Amorphous Polymers • When is a Pol ymer Amor phous ? Ex amp les • Wh y is a Polyme r Amo rphous ? • Amorphous Polyme r Pr operties • St ructure of Amor ph ous Pol ymer s – Long Range vsShort Range Order– Shape of Polymer C hains (Random Coil Models) – Experimental Co nfirmations (Neutr on Scattering) – Other Models (Non R andom Coils) • Dyn ami cs of Pol yme r Chai ns: Vis cos ity
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• Below TgMolecular motion is very localized (vibrations and few bond rotations)Hard, Brittle and High Modulus
• In the Tg Region
Onset of large-scale molecular motions (vibration and significant bond rotations)Soft, tough and lower Modulus.Properties depend on time/speed/frequency of perturbation
• Knowing the number of repeat units of a polymer chain, can we calculate its size ?
• Three basic models for linear polymer chains with various levels of approximationand sophistication.
– Random flight or freely jointed chain model:Assume the polymer chain can be described by a random flight in threedimensions (fixed bond length & random valence angle)
– Freely rotating chain model:Add the constraint of fixed valence angle to the previous model
– Hindered rotation model:Add the constraint that the dihedral angles describing the rotation of backboneatoms around single bonds cannot be random.