Demonstrating the tensile strength of polymers.

The principles of polymer chemistry and physics are often taught in lecture format. However, most of us would like to see the subject come alive, to see before our very eyes the fascinating and intimate details of polymer structure and behavior. This is the role of the classroom demonstration whether it is conducted by the lecturer or undertaken by the student. Most of us love to have a magician explain his tricks, even if we cannot emulate him. Similarly, students want to know the whys and wherefores of the behavior of the polymers that make up a large part of our environment.A compendium of polymer experiments, demonstrations, and review articles that have been published in this Journal appeared in 1983 (1). Another collection forms a chapter in a recent book on demonstrations (2). Sources of polymer samples also have been tabulated (3).A consideration of molecular size is essential to understanding the behavior of large molecules. It is, in fact, the key to most of the physical properties that make polymers useful. Dimensional rigidity or elasticity, strength, and durability that we associate with plastics, fibers, rubber, coatings, and adhesives all depend on the interactions of molecules that are orders of magnitude larger than familiar ones such as ethanol, benzene, or acetic acid. Of course, polymers themselves are even more familiar in some cases. Garbage bags and other packaging materials of polyethylene, home siding of poly(vinyl chloride), and foamed polystyrene cups for hot drinks are encountered daily. What is more, the technical, generic names are also well known as the trade names for many of these items.The term polymer implies the repetition of a single unit, the mer or monomer.

Rubber elasticity is a particularly satisfying topic for the teacher of polymer behavior because it combines the rigor and purity of statistical thermodynamics with the familiarity and homeliness of rubber bands and birthday party balloons. The interplay of thermodynamics with rubber goes back to 1806. Flory (1) gives a fascinating history of the early work and the subsequent developments which led eventually to a theory that incorporates the results of statistical mechanics. Treloar's book (2) is quite comprehensive in its treatment of rubber elasticity although several briefer treatments (1, 3, 4) can be recommended also.

A trisubstituted ethylene, 1-propene-1-ylidene dicyanate has been prepared via Knoevenagel reaction of acetaldehyde and malonitrile with p-alanine as a catalyst. This product has been copolymerized in bulkwith 2,2'-azoisobutyronitrile as an initiatorwith styrene and I-vinyl-2-pyrrolidone. Preliminary 'H and 13C NMR studies of the copolymers are in good agreement with an alternating structure besides minor proportions of homopolymers of styrene or 1 -vinyi-2-pyrrolidone. The propagation mechanism has also been studied with 'H-'H correlation speetroscopy.

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