15 15-1 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Introduction to Organic...

1515

15-1Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.

Introduction to Introduction to Organic Organic

ChemistryChemistry2 ed2 ed

William H. Brown William H. Brown

1515


Organic Organic PolymerPolymer

ChemistryChemistryChapter 15Chapter 15

1515


Organic Polymer Chem.Organic Polymer Chem. Polymer: from the Greek, poly + meros, many

parts. Any long-chain molecule synthesized by linking together single parts called monomers

Monomer: from the Greek, mono + meros, single part. The simplest nonredundant unit from which a polymer is synthesized

Plastic: a polymer that can be molded when hot and retains its shape when cooled

1515


Organic Polymer ChemOrganic Polymer Chem Thermoplastic: a polymer that can be melted

and molded into a shape that is retained when it is cooled

Thermoset plastic: a polymer that can be molded when it is first prepared, but once it is cooled, hardens irreversibly and cannot be remelted

1515


Notation & NomenclatureNotation & Nomenclature Show the structure by placing parens around the

repeat unit n = average degree of polymerization

Cl Cl Cl Cl Cl

Cl

is synthesized from

Cln

is written as

Poly(vinyl chloride)(PVC)

Vinyl chloride

1515


Notation & NomenclatureNotation & Nomenclature To name a polymer, prefix poly to the name of

the monomer from which the polymer is derived• if the name of the monomer is one word, no parens

are necessary• for more complex monomers or where the name of the

monomer is two words, enclose the name of the monomer is parens, as for example

poly(vinyl chloride)

poly(ethylene terephthalate)

1515


MorphologyMorphology Polymers tend to crystallize as they precipitate

or are cooled from a melt Acting to inhibit crystallization are their very

large molecules, often with complicated and irregular shapes, which prevent efficient packing into ordered structures

As a result, polymers in the solid state tend to be composed of ordered crystalline domains and disordered amorphous domains

1515


MorphologyMorphology High degrees of crystallinity are found in

polymers with regular, compact structures and strong intermolecular forces such as hydrogen bonds• as the degree of crystallinity increases, the polymer

becomes more opaque due to scattering of light by the crystalline regions

Melt transition temperature, Tm: the temperature at which crystalline regions melt• as the degree of crystallinity increases, Tm increases

1515


MorphologyMorphology Highly amorphous polymers are sometimes

referred to as glassy polymers• because they lack crystalline domains that scatter

light, amorphous polymers are transparent• in addition, they are weaker polymers, both in terms

of their high flexibility and low mechanical strength• on heating, amorphous polymers are transformed

from a hard glass to a soft, flexible, rubbery state

Glass transition temperature, Tg: the temperature at which a polymer undergoes a transition from a hard glass to a rubbery solid

1515


MorphologyMorphology Example: poly(ethylene terephthalate) (PET) can

be made with % crystalline domains ranging from 0% to 55%

OO

OO

nPoly(ethylene terephthalate)

(PET)

1515


MorphologyMorphology Completely amorphous PET is formed by cooling

the melt quickly• PET with a low degree of crystallinity is used for

plastic beverage bottles

By prolonging cooling time, more molecular diffusion occurs and crystalline domains form as the chains become more ordered• PET with a high degree of crystallinity can be drawn

into textile fibers and tire cords

1515


Step-Growth PolymersStep-Growth Polymers Step-growth polymerization: a polymerization in

which chain growth occurs in a stepwise manner between difunctional monomers

We discuss five types of step-growth polymers• polyamides• polyesters• polycarbonates• polyurethanes• epoxy resins

1515


PolyamidesPolyamides Nylon 66 (from two six-carbon monomers)

• during fabrication, nylon fibers are cold-drawn to about 4 times their original length, which increases crystallinity, tensile strength, and stiffness

+

Hexanedioic acid (Adipic acid)

1,6-Hexanediamine (Hexamethylenediamine)

O O

nHOC(CH2)4COH nH2N(CH2)6NH2heat

n +

Nylon 66

O O

C(CH2)4CNH(CH2)6NH 2nH2O

1515


PolyamidesPolyamides The raw material base for the production of

nylon 66 is benzene, which is derived from cracking and reforming of petroleum

catalyst

Cyclohexanone

catalyst

Benzene Cyclohexane

Cyclohexanol

+

air

OOOH O

3H2

HOC(CH2 )4COHHNO3

Hexanedioic acid (Adipic acid)

1515


PolyamidesPolyamides Adipic acid is in turn the starting material for the

synthesis of hexamethylenediamine

1,6-Hexanediamine (Hexamethylenediamine)

Ammonium hexanedioate (Ammonium adipate)

catalystHexanediamide (Adipamide)

heat

OO

OO

H2NC(CH2)4CNH2

4H2H2N(CH2)6NH2

NH4+ -

OC(CH2)4CO-

NH4+

1515


PolyamidesPolyamides Nylons are a family of polymers, the two most

widely used of which are nylon 66 and nylon 6 • nylon 6 is synthesized from a six-carbon monomer

• nylon 6 is fabricated into fibers, brush bristles, high-impact moldings, and tire cords

Caprolactam

1. partial hydrolysis

2. heatn

Nylon 6

nNH

O

NH(CH2)5C

O

1515


PolyamidesPolyamides Kevlar is a polyaromatic amide (an aramid)

• cables of Kevlar are as strong as cables of steel, but only about 20% the weight. Kevlar fabric is used for bulletproof vests, jackets, and raincoats

+

1,4-Benzenediamine(p-Phenylenediamine)

1,4-Benzenedicarboxylic acid (Terephthalic acid)

nKevlar

+

O

NH

COHnHOC

O O

nH2N NH2

CNHC

O

2nH2O

1515


PolyestersPolyesters Poly(ethylene terephthalate) (PET) is fabricated

into Dacron fibers, Mylar films, and plastic beverage containers

Poly(ethylene terephthalate) (Dacron, Mylar)

heat

+n

+

1,4-Benzenedicarboxylicacid

(Terephthalic acid)

1,2-Ethanediol(Ethylene glycol)

COHnHOC

O O

OO

C COCH2CH2O

nHOCH2CH2OH

2nH2O

1515


PolyestersPolyesters• ethylene glycol is synthesized from ethylene

• terephthalic acid is synthesized from p-xylene, which is obtained from petroleum refining

Ethylene oxide Ethylene glycolEthylenecatalyst

OCH2 =CH2

O2CH2 -CH2

H+, H2O

HOCH2 CH2OH

Terephthalic acidp-Xylenecatalyst

OO

HOC COHCH3H3CO2

1515


PolycarbonatesPolycarbonates

Phosgene

+

Disodium salt of Bisphenol A

Na+-O

CH3

CH3

O-Na+

Lexan(a polycarbonate)

+

Cl Cl

O

nO

CH3

CH3

O

O

2NaCl

1515


PolycarbonatesPolycarbonates Lexan is a tough transparent polymer with high

impact and tensile strengths and retains its shape over a wide temperature range• it is used in sporting equipment, such as bicycle,

football, and snowmobile helmets as well as hockey and baseball catcher’s masks

• it is also used in the manufacture of safety and unbreakable windows

1515


PolyurethanesPolyurethanes A urethane, or cabamate, is an ester of carbamic

acid, H2NCH2CO2H• they are most commonly prepared by treatment of an

isocyanate with an alcohol

Polyurethanes consist of flexible polyester or polyether units (blocks) alternating with rigid urethane units (blocks)• the rigid urethane blocks are derived from a

diisocyanate

+An isocyanate A carbamate

O

RNHCOR'RN=C=O R'OH

1515


PolyurethanesPolyurethanes• the more flexible blocks are derived from low-

molecular-weight polyesters or polyethers with -OH groups at the ends of each polymer chain

Low-molecular-weightpolyester or polyether

2,6-Toluenediisocyanate

+

n

A polyurethane

CH3

CNH NHCO-polymer-OCH3

N=C=OO=C=N

O

nHO-polymer-OH

O

1515


Epoxy resinsEpoxy resins Epoxy resins are materials prepared by a

polymerization in which one monomer contains at least two epoxy groups• within this range, there are a large number of

polymeric materials and epoxy resins are produced in forms ranging from low viscosity liquids to high melting solids

• the most widely used epoxide monomer is the diepoxide prepared by treating 1 mol of bisphenol A with 2 mol of epichlorihydrin

1515


Epoxy ResinsEpoxy Resins

O

CH3

CH3

OOO

A diepoxide

OCl Na+-O

CH3

CH3

O-Na+

Disodium salt of bisphenol AEpichlorohydrin

+

1515


Epoxy ResinsEpoxy Resins

H2NNH2

A diamine

O

CH3

CH3

O

An epoxy resin

HN

OH OH

NH n

O

CH3

H3C

OOO

A diepoxide

1515


Chain-Growth PolymersChain-Growth Polymers Chain-growth polymerization: a polymerization

in which monomer units are joined together without loss of atoms. For example:

catalyst

Ethylene Polyethylene

nCH2 =CH2 CH2 CH2 n

1515


PolyethylenesPolyethylenesMonomer

Formula

Polymer Name(s) and

Common Uses

polyethylene, Polythene;

break-resistant containers

and packaging materials

polypropylene, Herculon;

textile and carpet fibers

poly(vinyl chloride), PVC;

construction tubing

poly(1,1-dichloroethylene) Saran;

food packaging

CH

2

=CH

2

CH

2

=CHCH

3

CH

2

=CHCl

CH

2

=CCl

2

1515


PolyethylenesPolyethylenespolyacrylonitrile, Orlon;

acrylics and acrylates

polytetrafluoroethylene, Teflon;

nonstick coatings

polystyrene, Styrofoam;

insulating materials

poly(ethyl acrylate); latex paints

poly(methyl methacrylate), Lucite,

Plexiglas; glass substitutes

CH

3

CH

2

=CHCN

CF

2

=CF

2

CH

2

=CHC

6

H

5

CH

2

=CHCO

2

CH

2

CH

3

CH

2

=CCO

2

CH

3

1515


Radical Chain-GrowthRadical Chain-Growth Among the initiators used for radical chain-

growth polymerization are organic peroxides, which decompose as shown on mild heating

ΔO

O

O

O

Dibenzoyl peroxide

O

O

2 + 2CO2

A phenyl radical

A benzoyloxy radical

2

1515


PolymerizationPolymerization RadicalRadical: a molecule or ion containing one or

more unpaired electrons Fishhook arrowFishhook arrow: a curved and barbed arrow

used to show the repositioning of a single electron

To account for the polymerization of alkenes in the presence of peroxides, chemists propose a three-step radical chain mechanism

1515


PolymerizationPolymerization Step 1: chain initiation

• Chain initiation: a step in a radical chain reaction characterized by the formation of radicals from nonradical compounds

CH2=CH2 In-CH2CH2•+An alkyl radical

In•

In• + In•In In

1515


PolymerizationPolymerization Step 2: chain propagation

• Chain propagation: a step in a radical chain reaction characterized by the reaction of a radical and a molecule to give a new radical

• Chain length, n: the number of times the cycle of chain propagation steps repeats in a chain reaction

In-CH2CH2• (n-1)CH2=CH2+ In-(CH2CH2)n•

In-CH2CH2• CH2=CH2+ In-CH2CH2CH2CH2•

1515


PolymerizationPolymerization Step 3: chain termination

• Chain termination: a step in a radical chain mechanism that involves destruction of radicals

CH2CH2• •CH2CH2

CH2CH2-CH2CH2

+

1515


Radical Chain-GrowthRadical Chain-Growth The first commercial polyethylenes produced by

radical polymerization were soft, tough polymers known as low density polyethylene (LDPE)• LDPE chains are highly branched due to chain-

transfer reactions• because this branching prevents polyethylene chains

from packing efficiently, LDPE is largely amorphous and transparent

• approx. 65% is fabricated into films for consumer items such as baked goods, vegetables and other produce, and trash bags

1515


Radical Chain-GrowthRadical Chain-Growth Chain-transfer reaction: the reactivity of an end

group is transferred from one chain to another, or from one position on a chain to another position on the same chain• polyethylene formed by radical polymerization

exhibits a number of butyl branches on the polymer main chain

• these butyl branches are generated by a “back-biting” chain transfer reaction in which a 1° radical end group abstracts a hydrogen from the fourth carbon back

• polymerization then continues from the 2° radical

1515


Radical Chain-GrowthRadical Chain-Growth

A six-membered transition state leading to 1,5-hydrogen abstraction

H H

n

nCH2=CH2

••

1515


PolymerizationPolymerization Propylene and other substituted ethylene

monomers can also be polymerized under a variety of experimental conditions• radical polymerization of propylene involves 2° radical

intermediates to give polypropylene, with methyl groups repeating on every other carbon

PolypropylenePropene(Propylene)

ninitatornCH3 CH=CH2 CHCH2

CH3

1515


Ziegler-Natta PolymersZiegler-Natta Polymers Ziegler-Natta chain-growth polymerization is an

alternative method that does not involve radicals• Ziegler-Natta catalysts are heterogeneous materials

composed of a MgCl2 support, a group IVB transition metal halide such as TiCl4, and an alkylaluminum compound

nCH2=CH2

TiCl 4/Al(CH 2CH3)2Cl

MgCl2Ethylene Polyethylene

1515


Ziegler-Natta PolymersZiegler-Natta Polymers• Step 1: formation of a titanium-ethyl bond

Ti Cl

Ti CH2CH3

+

+

MgCl 2 /TiCl 4particle

Al(CH2CH3)2Cl

Al(CH2CH3)Cl2

1515


Ziegler-Natta PolymersZiegler-Natta PolymersStep 2: insertion of ethylene into the titanium-carbon

bond

Ti CH2CH3

Ti CH2CH2CH2CH3

+ CH2 =CH 2

1515


Ziegler-Natta PolymersZiegler-Natta Polymers Polyethylene from Ziegler-Natta systems is

termed high-density polyethylene (HDPE)• it has a considerably lower degree of chain branching

than LDPE and, a result, has a higher degree of crystallinity, a higher density, a higher melting point, and is several times stronger than LDPE

• appox. 45% of all HDPE is blow-molded into containers

• with special fabrication techniques, HDPE chains can be made to adopt an extended zig-zag conformation. HDPE processed in this manner is stiffer than steel and has 4x the tensile strength!

1515


Recycling CodesRecycling CodesCode Polymer Common Uses

1PET

poly(ethyleneterephthalate)

soft drink bottles, householdchemical bottles, films, textile fibers

2HDPE

high-densitypolyethylene

milk and water jugs,grocery bags, bottles

3V

poly(vinylchloride), PVC

shampoo bottles, pipes,shower curtains, vinylsiding, wire insulation,floor tiles, credit cards

4LDPE

low-densitypolyethylene

shrink wrap, trash andgrocery bags, sandwich bags, squeeze bottles

1515


Recycling CodesRecycling CodesCode Polymer Common Uses

5PP

polypropylene plastic lids, clothing fibers, bottle caps, toys,diaper linings

6PS

polystyrene styrofoam cups, egg cartons, disposable utensils,packaging materials,appliances

7 all other plastics, mixed plastics

various

1515


End Chapter 15End Chapter 15

Organic Organic PolymerPolymer

ChemistryChemistry

Date post:	24-Dec-2015
Category:	Documents
Upload:	malcolm-baker
View:	216 times
Download:	1 times

15 15-1 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Introduction to Organic...

Documents