classification by mechanism step – growth chain – growth classification by type

Hanyang Univ.Hanyang Univ.

Spring 2007

Classification by Mechanism

Step – Growth

Chain – Growth

Classification by Type

Condensation

Addition

Classification by Bond

Radical

Ion

Chap 8. Polycondensation Reactions

For further details,

Click next homepage.

http://www.pslc.ws/mactest/synth.htm

Surfing to the internet


Spring 2007

Step Growth Polymerization

•The growing chains react with each other.

•Polymers frwo to high Mw at a slow rate.

•High Mw is formed at the end of polymerization.

•Long reaction time is needed to obtain high Mw and high conversion

Chain Growth Polymerization

•Monomer molecules add on to a growing polymer chain one at a time.

•Polymers grow to high Mw at a very fast rate

•High Mw is formed at the early stage.

•Monomer adds on the growing polymer chain via reactive active center.

What are differences between step and chain growth polymerizatoin?


Spring 2007

Addition versus Condensation polymerisation

• Condensation polymers (C): fewer atoms in the backbone because of formation of by-products

• Addition polymers (A): the repeating unit contains the same atoms as the monomer

OH OH

O O

2NH2 NH2

6 * N N *

O O

H Hn

4 6+

**

OO

n

**

n

OO


Spring 2007Characteristics of Step-Growth

Step-growth polymerization principle was used by Carothers in 1929.

HO C

O

CH2CH3OH CH2CH3 CH3 CH2 C

O

O CH2CH3

Synthesis of Ester

Carothers thought about following reaction.

OH C

O

R C

O

OH R' OHOHMany scientists were sure that one would get a ring-like moleculeO

R'O

RO O

But, if more acid and alcohol were used, ring would not form because of unstability of ring-shaped molecules more than six atom.

It seemed to him more likely that one would get long chainlike macromolecules like this


Spring 2007

JACS (Journal of American Chemical Society, 51, P. 2548 (1929))

“Polyintermolecular condensation requires as starting materials

compounds in which at least two functional groups are present

in the same molecule”

Characteristics of Step-Growth

OH C

O

R C

O

OH R' OHOH


Spring 2007

Extended by Flory

The reactivity of functional group is not correlated with complexity and size of molecule with

functional group.

HO R OH + HOOC R' COOH (complexity)

HO R OH (size)

HO R OH

This concept is useful to polycondensation type polymerization.

ex) OCNRNCO + H2NR`NH2 polyurea

Equal Functional Group Reactivity Concept


Spring 2007

This concept also can be applied to Chain-growth polymerization.

Olefins

Vinyl monomers

Unsaturated monomers

So, double bond in vinyl monomer is considered as bifunctional.


C C

H

H

H

H

C C OR

H

H

H

H

OR C C OR

H

H

H

H

CCC

H

H

H

H

H

H

C C

H

H

H

H


Spring 2007

I. Thermodynamic Approach

“In order to for a polymerization to be thermodynamically feasible, the

Gibbs-Free Energy change must be negative, that is, ΔGp < 0.”

G = HTS

GP = HPTSP : this equation is the basic of understanding about polymerization,

depolymerzation equilibrium



Spring 2007

GP = Gpolymer Gmonomer

= (HP – Hm) – T(SP – Sm)

= HP – TSP

Where HP : enthalpy change per monomer unit

SP : entropy change per monomer unit

GP < 0 Polymerization is spontaneous

GP > 0 Polymerization is not possible

GP = 0 monomer polymer

at this temperature is ceiling temperature.

(for both step and chain growth)



Spring 2007

II.Kinetic Approach

“A negative GP does not necessarily mean that polymerization occurs under

a particular set of reaction conditions and reaction sites”

e.g) should have

functional group

proper initiator

temperature etc.



Spring 2007

Stage 1

Consumptionof monomer

n n

Stage 2

Combinationof small fragments

Stage 3

Reaction of oligomers to give high molecular weight polymer



Spring 2007

1. Polyesterification by esterinterchange

2. Polyesterification and polyamidation by Schotten-Baumann Reaction

O

C Cl+

NH2

OH

O

x

OO

R" (OCR' C O R ) OH + (2 x 1)R" OH

O

x HO R OH + xR"OCR' C O R"



Spring 2007

3. Amidation by thermal dehydration of ammonium salt

4. Reaction of OCNRNCO + HOR’OH polyurethane

H2NR’NH2 polyurea

n46H NH (CH2) NH CO (CH2) CO OH + (2n 1) H2O

++

6 H3N(CH2) NH3

4OOC(CH2) COO

n

46n H2N(CH2) NH2 + n HOOC(CH2) COOH



Spring 2007

Well-studied, well characterized rexns

Well-understood rexns at least on an empirical basis.

X-linked, inefficient rexn.

OHOH

CH2CH2

CH2 OO CH2

polyfunctional

high MW, linear?CH2O+

OH


For further details,


http://www.chemheritage.org/EducationalServices/nylon/other/step/step.html



Spring 2007

W. Carothers

In step-growth polymerization, Carother's equation gives the number-average degree of

polymerization, Xn, for a given fractional monomer conversion, p.

eq. sCarother'P1

1DP

P1

1

M

M

N

NDP

P1MM

n

00n

0

P = extent of reaction

[M]= concentaration of monomer

Carother’s Equation

P 0 0.5 0.8 0.95 0.99 0.999

DPn 1 2 5 50 100 1000

When P = 0.995 DPn = 200.


Spring 2007

2f ifP1

1

fP2

2DP

fDP

2

f

2P

)2( )1(eqn From

)2(N

N

reactionafter molecules of moles ofNumber

monomers ofnumber InitialDP

)1(fN

)NN(2

initially groups functional ofNumber

used groups funtional ofnumber The P

n

n

0n

0

0

Generalized Carother's Eq.


f = number of average functional group per monomer

N0 = number of initial monomers

N0f = number of initial functional group

N = number of final molecules (monomer, dimer, polymer)


Spring 2007

ex) monomer=10, fg= 20

final molecules= 2

R.O) then R.US.U (if S.U ofnumber is DP

58.01

1DP

8.010

8

102

2)-2(10P

n

n


For further details about W.Carothers


http://www.chemheritage.org/EducationalServices/chemach/pop/whc.html



Spring 2007

DPn 200

Polymer yield = 99.5%

P = 0.995

Highly efficient Reaction

Absent of side Reactions

that is, a 99.5% consumption of functional group does not necessarily a 99.5% polymer yield or

99.5% yield of interunit linkages

Ex)

OH (CH2)5COOH

-CO2

OH (CH2)4CH3 + CO2

High monomer purity

Exact (on known) Stoichiometry

Four Requirements of Polycondensation

Exact (on known) equivalence of functional groups.

Molecular Weight Control of Polycondensation Reaction

Equivalence of Functional Groups.


Spring 2007

A. Types of monomer

a. AB type

HO COOH

b. AA and BB type

HOOC COOH HOCH2CH2OH

c. Three functional groups for crosslinked polymers

HOCH2CHCH2OH

OH

Kinetics (ref. chap 11 in book)


Spring 2007

B. Condensation of difunctional monomers. a.

b.

HOCH2CH2OHH+

(-H2O)* OCH2CH2 *

O

O

H2NCH2CH2CH2CO2H∆

(-H2O)

NH

O

* NHCH2CH2CH2C *

O



Spring 2007Kinetics (ref. chap 11 in book)

Polyesterfication as an example of polycondensation

- d[COOH] / dt = k [COOH][OH][acid]

Assumption : without strong acid catalyst condition, pure monomer and correct equivalent

- d[COOH] / dt = k3[COOH]2[OH] -COOH is considered as acid catalyst

- d[COOH] / dt = k3[COOH]3 [COOH] = [OH]

integral eqn

1 / [COOH]2 = 1 / [COOH]02 +2k3t

1 / (1-P)2 = 1+2[COOH]02k3t P = 1 – [COOH] / [COOH]0

COOH OH CO

O


Spring 2007

- d[COOH] / dt = [COOH]2(k3[COOH] + kcat[ H +] )

kcat » k3 k3 can be neglected.

-d[COOH] / dt = k2[COOH]2 k2 = kcat[H+]

integral eqn

1 / (1-P) = 1 + k2[COOH]0 · t


[COOH] = [COOH]0 (1-P)

PDPn

1

1tk [COOH] 1 20nDP

If you know the value of K2, you can calculate DPn at any time

Assumption : with strong acid catalyst condition, pure monomer and correct equivalent


Spring 2007Kinetics (ref. chap 11 in book)

ex)k 2 10 –2 l mole1sec1 , C0 3 mole sec l1 , DPn =50( k2 = kcat[H+] )

Reaction time = ?

if k 2 10 –4 l mole1sec1

Reaction time = ?

less than 30 min

about 45 hr


Spring 2007

Assumption : Independence between reaction time and molecular size

P: fraction of functional groups that have reacted in time t

1-P : fraction of functional groups remaining at time t

x-mer: randomly selected polymer molecule containing exactly x structural units.

Probability finding a reacted carboxyl group in molecules = P

Probability finding (x-1) number of reacted carboxyl group in molecules = P x1

Probability finding a unreacted carboxyl group in molecules = 1P

Probability finding x-mer = P x1(1-P)

Kinetics

Mw distributions of linear condensation polymers


Spring 2007

If there are N number of molecules, total x-mer number is

N x = N P x1(1-P)

N = N 0 (1 P)

N x = N 0 P x1(1P) 2

Mw distributions of linear condensation polymers .

0.045

0.010

0.020

P=0.95

P=0.98

P=0.99

Nx

100 220

Kinetics


Spring 2007

xNxnDP

1-x2

0

p)p1(

xN

NxW x

x

PnDP

wDP

p

p

WxxwDP

xw

1

79 pageodian 1

1

2.0MWD

4

213

312

21

)1(

41

)1(

1

)1(

1

P

PPpx

P

Ppx

Pxp

x

x

x

Kinetics


Spring 2007

Target Molecular weight

DPn is time – dependent

1) Quench (cooling) the polymerization at pre- determined time

heating unstable

HO R COOH HO COOH

HOOC OH

react as heating undesirable

Molecular Weight Control


Spring 2007

2) Regulation of monomer concentration

nonstoichiometric condition or adding monofunctional reactant.

HO R OH HOOC COOH

HOOC COOH

+ HOOC R' COOH

EXCESS

• Stable Polymer

• No more reaction.

can control & limit MW



Spring 2007

Nylon 66: Adding lauric acid or acetic acid, MW control

Possible melt spinning through viscosity control

melt viscosity

mw

undesirable



Spring 2007

Assume B-B unit slightly in excess

NA : number of A functional group

Nb : number of B functional group

r = NA / Nb = feed ratio

P : rate of A group at t

rP : rate of B group at t

Initial total number of molecules = (NA + NB) / 2Number of unreacted A= NA(1―p)

Number of unreacted B= NB(1―rP)Number of total chain end = Number of unreacted A and B

→ Number of total molecules after t = (Number of total chain end )/2

= [NA(1―p)+ NB(1―r p)]/2



Spring 2007

A. Greater than two functionality polymers. a. Alkyd-type polyester :

b. Phenol-formaldehyde resin :

c. Melamine-formaldehyde resin :

HOCH2CHCH2OH

OH

OH

N

N

N

NH2

H2N NH2

Network Step Polymerization


Spring 2007

B. Gelatin : High conversion of greater than two functionality.

a. Gel point : onset of gelatin.

sudden increase in viscosity.

change from liquid to gel.

bubbles no longer rising.

impossible stirring.



Spring 2007

C. Gel point conversion.

: critical reaction conversion. : average functionality.

rrpc

[

1

avf

cp

avc f

p2

o

o

N

NNp



Spring 2007

4.25

)32()23(

avf

D. Examples of gel point conversion.

O

O

O

HOCH2CHCH2OH

OH

3mol of 1 2mol of 4

Gel point conversion : 77% (Experiment)

83% (Calculate)



Spring 2007

DPn ∞

i

ii

N

fNavgf

Ni:Monomer have functional group, f i

ex) 2mole Glycerol 6OH

3mole Phthalic Acid 6COOH

total 5 mole 12 f.g

N, No , No favg=total functional group

2( No- N) = number of functional

group after reaction

avg

avg

pfN

NDPn

fN

NNP

2

2

)(2

0

0

0


4.25

12avgf

where DPn ∝

= critical extent of reaction at gel point

In case of ex.

Pc = 2/2.4 = 0.833

avgc f

p2


Spring 2007

A. Polyester

(Dacron, Mylar) ester interchange rexn is faster than direct esterification.

It is difficult to purify diacid.

Methyl ester is used commonly.

For termination, alcohol is removed by distillation of reaction mixture.

Example of condensation polymerization

For further details about Polyester


http://www.pslc.ws/mactest/pet.htm



Spring 2007

CH3OC COCH3 + HO(CH2)2OH2

O

HOCH2CH2OC COCH2CH2OH

O

O O

+CH3OH2

1.

2. O

HOCH2CH2OC COCH2CH2OH

O

n

O O

COCH2CH2OHOCH2CH2O-C H + HOCH2CH2OH(n-1)

n



Spring 2007

. nylon salt

NH2 (CH2)6 NH2n + HOOC(CH2)4COOHn n O2C(CH2)4CO2

H3N(CH2)6NH3

- -

+

H NH

(CH2)6 NH

C (CH2)4 C

O

OH

O

+ OH2(2n-1)

B. Nylon 66

For further details about Nylon


http://www.pslc.ws/mactest/nysyn.htm

http://www.pslc.ws/mactest/nylon.htm




Spring 2007

Kevlar poly(p-phenylene terephthalamide) -high strength

NH2 NH2

HN NHC

O O

n

HOOC COOH+

C

C. Aromatic Polyamide

For further details about Kevlar and Nomex


http://www.pslc.ws/mactest/aramid.htm




Spring 2007

Nomex poly(m-phenylene isophthalamide) -very good high temperature resistance

+NH2 NH2

HOOC COOH -HCl-H2O

CH2Cl2DMAc

The electron density of NH2 is reduced by aromatic ring. So, the nuclephilicity of aromatic

amine is reduced by –COOH.

High temperature is needed.

For faster reaction, diacid chloride is used.

Li C O

C

O


* Coordinated covalent bond by using Li ion


Spring 2007

O

OO

O

O

O

O

O

+ NH2NH2

DMAcDMFDMSO

Pyromellitic dianhydride p-aminoaniline

(PMDA)

HOOC COOH

O

CNH NH

[ ]n

-H2O

O

C

O

C

CC

N

O

N[ ]n

polyamic acid(amidatoin) soluble

poly(pyromellitimido,-1,4 phenylene)

insoluble

nn

D. Aromatic Polyimides



Spring 2007

Two step polymerization is used because precipitation is occured before high molecular

aromatic polyimide was formed.

• In first step, poly(amic acid) is formed at -70 oC

• The poly(amic acid) is cyclized over 150 oC.

• Aromatic polyimide is very high heat resistance, Kapton, H-film

• To improve solubility of poly(amic acid), CH2 group is introduced in aromatic amine or

isocyanate is used instead of amine.

For further details about Polyimides


http://www.pslc.ws/mactest/imide.htm




Spring 2007

NaO C8

CH3

CH3

ONa Cl

O

O

S Cl

-NaCl

O* O

CH3

CH3

*n S

O

O

+ DMAc

4,4'dichloro diphenyl sulfonehigh nucleophilicity

polysulfone

n n

amorphous polymer, good strength, good oxidation resistance, engineering plastic, membrane material

E. Aromatic Polysulfone

AMOCO PERFORMANCE Co. UDEL.

.



Spring 2007

NH2

NH2

NH2

NH2

HOOC COOH-H2O

N

NH

N

NH

* *n

+

F. Polybenzimidazole (PBI)



Spring 2007

NH2

NH2

+

O

250¡ÆC

OH_

O

amine, amide

-H2O 350~400¡ÆC

NH

N

NH

NH

OH

NH

NH2

C

NH

NH2

C

OH

CC

C



Spring 2007

1961 Synthesized by Marvel

Some problems :

stoichiometric problems, side reactions, oxidatio,…

Celanese Co. (http://www.celanese.com)

not burn easily, self-extinguishing, but still expensive $45/lb in 1985


Spring 2007

CH2

OCHCH2Cl +

ClH +

CH2

O

CH CH2 O O CH2 CH

OH

CH2 On

O

O O CH2 CH CH2

OH C

CH3

CH3

OH

(n+2)

(n+2)

Structoterminal propolymer (epoxy end-group)

G. Epoxy Prepolymers



Spring 2007

X-linking

CH

OH

CH2 + RC

CO

O

O

CH CH2

O

O

R

O

O

CH CH2

(f=2) as X-linking agent

In this case, epoxy prepolymer is structure pendant prepolymer (OH terminated)



Spring 2007

phthalic anhydrideO

O

O

maleic anhydrideO

O

O

pyromellitic anhydride

O

O

O

O

O

O

Curing Agnet


or

amines

Properties and Applications

Thermoset, high Chemical and solvent resistance, adhesion to many

substrates, impact resistance, structural applications


Spring 2007

O

O

O +

OH

OH

OH+ R

R'

O

OH

RR'

OO CH2 C

H CH2O

C

O

O

O

O

alkyd resin

H. Unsaturated Polyesters



Spring 2007

O

O

O +OH

OH OCH2

CH2

OC

O

*

O

* n

brittleness, softness depends on X-linking densityh.

Applications: bowling ball, helmet, auto part, air con



Spring 2007

C

O

ClCl+ OH OH

O* O C

O

*n + HCl

Lexan from GE

Tm = 270°C, Tg=150°C

high impact resistance, transparency, packaging, phone dial ring,

process similar to polyester synthesis

2stage,

①vaccum at 200°C

②300°C

I. Polycarbonate



Spring 2007

HO(CH2)nOH O C N (CH2)6N C O

OCN

CH2 NCO

NCO

NCO

CH3

+

diol HMDI (hexamethylene diisocyanate)

diol

+

4,4'-diphenylmethane diisocyanate

or

+

TDI (tolylene diisocyanate)

diol

J. Poly urethane



Spring 2007

diamine in water

Polymer film forming at the interface

diacid chloride in organic solvent

O

CR C

O

ClCl + HOR'OHnn

O

CR C

O

R'O ** n + 2n ClH

O

CR C

O

ClCl + H2NR'NH2nn

O

CR C

O

* N R'NH H

*n 2n ClH+

Interfacial Polymerization


Spring 2007

Cl Cl

O O

4H2N NH24

Adipoyl chloride 1,6-Diaminohexane

Cl NH

NH

H

O O

4 4

NaOH

HO NH

NH

H

O O

4 4n

6 carbondiacid

6 carbondiamine

Nylon-6,6Diamine, NaOH, in H2O

Adipoyl chloridein hexane

Nylon 6,6

Nylon-6,6


Spring 2007

Diamine, NaOH, in H2O

Adipoyl chloridein hexane

Nylon 6,6

Since the reactants are in different phases, they can only react at the phase boundary. Once a layer of polymer forms, no more reaction occurs. Removing the polymer allows more reaction to occur.

Nylon-6,6

classification by mechanism step – growth chain – growth classification by type

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