applications an3 analoqiss Pictorial Analogies V: Polymers John J. Fortman Wright State University Dayton. OH 45435
One of the most important applied areas of chemistry is that of polymers. Polymers have been likened to such things as chains of students (11,keight trains (2),or snaplock beads (3).The analogies pictured in this paper illustrate more advanced concepts about polymers, but they still could be acted out in class by students, if desired. However, not all teachers are comfortable with such class participation, and many high school or college students are emharassed to participate. Transparencies of these cartoons can be used in place of such activities or to summarize them following the class participation. Instead of starting with each student representing a monomer (I),start with boy-girl couples holding both
Addition Polymerization
edited by RON DELORENZO Middle Georgia College Cochran, GA 31 014
hands as an analogy to carbon-carbon double bonds in an unsymmetric alkene such as propene pictured in Figure 1. Addition ~olvmerizationoccurs when a "catalvst" t a ~ one s student on tge shoulder and joins them with one hank The student with the free hand must then break one of the two pairs of held hands of another couple and this continues to build up the polymer as in Figure 2. The students almost always will join hands boy to girl, and all facing forward without special instruction, and this illustrates head to tail polymerization. Note that these analogies relate to addition polymerization as opposed to condensation polymerization, but similar ideas could be developed for condensation polymers, if desired. When instructed to join hands between couples boy to boy and girl to girl the result is head to head and tail to tail Part of a presentation at the 9th Biennial Conference onchemical Education, Bozeman, MT July 26, 1986.
Head to Tail Polymerization B - G - B - G - B - G 1
Monomers Figure 1. Analogy to an alkene such as propene before polymerization.
Figure2. Analogy toa regular head to tail formof an addition polymer, such as polypropylene.
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Syndiotactic
Head to Head, Tail to Tail B - G - G - B
- B - G 1
New Bonds are Left to Left or Right to Right Hands
Figure 3. Analogy to a head to head, tail to tail form of an addition polymer such as polypropylene.
Figure 6. Analogy to a syndiotactic polymer form.
Atactic Random
Mixture of New Bonds with Right to Left, Right to Right , and Left to Left Figure 4. Analogy to a random linkage in a polymer such as polypropylene.
lsotactic All Front
All Left to Right Hand Figure 5. Analogy to an isotactic form of a pOlymer. polymerization. This is illustrated in Figure 3. Obviously, a random chain order involving head to tail as well as head to head and tail to tail also can be illustrated as in Figure 4.
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Journal of Chemical Education
Figure 7. Analogy to an atactic polymer structure.
As noted, students invariably will link hands between couples with right to leR hand coupling so as to all face in the same direction, as shown in Figure 5. This illustrates an isotactic polymer that would have all appended groups on the same side of the chain, for instance, the methyl groups on isotactic polypropylene. In Figure 6 i s illustrated the syndiotacticpolymer chain with alternating sides if the instructions are to join hands between wuples only left hand to left hand, or right hand to right hand with someone of the opposite sex. If hands are joined in all possible combinations, the linkage analogous to an atactic polymer results which is depicted in Figure 7. Photocopies of these cartoons of suitable size for making overhead transparencies by photowpier or thermofax will be sent on request. Acknowledgment Thanks go to B m Stiver, an artist in the Media Services Department a t Wright State, for his skills, and to the chemistry department for their funds. Literature Cited 1.sarq"ia.A.M.J. C k r n Edue. 195s.63,w 1 . 2. Hayt, W. C. J. Chem Educ. ISM, 65.718. 3. Fortmao,3. J. J. C h .Edue 199%.69,323-324
