29-1 organicpolymerchemistry. 29-2 some definitions polymer:poly+meros polymer: from the greek,...

29-29-11

OrganicOrganicPolymerPolymerChemistryChemistry

29-29-22

Some DefinitionsSome Definitions

Polymer:Polymer: From the Greek, polypoly ++ merosmeros, many parts.• Any long-chain molecule synthesized by bonding

together single parts called monomers.

MonomerMonomer: From the Greek, monomono ++ merosmeros, single part.• The simplest nonredundant unit from which a polymer

is synthesized.

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

29-29-33

ContinuedContinued

Thermoplastic:Thermoplastic: A polymer that can be melted and molded into a shape that is retained when it is cooled.

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

29-29-44

Notation & NomenclatureNotation & Nomenclature

Show the structure by placing parens around the repeat unit:• nn = average degree of polymerization.

To name a polymer, prefix polypoly to the name of the monomer from which it is derived.• For more complex monomers or where the name of the

monomer is two words, enclose the name of the monomer in parens, for example poly(vinyl chloride).

StyrenePolystyrene

Poly(vinyl chloride) (PVC)

Vinyl chloride

synthesized from

29-29-55

Molecular WeightMolecular Weight

All polymers are mixtures of individual polymer molecules of variable MWs.• number average MW:number average MW: Count the number of chains of a

particular MW (Ni moles), multiply each number by the MW (Mi), sum these values, and divide by the total number of polymer chains.

• weight average MW:weight average MW:

= (Mass of fraction i)(fraction of all molecules having mass i)

MiMiNi

= (Mass of fraction i)(f raction of total mass of molecules having mass i)

29-29-66

ExampleExample

Sample has the unique chainsChainMW, Mi

MolesPresent, Ni

ChainMass, MiNi

120 0.10 12g

140 0.20 28

140 0.10 14

160 0.30 48

160 0.40 64

180 0.20 36

200 0.10 20

Mn = .10(120) + (.20+.10)(140)+ (.30+.40)(160) +.20(180)+.10(200)

(.10+.20+.10+.30+.40+.20+.10)

= 12+28+14+48+64+36+20

1.4=158

29-29-77

ExampleExample

Now for weight averaged MW

Mw = 120(12) + 140(28+14)+160(48+64)+180(36)+200(20)

(12+28+14+48+64+36+20)

ChainMW, Mi

MolesPresent, Ni

ChainMass, MiNi

120 0.10 12g

140 0.20 28

140 0.10 14

160 0.30 48

160 0.40 64

180 0.20 36

200 0.10 20

29-29-88

Polydispersivity IndexPolydispersivity Index

PDI = Mw/Mn measures the extent of different molecular weights.

PDI greater than or equal to 1.0

29-29-99

MorphologyMorphology

Polymers tend to crystallize as they precipitate or are cooled from a melt.

Acting to inhibit crystallization are that polymers are large molecules. Complicated and irregular shapes prevent efficient packing into ordered structures.

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

29-29-1010

Morphology: CrysatlineMorphology: Crysatline

High degrees of crystallinity are found in polymers with • regular, compact structures• strong intermolecular forces, such as hydrogen bonds

and dipolar interactions.

As the degree of crystallinity increases, the polymer becomes more opaque due to scattering of light by the crystalline regions.

Melt transition Melt transition temperature, Ttemperature, Tmm:: The temperature at which crystalline regions melt.• As the degree of crystallinity increases, Tm increases.

29-29-1111

Morphology: AmorphousMorphology: Amorphous

Highly amorphous polymers are sometimes referred to as glassy polymers.• Lacking crystalline domains that scatter light,

amorphous polymers are transparent.• They are weaker polymers, both in terms of their

greater flexibility and smaller mechanical strength.• On heating, amorphous polymers are transformed

from a hard glassy state to a soft, flexible, rubbery state.

GlassGlass transition temperature, T transition temperature, Tgg:: The temperature at which a polymer undergoes a transition from a hard glass to a rubbery solid. Put polystyrene cup in boiling water.

29-29-1212

• Example:Example: poly(ethylene terephthalate), abbreviated PET or PETE, can be made with crystalline domains of 0% to 55%.

nPoly(ethylene terephthalate)

29-29-1313

Completely amorphous PET is formed by quickly cooling the melt.• PET with a low degree of crystallinity is used for

plastic beverage bottles.

More crystallline formed by slow cooling, 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.

29-29-1414

Step-Growth PolymersStep-Growth Polymers Step-growth polymerization:Step-growth polymerization: A polymerization in which chain growth

occurs in a stepwise manner between difunctional monomers. Many chains initiated at same time. All monomeric -> mostly dimeric -> mostly trimers. Etc.

five types of step-growth polymers:• Polyamides

• Polyesters

• Polycarbonates

• Polyurethanes

• epoxy resins

29-29-1515

Polyamides Nylon 66Polyamides Nylon 66

Nylon 66 (from two six-carbon monomers).

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

Hexanedioic acid(Adipic acid)

1,6-Hexanediamine(Hexamethylenediamine)

Nylon 66

29-29-1616

Nylon 66, source of Hexanedioic AcidNylon 66, source of Hexanedioic Acid

• 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

Hexanedioic acid(Adipic acid)

COOHCOOH

29-29-1717

Nylon 66, source of the 1,6 hexanediamineNylon 66, source of the 1,6 hexanediamine

• Hexanedioic acid is the starting material for the synthesis of hexamethylenediamine.

H2NNH2

O-NH4+

4H2 H2NNH2 catalyst

1,6-Hexanediamine(Hexamethylenediamine)Hexanediamide

(Adipamide)

Ammonium hexanedioate(Ammonium adipate)

29-29-1818

Polyamides, Nylon 6Polyamides, Nylon 6

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 hydrolysis2. heat n

Nylon 6

29-29-1919

Polyamides, KevlarPolyamides, Kevlar

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

COHnHOC

nH2N NH2

2nH2 O

29-29-2020

Polyesters, PETPolyesters, PET

Poly(ethylene terephthalate), abbreviated PET or PETE, is fabricated into Dacron fibers, Mylar films, and plastic beverage containers.

heatHO

1,4-Benzenedicarboxylic acid(Terephthalic acid)

1,2-Ethanediol(Ethylene glycol)

+2nH2 O

Poly(ethylene terephthalate)(Dacron, Mylar)

29-29-2121

PET, source of glycol and terepthalic acidPET, source of glycol and terepthalic acid

• Ethylene glycol is obtained by air oxidation of ethylene followed by hydrolysis to the glycol.

• Terephthalic acid is obtained by catalyzed air oxidation of petroleum-derived p-xylene.

Terephthalic acidp-XylenecatalystHOC COHCH3

CH2=CH2O2

CH2-CH2

H+, H2OHOCH2CH2OH

Oxirane(Ethylene oxide)

1,2-Ethanediol(Ethylene glycol)

Ethylenecatalyst

29-29-2222

Polycarbonates, LexanPolycarbonates, Lexan

• To make Lexan, an aqueous solution of the sodium salt of bisphenol A (BPA) is brought into contact with a solution of phosgene in CH2Cl2.

Phosgene

Disodium salt of Bisphenol A

Lexan (a polycarbonate)

29-29-2323

Phase transfer catalysis.Phase transfer catalysis.

The sodium salt of bisphenol A is water soluble while the phosgene is not. Immiscible. No reaction.

Solution: Phase transfer catalysis. NBu4+ and a

negative ion can go back and forth between the two phases.

NBu4+ brings bisphenolate ion into organic phase

Reaction occurs with phosgene producing Cl-

NBu4+ brings chloride ion into water phase.

29-29-2424

Polycarbonates, LexanPolycarbonates, Lexan

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.

29-29-2525

PolyurethanesPolyurethanes

A urethaneurethane, or carbamate, is an ester of carbamic acid, H2NCH2COOH.• They are most commonly prepared by treatment of an

isocyanate with an alcohol.

Polyurethanes consist of flexible polyester or polyether units alternating with rigid urethane units.• The rigid urethane units are derived from a

diisocyanate.

+An isocyanate A carbamate

RNHCOR'RN=C=O R'OH

O Addition to the N=C bond

29-29-2626

PolyurethanesPolyurethanes

• The more flexible units are derived from low MW polyesters or polyethers with -OH groups at the ends of each polymer chain.

CH3N=C=OO=C=N nHO-polymer-OH

CNH NHCO-polymer-OCH3 OO

Low-molecular-weightpolyester or polyether

2,6-Toluenediisocyanate

A polyurethane

29-29-2727

Epoxy ResinsEpoxy Resins

Epoxy resins are materials prepared by a polymerization in which one monomer contains at least two epoxy groups.• Epoxy resins are produced in forms ranging from low-

viscosity liquids to high-melting solids.

29-29-2828

• The most widely used epoxide monomer is the diepoxide prepared by treating one mole of bisphenol A with two moles of epichlorohydrin.

A diepoxide

OCl Na+-O

the disodium salt of bisphenol A

Epichlorohydrin

29-29-2929

• Treatment of the diepoxide with a diamine gives the resin.

H2NNH2

A diamine

An epoxy resin

A diepoxide

Note the regioselectivity

29-29-3030

ThermosetsThermosets

Bakelite was one of the first thermosets.

29-29-3131

Chain-Growth PolymersChain-Growth Polymers

Chain-growth polymerization:Chain-growth polymerization: A polymerization that involves sequential addition reactions, either to unsaturated monomers or to monomers possessing other reactive functional groups.

Reactive intermediates in chain-growth polymerizations include radicals, carbanions, carbocations, and organometallic complexes.

29-29-3232

Chain-Growth PolymersChain-Growth Polymers

We concentrate on chain-growth polymerizations of ethylene and substituted ethylenes.

• On the following two screens are several important polymers derived from ethylene and substituted ethylenes, along with their most important uses.

An alkene

29-29-3333

PolyethylenesPolyethylenes

CH2=CH2

CH2=CHCH3

CH2=CHCl

CH2=CCl2

MonomerFormula

Common Name

Polymer Name(s) andCommon Uses

Ethylene

Propylene

Vinyl chloride

1,1-Dichloro-ethylene

Polyethylene, Polythene;break-resistant containersand packaging materials

Polypropylene, Herculon;textile and carpet fibers

Poly(vinyl chloride), PVC;construction tubing

Poly(1,1-dichloroethylene), Saran; food packaging

29-29-3434

PolyethylenesPolyethylenes

CH2=CHCN

CF2=CF2

CH2=CHC6H5

CH2=CHCOOEt

CH2=CCOOCH3

Acrylonitrile

Tetrafluoro-ethylene

Styrene

Ethyl acrylate

Methylmethacrylate

Polyacrylonitrile, Orlon;acrylics and acrylates

Poly(tetrafluoroethylene), PTFE; nonstick coatings

Polystyrene, Styrofoam;insulating materials

Poly(ethyl acrylate); latex paintsPoly(methyl methacrylate), Plexiglas; glass substitutes

29-29-3535

Radical Chain-GrowthRadical Chain-Growth

Among the initiators used for radical chain-growth polymerization are diacyl peroxides, which decompose on mild heating.

Dibenzoyl peroxide

A phenyl radical

A benzoyloxy radical

29-29-3636

Another common class of initiators are azo compounds, which also decompose on mild heating or with absorption of UV light.

Azoisobutyronitrile (AIBN)

or hN NN

C NN CN+2

Alkyl radicals

29-29-3737

Radical polymerization of a substituted ethylene.• chain initiation

• chain propagation

or h 2In

29-29-3838

• chain termination.

radical coupling

dispropor- tionation

29-29-3939

Radical reactions with double bonds almost always gives the more stable (the more substituted) radical.• Because additions are biased in this fashion,

polymerizations of vinyl monomers tend to yield polymers with head-to-tail linkages.

head-to-tail linkages

R R R R R R R

head-to-tail linkages head-to-head linkage

R R R R R R R

29-29-4040

Chain-transfer reaction: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

butyl branches on the polymer main chain.

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

nCH2=CH2

29-29-4141

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.

29-29-4242

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 4B transition metal halide such as TiCl4, and an alkylaluminum compound.

CH2=CH2

TiCl4/ Al(CH2CH3)2ClMgCl2 n

Ethylene Polyethylene

29-29-4343

Mechanism of Ziegler-Natta polymerization.Step 1: Formation of a titanium-ethyl bond

Step 2: Insertion of ethylene into the Ti-C bond.

Ti Cl Ti+ +

MgCl2/ TiCl4particle

Diethylaluminumchloride

Ti Ti+ CH2=CH2

29-29-4444

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 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!

29-29-4545

Polymer Polymer StereochemistryStereochemistry

There are three alternatives for the relative configurations of stereocenters along the chain of a substituted ethylene polymer.

HR RH HR RH HR

Syndiotactic polymer(alternating configurations)

HR HR HR HR HR

Isotactic polymer (identical configurations)

HR HR HR HR RH

Atactic polymer(random configurations)

29-29-4646

Polymer StereochemistryPolymer Stereochemistry

In general, the more stereoregular the stereocenters are (the more highly isotactic or syndiotactic the polymer is), the more crystalline it is.• Atactic polypropylene, for example, do not pack well

and the polymer is an amorphous glass.• Isotactic polypropylene is a crystalline, fiber-forming

polymer with a high melt transition.

29-29-4747

IonicIonic Chain Growth Chain Growth

Either anionic or cationic polymerizations• Cationic polymerizations are most common with

monomers with electron-donating groups.

• Anionic polymerizations are most common with monomers with electron-withdrawing groups.

Styrene IsobutyleneVinyl ethersVinyl thioethers

StyreneCOOR COOR CN COOR

Alkyl methacrylates

Alkyl acrylates

Acrylonitrile Alkylcyanoacrylates

29-29-4848

Anionic Chain GrowthAnionic Chain Growth

Anionic polymerization can be initiated by addition of a nucleophile, such as methyl lithium, to an alkene.

Li ++ +

29-29-4949

An alternative method for initiation involves a one-electron reduction of the monomer by Li or Na to form a radical anion which is either reduced or dimerized to a dianion.

A radical anion

A dianion

Butadiene

A dimer dianion

radical couplingto form a dimer

Li +Li +

29-29-5050

sodium naphthalide may be used.

The naphthalide radical anion is a powerful reducing agent and, for example, reduces styrene to a radical anion which couples to give a dianion.

Sodium naphthalide(a radical anion)

Na+Na+

Naphthalene

29-29-5151

• The styryl dianion then propagates polymerization at both ends simultaneously.

A styrylradical anion A distyryl dianion

Styrene

Na+Na+

29-29-5252

Propagation of the distyryl dianion.

2. H2O

A distyryl dianion

Polystyrene

29-29-5353

Living polymer:Living polymer: A polymer chain that continues to grow without chain-termination steps until either all of the monomer is consumed or some external agent is added to terminate the chains.• after consumption of the monomer under living

anionic conditions, electrophilic agents such as CO2 or ethylene oxide are added to functionalize the chain ends.

29-29-5454

• Termination by carboxylation.

CO2 H3O+nCOO- Na+

29-29-5555

• Termination by ethylene oxide.

CH2CH2O-Na+

H2OCH2CH2OH

29-29-5656

CationicCationic Chain Growth Chain Growth

The two most common methods for initiating cationic polymerization are:• Addition of H+. Reaction of a strong proton acid with

the monomer.

• Ionization, as in SN1. Abstraction of a halide from the organic initiator by a Lewis acid.

Initiation by a proton acid requires a strong acid with a nonnucleophilic anion in order to avoid completion of the addition to the double bond• Suitable acids include HF/AsF5 and HF/BF3.

29-29-5757

Cationic Chain GrowthCationic Chain Growth

• Initiation by a protic acid.

• Lewis acids used for initiation include BF3, SnCl4, AlCl3, Al(CH3) 2Cl, and ZnCl2.

H+BF4-

+ BF4-R

n BF4-

R R R R R

29-29-5858

• initiation

• propagation

Cl + SnCl4 +

2-Chloro-2-phenylpropane

SnCl5-

2-Methylpropene

29-29-5959

• chain termination

+SnCl5

H+SnCl5-

29-29-6060

Ring-Opening Metathesis PolymerizationRing-Opening Metathesis Polymerization

• During early investigations into the polymerization of cycloalkenes by transition metal catalysts, polymers that contained the same number of double bonds as the monomers used to make them were formed.

• for example:

• this type of polymerization is known as ring-opening ring-opening metathesis polymerization (ROMP)metathesis polymerization (ROMP).

LiAl(C7H15)4

TiCl4,

Norbornene

ROMP polymer

1,2-Addition polymer

29-29-6161

• ROMP polymerizations involve the same metallocyclobutene species as in ring-closing alkene metathesis reactions.

A metalcarbene

M CH2CH2M

continuedpolymerization

redrawn

ROMP polymer from cyclopentene

29-29-6262

• all steps in ROMP are reversible, and the reaction is driven in the forward direction by the release of ring strain that accompanies the opening of the ring.

Ring strain[kJ (kcal)/mol]

125 (29.8) 113 (27) 24.7 (5.9) 5.9 (1.4)

29-29-6363

• ROMP is unique is that all unsaturation present in the monomer is conserved in the polymer.

• polyacetylene is prepared by the ROMP technique.

Cyclooctatetraene

metal-nucleophiliccarbene catalyst

nPolyacetylene

29-29-6464

• poly(phenylene vinylene) is prepared as follows.

OAcROMP

AcO OAc

-2nCH3COOH

nPoly(phenylene vinylene)

29-1 organicpolymerchemistry. 29-2 some definitions polymer:poly+meros polymer: from the greek,...

Documents

chettinadtech.ac.inchettinadtech.ac.in/storage/14-08-25/14-08-25-11-29-08-… ·...

single-molecule kinetics of nanoparticle...

1 levels of organization subatomic particles – electrons,...

molecule mag

schematic layout of glucan molecule three-dimensional shape...

teoria combinatoria (pdf) - acm.ciens.ucv.ve€¦ · 6.4...

organic molecule

drupal meros 1o

29 august 2012 lhp 20: water acrosticrhp 21: water molecule

single-molecule atomic force microscopy reveals clustering...

methane molecule

lecture 29 introduction to fluorescence...

genetics. if molecule y represents a dna molecule, then...

small molecule gated split-tyrosine phosphatases and … ·...

biophysics 05 molecule dbiophysics-05-molecule dancesances

xtizontas kalyterh sxesh - 2o meros

small molecule large molecule interactions

macromolecules of life: a monomer (from greek mono "one"...

inorganic compounds–water molecule structure inorganic...

molecule - ufl.co.nz · molecule molecule cod. 5601 low...