105

Hydrocarbon Derivatives, Organic Reactions, and Petrochemicals 445NEL

10.510.5Polymerization Reactions—

Monomers and PolymersIf you take a look around you, you will likely find that you are surrounded by plasticproducts of many shapes and sizes. They may include pens, buttons, buckles, and partsof your shoes, chair, and lamp. There are plastic components in your calculator, tele-phone, computer, sporting equipment, and even the building in which you live. What areplastics and what makes them such desirable and versatile materials?

Plastics belong to a group of substances called polymers: large molecules made bylinking together many smaller molecules, called monomers, much like paper clips in along chain. Different types of small molecules form links in different ways, by eitheraddition or condensation reactions. The types of small units and linkages can be manip-ulated to produce materials with desired properties such as strength, flexibility, high orlow density, transparency, and chemical stability. As consumer needs change, new poly-mers are designed and manufactured.

Plastics are synthetic polymers, but many natural polymers have similar propertiesrecognized since early times. Amber from tree sap, and tortoise shell, for example, canbe processed and fashioned into jewellery or ornaments. Rubber and cotton are plant poly-mers, and wool and silk are animal polymers that have been shaped and spun into usefulforms. In fact, our own cells manufacture several types of polymers—molecules so largeand varied that they make us the unique individuals we are. Proteins and carbohydratesare all very different natural polymers.

Polymerization is the formation of polymers from the reaction of monomer sub-units. These compounds have long existed in nature but were only synthesized by tech-nological processes in the 20th century. They have molar masses up to millions of gramsper mole.

Addition PolymersMany plastics are produced by the polymerization of alkenes. For example, polyethene(polyethylene) is made by polymerizing ethene molecules in a reaction known as addition polymerization. Polyethylene is used to make plastic insulation for wires, andcontainers such as plastic milk bottles (Figure 1), refrigerator dishes, and laboratorywash bottles. Addition polymers are formed when monomer units join each other in aprocess that involves the rearranging of electrons in double or triple bonds in themonomer. The polymer is the only product formed.

The monomers form dimers (from two monomers) and trimers (from threemonomers), and continue reacting to form polymers (from many monomers, dimers,and trimers).

Polypropylene, polyvinyl chloride (PVC), Plexiglas, polystyrene (Styrofoam®), andnatural rubber are also addition polymers. The production process for polypropylene isillustrated in Figure 2.

CC + C

H

C

H

+ C

H

C

H

CC + CC C

H

C

H

+ C

H

C

H

C

H

C

H

C

H

C

H

ethene (ethylene) part of polyethene(polyethylene)

H H H H H H

→ →

H H H HH H H H H H H HH H H H H HFigure 1For recycling purposes, plastics(especially containers) are codedwith a symbol for the type of plasticincorporated.1. polyethylene terephthalate (PETE)2. high-density polyethylene (HDPE)3. polyvinyl chloride (PVC)4. low-density polyethylene (LDPE)5. polypropylene (PP)6. polystyrene (PS)7. other or mixtures

Look for these symbols on plasticproducts and, of course, recycle the product when you are finishedwith it.

4

LDPE

5

PP

1

PETE

Plastics Under PressureMost plastics need to be heatedand melted during recycling, butthat same heat is damaging to theplastic, and degrades it into a lessuseful material. Researchers mayhave a solution to the problem: anew plastic that can be reformedunder pressure instead of heat,and can be recycled many times.This technology could makerecycling cheaper and much moreenvironmentally friendly.

www.science.nelson.com GO

EXTENSION +

Unit 5 - Ch 10 Chem30 12/21/06 11:33 AM Page 445

446 Chapter 10 NEL

Other Addition Polymers: Carpets, Raincoats, and InsulatedCupsThere are hundreds of different industrial polymers, all with different properties, andformed from different reactants.

PolypropenePropene also undergoes addition polymerization, producing polypropene, commonlycalled polypropylene. You may have used polypropylene rope (Figure 3), or walked onpolypropylene carpet.

The polymerization reaction in the formation of polypropene is very similar to that ofpolyethene. The propene molecule can be considered as an ethene molecule with thesubstitution of a methyl group in place of a hydrogen atom. The polymer formed con-tains a long carbon chain, with methyl groups attached to every other carbon atom inthe chain.

Figure 2The production of polypropylene from crude oil

naphthafractionfrom oil

purifiedpropylenemonomer

polymerization: chainformation is assistedby catalyst

polypropylenepowder ispurified

extrusioninto pellets

polypropylene pelletsshipped to processor

crude oil

C C +

polypropene (polypropylene)

C CC

propene monomers

C C + C C + C CC or C C

nCH3

H

H

H

CH3

H

H

H

CH3

H

H

H

CH3

H

H

H

CH3

H

H

H

CH3

H

H

H

CH3

H

H

H

Figure 3Polypropylene rope is one ofmany petrochemical products.



Polyvinyl ChlorideEthene molecules with other substituted groups produce other polymers. For example,polyvinyl chloride, commonly known as PVC, is an addition polymer of chloroethene.A common name for chloroethene is vinyl chloride. PVC is used as insulation for elec-trical wires and as a coating on fabrics used for raincoats and upholstery materials(Figure 4).

PolystyreneWhen a benzene ring is attached to an ethene molecule, the molecule is vinyl benzene,commonly called styrene. An addition polymer of styrene is polystyrene, often used tomake cups and containers. Look for the recycle symbol with a 6 and PS.

TeflonTeflon® is the common name for an addition polymer with nonstick properties that aremuch desired in cookware (Figure 5).

The monomer used to synthesize Teflon is the simple molecule tetrafluoroethene,CF2=CF2, an ethene molecule in which all hydrogen atoms are replaced with fluorineatoms. The absence of carbon–hydrogen bonds and the presence of the very strongcarbon–fluorine bonds make Teflon highly unreactive with almost all reagents. It is thisunreactivity that allows it to be in contact with foods at relatively high temperatureswithout “sticking.” The inert (unreactive) nature of Teflon makes it a very useful polymerin a wide variety of applications. There is, however, some controversy about its safety, asyou will discover in the following Web Activity.

Section 10.5

C C +

polyvinyl chloride (PVC)

C CCC C

vinyl chloride monomers

+ C C + C CC or C C

nCl Cl Cl Cl Cl Cl Cl

H H H H H H H H H H H H

H H H H

H H

HH H

C C +

polystyrene

C CCC C

styrene monomers

+ C C + C CC or C C

n

H H H H H H H H H H H H H H

H H H HHH H

C C +

polytetrafluoroethene (Teflon)

C CCC C

tetrafluoroethene

+ C C + C CC or C C

nF

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

Figure 4Polychloroethene or polyvinylchloride is used for upholstery.

Figure 5The invention of Teflon has made lifeeasier in many ways.

Unit 5 - Ch 10 Chem30 1/18/07 2:17 PM Page 447

448 Chapter 10 NEL

Practice1. Draw a structural formula of three repeating units of

(a) a polymer of but-1-ene (b) a polymer of vinyl fluoride (c) a polymer of 1-chloro-1,2,2-trifluoroethene(d) Predict the properties of the polymer in (c) in terms of solubility in organic

solvents, rigidity, and resistance to heating.

2. Draw a structural formula of the monomer of the following polymer:

3. What monomer could be used to produce each of these polymers?

(a)

(b)

4. What functional group(s), if any, must be present in a monomer that undergoes anaddition polymerization reaction?

5. Addition polymers may be produced from two different monomers, called co-monomers. Saran™, the polymer used in a brand of food wrap, is made from themonomers vinyl chloride and 1,1-dichloroethene. Draw structural formulas for eachmonomer, and for three repeating units of the polymer, with alternating co-monomers.

6. (a) What are the typical properties of a plastic? (b) What types of bonding would you expect to find within and between the long

polymer molecules?(c) Explain the properties of plastics by referring to their bonding.

7. Polymerization is a term used for a crude-oil refining process that converts smallalkenes into gasoline-sized molecules. The polymerization process is controlled toproduce dimers and trimers only (not large polymers), using phosphoric acid as acatalyst. Provide a structural formula equation for the reaction of(a) three molecules of ethene(b) propene and but-1-ene(c) but-1-ene and but-2-ene

8. Find out from your community recycling facility what types of plastic products areaccepted for recycling in your area. If there are some plastics that are not accepted,find out the reason. Summarize your findings in a well-organized table.

H

F

C

H

C

CH3 H

F

C

H

C

CH3 H

F

C

H

C

CH3

CH3

CH

CH3

CH

CH3

CH

CH3

CH

CH3

CH

CH3

CH

F

C

F

C

ClCH3

F

C

F

C

ClCH3

F

C

F

C

ClCH3

DID YOU KNOW ??Addition MonomersEthene and its double-bondedderivatives are monomers forpolymers with a wide variety ofproperties. Some of thesemonomers include:

monomer of PVC

monomer of Saran™ wrap

monomer of instant glue

monomer of acrylic

H

H

C

H

C

CI

H

H

C

H

C

CN

H

COOCH3

C

H

C

CN

H

Cl

Cl

C

H

C

WEB Activity

Web Quest—Teflon: Healthy or Hazardous?Cooks used to coat pots and pans with butter or oil to keep food from sticking, but the resultwas greasy high-fat food. The invention of Teflon®, a non-stick cooking surface, changed allthis. Recently, concern has been growing regarding the possibility that Teflon® releases toxicchemicals if it gets too hot. Research the pros and cons of Teflon®, and decide for yourself ifthe risks are worth the benefits.


Unit 5 - Ch 10 Chem30 12/21/06 11:33 AM 48


Condensation PolymersSome polymers, including the synthetic fibres nylon and polyester, and natural polymerslike proteins and DNA, are produced by condensation polymerization reactions. Thesereactions involve the formation of a small molecule (such as H2O, NH3, or HCl) fromthe functional groups of two different monomer molecules. The small molecule is said tobe “condensed out” of the reaction. The monomer molecules bond at the site where atomsare removed from their functional groups. To form a condensation polymer, the monomermolecules must each have at least two functional groups, one on each end.

Comparing Natural with Synthetic PolymersResearch chemists have found that Nature has many well-designed molecular structuresthat are polymers. Many synthetic condensation polymers are structural analogs of thenutrient molecules found in foods: they have structures similar to those of lipids (fatsand oils), proteins, and carbohydrates. Over the next few pages, there is a classificationand description of some of these natural polymers: proteins and carbohydrate poly-mers. Most of us recognize these classes of compounds as categories of foodstuffs. Foodlabels usually list the mass of fat, protein, and carbohydrate per serving.

A synthetic compound that has a similar chemical structure to a naturally occurringsubstance is called a structural analog. For example, nylon is a structural analog of pro-tein, but not a functional analog (Figure 6). Functional analogs are synthetic compoundsthat perform the same function as a naturally occurring substance but do not neces-sarily have similarities in chemical structure. For example, synthetic sweeteners are func-tional analogs of sweet carbohydrates: sugars. Chemists who study natural chemicals inorder to prepare synthetic copies are called natural-product chemists.

Lipids and PolyestersLipids (fats and oils) are formed by esterification reactions between glycerol (propane-1,2,3-triol) and fatty acids (long-chain carboxylic acids). Since glycerol has three hydroxyl(–OH) groups, three molecules of fatty acid can react with each glycerol molecule toform a tri-ester. This reaction is a condensation reaction that is not, strictly speaking, apolymerization reaction: The largest molecule formed is a tri-ester.

Section 10.5

WEB Activity

Case Study—Recycling PlasticsMuch of the plastic we use today is collected. We sometimes think of collecting as "recycling,"but true recycling only happens if the plastic is used to make a product similar to the originalone. How is recycling done? Investigate several Web sites and gather information to write aprocedure for processing recycled plastic. Also, collect some pros and cons from multipleperspectives concerning the use of plastics.


Natural Product Lipids Proteins Carbohydrates(food nutrient molecules) ↓ ↓ ↓Structural Analog Polyesters Nylon Cellulose Polymers(synthetic polymers)

Figure 6Food nutrients and their syntheticstructural analogs are an example of natural product chemistry, wherechemists copy and modify the structure of chemicals found innature.

Aboriginal TechnologiesAboriginal peoples used manynatural materials to create usefultechnologies. For example,Aboriginal peoples invented thebirch-bark canoe, seal-skin kayak,rawhide and willow snowshoes,and animal skin tipis. The naturalpolymers, such as cellulose andprotein, in these Aboriginaltechnologies have, in some cases,been replaced by syntheticpolymers.

DID YOU KNOW ??

Photodegradable Polymers James Guillet (1927–2005), aCanadian green-chemist, used hisfascination with photosynthesis toinspire his study of thephotochemistry of syntheticsystems. While on holidays in theBahamas, he was disturbed by thequantity of plastic litter andrealized that, with his knowledge,he could “make it disappear.”Guillet registered three patents forphotodegradable polymers in 1970.Unfortunately, his invention wasnot widely embraced. Self-interests lobbied against his“human-made plastics.”

DID YOU KNOW ??


450 Chapter 10 NEL

glycerol � saturated fatty acid 0 saturated fat � water

glycerol � unsaturated fatty acid 0 unsaturated oil � water

At one time, unsaturated fats were considered to be healthier in the diet than saturatedfats and oils. Unsaturated oils are generally liquids at room temperature. To change theoil into a solid (such as margarine), the unsaturated fat is partially hydrogenated toremove some of the double bonds and increase the melting point. Subsequent researchshowed that, although unsaturated fats were healthier, the hydrogenation process createdunhealthy transformed fats.

C OH

C OH

C OH

3 CH3 (CH2)7 (CH2)7+ C C

OH

O

C

(CH2)7 CH3C C

OC

O

OC

O

C (CH2)7

OC

O

(CH2)7 CH3C CC (CH2)7

(CH2)7 CH3C CC (CH2)7

propane-1,2,3-triol(glycerol)

9-octadecenoic acid(oleic acid)

glyceryltri (9-octadecenoate)(triolein, an unsaturated cis fat present in olive oil )

H

H H

H

H

H

H H H

H H

H H

H

H

H

H

H H

H

3 O+

C OH

OH

O

H

H

C17H35

C

H

OOHH C

C OH

H

3 C17H35+ C

O

C H

OC

O

octadecanoic acidor stearic acid

(fatty acid)

propane-1,2,3-triol(glycerol)

glyceryltrioctadecanoate or tristearin or glyceryltristearate

(saturated fat present in butter and lard )

C

C17H35

H

H

H

H

H

OC

O

C C17H35

H

3 O+


BIOLOGY CONNECTION

Correlation versus Causeand EffectMany biochemistry studies relatedto food are correlational studies.These studies look for a correlation(relationship) between twovariables (without being able tocontrol all other variables—as acause–effect study would). Forexample, scientists found a strongcorrelation between saturated fats(and transfats), and artery andheart diseases. Chemistsresponded with creative solutions(Figure 7).

Figure 7Butter and margarine areexamples of saturated andunsaturated fats (lipids). There aremany criteria that can be used toevaluate which is the best product.

Learning TipYou are not required to learnthe names of carboxylic acidsbeyond ten carbons. You alsodo not have to name thetriesters representing fats andoils. You should, however, learnthe general structures of

• polyalcohols (especiallypropane-1,2,3-triol),

• saturated and unsaturatedfatty acids, and

• triester fats and oils.



PolyestersWhen a carboxylic acid reacts with an alcohol in an esterification reaction, a water mol-ecule is eliminated and a single ester molecule is formed. The two reactant molecules arelinked together into a single ester molecule. This esterification reaction can be repeatedto form not just one ester molecule, but many esters joined in a long chain, a polyester.This is accomplished using a dicarboxylic acid (an acid with a carboxyl group at each endof the molecule), and a diol (an alcohol with a hydroxyl group at each end of the mol-ecule). Ester linkages can then be formed end to end between alternating acid mole-cules and alcohol molecules.

Section 10.5

Practice9. Unsaturated lipids are generally more liquid (i.e., oils), and saturated lipids are

generally more solid (i.e., fats). Create a hypothesis to explain the difference betweenthe melting points of unsaturated versus saturated lipids.

10. The fatty acid C19H39COOH reacts with glycerol, C3H5(OH)3, to produce peanut oil.Write a structural formula equation to communicate this reaction.

11. The fatty acid CH3—(CH2)7—CH——CH—(CH2)7—COOH is hydrogenated. Write astructural formula equation for this chemical reaction.

TransfatA transfat has a double bondwhere the hydrogen atoms are onthe opposite side of the doublebond. Trans means across, so thehydrogen atoms are across thedouble bond from one another.

DID YOU KNOW ??

HO C

p-phthalic acid

C OH + +

ethylene glycol p-phthalic acidethylene glycol

O C C O CH2 CH2

a polyester (Dacron®)

O O

O O

H O CH2 CH2 O H C OHC + +H O CH2 CH2 OHHO

O O

+ H HO

n( (

C

HH

C

cisorientation

C

H

H

C

transorientation

HO OC�CH2�CH2�CO OH � H O�CH2�CH2�O H � HO OC�CH2�CH2�CO OH � →ethane-1,2-dicarboxylic acid ethane-1,2-diol

�OC�CH2�CH2�CO�OCH2�CH2O�OC�CH2�CH2�CO�� H2O(l)

If we were to depict the acid with the symbol �� , the alcohol with o�o, and theester linkage with o�, we could represent the polymerization reaction like this:

�� o�o � �� o�o → �� o�o��o�o�� waterpolyester

Dacron®, another polyester, is made from p-phthalic acid (p-dibenzoic acid) and ethane-1,2-diol (ethylene glycol). Note the two carboxyl groups in the dicarboxylic acidand the two hydroxyl groups in the polyalcohol that start the chain reaction.


452 Chapter 10 NEL

Proteins and NylonProteins are a fundamental structural material in plants and animals. Scientists estimatethat there are more than ten billion different proteins in living organisms on Earth.Remarkably, all of these proteins are constructed from only about 20 amino acids.Through a reaction that involves the carboxyl group and the amine (–NH2) group,amino acids polymerize into peptides (short chains of amino acids) or proteins (longchains of amino acids). The condensation reaction of the amino acids glycine and ala-nine illustrates the formation of a dipeptide. Condensation polymerization produces aprotein, with a molar mass tens of thousands to millions of grams per mole—thou-sands of monomers long.

The dipeptide reacts with itself or with more glycine and/or alanine. Of course, otheramino acids may be present to produce an even more complex peptide. The polypeptideproduced by polymerization is a protein with peptide (–CONH–) linkages. The fol-lowing general equation illustrates the formation of a protein from amino acids.

CH

CH3

CH2 CNH

H

O

HO

CH CN

CH3

H

H

O

HO

+

CO

HCN

O

HO

HO+

+ +alanineglycine watera dipeptide

CH2NH

HH

→

→

Practice12. Draw a structural formula equation to show a repeating unit of a condensation

polymer formed from the following compounds:

13. What functional groups must be present to form a polyester?

14. How are the reactions to form fats and to form polyesters similar and different?

HO CH2 CH2 CH2 CH2 OHHOOC CH2 CH2 COOH and

WEB Activity

Simulation—Molecular ModellingMolecular modelling has become more of a computer activity than a physical activity. Chemistsroutinely use interactive models to better understand how the shapes of compounds affect theirproperties. Check out some of the molecular modelling Web sites.


DID YOU KNOW ??Amines and AmidesTwo classes of organic compoundsthat are not studied in detail in thistextbook are amines and amides.The simplest amines have the —NH2(amino) functional group, as in R—NH2. The simplest amides havethe —CONH2 functional group in amolecule of R—CONH2. A polyamidemay be formed naturally ortechnologically by repeatedlyreacting a carboxyl group with anamino group. The —CONH— group iscalled an amide (or peptide) linkage.Proteins and nylon are polymersthat are called polyamides. Proteinpolymers are specifically calledpolypeptides.



Section 10.5

C

O

O H

+ N N

H

H

H

H

C

O

OH

→

4

C

H

H

( ) C

H

H

( )6

C C

O O

N N

H H4

amide linkage

C

HH

H

HO+( ) C

H

H

( )6 n

hexane-1,6-dioic acid + 1,6-diaminohexane + waterpart of the nylon 6,6 polymer chain→

N C C O � N

H O

R�

H

H HH H

N C C N C C �

H O

R�

H O

H

H O

R�H

C C OH

HH O

R�

polypeptide segmentamino acid 2amino acid 1

peptidelinkage

n

Purpose Design AnalysisProblem Materials EvaluationHypothesis ProcedurePrediction Evidence

To perform this investigation, turn to page 464.

Preparing Nylon 6,10 (Demonstration)Nylon was considered the “miracle” fibre when it was discoveredin 1935. At the time, nylon was unique because it was the firstsynthetic fibre produced from petrochemicals. It initiated an entirenew world of manufactured fibres. In this demonstration, sebacoylchloride, COCl(CH2)8COCl(l), reacts with 1,6-diaminohexane toproduce one type of nylon. For the prediction, write a condensedor line structural formula equation showing the formation of thepolymer.

PurposeThe purpose of this demonstration is to use your knowledge ofcondensation polymerization to explain the formation of a nylonpolymer.

ProblemHow does the combination of sebacoyl chloride and 1,6-diaminohexane form the polymer known as nylon 6,10?

DesignA solution of 1,6-diaminohexane is carefully poured on top of anaqueous solution of sebacoyl chloride. The nylon that forms at theinterface of the two layers is slowly pulled out of the mixtureusing forceps.

INVESTIGATION 10.5 Introduction Report Checklist

Many synthetic polymers, such as nylon, form in similar ways to proteins. Nylon is asynthetic condensation polymer. For both the natural polymer (protein) and the syntheticpolymer (nylon), the polymer forms by the reaction of a carboxyl group (–COOH) witha –NH2 group with amide linkages (–CONH–). Polymers with amide linkages are calledpolyamides. Amide linkages in proteins are called peptide linkages and the polymers arecalled polypeptides.

Nylon was synthesized as a substitute for silk, a natural polyamide whose structure nylonmimics. The onset of the Second World War speeded up nylon production to makeparachutes, ropes, cords for aircraft tires, and even shoelaces for army boots. It is the–CONH groups that make nylon such a strong fibre. When spun, the long polymer

NylonNylon was designed in 1935 byWallace Carothers, a chemist whoworked for DuPont; the name nylon is a contraction of New Yorkand London.

DID YOU KNOW ??


454 Chapter 10 NEL

chains line up parallel to each other, and the –CONH groups form hydrogen bonds with–CONH groups on adjacent chains.

KevlarTo illustrate the effect of hydrogen bonding in polyamides, consider a polymer with veryspecial properties. It is stronger than steel and heat resistant, yet is lightweight enough towear. This material is called Kevlar® (Figure 9) and is used to make products such as air-craft, sports equipment, protective clothing for firefighters, and bulletproof vests forpolice officers. What gives Kevlar these special properties? The polymer chains form astrong network of hydrogen bonds holding adjacent chains together in a sheet-like struc-ture. The sheets are in turn stacked together to form extraordinarily strong fibres. Whenwoven together, these fibres are resistant to damage, even that caused by a speeding bullet.

H H

O

CN C N

O O

CN C N nylon polymer chain

hydrogen bonding between chains

nylon polymer chain

O

H

H

C N

O

N

H

C

O

C

O

H

N N C

H

O

OC

CO

HN

NH

OC

CO

HN

NH

C

CO

HN

NH

C

CO

HN

NH

OO

O

C

CO

HN

NH

OC

CO

HN

NH

DID YOU KNOW ??Pulling FibresWhen a polymer is to be made intoa fibre, the polymer is first heatedand melted. The molten polymer isthen placed in a pressurizedcontainer and forced through asmall hole, producing a long strand,which is then stretched (Figure 8).The process, called extrusion,causes the polymer chains to orientthemselves lengthwise along thedirection of the stretch. Covalent orhydrogen bonds form between thechains, giving the fibres addedstrength.

hopper

pellets of polymer

molten polymer

hole

bobbin

DID YOU KNOW ??Paintball: A CanadianInventionThe sport of paintball was inventedin Windsor, Ontario. Paintballs werefirst used to mark cattle forslaughter and trees for harvesting,using oil-based paints in a gelatinshell. When recreational paintballuse demanded a water-based paint,the water-soluble gelatin shell wasmodified by adjusting the ratio ofthe synthetic and natural polymersused.

Figure 8Making a polymer

Figure 9The chemical structure of Kevlar,with hydrogen bonding betweenthe shaded polymer chains



Section 10.5

Practice15. What kind of polymerization does the formation of a polyamide (natural or synthetic)

involve?

16. Provide one example each of a natural and of a similar synthetic condensationpolymer.

17. Draw a structural formula representation of the nylon 6,8 repeating unit, formed byreacting H2N(CH2)6NH2 and HOOC(CH2)6COOH.

Natural or Artificial Polymers?From the time your grandparents were babies to the time youwere born, diapers have been made entirely of polymers.Cotton cloth diapers were, and still are, made of cellulose, anatural polymer. Nowadays, disposable diapers, made mainlyof synthetic polymers, are a popular choice. Which is better forthe baby? How do they affect our environment? The typicaldisposable diaper has many components, mostly syntheticplastics, that are designed with properties particularlydesirable for its function.

• Polyethylene film: The outer surface is impermeable toliquids, to prevent leakage. It is treated with heat andpressure to appear cloth-like for consumer appeal.

• Hot melts: Different types of glue are used to holdcomponents together. Some glues are designed to bondelastic materials.

• Polypropylene sheet: The inner surface at the leg cuffs isdesigned to be impermeable to liquids and soft to thetouch. The main inner surface is designed to be porous, toallow liquids to flow through and be absorbed by the bulkof the diaper.

Issue Design AnalysisResolution Evidence Evaluation

Issue ChecklistEXPLORE an issue

• Polyurethane, rubber, and Lycra: Any or all of these stretchysubstances may be used in the leg cuffs and the waist-band.

• Cellulose: Basically processed wood pulp, this naturalpolymer is obtained from pine trees. It forms the fluffyfilling of a diaper, absorbing liquids into the capillariesbetween the fibres.

• Polymethylacrylate: This crystalline polymer of sodiummethylacrylate absorbs water through osmosis andhydrogen bonding. The presence of sodium ions in thepolymer chains draws water that is held between thechains. The presence of water results in attractionsbetween the chains and causes the formation of a gel(Figure 10).

Manufacturers claim that grains of sodiumpolymethylacrylate can absorb up to 400 times their own massin water. If sodium ions are present in the liquid, they act ascontaminants, reducing absorbency because the attraction ofwater to the polymer chains is diminished. Urine alwayscontains sodium ions, so the absorbency of diapers for urine isactually less than the advertised maximum.

Figure 10Polymethylacrylate

dry in water

H

C

ONa

��

�

�

�

�

�

�

�

�

�


456 Chapter 10 NEL

Carbohydrates and Cellulose AcetateThe monomers of carbohydrates—compounds with the general formula Cx(H2O)y—aresimple sugar molecules. The sugar monomers undergo a condensation polymerizationreaction in which a water molecule is formed, and the monomers join together to forma larger molecule. For example, the sugar monomers glucose and fructose can formsucrose (table sugar) and water. Both starch and cellulose consist of long chains of glu-cose molecules. Simple sugar monomers are sometimes called monosaccharides; dimersare called disaccharides; and polymers are called polysaccharides.

Proponents of natural products argue that disposable diaperspose a long-term threat to our environment, filling wastedisposal sites with non-biodegradable plastics for futurecenturies. The industry has developed some new“biodegradable” materials—a combination of cellulose andsynthetic polymers, for example. Some of these materials haveproven too unstable to be practical, while others appear tobiodegrade in several years, which gives the diapers areasonable shelf life. The energy and raw materials needed tomanufacture the huge quantity of disposable diapers used isalso of concern. Diaper manufacturers and their supportersargue, however, that using the natural alternative—clothdiapers—consumes comparable amounts of energy in thelaundry. In addition, the detergents used in the cleaningprocess are themselves non-biodegradable syntheticcompounds made from petroleum products.

IssueDo cloth diapers pose less of a threat to the environment thandisposable diapers?

ResolutionConsumers should return to using cloth diapers in order toprotect the environment.

DesignWithin small groups, research the pros and cons of using clothdiapers. Gather information from a wide variety of perspectives.


DID YOU KNOW ??Maple Sugar and CornCanadian Aboriginal peoplesintroduced Europeans to maplesugar. Sugar (a disaccharide) can beobtained from sugar cane (fromSouth America) and sugar beets(from southern Alberta). Thegreatest contribution of Aboriginalagriculture is corn—one of the mostprolific and widespread crops inhuman history—from which weobtain corn syrup.

HH HOCH 2

CH OH2

+

O

HOOH

OH

OH

O CH OH2HOCH 2

HO

CH OH2

OO CH OH2

O

+H

H

H H

H

glucose + fructose sucrose + water

HO

HH H

H HOH

OH H

HOH

OHH

HOH

OH

→

→

H

HO

Starch for Energy; Cellulose for SupportStarchy foods such as rice, wheat, corn, and potatoes provide us with readily availableenergy. They are also the main method of energy storage for the plants that producethem, as seeds or tubers. Starches are polymers of glucose, in either branched orunbranched chains; they are, thus, polysaccharides.

We have, in our digestive tracts, very specific enzymes. One breaks down starch.However, the human digestive system does not have an enzyme to break down the otherpolymer of glucose: cellulose. Cellulose is a straight-chain, rigid polysaccharide withglucose–glucose linkages different from those in starch or glycogen. It provides structureand support for plants, some of which tower tens of metres in height. Wood is mainlycellulose; cotton fibres and hemp fibres are also cellulose. Indeed, it is because celluloseis indigestible that whole grains, fruits, and vegetables are good sources of dietary fibre.

It is the different glucose–glucose linkages that make cellulose different from starch.When glucose forms a ring structure, the functional groups attached to the ring arefixed in a certain orientation above or below the ring. Our enzymes are specific to the



Section 10.5


BIOLOGY CONNECTION

GlycogenAnimals also produce a starch-likesubstance, called glycogen, thatperforms an energy storagefunction. Glycogen is stored in themuscles as a ready source ofenergy, and also in the liver, whereit helps to regulate blood glucoselevels.

orientation of the functional groups, and cannot break the glucose–glucose linkagesfound in cellulose. Herbivores such as cattle, rabbits, termites, and giraffes rely on somefriendly help to do their digesting: They have specially developed stomachs and intestinesthat house enzyme-producing bacteria or protozoa to aid in the breakdown of cellu-lose.

In starch, glucose monomers are added at angles that lead to a helical structure, whichis maintained by hydrogen bonds between –OH groups on the same polymer chain(Figure 11(a)). The single chains are sufficiently small to be soluble in water. Thus,starch molecules are both mobile and soluble—important properties in their role asreadily available energy storage for the organism.

In cellulose, glucose monomers are added to produce linear polymer chains that canalign side by side, favouring interchain hydrogen bonding (Figure 11(b)). These inter-chain links produce a rigid structure of layered sheets of cellulose. This bulky and inflex-ible structure not only imparts exceptional strength to cellulose; it also renders it insolublein water. It is, of course, essential for plants that their main building material does notreadily dissolve in water. Cotton—A Natural Polymer

North American Aboriginalpeoples made extensive use ofcotton for clothing. This technologywas exported to Europe, where itcontributed to starting theindustrial revolution in Britain.Cotton is a natural carbohydrate(cellulose) polymer. There are nowregenerated (manufactured) fibresfrom cellulose, such as celluloseacetate and cellulose nitrate. In1850, long-fibre cotton comprisedover 50% of Britain’s exports. Themechanization and infrastructuredeveloped for processing cotton,and the resulting capital gained,helped to fuel and shape theIndustrial Revolution.

DID YOU KNOW ??

Figure 11The difference in linkages between glucose monomers gives very different three-dimensionalstructures.(a) In starch, the polymer takes on a tightly coiled helical structure.(b) In cellulose, the linked monomers can rotate, allowing formation of straight fibres.

OHH

HOHH

CH2OH

O

HH O

OHH

HOHH

CH2OH

O

HH O

OHH

HOHH

CH2OH

O

HH O

OHH

HOHH

CH2OH

O

HH O

starch(a)

OHH

H

HHOH

H

CH2OH

H OH

OHH

HOHH

CH2OH

H O

OHH

HOHH

CH2OH

H O

O

O

O

O

cellulose(b)

mini Investigation Starch and Cellulose

Use a molecular model kit and/or a computer program toconstruct and/or investigate molecular models of glucose,sucrose, starch, and cellulose.



458 Chapter 10 NEL

Cellulose Acetates—Structural Analogs of PolysaccharidesChemists have researched and developed polymers that are modifications of naturalpolymers. These natural–synthetic polymers are called biopolymers. For example, starchand cellulose have been made into synthetic polymers. An example is cellulose triacetate.Cellulose, a polysaccharide, is modified by reacting it with acetic acid, CH3COOH(l), andacetic anhydride, (CH3CO)2O(l), with sulfuric acid as a catalyst.

Cellulose triacetate is a polymer that is used in fabrics such as permanently pleated gar-ments, textured knits, and sportswear. There are other, similar, cellulose acetates.

Figure 12Invertase breaks sucrose down toglucose and fructose in somechocolates.

Practice18. Identify the functional groups present in a molecule of glucose and in a molecule of

fructose.

19. Describe several functions of polysaccharides and how their molecular structuresserve these functions in plants.

20. Compare the following pairs of compounds, referring to their structure andproperties:(a) sugars and starch (b) starch and cellulose

21. What are the distinctive features of carbohydrate molecules that, given a structuralformula, would allow you to classify them as carbohydrates?

22. Explain in terms of molecular structure why sugars have a relatively high meltingpoint compared with hydrocarbons of comparable size.

23. Describe, and then explain, the relative solubility of glucose, starch, and cellulose inwater.

DID YOU KNOW ??The Centre of the ChocolateSucrose, a disaccharide, is slightlysweeter than glucose but only halfas sweet as fructose. The enzymesucrase, also called invertase, canbreak sucrose down into glucoseand fructose—a mixture that issweeter and more soluble than theoriginal sucrose. The centres ofsome chocolates are made byshaping a solid centre of sucroseand invertase, and coating it withchocolate (Figure 12). Before long,the enzyme transforms the sucrosecentre into the sweet syrupy mixtureof glucose and fructose.

CH2OH

O O

OH

CH2OOCH3

OOCH3

OOCH3

OH

H

HO

HH

H

O

H

H HH

H

→

→cellulose

catalyst

cellulose triacetate

n n

WEB Activity

Case Study—Cellulose AcetateThis activity leads you through an exploration of the historical and current work done bypolymer chemists to use natural polymers to produce synthetic polymers with desiredcharacteristics and applications.




Section 10.5

Polymers are a common part our everyday world and include natural polymers (lipids(triesters), proteins, and carbohydrates) and synthetic polymers (e.g., nylon, celluloseacetate, and polyesters). For the structural formula equations of these polymers, see pre-vious pages.

Addition PolymersSynthetic Addition Polymer (e.g., polypropene)

Condensation Polymers (Structural Analogs)

Polyesters• Natural “Polyester” (e.g., butter):

glycerol � fatty acid → fat or oil � watere.g., C3H5(OH)3 � 3 C17H35COOH → C3H5(OOCC17H35)3 � 3 H2O

• Synthetic Polyester (e.g., Dacron)dicarboxylic acid � polyalcohol → polyester � watere.g., HOOC�C6H4�COOH � HO�CH2�CH2�OH →

[–OOC�C6H4�COO�CH2�CH2–]n � n H2O

Polyamides

• Natural (proteins; polypeptides):amino acid � amino acid � … → protein � watere.g., H2N�CH2�COOH � H2N�CHCH3�COOH →

[–NH�CH2�CONH�CHCH3�CO–]n � n H2O

• Synthetic (e.g., nylon 6,6):dicarboxylic acid � diamine → nylon � watere.g., HOOC�(CH2)4�COOH � H2N�(CH2)6�NH2 →

[�OC�(CH2)4�CONH�(CH2)6�NH–]n � n H2O

Polysaccharides

• Natural (e.g., starch):glucose � glucose → starch � waterglucose � glucose → cellulose � water(The glucose molecules that polymerize to produce starch or cellulose have slightly different stereochemical formulas.)C6H12O6 � C6H12O6 → [–C6H10O5–]n � n H2O

• Synthetic (e.g., cellulose triacetate):cellulose � acetic acid � acetic anhydride → cellulose acetate � ...[–C6H10O5–]n � CH3COOH � (CH3CO)2O → [–C6H7O5(OCH3)3–]n � ...

SUMMARY Polymers—Plastics, Fibres, and Food

C C C C

nCH3

H

H

H

CH3

H

H

H

→

Learning TipTry to equate the classificationof condensation polymers withthe three food groups whenorganizing your knowledge ofpolymers:

• polyesters include lipids andpolyester fabrics

• polyamides include proteinsand polyamide fabrics

• polysaccharides includecarbohydrates and, forexample, cellulose acetate.

Chemists create classificationsystems to help them organizetheir knowledge. Use the sameapproach to your advantage.


460 Chapter 10 NEL

Section 10.5 Questions1. Teflon®, made from tetrafluoroethene monomer units, is

a polymer that provides a non-stick surface on cookingutensils. Write a structural formula equation to representthe formation of polytetrafluoroethene.

2. Polyvinyl chloride, or PVC plastic, has numerousapplications. Write a structural formula equation torepresent the polymerization of chloroethene (vinylchloride).

3. Using a molecular model kit, construct models of the following monomers and polymers: (a) starch (d) polypropene(b) polyvinyl chloride (e) a polyester(c) nylon (f) cellulose acetate

4. As with most consumer products, the use of polyethylenehas benefits and problems. What are some beneficial usesof polyethylene and what problems result from these uses?Suggest alternative substances for each application.

5. Use the information in this section and from your ownresearch to continue gathering perspective statementsconcerning the statement that we should be saving morefossil fuels for petrochemical use in the future.

6. The first nylon product that was introduced to the public, in1937, was a nylon toothbrush called Dr. West’s Miracle-Tufttoothbrush. Earlier toothbrush bristles were made of hairfrom animals such as boar. From your knowledge of theproperties of nylon, suggest some advantages anddrawbacks of nylon toothbrushes compared with theirnatural counterparts.

7. Oxalic acid is a dicarboxylic acid found in rhubarb andspinach. Its structure is shown below.

Draw three repeating units of the condensation polymermade from oxalic acid and ethan-1,2-diol.

8. What is the synthetic polymer analog of each of thefollowing foods? (a) pasta(b) meat(c) butter

9. Suppose that two new polymers have been designed andsynthesized for use as potting material for plants. (a) List and describe the properties of an ideal polymer to

be used to hold and supply water and nutrients for aplant over an extended period of time.

(b) Design an experiment to test and compare the twopolymers for the properties you listed. Write a briefdescription of the procedures followed, and possibleinterpretations of experimental results.

10. When we purchase a product, we may want to consider notonly the source of its components, but also the requirementsfor its use and maintenance. In your opinion, how valid is theuse of the terms “organic,” “natural,” and “chemical” in thepromotion of consumer goods?

11. Starch and cellulose have the same caloric value whenburned, but very different food values when eaten byhumans. Explain.

12. Explain why the sugars in a maple tree dissolve in the sapbut the wood in the tree trunk does not.

13. Many consumer products are available in natural orsynthetic materials: paper or plastic shopping bags, woodor plastic lawn furniture, cotton or polyester clothing.Choose one consumer product and list the advantages anddisadvantages of the natural and synthetic alternatives,with particular reference to structure and properties of thematerial used as it relates to the function of the product.

14. Classify the type of polymerization for each of the followingpolymers: (a) polyethenes (c) polyamides(b) polyesters (d) polysaccharides

15. Research or use what you know to write a combination of aword, molecular formula, and structural formula equationfor each of the following chemical transformations: (a) starch (from grain) to glucose to ethanol(b) cellulose (from aspen trees) to glucose to methanol

Extension16. Alkyd (oil-based) paint is a polyester formed by reacting

glycerol (CH2OHCHOHCH2OH) with 1,2-benzenedicarboxylic acid (C6H4(COOH)2). Communicatethis reaction using a structural formula equation.

17. What functional group(s), if any, must be present in amonomer of a condensation polymer?

18. In an attempt to reduce body weight, many Canadians areconsidering low-carbohydrate or low-sugar diets. Based onyour knowledge of the chemistry of carbohydrates andsugars, comment on which of these diets might be moreeffective.

19. Natural rubber is made from resin produced by the rubbertree, Hevea brasiliensis.(a) Research the history of the use of rubber by Aboriginal

peoples long before Europeans came to the Americas. (b) Research the commercial invention, production, and

use of natural rubber, and the circumstances thatstimulated the development of synthetic rubber.

(c) Write a brief report on your findings.

20. Raymond Lemieux, from Lac La Biche, Alberta, was the firstchemist to artificially synthesize sucrose (in 1953). Consultthe biographical information of Lemieux. Describe hisinterest in science and one of his other accomplishments(other than the synthesis of sucrose).

21. Check the latest Alberta Chemical Operations Directory tosee if there are any new monomer and polymer chemicalplants in Alberta.

OO

HOC COH




105

Documents

c h h ethene ethylene

formation of polymers

new polymers

different natural polymers

plant polymers

synthetic polymers

animal polymers

addition polymerization