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Organic Lecture Series

OrganicOrganic PolymerPolymer ChemistryChemistry

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Organic Lecture Series FocusFocus onon thesethese areas:areas:

1) Know Definitions 2) Know the Organic Reactions 3) Be able to recognize the general class of ( polycarbonates, etc.)

2 Organic Lecture Series Organic • Polymer: from the Greek, poly + meros, many parts – any long-chain synthesized by bonding together single parts called • :Monomer from the Greek, mono + meros, single part – the simplest nonredundant unit from which a polymer is synthesized • : a polymer that can be molded when hot and retains its shape when cooled

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Organic Lecture Series Organic Polymer Chemistry

• : 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, (sometime called “”) hardens irreversibly and cannot be remelted

4 Organic Lecture Series PolymerPolymer ““Architecture”Architecture”

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Organic Lecture Series PolymerPolymer ““Architecture”Architecture”

6 Organic Lecture Series

vulcanized rubber

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Organic Lecture Series NotationNotation && NomenclatureNomenclature Show the structure by placing parenthesis around the repeat unit –n = average degree of

synthesized n synthesized from from n Cl Cl Styrene Poly(vinyl chloride) Vinyl (PVC) chloride

8 Organic Lecture Series NotationNotation && NomenclatureNomenclature

To name a polymer, prefix poly to the name of the monomer from which the 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)

synthesized n synthesized from from n Cl Cl Polystyrene Styrene Poly(vinyl chloride) Vinyl (PVC) chloride

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Organic Lecture Series MorphologyMorphology – Example: poly(ethylene terephthalate), abbreviated PET or PETE, can be made with % crystalline domains ranging from 0% to 55%

O O

O O n

Poly(ethylene terephthalate)

10 Terephthalic Organic Lecture Series

Manufacture:

HOAc Co or Mn

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Organic Lecture Series MorphologyMorphology • Completely amorphous PET is formed by cooling the melt quickly –PET with a low degree of crystallinity is used for plastic beverage bottles

12 Organic Lecture Series MorphologyMorphology • 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 and tire cords

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StepStep-Growth-Growth PolymersPolymers Organic Lecture Series Step-growth or condensation polymerization: polymerization in which chain growth occurs in stepwise manner between difunctional monomers (there is often a side product)

There are five types of step-growth polymers: 1. polyamides 2. 3. polycarbonates 4. 5. epoxy 14 Organic Lecture Series PolyamidesPolyamides • 66 (from two six-carbon monomers)

O HO + H 2N heat OH NH2 O Hexanedioic acid 1,6-Hexanediamine (Adipic acid) (Hexamethylenediamine)

OH N N n OH Nylon 66 – during fabrication, nylon fibers are cold-drawn to about 4 times their original length, which increases crystallinity, tensile strength, and stiffness 15

Organic Lecture Series PolyamidesPolyamides – the raw material base for the production of nylon 66 is benzene, which is derived from cracking and refining of petroleum

3H 2 O 2 catalyst catalyst

Benzene Cyclohexane

OH O HNO3 COOH + COOH

Cyclohexanol Cyclohexanone Hexanedioic acid (Adipic acid) 16 Organic Lecture Series PolyamidesPolyamides – adipic acid is in turn the starting material for the synthesis of hexamethylenediamine

O + - NH4 O - + heat O NH4 O Ammonium hexanedioate (Ammonium adipate)

O H N 4H 2 2 H N NH2 2 catalyst NH2 O 1,6-Hexanediamine Hexanediamide (Hexamethylenediamine) (Adipamide) 17

Organic Lecture Series PolyamidesPolyamides • 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 O H O NH 1. partial hydrolysis n N 2. heat n Caprolactam Nylon 6

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

18 Organic Lecture Series Manufacture of Caprolactam

OH O O N

NH NH2 OH H 2 SO4

The Beckman Rearrangement

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Organic Lecture Series PolyamidesPolyamides • is a polyaromatic amide ()

O O nHOC COH + nH 2 NNH2 1,4-Benzenedicarboxylic 1,4-Benzenediamine acid (p-Phenylenediamine) (Terephthalic acid) O O C CNH NH + 2nH2 O n Kevlar

– 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 20 PolyestersPolyesters Organic Lecture Series • Poly(ethylene terephthalate), abbreviated PET or PETE, is fabricated into Dacron fibers, Mylar films, and plastic beverage containers O O OH + HO heat HO OH 1,4-Benzenedicarboxylic acid1,2-Ethanediol (Terephthalic acid) (Ethylene glycol)

OO O +2nH2 O O n Poly(ethylene terephthalate) (Dacron, Mylar) 21

Polyesters Organic Lecture Series – ethylene glycol is obtained by air oxidation of ethylene followed by hydrolysis to the glycol

O H+ ,HO O2 2 HOCH CH OH CH =CH CH -CH 2 2 2 2 catalyst 2 2 Ethylene Oxirane 1,2-Ethanediol (Ethylene oxide) (Ethylene glycol) Ag●Alumina

– terephthalic acid is obtained by catalyzed air oxidation of petroleum-derived p-xylene

OO O2 H C CH 3 3 catalyst HOC COH p-Xylene Terephthalic acid

22 PolycarbonatesPolycarbonates Organic Lecture Series

– to make Lexan, an aqueous of the sodium salt of bisphenol A is brought into contact with a solution of phosgene in CH2Cl2 in the presence of a phase-transfer catalyst

O CH3 + Na - O O- Na + + Cl Cl Phosgene CH3 Disodium salt of Bisphenol A O CH3 O O + 2NaCl n CH3 Lexan (a polycarbonate) 23

PolycarbonatesPolycarbonates Organic Lecture Series • 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

24 Polyurethanes Organic Lecture Series •A urethane, or carbamate, is an

ester of carbamic acid, H2NCOOH – they are most commonly prepared by treatment of an isocyanate with an alcohol

O RN=C=O+ R'OH RNHCOR' An isocyanate A carbamate

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Organic Lecture Series MechanismMechanism ofof UrethaneUrethane FormationsFormations

26 Polyurethanes Organic Lecture Series

O RN=C=O+ R'OH RNHCOR' An isocyanate A carbamate

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

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Polyurethanes Organic Lecture Series

– the more flexible blocks are derived from low MW polyesters or polyethers with -OH groups at the ends of each polymer chain

CH 3 O=C=NN=C=O + nHO-polymer-OH Low-molecular-weight polyester or polyether 2,6-Toluene diisocyanate O CH 3 O CNH NHCO-polymer- O n

Apolyurethane 28 Organic Lecture Series EpoxyEpoxy ResinsResins •• EpoxyEpoxy resinsresins 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- liquids to high-melting solids

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Organic Lecture Series EpoxyEpoxy ResinsResins

– the most widely used epoxide monomer is the diepoxide prepared by treating 1 mole of bisphenol A with 2 moles of epichlorohydrin CH O 3 +- - + Cl + Na O O Na Epichlorohydrin CH3 the disodium salt of bisphenol A

O CH3 O O O

CH3 A diepoxide 30 Organic Lecture Series EpoxyEpoxy ResinsResins – treatment of the diepoxide with a diamine gives the

O CH3 O O O

CH3 A diepoxide

NH 2 H2 N A diamine

CH OH 3 OH H N O O N H n CH3 An epoxy resin 31

Organic Lecture Series ““Dissolving”Dissolving” Stitches LactomerLactomer®®

(α-hydroxyacetic acid)

(α-hydroxypropionic acid) 32 Organic Lecture Series ChainChain-Growth-Growth PolymersPolymers • 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 include radicals, carbanions, carbocations, and organometallic complexes

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Organic Lecture Series Chain-Growth Polymers • The focus in this section is chain-growth polymerizations of ethylene and substituted ethylenes

R R

An n

– on the following two slides are several important polymers derived from ethylene and substituted ethylenes, along with their most important uses

34 Radical Chain-Growth Organic Lecture Series • Among the initiators used for radical chain- growth polymerization are diacyl peroxides, which decompose on mild heating

O O O O Δ Dibenzoyl peroxide O

O 2 + 2 2CO2

A benzoyloxy A phenyl radical radical

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Organic Lecture Series Radical Chain-Growth • Another common class of initiators are azo compounds, which also decompose on mild heating or with absorption of UV light

Δ or hν 2 + N: N: NN N C CN N C Azoisobutyronitrile (AIBN) Alk yl radicals

36 Radical Chain-Growth Organic Lecture Series of a substituted ethylene chain initiation (free radical addition to an alkene)

Δ or h υ In-In 2In

In + In R R

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Radical Chain-Growth Organic Lecture Series • Radical polymerization of a substituted ethylene – chain initiation Δ or h υ In-In 2In

In + In R R – chain propagation

In In + R R R R

In + In n n R R R R R etc. 38 Organic Lecture Series Radical Chain-Growth – chain termination

radical coupling In In nn R R RR In 2 n R R

dispropor- H tionation In In n + n R R R R

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Organic Lecture Series Disproportionation-radical chain reactions are terminated by intermolecular H transfer H H H In In H R R R R

In In

R R R R

40 Radical Chain-Growth Organic Lecture Series

• 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

RRRR RRR

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

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Radical Chain-Growth Organic Lecture Series • 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:

H H

A six-membered transition state leading to nCH2 =CH2 1,5-hydrogen abstraction

n

42 Organic Lecture Series Radical Chain-Growth • The first commercial 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 43

Organic Lecture Series Ziegler-Natta Polymers • Ziegler-Natta chain-growth polymerization is an alternative method that does not involve free radicals & less branching – Ziegler-Natta catalysts are heterogeneous

materials composed of a MgCl2 support, a Group 4B transition halide such as

TiCl4, and an alkylaluminum compound

TiCl4 /Al(CH2 CH3 )2 Cl CH 2 =CH2 Mg Cl2 n Ethylene Polyethylene

44 Ziegler-Natta Polymers Organic Lecture Series

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

Mg Cl2 /TiCl4 particle Cl Ti Cl + Cl Al Ti + Cl Al

Diethylaluminum chloride Step 2: insertion of ethylene into the Ti-C bond

Ti + CH2 =CH2 Ti

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Ziegler-Natta Polymers Organic Lecture Series • 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

46 Ziegler-Natta Polymers Organic Lecture Series • Polyethylene from Ziegler-Natta systems is termed high-density polyethylene (HDPE) – approx. 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.

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Organic Lecture Series Polymer • There are three alternatives for the relative configurations of stereocenters along the chain of a substituted ethylene polymer

R H RHH RHRHR

Isotactic polymer (identical configurations)

RRH HHRRHHR RHH RHRHRRH

Syndiotactic polymer Atactic polymer (alternating configurations) (random configurations)

48 Polymer Stereochemistry Organic Lecture Series In general, the more stereoregular the stereocenters are (the more highly isotactic or syndiotactic the polymer is), the more crystalline it is – the chains of atactic polyethylene, for example, do not pack well and the polymer is an amorphous glass – isotactic polyethylene, on the other hand, is a crystalline, -forming polymer with a high melt transition

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IonicIonic ChainChain GrowthGrowth Organic Lecture Series May be either anionic or cationic polymerizations cationic polymerizations are most common with monomers with electron-donating groups δ+ δ+ δ+ OR SR

Styrene Isobutylene Vinyl ethers Vinyl thioethers

50 IonicIonic ChainChain GrowthGrowth Organic Lecture Series anionic polymerizations and most common with monomers with electron-withdrawing groups

- - CN δ- δ δ δ- COOR COOR CN COOR Styrene Alkyl Alkyl Acrylonitrile Alkyl methacrylates acrylates cyanoacrylates

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AnionicAnionic ChainChain GrowthGrowth Organic Lecture Series

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

R' R' R' R RLi+ + Li +

R' R' R etc.

52 Organic Lecture Series AnionicAnionic ChainChain GrowthGrowth • 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

+ Li + Li Butadiene A radical anion

radical coupling Li to form a dimer

+ Li + Li + Li + Li A dimer dianion A dianion 53

Organic Lecture Series AnionicAnionic ChainChain GrowthGrowth • To improve the efficiency of anionic polymerizations, soluble reducing agents such as sodium naphthalide are used

THF + Na Na+ : Naphthalene Sodium naphthalide (a radical anion) – the naphthalide radical anion is a powerful reducing agent and, for example, reduces styrene to a radical anion which couples to give a dianion 54 Organic Lecture Series AnionicAnionic ChainChain GrowthGrowth

Na +

Styrene Na + Na + Na +

A styryl radical anion A distyryl dianion

– the styryl dianion then propagates polymerization at both ends simultaneously

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Organic Lecture Series AnionicAnionic ChainChain GrowthGrowth • propagation of the distyryl dianion

1. 2n Na+ Na+ 2. H2 O

A distyryl dianion

n n

Polystyrene

56 Organic Lecture Series AnionicAnionic ChainChain GrowthGrowth “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

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Organic Lecture Series AnionicAnionic ChainChain GrowthGrowth

–termination by carboxylation

+ : n H O n CO2 - + 3 Na+ COO Na

n COOH

58 Organic Lecture Series AnionicAnionic ChainChain GrowthGrowth –termination by ethylene oxide

n Na+ O

nnH O - + 2 CH2 CH2O Na CH2 CH2OH

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CationicCationic ChainChain GrowthGrowth Organic Lecture Series • The two most common methods for initiating cationic polymerization are – reaction of a strong proton acid with the monomer – 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 addition to the double bond

– suitable include HF/AsF5 and HF/BF3

60 CationicCationic ChainChain GrowthGrowth Organic Lecture Series

– initiation by a protic acid

R

+ - R R H BF4 - R H3 C +BF4 R R H C 3 + R - n BF4 RRRR R

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

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CationicCationic ChainChain GrowthGrowth Organic Lecture Series – initiation

- Cl + SnCl4 + SnCl5

2-Chloro-2-phenylpropane – propagation

+ + + 2-Methylpropene

n

+ n +

62 CationicCationic ChainChain GrowthGrowth Organic Lecture Series

–chain termination

H2 O n + - SnCl5

+ - + H SnCl5 n OH

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