Historical Background

Ages ago - Natural Fibers Ex. Wool, silk, cotton

In 1736, Charles Marie de La

Condamine introduced the para

rubber tree (natural rubber).

Hevea brasiliensis

“Crying tree”

(para rubber) Latex Coating Natural (hevea) rubber known as

polyisoprene in its synthetic form.

1839-Charles Goodyear

Vulcanization: Transformation of sticky natural rubber to a useful

elastomer for tire use

Historical Background

S8

1843-Charles Goodyear Ebonite High % vulcanization (1st synthetic plastic made from natural rubber)

Fountain pen bodies smoking pipe mouthpiece bowling balls

Synthetic Polymers Started

cellulose cellulose nitrate

1847 “Cellulose nitrate”

1860s -Parkes (Electrical industry) and Hyatt (Billiard balls)

“Celluloid” (1st artificial thermoplastic)

Cellulose nitrate+ Camphor (as plasticizer)

1907-Leo Baekeland “Bakelite”

(thermosetting phenol-formaldehyde resin)

Bakelite letter opener

Bakelite distributor rotor

Bakelite radio

Bakelite telephone 1st truly synthetic plastic

On further heating with HCHO, novalac undergoes cross-linking to an infusible solid called bakelite. It is hard scratch and water resistant.

Nobel Prize-Chemistry 1953 for “his discoveries in the field of macromolecular chemistry”

Hermann Staudinger

1920 “Macromolecular Hypothesis”

Demonstrations of both synthetic and natural polymers

Polymer is a giant molecule

A chain of paper clips (above) is a good

model for a polymer such as polylactic acid (below).

long chains of short repeating

molecular units linked by covalent bonds

Development of commercial polymers

1927 PVC 1947 Epoxy resins

1931 PMMA & Neoprene 1948 ABS

1938 Nylon 1957 HDPE

1941 LDPE

1943 Silicones

Polymer –is a large molecule consisting of a number of repeating

units with molecular weight typically several thousand or higher

Polymers are made up of many Monomers

Many units One units

Repeating unit – is the fundamental recurring unit of a polymer

Monomer - is the smaller molecule(s) that are used to prepare a

polymer

Oligomer –is a molecule consisting of reaction of several repeat

units of a monomer but not large enough to be consider a polymer

(dimer , trimer, tetramer, . . .)

Degree of polymerization (DP)- number of repeating units

Polymer science is relatively a new branch of science . It deals with chemistry

physics and mechanical properties of macromolecule .

Definitions

Polymers vs Macromolecules

Polypropylene (PP)

DNA

3

2 1

Nylon 6,6

Zig-zag conformation

POLYETHYLENE

Substituent groups such as –CH3, -OCOCH3, CN, Cl or –Ph that are attached

to the main chain of the skeletal atoms are known as pendant groups. Their

structure and chemical nature can offer unique properties on polymer.

Classification of Polymers

A. Classification by Origin

• Natural Polymers

-Biological Origin - enzymes, nucleic acids, proteins

-Plant Origin – cellulose, starch, natural rubber

•Synthetic Polymers

- Fibers

- Elastomers

- Plastics

-Adhesives

3.Classification by Polymerization Mechanism

Classification of polymers to be suggested by Carothers

Addition polymers are produced by reactions in which monomers are added

one after another to a rapidly growing chain. Most important addition polymers

are polymerized from ethylene based polymers.

Trioxane

Ring opening polymerization

Polyoxymethylene

•Initiation

•Propagation

•Termination Unsaturated (C-C double bond)

(ethylene based monomers)

2.Classification by Polymerization Mechanism

Condensation polymers are obtained by random reaction of two molecules.

A molecule participating in a condensation reaction may be a monomer, oligomer, or high molecular

weight intermediate each having complementary functional end units, such as carboxylic acid or

hydroxyl groups. Typically condensation polymerizations occur by the liberation of a small molecule in

the form of gas, water, or salt.

More recently, another classification scheme based on polymerization kinetics has been adopted

over the more traditional addition and condensation categories.

• Step growth

• Chain growth

3.Classification by Polymer Structure

Classification by Chain structure (molecular architecture)

(a) linear

(c) network

Branched polymers have side chains, or branches, of significant

points (known as junction points), are characterized in terms of the

number and size of the branches

The basic functionality required for forming even a linear chain is two

bonding sites.

Higher functionality yields branched or even crosslinked or networked

polymer chains.

(b) branch

Network polymers have three dimensional structures in which each

chain is connected to all others by a sequence of junction points and

other chains. Such polymers are said to be crosslinked and

characterized by their crosslink density, or degree of crosslinking,

which is related to the number of junction points per unit volume

Non linear polymers may be formed by polymerization, or can be prepared by linking together (ex.

crosslinking) pre-existing chains.

(d) ladder polymer

2.Classification by Polymer Structure

Classification by Chain structure (molecular architecture)

Ladder polymers constitute a group of polymer with a regular sequence of crosslinks.

diacetylene

2.Classification by Polymer Structure

Classification by Chain structure (molecular architecture)

(g) dendrimer

Dendrimers are repeatedly branched, roughly

spherical large molecules.

4.Classification by Polymer Structure

Classification by Monomer Composition

contain only one type of repeat unit (A))-A. Homopolymer

contain two different repeating units (AB)-B. Copolymer

If there are three chemically different repeating unit, it is then called terpolymer

Poly(styrene-co-acrylonitrile) (SAN)

Type of Copolymers

Random copolymer : -A-B-B-A-B-A-A-B-

-two or more different repeating unit are distributed randomly

Alternating copolymer : -A-B-A-B-A-B-A-B-

-are made of alternating sequences of the different monomers

Block copolymer : -A-A-A-A-B-B-B-B-

-long sequences of a monomer are followed by long sequences of

another monomer

Graft copolymer : -A-A-A-A-A-A-A-A-

-Consist of a chain made from one type of monomers with branches

of another type

B-B-B-B-B-

5.Classification by Thermal Behavior

A thermoset is a polymer that, when heated, undergoes a chemical change to produce a

cross-linked, solid polymer.( Ex: urea-formaldehyde, phenol-formaldehyde, epoxies)

Thermoplastic polymers soften and flow under the action of heat and pressure. Upon

cooling, the polymer hardens and assumes the shape of the mold (container).

(Ex: polyethylene, polystyrene, and nylon)

Inorganic Polymers

polydimethylsiloxane

O Si

CH3

CH3

n

N P

Cl

Cl

n

Poly(dichlorophosphazene)

Polyelectrolytes

H2C

HC

COOH

n

H2C C

COOH

n

CH3

Poly(acrylic acid) Poly(methacrylic acid)

A. Types of Nomenclature

a. Source name : to be based on names of corresponding monomer

Polyethylene, Poly(vinyl chloride), Poly(ethylene oxide)

b. IUPAC name : to be based on CRU, systematic name

Poly(methylene), Poly(1-chloroethylene), Poly(oxyethylene)

c. Functional group name :

According to name of functional group in the polymer backbone

Polyamide, Polyester

Nomenclature

d. Trade name : The commercial names by manufacturer Teflon, Nylon

e. Abbreviation name : PVC, PET

f. Complex and Network polymer : Phenol-formaldehyde polymer

Nomenclature

Vinyl polymers

A. Vinyl polymers

a. Source name : Polystyrene, Poly(acrylic acid),

Poly(α-methyl styrene), Poly(1-pentene)

b. IUPAC name : Poly(1-phenylethylene), Poly(1-carboxylatoethylene)

Poly(1-methyl-1-phenylethylene), Poly(1-propylethylene)

CH2CH

Polystyrene Poly(acrylic acid)

Poly(α-methylstyrene) Poly(1-pentene)

CH2C

CH3

CH2CH

CO2H

CH2CH

CH2CH2CH3

B. Diene monomers

Source name : 1,2-Poly(1,3-butadiene) 1,4-Poly(1,3-butadiene)

IUPAC name : Poly(1-vinylethylene) Poly(1-butene-1,4-diyl)

CH2CH CHCH 2CH2CH

HC CH2

1,2-addition 1,4-addition

Vinyl polymers

Vinyl copolymer

Type Connective Example

Unspecified -co- Poly[styrene-co-(methyl methacrylate)]

Statistical -stat- Poly(styrene-stat-butadiene)

Random -ran- Poly [ethyelene-ran-(vinylacetate)]

Alternating -alt- Poly[styrene-alt-(maleic anyhride)]

Block -block- Polystyrene-block-polybutadiene

Graft -graft- Polybutadiene-graft-polystyrene

* A statistical polymer is one in which the sequential distribution of the monomeric units obeys the statistical laws. In the case of random copolymer, the

probability of finding a given monomeric unit at any site in the chain is independent of the neighboring units in that position.

Polystyrene-graft-polybutadiene

Polystyrene-block-polybutadiene

* Representative Nomenclature of Nonvinyl Polymers

Poly(hexamethylene Poly(iminohexane-

sebacamide) or Nylon6,10 1,6-diyliminosebacoyl)

Monomer Polymer Source or IUPAC name

structure repeating unit Common Name

O

H2C CH2

HOCH2CH2OH

H2N(CH2)6NH2NH(CH2)6NHC(CH2)8C

O O

HO2C(CH2)8CO2H

Poly(ethylene oxide)

Poly(ethylene glycol) Poly(oxyethylene)

Poly(oxyethylene) CH2CH2O

CH2CH2O

Abbreviations

Abbreviation Name

PVC Poly(vinyl chloride)

HDPE High-density polyethylene

LDPE Low-density polyethylene

PET Poly(ethylene terephthalate)

ABS Arcylonitrile-butadiene-styrene resin

PBT Poly(butylene terephthalate)

PE Polyethylene

PMMA Poly(methyl methacrylate)

PP Polypropylene

PS Polystyrene

PTFE Poly(tetrafluoroethylene)

PEO Poly(ethylene oxide)

Thermal Responses of Simple Molecules

Water exists at three distinct

physical states-solid, liquid and

gas (vapor)

Transitions between these

states occur sharply at constant

, well defined temperatures.

Thermal Responses of Polymers-1

Polymers do not exist in the

gaseous state. At high T they

decompose.

The transition between solid and

liquid forms of a polymer is rather

diffuse and occurs over a

temperature range, whose

magnitude (of the order of 2-10 °C)

depends polydispersity of the

polymer

Thermal Responses of Polymers-2

The molecular motion in a polymer sample is promoted by its thermal agitation

It is opposed by the cohesive forces between structural segments (groups of atoms)

along the chain and between neighboring chains.

The cohesive forces and thermal transitions in polymers depend on the structure of the

polymers.

The glass transition temperature, Tg

The crystalline melting point, Tm

Temperatures at which

physical properties of

polymers undergo drastic

changes

Tg—transition from the hard and brittle glass into softer rubbery state (amorphous polymer- in the

amorphous regions of semicrystalline polymer)

Tm– corresponds to the temperature at which the last crystallite starts melting

depends on the crystallinity and size distribution of crystallites

Knowledge of thermal transitions is important in ;

The selection of proper processing and fabrication conditions

Characterization of physical and mechanical properties of a material

Determination of appropriate end uses

Amorf

Yarı kristal

kristal

sıvı sıvı

sıvı

katı

zamksı

kauçuğumsu

camsı camsı

esnek termoplastik

Tg

Te

T

Tam kristal ve yarı kristal maddelerde davranış değişiklikleri belirgin, amorf maddelerde camsı geçiş dışındakiler derecelidir.

Amorf, yarı kristal ve kristal maddelerde ısıl geçişler sırasında gözlenen davranış değişiklikleri

Polimer Kimyası Prof. Dr. Mehmet Saçak (5. Baskı, Gazi Kitapevi)

Glass Transition Temperature

Polimer Kimyası Prof. Dr. Mehmet Saçak (5. Baskı, Gazi Kitapevi)

Thermal Transitions

1st order transition 2nd order transition

Abrupt change in a fundamental

property such as enthalpy (H) and

volume (V)

Melting is a first order thermodynamic

transition

First derivative of properties such as

enthalpy (H) and volume (V) changes

p p )T

H(C

Capacity Heat

p)T

V(

V

1

tCoefficienExpansion Thermal

Both Cp and change abruptly at Tg.

fo VVV

))((

(constant) V

V

*

*

f

T

VTTVV

V

Vf f

gff

f

21

g )(

f

fgTTff

Free Volume Theory S

pe

cific

Vo

lum

e

Vf*

Vf

Vo

Tg

Temperature

(T)

Free Volume Fraction

Thermal expansion coefficient (above Tg)

This theory considers the free volume (Vf) of a substance as the difference between its

specific volume (total volume) (V) and the space actually occupied by the molecules (Vo)

Thermal expansion coefficient (below Tg)

For whole range of glassy polymers, fg is remarkably constant and this concept of free

volume found important use in the analysis of the rte and temperature dependence of

viscoelastic behavior of polymers between Tg and Tg+100K

Structural Features;

Chain Flexibility (stiffness, polarity,

steric hindrance)

Interchain Attractive Forces

Geometric Factors

Copolymerization

Molecular Weight

Branching and Crosslinking

Crystallinity

External Variables;

Plasticization

Pressure

Rate of Testing

Factors Affecting Tg

Chain flexibility is determined by the ease with which

rotation occurs about primary valence bonds. Polymers

with low hindrance to internal rotation have low Tg values

Long-chain aliphatic groups (ether-ester linkages) enhance flexibility

Cyclic structures stiffen the backbone

Chain Flexibility

Bulky side groups that are stiff and close to the backbone cause steric hindrance , decrease

chain mobility and hence raise Tg

Chain Flexibility

The influence of the side group in enhancing chain stiffness depends on

the flexibility of the group and not its size.

In fact, side groups that are fairly flexible have little effect within each

series; instead polymer chains are forced further apart.

This increases the free volume, and consequently Tg drops.

Chain Flexibility

Polymers that have symmetrical structure

have lower Tg than those with asymmetric

structures.

The additional groups near the backbone

can be accommodated in a conformation with

a “loose” structure. The increased free

volume results in a lower Tg.

Geometric Factors

Double bonds in the cis form reduce the energy barrier

for rotation of adjacent bonds, “soften” the chain, and

hence reduce Tg

Geometric Factors

The effect of polarity

The steric effects of the pendant group in series (CH3, Cl, CN)

are similar but the polarity increases so Tg increases.

Interchain Attractive Forces

Hydrogen Bonding

Ionic Bonding Any structural feature that tends to

increase the distance between polymer

chains decreases the cohesive energy

density and hence reduces Tg.

In the polyacrylate series shown above,

the increased distance between chains

due to the size of the alkyl group, R,

results in reduced Tg.

Interchain Attractive Forces

To be able to control the Tg and Tm independent of each other is very difficult, but it is

solved to some extent by copolymerization of polyblending.

A copolymer system may be characterized by:

geometry of the resulting polymer (random, alternating, graft or block)

The compatibility (miscibility) of two monomer

Isomorphous Systems (Homogeneous Copolymers or Compatible Polyblends

In isomorphous systems, the component monomers occupy similar volumes and are capable of replacing

each other in the crystal system.

Copolymerization merely shifts the Tg to the position intermediate between those of the two homopolymers; it

does not alter the temperature range or the modulus within the transition region

2 and 1 components of fractions volumeare V and V

rshomopolyme individial of T are T andT

;where

(1) TVTVT

21

gg2 g1

2g21g1g

Variation in Tg

with copolymer

composition

Copolymerization

Nonisomorphous Systems In nonisomorphous systems, the specific volumes of the monomers

are different. In this case, the geometry of the resulting polymer becomes important.

Random and Alternating: The increased disorder resulting from the random or alternating distribution of

monomers enhances the free volume and consequently reduces Tg below that predicted by Equation 1.

Variation in Tg with

copolymer composition

2 and 1 components of fractions weight are Wand W

rshomopolyme individial of T are T andT

;where

(2) T

W

T

W

T

1

21

gg2 g1

2g

2

1g

1

g

Examples of this type are methyl methacrylate–acrylonitrile,

styrene–methyl methacrylate, and acrylonitrile–acrylamide

copolymers. (Line 2-next graph)

It is also possible that monomers involved in the copolymerization

process (as in the copolymers methylacylate–methylmethacrylate

and vinylidene chloride–methylacrylate) introduce significant

interaction between chains. In this case the Tg will be enhanced

relative to the predicted value (line 3 –next graph)

Copolymerization

Block or Graft Copolymers (incompatible Copolymers): For block or graft copolymers in which the

component monomers are incompatible, phase separation will occur. Depending on a number of factors

— for example, the method of preparation — one phase will be dispersed in a continuous matrix of the

other. In this case, two separate glass transition values will be observed, each corresponding to the Tg of

the homopolymer.

Polyblends of polystyrene (100 ) and 30/70 butadiene- styrene copolymer

Copolymerization

Molecular Weight

At a given temperature, therefore, chain ends provide a higher free volume for molecular motion.

As the number of chain ends increases (which means a decrease in Mn), the available free

volume increases, and consequently there is a depression of Tg.

The effect is more pronounced at low molecular weight, but as Mn increases, Tg approaches an

asymptotic value.

constant a K

weightmolecular infinitean of TT where

M

KTT

gg

ngg

Crosslinking and Branching

Crystallinity

Crosslinking involves the formation of intermolecular connections through chemical bonds, and this results

in chain mobility and Tg increases.

For lightly crosslinked systems like vulcanized rubber, Tg shows a moderate increase over the un

crosslinked polymer.

For the highly crosslinked systems like phenolics and epoxy resins, the Tg is virtually infinite.

Like long and flexible side chains, branching increases the separation between chains , enhances free

volume and decreases Tg

In semicrystalline polymers, the crystallites may be regarded as the physical cross-links that to

reinforce or stiffen the chain. So Tg will increase with increasing crystallinity.

Kelvin degreesin are T and T where

polymers calunsymmetrifor 2/3

polymers lsymmetricafor 2/1

T

T

mg

m

g

Plasticization

Plasticity is the ability of material to undergo plastic or permanent deformation.

Plasticity is the process of inducing plastic flow in a material. In polymers, this can

be achieve by addition of low molecular weight organic compounds (plasticizers).

Plasticizers are nonpolymeric, organic liquids of high boiling points. They are

miscible with the polymer, and should remain in the polymer. (Very low Tg

between -50 °C and -160 °C)

Addition of a small amount of plasticizer drastically reduces the Tg of polymer.

Effect of plasticizer in reducing Tg

Plasticizers function through a solvating action by increasing

intermolecular distance, thereby decreasing intermolecular

bonding forces.

The addition of plasticizers results in a rapid increase in chain

ends and hence an increase in free volume.

A plasticized system may also be considered as a polyblend,

with the plasticizer acting as the second component

Crystalline Melting Point

Melting in crystalline polymeric systems.

• The macromolecular nature of polymers and the existence of molecular

weight distribution (polydispersity) lead to a broadening of Tm.

• The process of crystallization in polymers involves chain folding. This creates

inherent defects in theresulting crystal. Consequently, the actual melting point

is lower than the ideal thermodynamic melting point.

• Because of the macromolecular nature of polymers and the conformational

changes associated with melting, the process of melting in polymer is more

rate sensitive than that in simple molecules.

• No polymer is 100% crystalline.

Melting represents a true first order thermodynamic transition characterized by the discontinuities in the

primary thermodynamic values (heat capacity, specific volume (density), refractive index and tranparency.

melting during change entropyS

melting during change enthalpyH where

S

HT

0THG

m

m

m

mm

mmmm

Factors that determine crystallization

tendency;

Structural regularity

Chain Flexibility

Intermolecular Bonding

Factors Affecting

The Crystalline Melting Point Tm

states twoin the moleculesbetween order of degreein differenceS

states liquid and ecrystallin in the chains

between energies cohesive in the difference theH

process

m

m

where

S

HT

libriumPesudoequi

m

mm

Hm is independent of molecular weight. Polar groups on the chain would

enhance the magnitude of Hm

Sm depends not only molecular weight, but also on structural factors like chain

stiffness. Chains that are flexible in the molten state ( large number of

conformations than stiff chains) result in a large Sm

Trend of crystalline melting point in homologous

series of aliphatic polymers.

The melting points approach that of

polyethylene as the spacing between

polar groups increases.

For the same number of chain atoms

in the repeat unit, polyureas,

polyamides, and polyurethanes have

higher melting points than polyethylene,

while polyesters have lower.

Ym =molar melt transition function

Intermolecular Bonding-1

The melting points of the nylons reflect the density of hydrogen forming amide linkages.

The densities of interunit linkages in polycaprolactone (ester units) and polycaprolactam

(amide units) are the same, but the amide units are more polar than the ester units.

Intermolecular Bonding-2

Effect of Structure

Tg ( °K)

Kelvin degreesin are T and T where

polymers calunsymmetrifor 2/3

polymers lsymmetricafor 2/1

T

T

mg

m

g

Chain Flexibility

Polymers with rigid chains would be expected to have higher melting points than those

with flexible molecules

On melting, polymers with stiff backbones have lower conformational entropy changes

than those with flexible backbones.

Chain flexibility is enhanced by the presence of such groups as –O– and –(COO)– and by

increasing the length of (–CH2–) units in the main chain.

Insertion of polar groups and rings restricts the rotation of the backbone and consequently

reduces conformational changes of the backbone

The effect of colpolymerization on Tm depends on the value of compatibility of comonomers.

If the comonomers have similar specific volumes, they can replace each other in the crystal lattice

(isomorphous systems), and Tm will vary smoothly over the entire composition range.

If the copolymer is made from monomers each of which forms a crystalline homopolymer, the

degree of crystallinity and the crystalline melting point decreases as the second constituent is added

to either of the homopolymers.

The Tm of the copolymer (in the second case);

component (major) izingorcrystallr homopolyme theoffraction mole X

fusion ofheat H

;

ln11

m

heat

where

XH

R

TT mmm

Block and graft copolymers with sufficiently long homopolymer chain sequences crystallize

and exhibit properties of both homopolymers and have two melting points, one for each type

of chain segment.

Copolymerization