l2 mw sp relation

7/30/2019 L2 MW SP Relation

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Dr. S.Ray_Chem Engg_NIT Agratala 1/9/2013

olymer Processing Engineering 1

1

2

Structure-processing-property relationships


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1-Primary bonds : the covalent bonds that connect the atoms of the main chainhain

22-- Secondary bonds : nonSecondary bonds : non covalent bonds that hold one polymer chain to anothercovalent bonds that hold one polymer chain to anotherincluding hydrogen bond and other dipoleincluding hydrogen bond and other dipole dipole attractiondipole attraction

33--Crystalline polymer : solid polymers with a high degree of structural order andCrystalline polymer : solid polymers with a high degree of structural order andrigidityrigidity

44-- Amorphous polymers : polymers with a low degree of structural orderAmorphous polymers : polymers with a low degree of structural order

55--SemiSemi crystalline polymer : most polymers actually consist of both crystallinecrystalline polymer : most polymers actually consist of both crystallinedomains and amorphous domains with properties between that expected for adomains and amorphous domains with properties between that expected for apurely crystalline or purely amorphous polymerpurely crystalline or purely amorphous polymer

66--Glass : the solid form of an amorphous polymer characterized by rigidity andGlass : the solid form of an amorphous polymer characterized by rigidity andbrittlenessbrittleness

Amorphous Crystalline


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5

Van de Waals Forces ~ 2-20 kJ/mol

1. Dipole-Dipole InteractionKTR

ED 6

2

2

2

1

3

2 = ~ 13-21 kJ/mol

2. Induced Dipole-Dipole InteractionR

EI 6

2

222

11 += ~ 6-13 kJ/mol

3. Dispersion Interaction

+=

RII

IIEL 6

21

21

21

2

3 ~ 0.8-8 kJ/mol

dipole moment, polarizability, I ionization energy, R intermolecular distance


Intermolecular Interactions defining polymer structure and properties

6

Hydrogen Bonding

Proton Donors:

Proton Acceptors:

Oxygen Nitrogen

Why are nylons strong and tough? Why nylons have high melting

temperature (~250C)?

-X-H Y- ~ 20-40 kJ/mol

~ 4-5 (


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7

Ionic Interactions

Polyeletrolytes or Ionomers

Polyelectrolyte multilayers

on silicon wafer

8

Molecular Conformations

What determines molecular conformations?

staggered eclipsed

anglevalU

rotatU

stericUU

..)( ++=

2

jj

j

angle.val

)3(

rotat

6

i

i

iiSteric

)(2

kU

)3cos1(2

UU

bR)R

exp(aU

====

++++====

====

Potential Energy of a Molecule:


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9

Zig-Zag versusHelix

stablegauche(+) gauche(-)

stable

~+15 ~-15

CH2CH2n

PolyethyleneCF2CF2

n

Polytetrafluoroethylene

CH3-CH2-CH2-CH3

10

The different possible spatial arrangements are called the tacticityof the polymer.

For monosubstituted ethylene, such as a vinyl polymers, everyother carbon atom is a chiral center and are referred to aspseudochiral centers

If the R groups on successive pseudochiral carbons all have thesame configuration, the polymer is called isotactic

When the pseudochiral centers alternate in configuration from onerepeating unit to the next, the polymer is called syndiotactic.

If the pseudochiral centers do not have any particular order, but infact are statistical arrangements, the polymer is said to be atactic.

Polymer Tacticity


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In Fisher projections the R groups are placed either up or down.

a) all up (or all down) indicates the isotactic structure:

b) alternating up and down indicates syndiotactic:

c) random up and down indicates atactic:

Polymer Tacticity

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Polymer Tacticity

X=CH3Y=H

R R R R R R

isotactic

isotactic PP

R S R S R S

syndiotactic

syndiotactic PP

C

H3C CH2CH3

H Cl

S

C

H3C CH2CH3

Cl H

R

Atactic (non-atactic)

S R R R S R S S R S R

atactic PP


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The isotactic and syndiotactic (also known as stereo-regular)polymers are both crystallizable because of their regularityalong the chain. However, their melting temperatures are not thesame.

Atactic polymers, on the other hand, are usually completelyamorphous unless the side group is so small or so polar as topermit some crystallinity.

Polymer Tacticity structure-property relationship

14

States of Thermoplastics Polymers

Thermoplastics Polymers

Crystallinee.g. polyethylene,polypropylene, etc.

Amorphouse.g. polystyrene,polyacrylates, etc.

Liquid Crystallinethermotropic or lyotropic,main-chain or side-chain

LC polymers (LCPs)

Amorphous: No long range order, only short range order. Like gas and liquid.Important parameter: Glass Transition Temperature (Tg)

Glassy state (hard) Tg Rubbery state (soft)

Crystalline: Long range order, including positional, orientational, and conformational orders.Like crystals or solids.Important parameter: Melting Point (Tm)

crystallization

melting


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77 Crystalline melting temperature (TCrystalline melting temperature (Tmm ) : temperature at which crystalline) : temperature at which crystallinePolymer converts to a liquid or crystalline domains of a semi crystallinePolymer converts to a liquid or crystalline domains of a semi crystallinePolymer melt (increased molecular motion )Polymer melt (increased molecular motion )

88-- Glass transition temperature (Glass transition temperature (TTgg ) : temperature at which an amorphous) : temperature at which an amorphouspolymer converts to a liquid or amorphous domains of a semi crystallinepolymer converts to a liquid or amorphous domains of a semi crystallinepolymer meltpolymer melt

99 Thermoplastics (plasticsThermoplastics (plastics )) :polymers that undergo thermally reversible:polymers that undergo thermally reversibleInterconversionInterconversion between the solid state and the liquid statebetween the solid state and the liquid state

1010-- ThermosetsThermosets : polymers that continue reacted at elevated temperatures: polymers that continue reacted at elevated temperaturesgenerating increasing number ofgenerating increasing number of crosslinkscrosslinks such polymers do not exhibitsuch polymers do not exhibitmelting or glass transitionmelting or glass transition

1111-- LiquidLiquid crystalline polymers : polymers with a fluid phase that retainscrystalline polymers : polymers with a fluid phase that retains

some ordersome order1212-- ElastomersElastomers : rubbery , stretchy polymers the effect is caused by light: rubbery , stretchy polymers the effect is caused by lightcrosslinkingcrosslinking that pulls the chains back to their original statethat pulls the chains back to their original state

Temperature

3

9

67

8

4

5

Glass phase (hard plastic)

Rubber phase (elastomer)

Liquid

Leathery phase

Log-stiffn

ess


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Glass TransitionMelting

Property of the amorphous region Below Tg: Disordered amorphous

solid with immobile molecules Above Tg: Disordered melt A second-order-like transition

Property of the crystalline region Below Tm: Ordered crystalline solid Above Tm: Disordered melt A first-order transition

-like

Melting versusGlass Transition

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Higher Order Polymer Structures

Second Order Structures - Conformation

extended chain random coil folded chain chain helix

Third Order Structures Micromorphology

non-entangled entangled fringe micelle crystal chain-folded crystal

Fourth Order Structures Macromorphology

crystallinespherulites

double gyroid ofABC terpolymers


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20


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Molecular Weight of Polymers

1. Molecular Weight (MW) = Degree of Polymerization (DP) M0

CH2CH21000

MW = 1000 M0 (28) g/mol = 28,000 g/mol

Number-average DP

MMDP nn 0/=

Weight-average DP

MMDP ww 0/=

Number-average Molecular Weight

===

iMiwi

iiiin N

MNMxM 1

Weight-average Molecular Weight

=

==

MN

MNM

MN

MNMwM

ii

iii

ii

iiiiw

2

2. Average Molecular Weights of Polymers

A set of values {M1, M2, . . ., Mn}. The probability of each value is {P1, P2, . . ., Pn}.

The average is . So, the average depends on the probability.

=1iiiMP

=

=

1

1

ii

iii

P

MP

1. A number-average molecular weight Mn : divide chains into series of size

ranges and then determine the number fraction Ni of each size range

where Mi represents the mean molecular weight of the size range i, and N i is thefraction of total number of chains within the corresponding size range

To create a solid with useful mechanical properties the chain must be long !!One may describe chain length in terms of polymer average molecular weight,which can be defined in several ways:

Molecular weight averages

2. A weight average molecular weight Mw is based on the weightfraction wi within the size ranges:

Mn = Mi Ni/ Ni

Mw = Mi W i/ W i


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(1) The number-average molecular weight for a

discrete distribution of molecular weights is givenas

where N is the total number of molecular-weight

species in the distribution.

(2) The weight-average molecular weight is given as

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Z-average Molecular Weight (melt elasticity)

==

==

MN

MN

MwMw

MMwMw

MzMii

ii

ii

iii

ii

iiiiz 2

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Viscosity-average Molecular Weight (viscosity)

=

+

MN

MNM

ii

aii

a

v

1/1

a is viscosityparameterbetween 0.5 and 1.0

Generally:

MMMM zwvn


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A measure of the molecular-weight distribution (MWD) is given by the ratios ofmolecular -weight averages.

For this purpose, the most commonly used ratio is Mw/Mn, which is called thepolydispersity index or PDI.

PDI= Mw/Mn

Mw/Mn = 1 monodispersePolymer sample consisting of molecules all of which have the samechain length

Mw/ Mn > 1 polydispersePolymer consisting of molecules with the variety of chain length

0 200,000 400,000 600,000 800,000 1,000,000

4.0

3.0

2.0

1.0

0

Mi (g/mol)

104wi

MM pn = g/mol000,100

g/mol900,199=Mw

g/mol850,299=M z

g/mol000,165=Mv

1=wi



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Molecular Weight Distribution (MWD)

M

MMWD

n

w=

Perfectly MonodisperseMWD = 1.0

Monodisperse (general term)1.0 < MWD 1.1

PolydisperseMWD > 1.1

Living polymerization:1.0 < MWD 1.1

Radical polymerization:1.5 < MWD 2.0

Condensation polymerization:MWD ~ 2

Ziegler-Natta polymerization:5 < MWD < 30


28

CH2CH2 n

polyethylene (PE)

MW = 105

g/molN = 7143 CH2a = 0.154 nm

random coil

extended chain

Rg = N0.5a= 13.0 nm

Rg (radius of gyration)

Lex = Na = 1100.0 nm= 1.1 m

An Example Polymer - Polyethylene

CH2=CH2ethylene


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Start Destination Miles

1: A 2: B 210

2: B 3: C 90

3: C 4: D 620

4: D 5: E 2790

Suppose that you want to travel from place A to place E, visiting yourfriends along the way. Unfortunately your friends live only on the easternand western coasts, leading to a somewhat unconventional journey.

An Exercise

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The number-average of the miles traveled in the four legs of thejourney is 928 miles. This is the average distance traveled in eachleg of the journey. It places equal emphasis on each leg.

An Exercise - continued

miles5.927

1111

2790162019012101

=

+++

+++=

==

N

MNMxM

i

iiiin

Number-average


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miles8.22152790162019012101

27901620190121012222

2

=+++

+++=

=

==

MN

MNM

MN

MNMwM

ii

iii

ii

iiiiw

The mass-average of the miles traveled in the four legs of thejourney is 2216 miles. This average places a greater emphasison the leg of the journey with the largest "mass" - that is thefourth leg in which you travel 2790 miles. It is morerepresentative of the major part of your journey.

Mass-average

An Exercise - continued

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Property - Molecular Weight Dependence

1. Glass Transition MW Dependence

10-4

Mn

Tg

(C)

PMMA

M

KTT

n

gg =

K is a polymer-related constant.


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2. Viscosity MW Dependence

M < Mc, no entanglement M > Mc, entanglement

Mc critical MW

3.4

1.0

topologicalentanglement


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Entanglements affects solubility of polymers

Polymers chains tends to entangle beyond criticallength and when entangled, polymers cant movelaterally but move along their lengths (think chowmein)

Polymers that are long enough to entangle

need to disentangle before dissolutionSolvent diffuses into the solid and swells thematerial, allowing space for movement and thenslow longitudinal diffusion allows single chainsto dissolve

l2 mw sp relation

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