Polymer Morphology - Amorphous Polymers Flashcards
What are five unique features of polymeric materials?
- Synthesis
- Average molecular weight and molecular weight distribution
- Types of bonding
- Semicrystalline morphology
- Viscoelasticity
What do viscoelastic properties depend on?
temperature and time
What do viscoelastic materials have?
Both elastic and viscous behavior
What are the amorphous states?
- Melt state
- Glassy state
- Solution state
What is a polymer chain in the amorphous state described as?
Random coil
When is a glassy polymer amorphous?
below Tg
When is a rubbery polymer amorphous?
above Tg
When is a semicrystalline polymer amorphous?
above Tm and between crystals (T<Tm)
What temp is the amorphous state stable?
above Tm
why do some polymers not crystallize?
- crystallization kinetics too slow
- structure is not conductive to order
What is negatively impacted by increased branching?
degree of crystallinity in an amorphous polymer
When is molecular motion very localized?
Below Tg for amorphous polymers
What happens below Tg for amorphous polymers?
- High modulus
- Hard and brittle
When does the onset of large scale motions take place?
Around Tg for amorphous polymers
What happens around Tg for amorphous polymers?
- Time/speed/frequency of perturbation dependence
- Lower modulus
- Soft and tough
What type of region is below the Tg when a polymer is amorphous?
Glassy
What is the structure of amorphous polymers?
- Short range order
- No long range order
What are the 3 basic models for linear polymer chains?
- Random flight or freely jointed chain model
- Freely rotating chain model
- Hindered rotation model
What is the freely rotating chain model?
- Valence angles are identical and fixed
- Bonds can rotate freely
What is the hindered rotation chain model?
- Rotations around single bonds along chains are not free
What causes hindered rotations in a chain model?
Steric repulsions
