Chemistry XXI Unit 3 How do we predict properties? DISCUSSION Central goal: To make predictions of the physical properties of substances based on their molecular structure.

Chemistry XXI Amazing Diapers Disposable diapers are made of a variety of polymeric materials, natural and synthetic. Different polymers serve different purposes based on their physical properties.

Chemistry XXI Let’s Think Imagine you have to design a new baby diaper. You should choose the material for the diaper’s filling. a)Which of these two polymers would you choose? Why? b)Would you suggest to use a crosslinked polymer or not? Why? c)Would you suggest to use the polymeric material in pellet form of finely shredded? Why?

Chemistry XXI Filling Cross-linking can help create a network that better hold water Cellulose Normally used in shredded form (maximize surface area)

Chemistry XXI Let’s Think The filling needs to be enclosed in a water impermeable flexible container that keeps water from leaking a)Which of these three polymers would you choose to build the container? Why? b)Would you suggest to use a cross-linked polymer or not? Why? LDPE Crosslinking  Rigidity

Chemistry XXI Let’s Think Cellulose Polyethylene The polyethylene container does not let water go out, but should not allow water to go in. So, how the diaper works? Another Substance? H2OH2O Design a substance that could do this. Cellulose Polyethylene H2OH2OH2OH2O H2OH2OH2OH2O

Chemistry XXI Surfactant-Amphiphile

Chemistry XXI Let’s Think One of the main components of modern disposable diapers is sodium polyacrylate. How would you explain its high absorption capacity? Would the polymer absorb more or less sea water than fresh water? Why?

Chemistry XXI Let’s Think Cu 2+ How would you expect the absorption capacity of this polymer change if Na + ions are replaced by Cu 2+ ? Why?