or to repair a hernia? Some polymers are biocompatible and now used to replace or repair body parts.

a. List four properties that would be desirable for polymers used within the human body.

1) Non-Toxic
2) Low Cost
3) Inert to Body Fluids
4) Durable

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 store 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 first contact lenses were made from a polymer called polyacrylamide. Rigid gas-permeable lenses then became available. These lenses are a combination of PMMA, silicones and fluoropolymers. It has to be lightweight, non-toxic, permeable to oxygen and flexible.

c. What is the difference in the material used in “hard” and “soft” contact lenses? How do the differences in properties affect the ease of wearing of contact lenses?

Hard contacts lenses are made from PMMA, a material that is inflexible and does not oxygen to pass through, soft contact lenses on the other hand are made of Silicone, this materials allows for oxygen to pass through and is flexible, making soft contacts more comforting to the eye.