0.7 Polymers

Macromolecules: Natural and Synthetic Polymers

Objectives

In this laboratory you will become familiar with the classifications of polymers by synthesizing and examining several of the following:

• a cross-linked condensation copolymer (Glyptal ${}^{\text{TM}}$ resin)
• a branched addition polymer (polymethylmethacrylate)
• a loosely cross-linked silicon-based condensation polymer (a polymethylsiloxane)
• a cross-linked polyvinyl alcohol

Additional information about polymers can be found in Chapter 12 of your textbook.

 grading

Your grade will consist of the following:

• Pre-lab (10%)
• Correctness and thoroughness of your observations and the answers to the questions on the report form (80%)
• TA evaluation of lab procedure (10%)

Before Coming to Lab . . .

• Complete the pre-lab exercise
• Read the introduction and any related materials provided to you

NOTE: If you wear contact lenses, for this week’s lab, you may prefer to wear your prescription glasses. 

Introduction

Approximately 50% of the industrial chemists in the United States work in some area of polymer chemistry, a fact that illustrates just how important polymers are to our economy and standard of living. These polymers are essential to the production of goods ranging from toys to roofing materials. So what exactly are polymers? Polymers are substances composed of extremely large molecules termed macromolecules, with molecular masses ranging from ${\text{10}}^4$ to ${\text{10}}^8$ amu. Macromolecules consist of many smaller molecular units, monomers, joined together through covalent bonds. The molar mass of the polymer is quoted as an average molar mass.

Both natural and synthetic polymers are ubiquitous in our lives: elastomers (polymers with elastic, rubber-like properties), plastics (the first plastic was used in 1843 to make buttons), textile fibers, resins, and adhesives. The more common polymers include acrylics, alkyds, cellulosics, epoxy resins, phenolics, polycarbonates, polyamides, polyesters, polyfluorocarbons, polyolefins, polystyrenes, silicones, and vinyl plastics, to name but a few.

Naturally occurring macromolecules are derived from living things: wood, wool, paper, cotton, starch, silk, rubber and have provided us for centuries with materials for clothing, food, and housing. Starch, glycogen, and cellulose are all polymeric versions of the monomer glucose. Again, we see that minor structural variations create chemicals with very different properties. Proteins are macromolecules composed of monomeric units of alpha amino acids; nucleic acids are composed of subunits (nucleotides) containing a nitrogeneous base, sugar and phosphate groups. Natural rubber is a latex exudate of certain trees and composed of monomers called isoprene units. The usefulness of latex was first discovered by Lord Mackintosh in Malaysia in the last century and provided the foundation of his waterproof rainwear empire.

The temptation to improve upon nature has always been great and has rarely been resisted. When scientists linked the special properties of these substances (physical properties such as tensile strength and flexibility) to the sizes of their molecules the next logical step involved chemical modifications of naturally occurring polymers.