CHAPTER

21

Chemical Classifications:

1. Addition Polymers

IL Condensation Polymers

Polymer Structures:

I. Linear Polymers

II. ·Branched Polymers

ill. Cross-linked Polymers

IV. Copolymers

Polymer C.hemistry

- -- - -----

. Introduction Polymers are large molecules that contain small repeating units. Tre o--' s' ::: ~~,Sat become these units in the polymer are called monomers. Polymers are also =--.-- -~a· their high molecular masses. They are in the range of several thousand _ ~ z ~ ::" s - - - · ·; "" Among important naturally occurring polymers are proteins, cellulose, silk, and -- :!L ?'lZS:ics c-::.: c:... · - • <: S::le!'s such as lucite, formica, nylon, dacron, and polystyrene are purely synthetic ~"' ~ ~ c'<=:fsts

Chemical Classification

A. Addition Polymers: The processes by which monomers are~· ~== ~ iecules are used to classify polymers. Some monomers contain one or more an initiator use their :rt-electrons to form new bonds between ,_ _ _ :--- ~"""""'· · ...; _ ly-rr>:rs have lost much of their unsaturation in creating these new bonds. Polymers ~~- ·-~ ~ cc.- eC. adtiition poly-mers because each monomer unit adds to the growing polymer ~:r:-=s :e · :t=>ee basic types and the processes take their names from the chemical type of the c:at21_ • __ • • r--" · c, a. Free Radical. (Equations la, b, c). Examples of addition po · .: -=-~ __ ~ e, polysty­rene, lucite, neoprene rubber, polyvinyl chloride, and

COOMe COOMe COO e I I I

A:-+ CH2 :::::C- A~CHz-C:- + CHz= C - A -I I I CH?. CH3 ~

Equation la: Anionic Polymerizatio of

Chapter 21 Polyme r Chemistry 493

R+ + CH2 = CH - R"""' CH2 - CW + CH2 = CH - R- CHz- CH - CHz - C'JY - polymer I . I f I I c~3 c~ c~ ~ :na

Equation lb: Cationic Polymerization of Propylene

R• + CH2 = CH- R-CHz-CH• +CH2 =CH- R-CHz - CH - - - · • - polymer © © © I

Equation lc: Free Radical Polymerization of Sty::-e:Je

B. Condensation Polymers: The chemistry of condensation polymers in weight compound (usually water) when two monomers combine. In o two reacting monomers must contain at least two functional groups or more sites on the monomers. Polyesters and polyamides make up tion polymers (e.g., nylon and dacron). (Equations 2a, b).

HO- CH2 - CHz- OH + HOOC -Q-coOH + HO- CHz- CR - - '=- _:-- - = catalyst

HO- CH2 - CH2 - OOC -<Qr- COO- CH2 - ~-

Equation 2a: Condensation Polymerization-~ : -- ~

catalyst NHz =--(CHz)6 ~ NH- OC- (CH2) 6 - CO- NH- (CHz)5 - - --=-::- -=-

Equation 2b: Condensation Polymerization- _-~-? .=.

Structural Classification

A. Linear Polymers: If the polymers link together in long, uninterrup­polymers. (Equation 3a.)

B. Branched Polymers: If some of the units that make up the polyme= cc:::::C:::::=;. group, then the macromolecule can grow branches from the main -different solubilities, melting points, and properties when compared--- - -

C. Cross-lipked Polymers: Linear polymer chains can be synthesizeri. - -tiona! groups on them. After the initial polymer chains have fo the reaction of these extra functional groups. The result is a large ----=--- .... -,-r--.,.....,..-.:>-:. joined together into a single, very high-molecular weight polyme::- -=- ::._ s;::=::c;;::ci~ ,__,....._:.....:::

solvent. The uncross-linked polY.mer is used at its desired locatio::i =-- -proquct. (See equation 3c.)

D. Copolymers: To modify the properties of simple polymers, two -carrying out condensation polymerizations. These copolymers cc:::;.

For random copolymers, different monomers are placed in the The monomer units occur in random order in the final polyme::. ~ _ -small polymer chains (oligomers) are grown from a single mm the reaction mixture. This process may be repeated through se, - - --sists of"discrete blocks of single monomer chains alternating w±::::: ·;:c::=:::=

14

COOH

Equation 3a: ,_

· Equation 3b:

Equation 3c:

Equation 3d: -

Equation 3e:

A-A- A- A- A- A- A-A-A

Linear Polymer

A I

A-A-A- A- A- A- A- A-A-A-A I I I A A A I I A A-A

I A

Branched Polymer

A-A-A-A- A- A- A- A-A-A-A-A I I

A-A-A-A- A- A- A- A- A- A-A-A I

A-A-A-A- A- A- A- A- A- A-A-A I I A-A-A- A- A- A- A- A- A- A-A-A

Cross-linked Polymer

A-A-B-A- B- B- A- B- A- A-A-B

Random Copo er

B-B-B-B- A- A- A- B-B- B- A-A -- - - - - ----. --~------ - --- ---------- - - -- - - --·-

B ock Copolymer

Chapter 21 Polymer Chemistry 495

I ~

LAB XXI ~ A

Difficulty Level

Basic

KeyWords

Polyacrylates Vmyl polymer

Background

Free Radical Polymeriza ·on

Pendant group Free radical polymm?Z;llc:l

The final nature of the polymer depends on the type oi ~-~a= ~-cc ~~=­groups or substituents attached to the original acrylic ~

Materials

Methyl methacrylate

heat

0 II C- 0 - 0 -

©J -Benzoylpe

The followirig procedure may be carried out with ·-.::..

v

produced should then be compared to see how altP · ._:: - - ,....=-~""": ;::::a:±:=~

Initiator

rate of polymerization and the properties of the ~- _ ::::=:::;.:==:::::::o. ethyl acrylate, cyclohexyl acrylate, and 2-methyfb

Lab XXI A Free Radical Polymerization

1. In a 4-inch test tube, place 2 mL of methyl methacrylate. Add a few crystals of benzoyl perox-ide. Stir the mixture with a glass rod to ensure that the peroxide is uniformly distrib-uted in the monomer.

2. Place the test tube in a 150 mL beaker half full of boiling water. Heat the methyl methacrylate for 30 minutes.

3. At the end of this time, remove the test tube from the boilii:tg water, and allow it to cooL

4. Wrap the test tube in a clOth towel; gently crush it with a hammer.

5. Carefully remove the pol~er casting from the broken glass .

. 6. 'fum in your polymer to your instructor.

-~ r I

~ r - . i ~-:. f -~

I ~-:. r I

~-=-r , ~--=-r _.....,

k-:11 r !

~=-r I =-r I r.

1Dil.OO :rr

0 n C-O-CH3 I

CH,=C I CH,

~00~--r---.----.--------~------.. -------.,-------~

-

©Aldrich Chemical Company, =

QUESTIONS

1. Draw the structure ( 4 monomer units) of a head-to-tail polymer:. -n-o you expect its properties -~ _ different from those of the head-to-head compound?

2. Heating the methyl methacrylate rapidly produces a bubbly matri2' are these bubbles no the material is heated slovvly?

3. Can you correlate the different properties of the polymers this experiment?

ADDITIONAL READINGS

structures of the monomers

Carey, F.A. Organic~Cfwrn:i:stry;~~~a. New York: McGraw-Hill, 1992: 24?--246.

Ege, SA9igli"hic Chemistry, Srd ed. Lexington, Massachusetts: D.C. Heath & Co., 994: 1251-1265.

Fessenden, R.J. and J.S. Fessenden. Organic Chemistry, 5th ed. Paciiic Grore, California: Brooks/Cole Pub~= 1994:264.

McMurry, J. Organie Chemistry, 3rd ed. Pacific Grove, California: Brool;stCo e • l:ishlng Co., 1992: 1188.

Morrison, R.T. and R.N. Boyd.· Organic Chemistry, 6th ed. Englewood GIEs, ew Jersey: Prentice-Hall, 1992: 1

Solomons, T.W.G. Or:ganic Chemistry, 5th ed. New York: John Wiley & Sons, 1992: 388.

Streitwieser, A.·, C.H. Heathcock and E.M. Kosower. Introduction to Orga:nic Chemistry, 4th ed. New York: Mai~Zt Publishing Co., 1992: 1141-1143.

Vollhardt, K.P.C. and N.E. Shore. Organic Chemistry, 2nd ed. New York: =.3.. Freeman & Co., 1994: 445.

Wade, L.G. Jr. Organic Chemistry, 3rd ed. Englewood Cliffs, New Jersey: Prentice--Hall, 1987: 1284-1292.

Lab XXI A Free Radical Polymerizatio~

-·

Mix up your own batch of one of the world's f1rst synthetic materials

N 1938 THE E.I. DUPONT DE NEMOURS Company, known at the time mainly as a maker of explosives, announced what was arguably the single most important invention

in the history of legwear: nylon. Nylon wasn't discovered by accident or

extracted from a natural source. It was one of the first materials engineered from scratch, based on an understanding of polymer chemistry and a desire to plug what was, apparently, a serious hole in the hosiery industry. The company promised that this magical product would finally free the modern woman from the yoke of expensive, run-prone silk stockings. And it worked! There were widespread reports of mobs becoming restless,

When molecules of hexamethylenediamine

and sebacoyl chloride link together to create

chains thousands of atoms long, you get nylon.

Stir Up Some Nylon 55

if not violent, in the minutes before the opening of a store rumored to have some of the new "nylons" in stock

Fortunately, nylon is now abundant, and if you have a chemicals catalog handy, it's not that difficult to make yourself. When molecules of hexamethylenediamine and sebacoyl chloride link together in an alternating pattern to create chains thousands of atoms long~which happens spontaneously anytime these chemicals come in contact with each other~you get nylon.

The recipe I used is based on the Tequila Sunrise principle: two solutions with different densities layered in the same glass. The heavier, aqueous (water-based) hexamethylenediamine solution is on the bottom [here dyed with food coloring], and the lighter sebacoyl chloride is on top. A film of nylon appears instantly where the two layers meet. Gently pull the film with tweezers, and new nylon forms in its place, allowing you to produce a continuous thread dozens of yards long from an average-size glass.

Commercial nylon is made with the same chemical bonds through a slightly different reaction, and the resulting product is purified and melted down before being pulled into fibers. My homemade thread, on the other hand, is too thick and brittle for knitting. Oh well, I prefer my hose in French silk anyway.

HowT(!: Get Nylon from Liquid

ethylenediamine aminohexane) in

sodi um hydroxide liliters 0.2M sebacoyl

- e in hexane

C.alrmrlN pour the sebacoyl dl6ilril:llesolution on top

ethylenediamine out where to buy at

If you have ing the chemicals in

a bartender for help.

ers to grab the een the two

pull it up.

D 100 milliliter beaker or glass

D Tweezers D Rubber gloves D Safety glasses

3The thread will appear as fast as you pull it from

the mixture. You can collect it around anything that's convenient. I used a roll of paper towels stuck on a paint roller.

4 The final product: a continuous thread-from

bottles of chemicals.

NAMED FOR: A variation of the 'marketing claim

uno-run••

(2 o v.-t 1 s_X , r) -:::: U ) ( s . 11-- t-v..)

X :::c 2 -~ \) I"<. ~~ --6 (, 0 0(0 "1

Cs rvt. l\l '\ol4) (~) -=-(_so V"'l s)( · s-)

so c.o{ c~ ~ h.'\_ Is o-t 3 hA.. (\} to

7_ ' '1 0 JIV\.. l.s ~-o ~ () 'l «, '2_ 7.. _ ( M ls v-1 H0't)

")

'?. S ~\oe-,~ ,_d (___~ lat!'~vl Q.. l

·s C·, ,l '-{ ) l ~k-

o. ·2-M 3 0 1M-. l 5> c.r{

.2 . ~~ ~l e ..

l 4:1~,

-

<.....,_

P.O. Box 219 • Batavia, IL 60510 (800) 452-1261 • Fax (866) 452-1436

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'·Your Safer Source for Screor:e Supplies"

P ·on No. 377.10

The Preparation of Guar Gum Slime Introduction

Curiosity often overwhelms those who see an unrecognizable substance. "What is itT" they wonder, ·~--nat can it be?" Capture your students' attention with this "goopy" slime recipe.

Concepts

• Polymers

Materials

Guar gum, 0.5-1.0 g

Sodium borate solutio!), 4%, N~B407 , 5 mL

Water, distilled or deionized, 100 mL

Food coloring (optional), 1-2 drops

Balance

( - ,\ Safety Precautions

Graduated cylinder, 10-mL

Graduated cylinde~, 100-mL

' Small plastic cup, 5-8 oz

Stirring rod

Slime is generally considered nonhazardous; howeve r, it should not be ingested and should only be used in ~ Tl'.anner intended. It is not recommended rhat studenrs be allowed to take slime home. Slime wiU easily su1ir.. ciorhin..g. UJJl-.OlsteT}~ arul wood suifaces. With food coloring added, it will stain these suifaces and skin even more readily, .ear che:rr.ical • lash goggles. chemical-resistant gloves, and a chemical-resistant apron. Please review currenJ Mmeri.al Safe ' Data Sheets for ru:!tiiriar.al safef)~ handling, and disposal information. -- --- - - .

Procedure

1. Add 100 mL of distilled or deionized water to the small plastic cup. If desi..."C:d, add and stir.

2. Slowly and with constant stirring, add 0.5- 1.0 g of guar gum to the wa er. _'ore.· .r rho guar e

will form large, undesirable clumps. Stir unti l dissolved. The mixture will !:hie ·eil slie'

3. Add 5 mL of 4% sodium borate solution. Stir. The mixture should gel in 1- 2 minuies.

Dispusal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and sp:OCiilC

review all federal, state and local regulations that may apply, before proceeding. Slime may be thrown o• Suggested Disposal Method #26a

Tips

Use only distilled or deionized water. The ions present in tap water may interfere with the polymeriza··on the slime to turn watery after only an hour or two. Sii:ne made with distilled or deioillzed water " ill reuilll : and consistency for several days.

• Store the slime in an airtight container or bag to prevent it from drying out.

GHEM-FAX'~ .. makes science teacl7ing easier. 377.10

01271 0

Discussion

Guar gum, a natural polymer with a molecular weight of about 220,000 g/mole, is made ir Cyamopsis letragonolubus, a legume cultivated in India~§_l i vestock feed. Guar gum has 5- 8 times and is commonly used as a binding or thickening agent in foods and cosmetics.

Guar gum is a long-chain polyalcohol with 1 ,2-diol groupings capable of complexation with structures given below are oversimplified, but may help to visualize tb.e network complex as it exte

R R R

I I I HCOH H0""-8 / OH HC-·- 0 0 --CH

2 I I ""-~/ I + B

Hif ""-oH HC - -0/ ""-o - - 6H HCOH

I I I R R R

Guar gum Borate ion Cross-linked guar gum-borate gel

In addition to forming complexes with the borate ion, the interaction of long-chain polyalcoho the borate ion leads to crosslinking of different polymer chains, or sometimes part of the same three-dimens ional network of connected chains is formed. When the concentration of cross-linkerl immobilized within the network and a semisolid gel results. Because the borate ion can bond v."i particularly effective in creating three-dimensional gel networks from gums such as guar gum. Ol: gels are rubber cement, gelatin , fruit jellies, agar, and yogurt.

Connecting to the National St_andards

This laboratory activity relates to the following National Science Education Standards (1996):

Unifying Concepts and Processes: Grades K-12 Evidence, models, and explanation

Content Standards: Grades 5- 8 Content Standard A: Science as Inquiry Content Standard B: Physical Science, properties and changes of properties in matter Content Standard F: Science in Personal and Social Perspectives; science and technology · soc·o

Content Standards: Grades 9- 12 Content Standard A: Science as Inquiry Content Standard B: Physical Science, structure and properties of matter Content Standard F: Science in Personal and Social Perspectives, science and technolO£V · challenges

Acknowledgment

We would like to extend a special thanks to David A. Katz for providing us with the ins

Reference

Casassa, E. Z.; Sarquis, A.M.; Van Dyke, C. H. J. Chem. Ed. 1986, 63, 57.

Materials for The Preparation of Guar Gum Slime are available from Flinn

• Catakl!; No. Descri pt ion I G0039 Guar Gum, 1 00 g I S0363 Sodium Borate Solution, 4%, 500 ml I V0003 Vegetable dyes, Set I W0001 Water, Distilled, 1 Gallon I AP9081 Fluorescent Slime-Chemical Demonstration Kit I

Consult your Flinn Scientific Catalog!Refenmce Manual for current prices..

-2 -

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c.

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www.flinnsci.com • E-mail: flinn@fl' · com

Silicone Super Ball Introduction

Two solutions are mixed, forming a solid polymer that bounces when shaped into a ball.

Concepts

• Silicones • Polymers

Materials

Ethyl alcohol, CH3C~OH, 95%, 10 mL

Sodium silicate solution, (water glass), 20 mL

Graduated cylinder, 25-mL

Safety Precautions

Latex gloves

Paper or plastic cup small

Wooden splint

Ethyl alcohol is a dangerous fire risk; it is flammable. The addition of denaturant makes eth)' Sodium silicate solution is very alkaline; a skin irritant. Wear chemical splash goggles, chemical-resisimri _ resistant apron. Please review current Material Safety Data Sheets fo r additional safety, handling. anG=>!i""IM.i~==;;;;;:=~_

Procedure

1. Measure out 20 mL of sodium silicate solution using the 25-mL graduated cylinder. A ~ so

2. Measure out 10 mL of 95% ethyl alcohol and add it to the paper cup.

3. Stir the mixture with the wooden splint in a regular circular motion.

4. As the mixture solidifies, squeeze out the liquid with latex--gloved hands; place the solid in the palm ~

the solid into a ball.

5. While forming the ball, continue to gently press out the excess liquid.

6. Bounce the ball!

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general e -

ing the disposal of laboratory waste. The wood splint and excess product from the reac ·on may be dispo:;;.erl Suggested Disposal Method #26a.

Tips

• Adjust the amount of alcohol used (anywhere from 5 to 1- mL) balls will vary in how brittle they are.

observe the Cffi~:no~ between the superballs. The

• The silicone super ball is brittle and may crumble. It may be reformed by pressing - berncen

• The super ball should be stored in a closed or airtight container when no in use.

CHEM-FAXT~ . . makes science teaching easier.

palms of the hands.

758.00 102407

Discussion

The super ball is a variation of a simple silicone. Silicone is the term used to describe any mganosi1:i n oxide polyme£ in which the structural unit is usually:

R

I R R

I I Si-0 Si- 0 Si- 0

I R

I R n R

R is an organic, usually a methyl group.

Silicones are characterized by wide-range thermal stability, high lubricity, extreme water repe and ?t;~oc~JEJ]l!C<al inertness.

Their wide-ranging uses include adhesives, lubricants, protective coating paints, electric;al11' lSUIE:Iorr.. ~~~~­

prosthetic replacements for body parts, including implants.

Sodium silicate solution is produced by fusing sand (Si02)n and soda ash azCO:J in a furnace product, NazO (Si02)

0 is also called water glass. The reaction with ethyl alcohol produces a uper

silicone elastomer where the R is (- 0 - CH2CH3).

Connecting to the National Standards

This laboratory activity relates to the following National Science Education Standards (1996):

Unifying Concepts and Processes: Grades K-12 Evidence, models, and explanation Form and function

Content Standards: Grades 5-8 Content Standard B: Physical Science, properties and changes of properties in matter Content Standard E: Science and Technology Content Standard F: Science in Personal and Social Perspectives; science and technolo:gy -Content Standard G: History and Nature of Science, science as a human endea of~·~""'

Content Standards: Grades 9-12 Content Standard B: Physical Science, structure of atoms structnre and properties of matter, che -Content Standard E: Science and Technology Content Standard F: Science in Personal and Social Perspectives science and technology in locaL m!.lia;:~ challenges

Reference

Gardner, M.; Summerlin, L.; Borgeford, C. Selected Demonstrations from Berkeley l.C.E., S 19 _

Materials for Silicone Super Ball are available from Flinn Scientific, Inc..

Catalog No. Description I S0102 Sodium Sil icate Solution, 500 ml l E0009 Ethyl Alcohol, 95%, 500 ml l AP4444 Wood Splints, pkg ./100 I

Consult your Flinn Scientific Catalog/Reference Maru.tal fur

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