307 - key relationships

Molecular weight ↑ → entanglement ↑

Longer chains have more opportunities to become physically entangled.

Molecular weight ↑ → viscosity ↑

More entanglement makes polymer flow more difficult.

Molecular weight ↑ → toughness ↑

Greater entanglement makes crack growth more difficult.

Molecular weight ↑ → creep ↓

Entanglements restrict chain movement.

Branching ↑ → density ↓

Branches prevent efficient chain packing.

Branching ↑ → crystallinity ↓

Branches make ordered packing more difficult.

Free volume ↑ → Tg ↓

More space allows molecular movement at lower temperatures.

Crosslinking ↑ → molecular mobility ↓

Covalent links restrict chain movement.

Crosslinking ↑ → Tg ↑

Restricted molecular movement requires greater thermal energy.

Secondary bonding ↑ → Tg ↑

Stronger intermolecular forces make molecular movement more difficult.

Crystallinity ↑ → modulus ↑

Ordered crystalline regions resist deformation.

Crystallinity ↑ → strength ↑

Crystalline regions provide structural reinforcement.

Crystallinity ↑ → ductility ↓

Ordered structures restrict molecular movement.

Cooling rate ↑ → crystal size ↓

Rapid cooling favours nucleation over crystal growth.

Cooling rate ↓ → crystal size ↑

Slow cooling allows crystals more time to grow.

Shear rate ↑ → viscosity ↓

Polymer chains orient and slide past one another more easily.

Temperature ↑ → molecular mobility ↑

Chains can move and rearrange more easily.

Temperature ↑ → relaxation rate ↑

Internal stresses redistribute faster.

Frequency ↑ → polymer appears more elastic

Chains have less time to relax during each cycle.

Frequency ↑ → observed transition temperature ↑

Faster deformation shifts transitions towards higher temperatures.

Aging time ↑ → free volume ↓

The polymer moves towards equilibrium.

Aging time ↑ → stiffness ↑

Reduced free volume restricts molecular motion.

Strain rate ↑ → apparent strength ↑

Chains have less time to rearrange.

Temperature ↓ → brittleness ↑

Molecular mobility decreases.

Temperature ↑ → ductility ↑

Molecular mobility increases.

Higher molecular weight → craze stability ↑

More entanglements help stabilise craze fibrils.

Higher crosslink density → flow resistance ↑

Crosslinks prevent chains from freely moving past one another.

Higher crystallinity → thermal resistance ↑

Ordered crystalline regions generally remain stable to higher temperatures than amorphous regions.