Morfologi Polimer 1

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. 2

Tacticity: How groups are arranged along polymer 1. Stereochemistry 3

Tacticity: disubstituted monomers 4

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) 5

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Glass-rubber-liquid Amorphous plastics have a complex thermal profile with 3 typical states: Log(stiffness) Pa Temperature Glass phase (hard plastic) Rubber phase (elastomer) Liquid Leathery phase Polystyrene TgTg Tygon (plasticized PVC) PDMS polyisobutylene 7

Properties Affected : Specific Volume / Density Specific Heat, Cp Refractive Index Modulus Dielectric Constant Permeability 8

Rigid group in backbone Flexible polymer backbone Steric Hinderance Long plasticizing side groups Symmetrical substituents Polar functionalities Plasticizers 9

Factors influencing Tg 1. Chain flexibility Silicone > Ether > Hydrocarbon > Cyclic HC > Aromatics 10

– Tg = -55 deg.C 88 deg.C 2. Steric Bulk of Substituents Tg = -120  C 5  C -24  C -50  C Long side chains may act as plasticizers (C  6) 11

3. Molecular Symmetry Asymmetry increases chain stiffness. 4. Polar Interactions increase Tg Hydrogen bonding 5. Molecular Weight up to Critical Limit 6. Crosslinking Reduces Segment Mobility 12

3. Crystallinity in Polymers Sheaf-like arrangement of lamellae in a blend of polyethylenes System: Polyethylene (PE), Composition: LPE:BPE 3:1 An image of an alkane crystal taken by AFM System: Alkane, Composition: C 36 H 74 An image of a single crystal alkane System: Alkane, Composition: C 294 H 590 Single PE spherulite AFM Maltese cross spherulites 13

natural rubber(x30,000). Chain-folded lamellar crystallites (white lines) ~10nm thick extend radially. Crystalline structures in polymers 14

% Crystallinity: % of material that is crystalline. --TS and E often increase with % crystallinity. --Annealing causes crystalline regions to grow. % crystallinity increases. 15

Intramolecular interactions (  H f ) favor crystallization & higher T m Hydrogen bonding 20 kJ/mol Van der Waals: 2 kJ/mole 16

Molecular weight influence on Tm Melting temperatures of n-alkanes (up to C 100 ) as a function of chain length. 17

Methods for Inducing Crystallization in Polymers Slow cooling of molten polymer Annealing between T g and T m Evaporation of solvent Shear & disintanglement Stretching and alignment of macromolecules 18

Branching on Crystallinity Which one will be more likely to crystallize? 19

Linear crystallizes easier (HDPE = linear; LDPE = branched) 20

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Nucleation Rates between Tg and Tm 22

Primary Crystallization 23

Crystallinity (%) Cooling rate ( o C/s) Slow Cooling Quenching 24

Early stages of crystallation of PEEK in the presence of a carbon fibre. 25

Effects of Crystallinity 1)Strength: Stronger & Stiffer 2)Optical: Opaque (scattering by spherulites) 3)Higher density 4)Less Soluble 5)Less Permeable 26