report of the polymer core courle committee
Polymer Chemistry for Introductory ~eneralChemistry Courses Core Course Committee in General Chemistry
There exists a breadth in what is taught today as General or Introductory Chemistry. This breadth is typically limited by topics covered in popular texts and by specifications described by the ACS Committee on Professional Training. While the topics considered in this report are traditionally covered in introductory chemistry courses, the information can be introduced in other packages (as dynamic courses, synthesis courses). The committee was mindful that the breadth of materials already suggested for coverage in general chemistry exceeds the time limits of such courses. Thus we adhered to the principle of not adding topics, hut rather investigating ways in which polymer-related topics can be utilized: (1) without additional time specifically devoted to polymer science and (2) to enhance typically introduced topics by the use of polymer-related illustrations, etc. I. General Topics and Depth of Topics to be Covered
recognition of stereoregular possibilities-atactic, syndiotactic. isotactic: head-to-tail. 2) ~ o ~ d l y r n e r s Recognition of alternating, random, block, and graft forms. 3) Addition and Condensation Polymers and 4) Chain and Stepwise Growth Polymerizations Recoenition that most vinvl uolvmers are addition formed through chain"grdw& polymerization and that most oolmers containine heteroatoms in the backbone are conde&tion polymers Lrmed through classical condensation routes throueh polvmerization - stepwise arowth - . kinetics. 5) Molecular Weight Distribution Recognition that most synthetic and many natural polymers exist as a combination of chains of varying length; natural polymers as DNA and enzymes typically are singular in molecular weight.
A. Preferred Topics
1) Polymer, Macromolecule Definition (polymers are very large molecules formed hy linking together smaller molecules called monomers; every day examples-natural and synthetic (cf. section L below). 2) Importance All around us; forms the basis for plant (polysaccharides) and animal (protein, nucleic acids) life; about half of all chemists are concerned with polymers. 3) Rubbers (Elastomers),Fibers, and Plastics Examples including kinds (nylon, polystyrene) and uses (floor tiles, bottles); structure-property relationships (cf. 111-J). 5) Common Polymers Structural unit, examples of uses should he brief, general. Include polystyrene, polyethylene, polysaccharides, nylons, polyesters, nucleic acids, proteins, polyvinyl chloride, and inorganic polymers-glass, concrete, diamond, and graphite. 6) Typical properties Memory-mention only. (cf. 111-H);solubility (cf. Refs 1and 10); Form viscous solutions (cf. 111-1).
6.Optional Topics 1) Configurations Recognition of linear, branched, crosslinked structures; The Core Course Committee in General Chemistry consists of: Charles E. Carraher, Jr., Wright State University, Dayton, OH 45435 J. Arthur Campbell, Harvey Mudd College. Claremonl, CA 9171 1 Milton Hanson, Augustana College. Sioux Falls, SD 57102 Calvin Schildknecht, Genysburg College, Genysburg. PA 17325 Stanley Israel, University of Lowell. Lowell, MA 01854 Norman E. Miller, University of South Dakota, Vermillion. SD 57069 Eckhard Hellmuth, University of Missouri-Kansas City. Kansas City. MO64110
11. Polymers as Tools for Delivering Necessary Concepts
A. Preferred Topics
I) Importance of Shape and Chemical Nature Mode of linkage (cis-trans, etc.)-isoprene linked in cis form gives a soft, flexible rubber whereas in the trans form it becomes a hard, somewhat brittle polymer. Cellulose and starch are both polymers based on glucose, yet different linkage responsible for the difference in given organisms being able to metabolize each. Sequence-RNA messenger nucleic acids, proteins, enzymes. Shape-raw and cooked eggs differ in the shape of the protein chains and in their physical and biological properties; enzymes. 2) Need to Utilize Renewable Resources Production of nylon-66 using furfural as feedstocks derived from steam-acid digestion of corn cobs, oat hulls, bagasse or rice hulls. 3) Importance of Chemical Industry Over 15 million metric tons of plastics, 3.5 million metric tons of elastomers, and 10 million metric tons of fibers are produced annually in the USA, etc. 4) Importance of Knowing Whether a Reaction is Endothermic or Exothermic rene. 5) Importance of Synthetic Chemicals In Eueryday Life Paints-most latex coatings based on polymethylmethacrylate, etc. 6) Thermodynamics-Emphasizing that it is the Net Free Energy that is Important Students are gently introduced to thermodynamics and the quantities contained in AG = AH - TAS, the Gibbs Free Enerev "" relations hi^ for constant temnerature. Usine the convention that a negative G is needed for a reaction to oroeress in the direction noted, we know that for a vinvl poiym&zation AS will be negative, making the entropycontaining term positive, Volume 60
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acting against polymerization. Yet reaction occurs, through a large, negative H factor which results from the breakage of a r-bond of about 60 kcallmole bond strength, forming a u-bond of about 85 kcallmole bond strength leaving about a net 25 kcal/mole generated. 7) Illustrate Types and Importance of Types of Bondingand Spatial Considerations Most interactions are invernely proportional to distance. High density polyethylene is a linear polymer in which interchain attractions are primarily of the dispersion type. The dispersion forces are about 2 kcallmole per methylene unit. The maximum interaction then between the ~ o l v polyethylene is linear and regular in order witLut bulk; substitutes, regular packing is normal. The factor of regularity allows the chains to take better advantage of the dispersion forces leading to polyethylene crystals which are so cohesive as to be insoluble in all known solvents. (Polyethylene is dissolved through heating in appropriate solvents.) Low density polyethylene is branched, the branching discourages regular and close packing. Thus, the melting range of branched polyethylene is about 105 to 108°C with a density of above 0.86 glcc while linear polyethylene has a melting point of about 132°C and a density of about 0.92 to 0.97 glcc. The presence of polar units as in polyvinylchloride permit the chains to he attracted by dipole-dipole interactions of 2-6 kcallmole units in addition to the dispersion forces resulting in a higher melting product, 21Z°C. The packing of chains in polyamides is stabilized by the formation of strong hydrogen bonds between the amine and carboryl groups. When nylon is first made, the chains are randomly oriented. Often the polymer is melted and extruded into filaments which are stretched to 4 or 5 times their original length. This stretching orients the chains to lie more closely parallel to the filament axis. This reorientating results in a closer packing of the chains and an increase in tensile strength. It is important to note that the high melting point of nylon-66 (265°C) is the result of a combination of dispersion, dipole-dipole and hydrogen bonding forces between the polyamide chains. Ill. Timely Illustrations A. Natural Building Blocks The basic difference between plants and animals is the difference between their two basic macromolecular building hlocks-polysaccharides and proteins. B. Siloxanes In 1945 E. G. Rochow, a t the General Electric Research Laboratory, discovered that a silicon-copper alloy reacts with organic chlorides forming a new class of compounds, the organosilanes. These compounds react with water forming organosilane hydroxyls which in turn undergo condensation forming small to large siloxane chains containing Si-0 moieties. (CH3)2SiCl.+ Cu CH3CI+ Si-Cu (alloy) (CHs),SiC12+ H,O (CH.),Si(OH), + HCI CH,
--
I
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Journal of Chemical Education
loxanes. Early, these compounds were incorrectly called silicones and this name continues to be used. The Si-0 moiety is the same moiety found in many natural rocks, including granite, sand and quartz and in window glass, all networks of Si-0 units with an empirical formula of Si02. The structure of polysiloxanes can vary from linear to highly crosslinked with corresponding changes in the physical properties. Linear, short-chained polysiloxanes containing methyl siloxane units are widely used as cooking oils, greases, and lubricating oils. High molecular weight siloxanes are elastomers used as caulking compounds. Polysiloxane resins are crosslinked, thermoset products containing less than two alkyl or aryl groups per silicon atom. These resins give surface coatings which provide heat resistance, chemical resistance, and water repellency and are used in rain wear, as release resins in preparing nonstick surfaces as in muffin and bread pans, and m construction to make concrete and masonry water repellent. Fluid silicon resins are used as potting and encapsulating materials in electrical devices including comuuter anolications. .. Silicon rubbers are formed on vulcanization and have been used exteusivelv in the mace Dropram as soles of lunar boots . . and in the construction of air-tigk seals. Various forms of polysiloxanes have also found numerous biomedical applications. C. "Accidental"Discoveries There are numerous illustrations of "accidental" discoveries including the Goodyear scenario. While these are "accidental" in terms of being unexuected or unplanned, these are not "accidental" with>especi to recognition and the preparedness of the observer to take advantage of and extend the discovery. During the summer of 1938, koy Plunkett of duPont was studying the synthesis of fluorochlorohydrocarhon compounds. He needed about 100 lhs of tetrafluoroethylene for several projects. He constructed a small pilot plant for synthesis of the material, storing the tetrafluoroethylene in steel cylinders cooled with dry ice. The experiment involved passing the gaseous tetrafluoroethylene from one cylinder to another, monitoring the amount to he used in the ongoing svntheses. about 15 minutes an assistant noticed that the flow of tetrafluoroethylene had stopped though it was apparent that the majority of the gas remained undelivered. The valve was completely opened, hut to no avail; a wire was run through the valve opening, still no gas. Desperate, Plunkett cut the cylinder in half-no gas escaped-instead a white powder was found. Investigation of the white powder finally led to the marketing of the polymer Teflon. D. Polyurethanes The condensation of diisocyanates and diols yield polymers called polyurethanes. Polyurethanes are utilized as fibers (swimsuits and foundation garments), elastomers (industrial wheels, heel lifts), coatings (floors where high impact and abrasion resistance are required as dance floors; bowling pins) and foams (pillows and cushions). OCN-R-NCO + HO-R-OH ----c +C-~-R,-&&O -R-% The foams are made by incorporating chemicals that release a gas within the material during the polymerization or during the molding process. The effect is similar to that of baking powder releasing carbon dioxide in dough, causing it to rise. The resultant polymer or bread contains tiny gas-filled cavities giving the product a sponge-like quality. Polymeric foams are made in a number of different ways including mechanical agitation with gas forced through the polymer and use of blowing agent8 that decompose on heating.
Urethane foams are produced through use of excess diisocyanate giving polymers whose ends are preferentially isocyanate groups. The end-group isocyanates react with water or carboxylic acids giving off carbon dioxide. NaHC03 + H+ Polymer-NCO
-
+ H20
Nat
-
+ Hz0 + COz f
Polymer-NHz
+ COz f
E. Nylon
As women's hemlines rose in the 1930's. silk stockinzs were changedthis. I t in great demand, hut very expensive. could be woven into the sheer hosiery women desired and was more durable than silk. The first public sale of nylon hose was in Wilmington, Delaware on October 24,1939. They were so popular they had to be rationed. World War I1 caused the commercial use of nylon to cease until 1945. Nylon, the first fiber to result from a deliberate search, was also the first synthetic (man-made) material whose physical properties exceeded those of the analogous naturally occurring material (protein fiber). The search began in 1927 with the wooing of Wallace H. Carothers from Harvard by duPont. Carothers succeeded in synthesizing and forming nylon fibers some eight years later. By 1937 nylon appeared on the market as the bristles of toothbrushes and by 1940 as women's stockings. Today it is produced in many forms for many purposes a t an annual rate exceeding 8 lhs (4 kg) per person in the USA. ~ & n ~ ia sstrong fiber with a tensile strength of 4,000 to 6,000 kg/cm2, which is still only about one-fifth of the ultimate strength it would have if the molecules could be perfectly aligned. About half of the nylon fiber produced goes into tire cord. The remainder is used in ropes, cords, rugs, fish nets and lines, clothes, thread, hose, undergarments, coats, and dresses. As a plastic it is an engineering material substitute for metal in bearings, .. . cams.. aears. . rollers, and as housinas - and iackets on electrical wires. The discussion can he further developed noting the structural similarity of nylon to proteins and the production of nylon utilizing natural products.
ion
of resins which can separate both charged and polar organics and inorganics including important biological materials. H. Rubber-History and Memory Joseph Priestly invented the name "ruhher" because of its ability to rub out pencil marks. By 1920 most of the ruhber tree plantations were under the control of Great Britain and the Netherlands. Great Britain, in 1922, set up a program called the Stevenson Plan designed to control the price and supply of rubber. Under the direction of the foreign secretary, young Winston Churchill, the price of rubber increased fonr-fold over the next four vears. The rubber cartel was ioined by the Dutch and prices we;e controlled to the benefit df both countries until World War 11. The fall of Southeast Asia to Japan precipitated a desperate situation with regard to ruhher. The USA and European countries, including Germany, had learned to depend on ruhher tires for transportation, rubber belts for industrial production, etc. Typically it takes about 20 to 25 years for an industry to grow from infancy to maturitv. but USA ~roductionof svnthetic ruhher went from zero in i940 to 670,000 metric tons in 1944. Ironically, the fundamentals for the synthetic rubber production were developed in Germany. This synthetic rubber, Buna-S, a hutadiene (70 parts) and styrene (30 parts) product was initially synthesized on an industrial scale in Germany's I. G. Farbenindustrie in 1933. This rubber was not as good as natural rubber, but it was readily available and inexpensive with respect to cheap petroleum feedstock. While much of our ruhher remains the hutadiene-styrene type, other monomers are utilized to produce ruhher. One such rubber is neoprene, produced from chloroprene, which is resistant to chemicals, heat and oil. Another is based on a copolymer of hutadiene and acrylonitrile which is especially resistant to oils, fats, and industrial solvents and which performs well under high and low temperatures.
F'
F'
F. Mechanisms and Kinetics
The best studied reaction mechanism is that of the free radical polymerization of vinyl reactants as polystyrene. G. Ion Exchange Resins
paper being polymeric. Ion exchange resins are complex materials that vary both in inner and surface structure. Ion exchange is not new, for nature has made use of it in soils, sands, and rock and in living organisms even before man was aware of its importance. One of the earliest references to ion exchange is recorded in the Holy Bible. They could not drink of the waters of Marah, for they were bitter
. ..And he cried unto Jehovah; and Jehovah showed him a tree, and he cast it into the waters, and the waters were made sweet. Exodus 15: 23-25 Thus Moses may have applied ion exchange on an "industrial" scale. Aristotle, among others, recognized that salts from the oceans could be partially removed when percolated through certain sands. Later in history, in 1930, synthetic materials acting as ion exchangers were discovered by two Enelish chemists. Adams and Holmes. Thev observed that crushed phonograph records exhibited ion-exchange properties. This effect was the stepping stone in leading organic chemists to the synthesis of organic resins. A class of ion exchange resins known zeolites have been employed as softening agents. By the 1950's the zeolites were largely replaced by sulfonated polystyrene resins. Today there exists a wide array
-
I
I
H H CN The individual rubber polymer chains are held together by weak intermolecular, mainly dispersion forces. A few crosslinks are introduced during vulcanization. The weak intermolecular bonding permits ready elongation to a point where further stretchinirequires breakage of primary bonds introduced as crosslinks. Crosslinking directly affects many nhvsical of volvmers. Stvrene-butadiene rubbers. " ~ronerties . . . " change from soft to hard as the amount of crosslinking increases from several links per chain to up to 60%of the chain. The initial elongation (distortion) of mildly crosslinked materials is large, reaching a point where there is little strain for a large amount of applied stress. A rubber band can be quickly and efficientlv utilized to illustrate this voint as well as the memory aspect of returning to the origikal shape and size. Another ready illustration is our skin which is a somewhat ela-ti, miiterih. Srtdrnts tall hr enwuragrd tr, tug at their skin imd relate rhe r(wlts trg the rubber b:md with resvert tu the elastic properties. Some polymeric materials such as metals can be bent and returned to their original shapes only a limited number of times; eventually, they break. But many polymers, called elastomers, can be stretched over ten times their normal length and returned to their original dimensions thousands of times. Only polymeric materials can do this. This returning to the original size and shape is called memory. Most polymeric materials exhibit some memory, but only rubbers possess almost perfect memories. Volume 60
Number 11 November 1983
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Lastly, trees which produce rubber latex are heing considered as alternative fuel and petrochemical sources (the worm has turned once again). I. Resistance to Flow Hirh viscositv or resistance to flow is another aeneral polymer characteristic. Because the long polymer cbain is arranged in a number of flow planes, a friction or drag between planes opposes free flow. his can he shown by preparing equal concentrations of a polvmer, such as polvvinvl . . ~. . alcohol, and :in inorganic a h , such i ~s?< d i ~ l,.hltride, n~ in w t w . If test r u l ~ .;Ire i fillrd H I I I I ~ M c ~ m 1 ~ 1with ~ 1tach ~ ~ 111ufion 1~ and then stoppered and inverted, the ai; bubble will rise to the top much more slowly in the polymer solution because of its higher viscosity. J. Polymer Structure-Property Relationships Polymeric materials can be divided into three broad categories-rubbers (elastomers), fihers, and plastics. Elastomers are high polymers possessing chemical and/or ~ h v s i c a lcrosslinkinr. For industrial application the "use" temperature must heabove the glass tr&sition temperature, T,, (to allow for full "chain" mobility), and its normal state (unextended) must be amorphous. The restoring force, after elongation, is largely due to entropy. As the material is elongated, the random chains are forced to occupy more ordered positions. On release of the applied force the chains tend to ieturn to a more random state.Gross, actual mobility of chains must be low. The cohesive energy forces between chains should he low to permit rapid, easy expansion. In its extended state a chain should exhibit a high tensile strength, whereas a t low extensions it should have a low tensile strength. Crosslinked vinyl polymers most often meet the desired property requirements. The material after deformation should return to its original shape because of the crosslinking. This property is often referred to as a rubber's "memory." Fiber properties include high tensile strength and high modulus (high stress for small strains). These can he obtained from high molecular symmetry and high cohesive energies between chains, both requiring a fairly high degree of polymer crystallinity. Fibers are normally linear and drawn (oriented) in one direction, producing high mechanid properties in that direction. Typical condensation polymers, such as polyester and nylon, often exhibit these properties. If the fiher is to he ironed, its T, should be below 300°C. Branching and crosslinkina are undesirable since they disrupt crystalline formation even though a small amount bf crosilinkkg may increase some phvsical properties if effected after the material is suitably drawn indprocessed. Products with properties intermediate between elastomers and fihers are grouped together under the heading "plastics." Some polymers can be classified within two categories, with properties heing greatly varied by varying molecular weight, end groups, processing, crosslinking, plasticizer, and so on. Polyesters in their more crystalline form hehave as a fiber, whereas less crystalline forms are generally classified as plastics. K. ldeal Rubber and ldeal Gas For more advanced students, it may be of interest to compare and contrast an ideal rubber with an ideal gas. The "rubber hand" exercise can he readily, effectively, and economically utilized to introduce the topic of ideal rubbers. L. Readings Followinr are readilv available, referenced articles on polymer topics written a t a level suitable for beginning chemistrv courses. References are aiven in the following section a n d i r e cited as to numerical order and page(s). F& instance, the citation "addition polymers-23338-342,'' refers to reference 23 which is a hook by Jones e t al., "Chemistry, Man and Society," and information on the topic is found on pages 338 to 342 of the book.
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Journal of Chemical Education
Addition polymers-23:338-342; 24608-614 Additives-23352-355 Bonding-2; 31:660,661 Chain-growthpolymerization-26:665669 Condensation polymers-24:614-617 Canfieurationand Conformation-2: 1 2 copoiymers-26:671-672 Disposal-l Fabricatian-23357-360 Flammability-5 Flow Prnperties-1 ~uture-6 Inorganic polymers-21 Medical uses-4 Mrmorv-1 - -~~~~~ Models-7-10; 12; 14-19 Molecular weight and distribution-13; 26:675-679 Nucleic acids-3; 21:731-739; 22:64&652; 25588-593; 27:719
.-.
797
Nylon-23347-349; 29384-388; 30:397-399 Paper-30:390-395 Physical Properties-1; 22641; 26:679-683; 28:67&681; 31:660663 Plasticizers-23:353; 30:406,437 Polyethylene-29:378-381 Polymerization-30:399-403
Polyvinyl chloride-24:610-612 Palysaccharides-24621423
Proteins-% 21:724-731: 22642-643: 24623-633: 27:711-719
21 -, -References , a) Chem~stry51(5),1978 (1) What Are Polymers? C. Carraher, 6-10. (2) Sizes and Shapes of Giant Molecules, A. Tonelli, 11-13. (3) Biopolymers and the Origin of Life, 3. Ferris, 14-16. (4) Role of Polymers in Medicine and Surgery, S. Shalaby and E. Pearce, 17-21. (5) Fire and Polymers, G. L. Nelson, 22-27. (6) Polymers for the Future, H. F. Mark, 28-30. OF CHEMICAL EDUCATION b) JOURNAL (7) Simple Models for Polymer Stereoehemistry,F. Rodriguez, 45,507 (1968). (8) Disposable Macromolecular Model Kits, I. Nicholson, 46, 671 . - 119fi91 (9) Demonstration-Ordered Polymers, P. Mazzocchi, 50,505 (1973). (10) Polymer Models, C. Carraher, 47,581 (1970). (11) Demonstrating Rubber Elasticity, F. Rodriguez, 50, 764 (1973). (12) Conformation of Macromolecules, D. Napper, 67, 305 119691. , - ~ , Polymer Molecular Weight Distribution, D. Smith and J. Raymonds, 49,577 (1972). Models for Linear Polymers, P. Morgan, 37,206 (1960). Models Illustrating the Helix-Coil Transition in Polypeptides, H. Hayman, 41,561 (1964). Models of the Palweotide-Helixand of Protein Molecules. PolyethGkne and pipecleaner Models of Biological Polymers, H. Pollard, 43,327 (1966). The Law Cost Construction of Inorganic Polymer Models Using Polyurethane, M. Mrvosh and K. Daugherty, 52,239 (1975). (19) Biopolymer Models of Nucleic Acids, E. Barrett, 56,168 ,,nnn> ,rr,ir,.
(20) Stress-Strain Behavior of Rubber, C. Arends, 37,4111969). OF CHEMICAL EDUCA(A complete listing of JOURNAL TION articles dealing with polymers is found in "Polymer Chemistry: An Introduction," R. Seymour and C. Carraher, Marcel Dekker, New York, 1981, pp 535-539; An extensive listine of trade or brand names is also found in this book on pf501-533.)
cl Current Textbooks1
(21) "Chemistry: A ~ o d e r Introduction," n 2nd ed., Cherim and
Kallan, W. B. Saunders Co. (22) "Fundamentals of Chemistry,"4th ed., F. Brescia, J. Arents, H. Meilichad, A. Turk, Academic Press. (23) "Chemistry, Man and Society," 2nd ed., M. Jones, J. Netterville, D. Johnston. and J. Woods, W. B. Saunders Ca. (24) "Chemical Principles," 4th ed., W. Masterton and E. Slowinski, W. B. Saunders. (25) "Foundations of College Chemistry," 3rd ed., D. Murphy and V. Rousseau, John Wiley & Sons. (26) "Chemistry: The Universal Science," F. Pilar, AddisonWesley. (27) "General Chemistry," J. March and S. Windner, MacMillan. (28) "Chemistry, A Study of Matter," 3rd ed., W. Lippincott and A. Garrett, John Wiley. (29) "Inside Chemistry," C. Campton. (30) "Chemistry: The Unending Frontier," J. A. Campbell, Goodyear Publishing Co. (31) "Chem One," 2nd ed., J. Waser, K. Trueblood, and C. Knabler, McGraw-Hill. IV. Textbook Evaluation A survey of 33 of t h e m o s t populargeneral chemistry texts (survey t o majors texts; one a n d two semester) published from 1978-80 was made, aimed a t assessing what polymer-related topics are commonly contained i n introductory texts, to gain information concerning extent a n d depth of coverage, a n d for comparison with what might b e expected t o b e included concerning polymer topics. T h e results of this survey helped i n formulating the recommendations given i n P a r t s 1-111. Following are summary statements including recommendations relative t o this survey. 1) Overall, the majority of texts (20)were deemed to he satisfactory in level and extent of coverage. The mast complete coverages, as a rule, were made by texts aimed at nonmajors, though a number of the best-selling majors~level texts rated outstanding. 2) Almost all texts (32) included the definition of polymers and noted that they were all around us and important. 3) Integration of polymers as illustrations throughout the texts (at properjunctures) was largely lacking, probably since the concept of integration of materials and examples has yet to mature and the concept that polymers should be included within introductory texts is new. Integration of polymer topics should be encouraged. It is possible that a unified approach regarding biopolymers, synthetic organic polymers, and inorganic polymers may be advantageous (i.e., recognize that they are all polymers often with similar properties). 4) While the majority of texts included accurate information, several included misleading or inaccurate information concerning polymers. The Core Committee has agreed to assist textbook writers on request. V. Summary A. Tools It is difficult to teach without the proper tools; the textbook is one such critical tool. There exists a maioritvof . introductorv level textbooks which cover polymer topics in sufficient depth a n d breadth t o allow teachers a eood choice of sound texts. T h e r e also exist sufficient teaching aids, etc., t o allow t h e building u p of basic topics. Finally, there exists sufficient experience within a n d without the committee t o demonstrate t h a t many important topics typically covered in introductory courses can b e enriched (not enlarged) through t h e use of polymer illustrations. 6.Allocation o f Time T h e number of topics (supposedly) necessary for introductory courses is growing beyond reasonable bounds. With this in mind, t h e Core Course Committee h a s attempted to
.
'
Contains only texts referenced in Part 1-Topics. Inclusion or exclusion does not reflect an opinion by the Committee.
emphasize polymer topics as enrichment, substitute items t o assist the teacher t o more easily, clearly, a n d broadly present t h e basic concepts of chemistry. I n general the committee believes t h a t 5-10% of t h e actual lecture a n d laboratory experience should b e related t o polymer concepts a n d illustrations. C. illustrative Exam Questions T h e following questions a r e given as illustrative of t h e b r e a d t h a n d d e p t h of coverage t h a t t h e Committee feels is suitable. I . Problems and Answers a) Name 5 polymers you encounter daily. Answer Could include both naturaCas starch, DNA, proteins, wool, cellulose-and synthetic-as polyesters, nylons, polystyrene, polyethylene, polyvinyl chloride. h) Polv~thvleneis ~roducedin excess of 4 million metric tons in
were completely burned in the presenceof excessair, how many moles of C02 would be produced? Answer: tCHzCH2-fz 3 0 2 2C02 2HzO Ten grams of polyethylene is 10g/28g/grepeating unit = 0.357 mole repeating units of polyethylene which gives twice the number of moles of COz or 0.714 moles. This problem illustrates the magnitude of chemistry (amount of polyethylene praduced), application of chemistry (uses), combustion products and a weight-weight calculation. N!I1,wart. pr nlucrd for u.+ . t s ~ \ n r h r tiillers ~ r n, r l n I. rd, rwr.. cllnl,~ o d c r g m n t n those. ~ . and c1rri.r. 11) ~rnmnt..:n rwr:, ,.I I n.i.li.,n metric runs in 1hc US:\ \c:vly. \\'hkh t.1 111t t a > l lowing repeat units is a nylon?
-
+
21
H
0
I Il (a) +N-0--C-R+
+
0
H
H
0
(b) f
/I
(d) f R--C---0-R-0--C (4 XH~-CH. j
I/j
d) A b u t 2 million metric tons of polyester fibers are utilized yearly in permanent press and "wash and wear" garments, felts, and tire cords. Circle the physical properties which are required for a fiber. (a) high tensile strength (b) easily and rapidly expandable ( e ) high modulus (high stress for small strains) id) water soluble Answer: (a), (c) should be circled. e) Define copolymer. Answer: A polymer chain containing repeat units from more than one monomer.
2. Problems a ) Draw the monomer used to prepare polyethylene. h) What is the maximum molecular weight polymer molecule that can be prepared from l O P g of gaseous ethylene? el. A . oolvmer . was found to contain onlv carbon. hvdroeen. and oxygen with 65.6% carbon and 9.38% hydrogen. Wcat is its empirical formula? dl How many moles of ethylene gas are required to manufacture a 150-9 polyethylene bottle? Cellulose consists of about 1,000C6H& units linked together. What are the percentages of C, H, and 0 in cellulose? Acrvlonitrile. H?C=CHCN, is a commerciallv. imoortant . monomer which forms ~olvacrvlonitrile.utilized in the mano-
chain -. .-....
Given aqueous solutions of polyvinyl alcohol, sucrose, and sodium chloride (0.1 gI100 ml each), which would have the lowest freezing point? Lowest melting point? Volume 60 Number 11
November 1983
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