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Morfologi Polimer

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• Chemical structure of polymer has profound effect on physical properties of polymer i.e. strength, durability, transparency, heat resistance, weather resistance, spinnability, resilience and flammability.

• Polymer properties make polymer is commercially produced.

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Tacticity: How groups are arranged along polymer

R R R R R R R R R RR

isotactic

R R R R R R R R R RR

syndiotactic

Vinyl Monomers

R R R R R R R R R RR

atactic

1. Stereochemistry

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Tacticity: disubstituted monomers

R R R R R R R R R R

R R R R R R R R RR

R

R R R R R R R R R R

R R R R R R R R R

RR

isotactic

syndiotactic

H

Polymer

R

H

Polymer

R

Looksing at indicated atoms from the left

H

Polymer

R

R

Polymer

H

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2. Glass transition temperature (Tg)

The glass transition temperature (Tg) describes the temperature at which amorphous polymers undergo a second order phase transition from a rubbery, viscous amorphous solid (fresh spaghetti) to a brittle, glassy amorphous solid (3 days old Spaghetti)

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Glass-rubber-liquid

Amorphous plastics have a complex thermal profile with 3 typical states:

Log(stiffness)Pa

Temperature

3

9

6

7

8

4

5

Glass phase (hard plastic)

Rubber phase (elastomer)

Liquid

Leathery phase

Polystyrene

Tg

Tygon (plasticized PVC)

PDMS

polyisobutylene

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Properties Affected :• Specific Volume / Density• Specific Heat, Cp• Refractive Index• Modulus• Dielectric Constant• Permeability

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• Rigid group in backbone

• Flexible polymer backbone

• Steric Hinderance

• Long plasticizing side groups

• Symmetrical substituents

• Polar functionalities

• Plasticizers

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Factors influencing Tg

1. Chain flexibility• Silicone > Ether > Hydrocarbon > Cyclic HC

> Aromatics

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– Tg = -55 deg.C 88 deg.C•

2. Steric Bulk of Substituents

Tg = -120C 5C -24C -50C

Long side chains may act as plasticizers (C 6)

O O

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3. Molecular Symmetry Asymmetry increases chain stiffness. 4. Polar Interactions increase Tg Hydrogen bonding5. Molecular Weight up to Critical Limit6. Crosslinking Reduces Segment Mobility

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3. Crystallinity in Polymers

Sheaf-like arrangement of lamellae in a blend of polyethylenesSystem: Polyethylene (PE), Composition: LPE:BPE 3:1

An image of an alkane crystal taken by AFMSystem: Alkane, Composition: C36H74

An image of a single crystal alkaneSystem: Alkane, Composition: C294H590

Single PE spherulite AFM

Maltese cross spherulites

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natural rubber(x30,000).• Chain-folded lamellar crystallites (white lines) ~10nm thick extend radially.

Crystalline structures in polymers

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crystalline region

amorphous region

• % Crystallinity: % of material that is crystalline. --TS and E often increase with % crystallinity. --Annealing causes crystalline regions to grow. % crystallinity increases.

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Intramolecular interactions (Hf) favor crystallization & higher Tm

Hydrogen bonding20 kJ/mol

Van der Waals: 2 kJ/mole

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Molecular weight influence on Tm

• Melting temperatures of n-alkanes (up to C100) as a function of chain length.

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Methods for Inducing Crystallization in Polymers

• Slow cooling of molten polymer• Annealing between Tg and Tm

• Evaporation of solvent• Shear & disintanglement• Stretching and alignment of macromolecules

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Branching on Crystallinity

Which one will be more likely to crystallize?

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Linear crystallizes easier (HDPE = linear; LDPE = branched)

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Nucleation Rates between Tg and Tm

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Primary Crystallization

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Cry

sta

llin

ity (

%)

Cooling rate (oC/s)

10

20

30

40

00.01 0.1 1.0 10 100

Slo

w C

oolin

g

Quench

ing

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Early stages of crystallation of PEEK in the presence of a carbon fibre.

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Effects of Crystallinity

1) Strength: Stronger & Stiffer

2) Optical: Opaque (scattering by spherulites)

3) Higher density

4) Less Soluble

5) Less Permeable