1.3

Basic Terms and Concepts in Polymer Chemistry

Polymer Chemistry

History of Macromolecular Chemistry

1922 De!nition of the term polymer by Hermann Staudinger1953 Nobel Prize for Hermann Staudinger (concept)1963 Nobel Prize for Karl Ziegler and Giulio Natta (ole!n polymerization)1974 Nobel Prize for Paul J. Flory (polymers in solution)

1901 Polyacrylates (Rhm Chemie)1928 Plexiglass (Rhm Chemie)1930 Polystyrol, Polyacrylonitrile (BASF)1934 Polyvinylchloride (BASF)1937 Polyamides (DuPont, BASF), Polyurethanes, Polybutadiene (IG Farben)1939 Polyethylene, LDPE (ICI)1945 Poly(ethylene terephthalate) (ICI)1946 Te"on (DuPont)1952 Polyethylene, HDPE (Ziegler)1954 Polypropylene (Natta)

Mhlhaupt, Angew. Chem. Int. Ed. 2004, 43, 1054.51

Polymer Chemistry Staudinger, Helv. Chim. Acta 1922, 5, 785.

Denition of a Polymer

prop

erty

number of repeating units0 4 8 12 16

52

Denition of a polymer according to Hermann Staudinger:A polymer is a large molecule constituted from (identical) smaller structural repeating units with a length sucient such that molecules with n and n+1 repeating units are in

If properties are indistinguishable, polymers are also inseparable; polymers are polydisperse!

Polymer Chemistry

Polymer Types, Architectures, Microstructures

linear star branched hyperbranched network

random AB diblock ABC triblock segmented graft

Copolymers: dierent types of repeating units (and microstructures)

miktoarm starABA triblockalternating tapered brush

53

Homopolymers: one type of repeating units (but dierent architectures)

Polymer Science

Molecular Weight (MW) and Molecular Weight Distribution (MWD)

54

Polymers do not have dened molar masses but molecular weight distributions (MWD) Dierent molecular weight averages, width, and shape Molecular weight averages are moments of the molecular weight distribution

1

0

log MW

Mw Mz

MnMp

Mn =niMini

number average molecular weight

Mw =niM2iniMi

weight average molecular weight

Mz =niM3iniM2i

centrifuge average molecular weight

Mz+1 =niM4iniM3i

z+1 average molecular weight

molecular weight distribution

Polymer Chemistry

Molecular Weight Averages and Polydispersity Index

55

Mn =niM ini

=4 9000 + 4 1000

4 + 4= 5000

Mw =niM 2ini M i

=4 90002 + 4 10002

4 9000 + 4 1000= 8200

PDI =M wMn

= 1 .64

Mn =niM ini

=8 5000

8= 5000

Mw =niM 2ini M i

=8 50002

8 5000= 5000

PDI =MwM n

= 1 monodisperse (molecularly uniform)

polydisperse

Polymer Science

Thermal Transitions of Polymers

highly crystalline

partially crystalline

amorphous, glassy

polymer meltmelting transitionTmglass transition

Tg

56

Polymer Science

Thermal Transitions of Polymers

57

Analysis of thermal transitions with Dierential Scanning Calorimetry (DSC)en

thalp

y

temperature

Tg

Tm

Tg

melting

crystallization

enthalp

ytemperature

Tg

Tm

melting

crystallization

Tg crystallization

Tg

Tg

Tm

melting

crystallization

crystalline polymer

amorphous polymer

partially crystalline polymer

slow

fast

Polymer Science

Mechanical Properties of Polymers

58

exible polymers (Tg < r.t.)

rigid polymer chains (Tg > r.t.)

amorphous thermoplast crystalline thermoplast duromer ber

!ber axis

viscous liquid thermoplastic elastomer elastomer

Polymer Science

Determination of Mechanical Properties of Polymers by Tensile Testing

59

strain

stres

s thermoplast

ber

elastomer

Youngs modulus E (slope in the elastic deformation region) is a measure for stiness Energy at break (area under stress-strain curve) is a measure for toughness Yield stress (maximum at the end of the elastic deformation region) is a measure for strength

Polymer Chemistry

Step-Growth Reactions

60

O

O

HOOH

HO OHn + n

O

O

OO OH

H

n

n H2O

O

HO NH2 n H2On

O

NH

n

N

N COCO

OHHO OO

O

N

O

NH H

N COn + n

n

Polycondensations

Polyadditions

poly(ethylene terepththalate) (PET)terepththalic acid ethylene glycolAA monomer BB monomer

Nylon-66-aminohexanoic acidAB monomer

linear poly(urethane)bisphenol A toluene diisocyanate (TDI)AA monomer BB monomer

Polymer Chemistry

Origin of Polydispersity and MW Limitations in Step Growth Reactions

61

A6 B

B

A

B AB

AB

AB

A

A

B

B

ABA

M n = 2 .0M w = 2 .4

PDI = 1.2conversion = 50%

Polymer chain growth is a statistical process Conversion limits molecular weight

Polymer Chemistry

Chain Polymerizations

62

O O

N2N NNC CN 2 CN

CNO OMe

n

O OO OCN

n

O OMe

O OCN CN

Example: Radical polymerization

initiator decomposition

initiation

propagation (chain growth)

Initiator decomposition and initiation are statistical processes, but not responsible for molecular weight distribution and limitation

Polymer Chemistry

Chain Termination and Transfer Reactions in Radical Chain Polymerizations

63

O OO OCN

nO OO OCN

nOO OO CN

n

O OO OCN

n

H

OO OO CN

n

OO OO CN

n

+

+O OO OCN

nOO OO CN

n

+H

O OO OCN

n

H

O OO OCN

n

+ H

combination

disproportionation

transfer

termination

termination

Example: Radical polymerization

Termination and transfer reactions are statistical processes that cause molecular weight distribution and limit molecular weight

Polymer Chemistry

Living Chain Polymerizations

64

Example: anionic polymerization

CHCH

CH CH

n

n

CH

n

CH2

n

Li Li

Li Li

LiH O H

Li OH

initiation

propagation (chain growth)

quenching

Initiation is fast (but not ininitely fast), termination and transfer reactions are absent, growth is not a statistical processes; narrow MWD and controlled MW

Polymer Chemistry

Summary of the Polymerization Mechanisms

65

Step Growth Chain Growth Living

10 1

conversion

degr

ee of

polym

erizt

ation

P n

10 1

conversion

geleffect

inductionperiod

glasseffect

degr

ee of

polym

erizt

ation

P n

10 1

conversion

degr

ee of

polym

erizt

ation

P n

Carothers equation

kinetic control

conversion and initiator control

=1

1

=

=

1

0

0log MW

weigh

t fra

ction

1

0

0log MW

weigh

t fra

ction

1

0

0log MW

weigh

t fra

ction

SchulzFlory distribution Poisson distributionSchulzFlory distribution

Polymer Chemistry

Summary of the Polymerization Mechanisms

66

Step Growth Chain Growth Living

10 1

conversion

degr

ee of

polym

erizt

ation

P n

10 1

conversion

geleffect

inductionperiod

glasseffect

degr

ee of

polym

erizt

ation

P n

10 1

conversion

degr

ee of

polym

erizt

ation

P n

Carothers equation

kinetic control

conversion and initiator control

=1

1

=

=

2

1

2

0 1conversion conversion

polyd

isper

sity i

ndex

PDI

1

2

1

0 1

polyd

isper

sity i

ndex

PDI

0 1conversion

polyd

isper

sity i

ndex

PDI

gel and glasseffect

= 1 +1

inductionperiod

PDI = 1 + conv

Applications of Polymers

Optical Fibers and Components

Packaging MaterialsThermal Insulation Materials

Structural Materials

67