Polymer Lectures 08 Given

8/3/2019 Polymer Lectures 08 Given

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SYNTHETIC ORGANICPOLYMERS

Convenor: Dr. Fawaz Aldabbagh


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Polymers are large molecules made up of repeating units called Monomers

The synthetic process is Polymerization.

E.g.

CH2

CH2 CH2 CH2

OCH

2CH

2O

Monomer

Polymerization

Polymer

n

Monomer

Polymerization

Polymern

Note define repeating unit in terms of monomer structure

Degree of Polymerization is the number of monomer units in a Polymer

However, for synthetic polymers it is more accurate to state average degree ofpolymerization ( )DP


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A polymer prepared from a single monomer is a homopolymer

If two or more monomers are employed, the product is a copolymer

Linear polymer has no branching

Graft copolymer is an example of a branched network


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Two main classifications of Polymerization

Addition reaction orChain growthMolecular weight increases by successively adding monomers to a reactive polymer

chain end resulting in high molecular weights at low conversions.

STEP reaction or growthPolymers are formed by linking monomer molecules to form dimers, trimers and

higher species in a step-wise fashion. The most abundant species react, and thus

high molecular weight formed only beyond 99% conversion.

Polymerization Conversion (p)

=

M0 - Mt

M0P

M0 = initial number of monomer molecules

Mt= Number of monomer molecules at time t


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Ionic Chain (addition)-Growth Polymerization

The choice of ionic procedure depends greatly on the electronic

nature of the monomers to be polymerized

CO2R CO2R CN CO2R

CN

OR SR

N

Vinyl monomers with electron-donating groups

Vinyl monomers with electron-withdrawing groups

Monomers and reagents should be scrupulously purified; water and oxygen

should be removed.

Polymerizations carried out at very low temperatures

Anionic Polymerization

Cationic Polymerization


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Anionic Polymerizations

Initiators include alkyl lithiums and sodium amide


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Cationic Polymerization -- the formed carbocation must be quite stable

OROR

H+

+

H+

+

Stable tertiary carbocation

stable oxonium ion

BF3/H2O

n

E.g. proton initiates polymerization of isobutane (2-methylpropene)

Adhesive, sealant, insulating oil, lubricating oil


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CNCNCN

OHH

CNCNCN

H

acid

nn

+ OH

_

_

OMe OMe OMe

H H

OHH

OMe OMe OMen

+

base

n

+ H3O+

Reactions of water with reactive carbanions and carbocations

Note viable substrates for anionic polymerizations do not have E-protons


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Chain Reaction: Free Radical Polymerization

RO OR

Ph

Ph

RO

2RO

RO +

Ph

RO

Ph

RO

n

Ph

Ph

n

Initiation

Propagation

Random Termination

Dead chainsDead chains


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Conventional Radical Polymerization

Advantages

1/wide range of vinyl monomers polymerizable2/can be carried out in bulk, water, organic solvents and other solvents

3/no rigorous purification or drying of reagents required

Conditions: Usually heat required for initiation

Initiator decomposition time should be considered

- Amount of initiator, reaction temperature and initiator half-life (slow decomposition)

Initiation Rate = Termination Rate - steady state kinetics apply

Overall,

[radical concentration] = low

Since termination (disproportionation and coupling mechanism) is random, a broad

MWD results. This polymer is dead (cannot initiate new monomer additions).


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Examples of Polymers Prepared by Radical Polymerization

H

H

H

H

H

H

CN

H

H

H

O

MeO

H

H

H

O

Me O

CH2CH

CH2CH

CN

CH2CH

O

OMe

C

CH2CH

O

C O

Me

n

n

n

n

Poly(styrene)

Poly(acrylonitrile)

Poly(vinylacetate)

Poly(methylacrylate)

Monomer Polymer

n

n

n

n


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Advantages of Radical Polymerization

1. Wide variety of vinyl monomers can be polymerized (electron rich and

deficient DBs)

2. Can be carried out in bulk and in a wide variety of solvents, which include

water and organic solvents

3. No rigorous purification of reagents or drying of solvents required

4. Rapid formation of high molecular weight polymer after small conversions of

monomer to polymer ( chain (addition) polymerization)

5. Living/controlled polymerizations enable easy formation of block copolymers

and sophisticated architectures

75% of commercial polymers are made by radical polymerizations

Some monomers can only be polymerized by radical means, e.g. acrylic acid (AA)

C C

C

HH

H

O

OH

H

C

H

C

H

COOH

n

AIBN

Ion-exchange resins, smart polymers


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Polar Effects are important in radical polymerizations, and can give

alternating copolymers

Ph

R

Ph

R

CN

CN

H

H Ph

Ph

R

CN Ph CN

n

Radical Polarity


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Chain Reaction initiation, propagation, termination

DP

50 100

conversion

DP

50 100

conversion

Chain polymerization with termination

Chain polymerization without termination

Living

e.g. conventional radical polymerization

e.g. nitroxide-mediated radical polymerization(NMP)

DP =[monomer]

[Initiator]

Life time of polymer radical chain is about 1 second

Initiator added so to slowly decompose throughout

polymerization time

Typically, rate of initiation = rate of termination

Therefore, [propagating radical] remains constantSteadyState

Initiator decomposes quickly, and polymer chains have long life times


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P T P + T

Nitroxide-mediated Controlled/living Radical Polymerization (NMP)

propagation

T = Nitroxide

P =Propagating radical

Features:

1. Molecular weight increases linearly with conversion

2. Narrow molecular weight distributions obtained

3. Polymer chains contain living ends enabling chain extension or block

copolymer synthesis

A TAAAAn

A BBBBAAAA

n

n

B T

AAAAAn

B n

+ T propagation

Block copolymer synthesis

T is sterically congested


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TT

T

TT

T

Conventional Radical Polymerization

Controlled Radical Polymerization

Broad MWD

Dead Polymer

Narrow MWD

Living Polymer

Life time of radicals extended from 1 second to hours, as the radicals

do not get involved in irreversible bimolecular termination reactions,

since radicals are trapped by nitroxide reversibly

Initiator must decompose quickly to insure narrow MWD


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Example ofBlock Copolymer Formation

Ph

Ph

Ph

N

O

P

O

OEt

OEt

Ph

Ph

O

N P

O

OEt

OEt

O

OMe

Ph

Ph

O

O OMe

N

PO

O

O

AIBN, heat

SG1

n-1

n

+

SG1

n-1

m

n-1 m

D : n = 60: m =20

propagation

n = 60

m =20

heat

Ph

Ph O OMe

n-1 m

D : n = 60: m =20

Please correct block copolymer structure in questions

Reversible trapping added to

propagation to prevent

irreversible termination

First living poly(styrene) block

heated in the presence of methylacrylate to give diblock D


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C C

H

H C

Me

O

MeO

CH2

C

O

OMe

C

Me

n

n

Poly(methyl methacrylate)

perspex

Nitroxides cannot control MMA Polymerizations

N

O

P

O

OEt

OEtC C

CH3

CO2Me

H

H

H

H

C C

CH2

CO2Me

N

OH

P

O

OEt

OEt

+

PMMASG1

PMMA=

+

SG1-H

disproportionation

MMA

AIBN

McHale, Aldabbagh, Zetterlund, J. Polym. Sci. Part A: Polym. Chem. 2007, 45, 2194-2203


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Alternating, Block and Graft Copolymers are made by radical copolymerization

macromonomer

excess small

monomer

Graft Copolymer

AIBN, heat

Graft Copolymer Formation


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Recent Example of a Graft Copolymer Synthesis

+ Copolymerization

macromonomer monomerGraft copolymer

Poly(AA) NIPAM

C

H

CH2

C

H

CH2

CH2n

Br

CO

OH

CO

OH

C

C

H

H

C

O

OCH2CH

3

+

CH2

CH

C O

NCH

CH3

CH3

H

N-Isopropylacrylamide

NIPAM monomer (excess)

McHale, Aldabbagh, Carroll, Yamada, J. Polym. Sci. Part A: Polym. Chem. 2007, 45, 4394-4400

Poly(acrylic acid) macromonomer

Insoluble in water above the lower critical solution temperature (LCST)


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0.0

0.1

0.2

0.3

0.4

0.5

0.6

2 3 4 5 6 7 8

logM

W(

log

M)

Copolymerization of Poly(AA) Macromonomer with NIPAM in ethanol at 60 C

macromonomer4%

19%

63%

40%

Shift to higher MW


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Insoluble in water Soluble in NaOH (aq)Graft copolymerin NaOH solution(40C)

Graft copolymer

in NaOH (50C)

Poly(NIPAM)in water(40C)

+ Copolymerization

macromonomer MonomerGraft copolymer

Poly(AA) NIPAM

Dual-Responsive Smart Graft Copolymer

McHale, Aldabbagh, Carroll, Yamada, J. Polym. Sci. Part A: Polym. Chem. 2007, 45, 4394-4400Gibbons, Carroll, Aldabbagh, Yamada, J. Polym. Sci. Part A: Polym. Chem. 2006, 44, 6410-6418


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Ziegler-Natta Chain (Addition) Polymerization

C C

H

H H

H

n

TiCl4/AlEt3

1-4 atm, rt

Milder conditions than radical polymerization

HDPE (high density poly(ethylene) is 3-10 times stronger than LDPE

Less cross-linking, as terminal DBs less reactive than substituted DBs of radical

polymerization

Cl3Ti

H H

Ti

Cl

Cl

ClH+

Termination reaction

Few monomers polymerized by Z/N


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Ziegler-Natta Addition Polymerization

Isotactic polymerization

R

Cl

R

Cl3Ti R AlR

2Cl

Cl3Ti

R

Cl3Ti R

R

Cl3Ti

RCl

3Ti

Cl3Ti

R

Cl3Ti

R

Cl3Ti

R

TiCl4 / AlR3

1-4 atm, rtn

TiCl4 + AlR3 Cl3Ti AlR2

+

n

Wcomplex

Tcomplex


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Stereochemistry and Polymers

Many useful pol ymers, such as pol y(styrene),

poly(acrylonitrile) and poly(vinyl chloride) are atacticas

normally prepared. Customized catalysts that effect

stereoregular polymerization of poly(propylene) andsome other monomers have been developed, and the

improved properties associated with the increased

crystallinity of these products has made this an

i m p o r t a n t f i e l d o f i n v e s t i g a t i o n .

The properties of a given polymer will vary considerably with its tacticity.Atacticpoly(propylene)

is useless as a solid construction material, and is employed mainly as a component of adhesivesor as a soft matrix for composite materials. In contrast, isotacticpolypropylene is a high-melting

solid (ca. 170 C) which can be molded or machined into structural components.

Because poly(propylene) rope is so light, it is the only rope that floats. For

this reason, it is very popular among ropes for pool makers and water

sports. Also when wet it is flexible and does not shrink.

Amorphous polymer melts to

a hard rubbery, glassy state


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Step-growth Polymerization

Step-polymers are made by allowing difunctional monomers with

complementary functional groups to react with one another

Condensation between two molecules

C C

O O

OCH2CH2

O

n

O O

OMeMeO

OH

OH

+

Poly(ethylene terephthalate)terephthalic acid ethylene glycol

PETThis is an example of a poly(ester)

The reaction is a transesterification Recyclable plasticbottles and textile

fabrics

Using a condensation reaction


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Self-Condensation or Ring-Opening Polymerization

First patented by Dupont

Nylon 6 is made by heating caprolactam to about 250 C with about 5-10% water

These are poly(amides) bristles of toothbrishes,

s t o c k i n g s , r o p e , t i r e s , c a r p e t f i b r e

First patented by BASF

260-280 C

250 psi

- H2O

MW = 10,000, m.pt. 250 C, fibres stretched (to increase strength) to 4 times their length

High temp. to drive off water

Also opened by

cations & anions

Molten nylon spun

into fibres


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1. Polymers retain their functionality as end groups at the

end of the polymerization

2. Only a single reaction is responsible for polymer formation

3. Molecular weight increases slowly even at high

conversion. This is given by the Carothers equation,

where conversion is (p)

DP =1

1 -p

At 98% conversion, the degree of polymerization is only 50%

4. Exact stoichiometric balance and very pure monomers

are required to achieve high molecular weights

Larger chains react only at veryhigh conversion

5. Equilibrium reactions necessary to remove by-product


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Step-addition no by-products

CH2

O

O

O

O

CH2

6

+6

n

CH2N2 [ CH2 ] + N2nBF3

Chain-growth condensation

NN CC OO

OH

OH

NN

H

O

H

O

OO

+

nPoly(urethane)

Insulation foam, HP adhesives, sealants,

carpet underlay

180 C

Bayer-patented

Lower Temp. than condensation reactions

Impurity found in diazomethane

bisdienebenzoquinone

Cyclic diene held cis is very reactivee.g. dicyclopentadiene

rt


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Time for litter to biodegradeProduct Time to biodegrade

Paper 2-5 months

Wool socks 1 to 5 years

Plastic coated paper milk cartons 5 years

Plastic bags 10 to 20 years

Nylon fabric 30 to 40 years

Aluminum cans 80 to 100 years

Plastic 6-pack holder rings 450 years

Glass bottles 1 million years

Plastic bottles Forever


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Plastic resin identification codes (1)

Codes Descriptions Recycled products

Polyethylene terephthalate (PET, PETE) is clear, tough, and

has good gas and moisture barrier properties. Commonlyused in soft drink bottles and many injection molded. Other

applications include strapping and both food and non-food

containers. Cleaned recycled PET flakes and pellets are in

great demand for spinning fiber for carpet yarns, producing

fiberfill and geo-textiles.

Fiber, tote bags, clothing,

film and sheet, food andbeverage containers, carpet,

strapping, fleece wear,

luggage and bottles.

High Density Polyethylene (HDPE) is used to make bottles for

milk, juice, water and laundry products. Unpigmented bottlesare translucent, have good barrier properties and stiffness,

and are well suited to packaging products with a short shelf

life such as milk. Because HDPE has good chemical

resistance, it is used for packaging many household and

industrial chemicals.

Bottles; pipe, buckets,

crates, flower pots, gardenedging, film and sheet,

recycling bins, benches,

dog houses, plastic lumber,

floor tiles, picnic tables,

fencing.

Polyvinyl Chloride or PVC has excellent chemical resistance,

good weatherability, flow characteristics and stable electrical

properties. The vinyl products can be broadly divided into

rigid and flexible materials. Bottles and packaging sheet are

major rigid markets, but it is also widely used as pipes and

fittings, siding, carpet backing and windows. Flexible vinyl is

used in wire and cable insulation, film and sheet, floor

coverings synthetic leather products, coatings, blood bags,

medical tubing and many others.

Packaging, binders, decking,

paneling, gutters, mud flaps,

film and sheet, floor tiles

and resilient flooring, cables,

mats, cassette trays,

electrical traffic cones,

boxes, garden hose, mobile.


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Plastic resin identification codes (2)

Codes Descriptions Recycled products

Low Density Polyethylene (LDPE) used predominately in filmapplications due to its toughness, flexibility and relative

transparency, making it popular for use in applications where

heat sealing is necessary. LDPE is also used to manufacture

some flexible lids and bottles and it is used in wire and cable

applications.

Shipping envelopes,garbage can liners, film

and sheet, furniture,

compost bins, paneling,

trash cans, landscape

timber, lumber

Polypropylene (PP) has good chemical resistance, is strong, and

has a high melting point making it good for hot-fill liquids. PP is

found in flexible and rigid packaging to fibers and large molded

parts for automotive and consumer products.

Automobile battery cases,

signal lights, battery

cables, brooms, brushes,

oil bins, funnels, bicycle

racks, trays pallets,

sheeting.

Polystyrene (PS) is a versatile plastic that can be rigid or foamed.

General purpose polystyrene is clear, hard and brittle. It has a

relatively low melting point. Typical applications include

protective packaging, containers, lids, cups, bottles and trays.

Light switch plates, vents,

thermal insulation, desk

trays, rulers, license plate

frames, foam packing,

foam plates, utensils

Other. Use of this code indicates that the package in question is

made with a resin other than the six listed above, or is made of

more than one resin listed above, and used in a multi-layer

combination.

Bottles, plastic lumber


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Recycling of plastic containers and wrapping

Chemical Recycling by Eastman Kodak

C C

O O

OCH2

CH2

O

C C

O O

OMeMeO

OH

OHn

+

CH3OH

These monomers are purified by distillation or recrystallization and used

as feedstocks for further PET film manufacture.

H+

methanolysis

PET


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Representative Exam Questions

1. Using one appropriate monomer for each polymerization classification, discuss the mechanism and

kinetics;

(a) Step-growth, b) conventional (non-living) chain (addition), c) living chain (addition) polymerizations.

In your answer give details of reaction conditions and reagents required.

2. (a) Discuss the stability of nitroxide radicals, and there use in living radical polymerizations.

(b) Why is it not possible to control the radical polymerization of methyl methacrylate with nitroxides?

3. How would you prepare the following polymers? Give reaction conditions, reagents and detailed

mechanisms for each polymerization. Name polymers A-D.

Ph

PhO OMe

n n n

A

BC

n-1 m

D : n = 60: m =20

4. Draw structures of the polymers obtained from the following reactions;

CO2Me

MeO2C OH OH

O

+H+

KOH

5. Give one example of an isotatic polymer and block and alternating copolymer. Provide reactions (with

conditions) and mechanisms for their synthesis.

Documents

Polymer Lectures 08 Given