Polymer Chemistry in High School Roger Stucki Excelsior Springs High School, Excelsior Springs, MO 64024
A teacher needs to answer four questions when adding a unit to a course: Why? What? When? and How? This paper suggests some ideas that the high school teacher might use to answer these questions when considering the addition of polymer chemistry to the general chemistry curriculum. Each of the final three questions has to he answered according to the level of the students, the current curriculum being taught, and the time and facilities available.
analogy of the condensation reaction of ethylene glycol and terephthalic acid to form a polyester
Why?
The "why" is simple. Polymer chemistry is an area which pervades our everyday lives. In fact, hiopolymers make life possible. Both the range of polymer applications and the number of people involved with industrial polymers are enormous. Approximately 50% of all professional chemists work within the area of polymer chemistry ( I ) . Two of the most important things in a teenager's existence, clothes and automobiles, are dependent upon polymer chemistry. This is usually sufficient to create a high level of interest in this topic. What?
An introduction to polymers might include as little as the meaning of some basic terms, e.g., monomer and polymer. This can be done by example using such common materials as ethylene and polyethylene. The next extension might he examination of the basic polymer types. I prefer to do this by considering the types of reactions involved in preparation of polymers. Specifically, I recommend discussion of addition (chain-reaction) and condensation (step-growth) polymers. Examples of polymers students might find most interesting appear in Table 1.The instructor needs to be careful at this point because it is very easy to overwhelm the student with too many examples. I t is best to concentrate on a few easily understood cases. The unit on polwners might also include co~olwners, thermoplastic and thermosetting polymers, the roie df cata: Iysts, natural polymers (such as cellulose and rubber), and biopolymers like proteins and carbohydrates.
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to f o m polymer or the reaction of hexamethylenediamineand a d i ~ i acid c to form nvlon
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peptide link Another common area covered in introductory chemistry is the nature of catalysts and initiators. The instructor could use the role of peroxides in the polymerization of styrene to polystyrene as an example of how an initiator might work.
The obvious place for polymers is within the context of organic chemistry since most are hydrocarbon compounds. Unfortunately, many of us all too often "run out of time" hefore getting to organic chemistry. I have been guilty of this myself. Textbook authors are not the most helpful people in this regard either. Organic chemistry is rarely placed in a prominent area of the text, and it often occupies aplace near the end of the hook. This sends a message to students and teachers alike that other topics are more important. Teachers in hiah school need to make an effort t include this immrtant area>f chemistry in the general chemistry curriculum. An alternate idea is to integrate polymer topics throughout the course. For example, during a unit on acids and bases, nearly every chemistry teacher includes the neutralization reaction between sodium hydroxide and hydrochloric acid.
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I t would not he very difficult a t this point to introduce the 1092
Journal of Chemical Education
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NH&H&NC(CHJ,COH HOH a polyamide or finally to introduce some biochemistry with a reaction of amino acids.
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How?
If possible, let the students introduce the topic themselves. You might pose this question to your class, "How does chemistry affect your everyday life?" or "How would things change if all the chemical advances over the last 25 to 30 years suddenly vanished?'' Usually in the course of the discussion someone realizes that if these advances were suddenly wiped out, the entire class would he virtually naked. This observation not only awakens the most distinterested student, hut also leads into a discussion of nylons, polyesters, and other synthetic fibers. From this point the instructor can proceed into an elementary discussion of what a polymer is. In the heginning, i t is best to eliminate any chalkboard diagramming of monomer and polymer structure. Instead illustrate the idea of a monomer and polymer using familiar objects such as paperclips by building individual clips (monomers) into chains (polymers). Copolymers could be illustrated using clips of different sizes or shapes. Things that "polymerize" spontaneously such as coat hangers, fish hooks, and Christmas tree ornament hangers can be discussed. Using students to represent monomers is another good idea which can he fun for the class as well as instructional ( 6 ) . A polymer "reaction" can he demonstrated by placing coat hangers in a large grocery hag, and allow them to "react" by shaking the hag. If the hangers are randomly placed in the hag, the end result is generally a tangled mass, an impressive demonstration of a "coat hanger polymer." A similar demonstration could he used to illustrate the cross-linking of sulfur in the vulcanization or rubber. Using
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chains of n a ~ e clins r to illustrate rubber oolvmers and ooened paper clips ior suifur, put the "reactants" in a containdr and "heat" (shake vigorously). The "sulfw" clips will usually cause the chains to snag together to form a cross-linked polymer. After polymers are introduced with the simple models, the chalkboard structures will he much more meaningful and more advanced topics become more easily discussed. Ideally, students can perform experiments with polymers during this unit. Some possihle activities include the synthesis of nylon and the conversion of cellulose into thread (7,s).Still other ideas are presented in Table 2. The instructor needsto exercise a great deal of care in the selection of polymer experiments. Many involve compounds which are not able to be properly stored and used in typical high school facilities in addition to being too dangerous for high school students to use Whatever ideas you decide to accept, modify, or reject, the important thing is that you include some polymer chemistry in your general chemistry course. I t is a tremendously important area, and i t contains a lot of good chemistry. Literature Cited 11) Harria,F. W.,J.CHBM.EDUC.,S~,~~~, (1981). . andBacon, Ino.,Boatan,1981, 12) Sfine, WilliamR.,"Applied Chemistry: 2nd 4.Allyn n 11"
