Polymers Flashcards
(23 cards)
Only hydrogen bonding or/and Van de Waals between chains
Thermoplastics
Secondary (weak) bonds melt at glass transition temperature (Tg)
Thermoplastics
Chains can slide over each other and flow at high T
Thermoplastics
Can be melted and recast
Thermoplastics
Extensive covalent cross-links
Thermosets
Very rigid, cannot deform much
Thermosets
CANNOT be melted and cast
Thermosets
Few covalent cross-links
Elastomers
“Memory” of chain positions, even after large extensions
Elastomers
CANNOT be melted or cast
Elastomers
Primary bonds, strong and stiff, maintained at high temps
Covalent cross-links
Secondary bonds, weak and not stiff, “melt above Tg
Hydrogen or Van der Waals
Chains entangle, side groups interact
Mechanical interactions
Drawn fibers from melt, very stiff (covalent bonds)
Aligned fibers
Chains fold and generate structure, can form spherical shape (“spherulite”)
Crystalline
Less dense than crystalline, lower modulus
Amorphous
NO covalent cross links between chains
Thermoplastics
Strong dependence on temperature, rigid when T < Tg (secondary bonding between chains), rubber-like when T > Tg (secondary bonds melt)
Thermoplastics
Contain extensive covalent cross-links, formed by resin and hardener
Thermosets
Occasional cross-links, between thermoplastics and thermosets
Elastomers
Secondary bonds melt at room temp
Elastomers
Applied stress leads to straightening of chains (large deformations)
Elastomers
Light cross-linking provides “memory” of original configuration, returns to original shape upon unloading
Elastomers
