Experiment 2

The Structure and Properties of Polymers

Procedure and Results

Procedure

1. Cross-linked PVA

a) Effect of cross-linking on viscosity: Pour 100 ml of 2% PVA/water solution into each of 4 beakers. To each of the beakers add 1.0, 1.5, 2.0, and 2.5 ml, respectively of a 4% borax solution with vigorous stirring. To measure the viscosity of your solutions take a glass funnel, and use paper tape to mark it as shown in the figure. Mark "a" should be about 1 cm below the top of the funnel, and mark "b", about 2 cm below mark "a."

Place your finger over the bottom of the funnel and fill the funnel with one of your polymer solutions. Let the solution drain into a beaker. Measure the time required for the solution to drain from mark "a" to mark "b." The time required for the solution to drain is a measure of its viscosity. The longer the drainage time, the greater the viscosity. Repeat the measurement to test the reproducibility of your measurement. Wash the funnel with hot tap water, rinse it with acetone and allow it to dry thoroughly. Be careful not to remove the tape from the funnel. Repeat the measurement with your other solutions.

This measurement must be done for the 2% PVA with no borax added and also for each of the four solutions with added borax.

b) Preparation of a "slime:" Pour 100 ml of the 4% PVA solution into a beaker and add 10 ml of the 4% borax solution, again, with vigorous stirring. Compare the properties of the resulting gel with those of the others prepared previously. How do you explain the differing properties?

This gel is nontoxic, can be handled safely by children, and represents an interesting way to introduce polymers to children.

2. Bakelite

A sample of this polymer will be prepared by your instructor. Compare the properties of this polymer with the PVA and Slime. Consider the difference between the types of crosslinking in the two polymers and how this affects the properties.

Results

The Results section of your report should contain the following information:

1. A data table for the viscosity measurement in the form drainage time (sec) versus volume (mL) of borax solution.

2. A graph of this data. Some hints for graphing are available.

3. A description of the properties of the "slime" that you prepared.

4. A description of the properties of Bakelite.