Elastomers-Polyurethanes Flashcards
Behavior of elastomers
Elastic behavior over very large strains
Molecular arrangement of elastomers
Amorphous
Glass Transition temperature
Above Tg: at room temperature
What can delay the plastic deformation of elastomers?
Crosslinking
Processing of elastomers
Thermoset
Polyurethane characteristics (elastomer)
Tough, elastomeric, good fatigue resistance
Uses of polyurethanes (elastomer)
Pacemakers, artificial hearts, blood-contacting applications
What type of copolymer are polyurethanes (elastomer)
Block copolymer
hard (glassy) and soft (rubbery) segments
What reacts to make polyurethane
Diisocyanates and diols
What is a concern that occurs due to the presence of isocyanates
Cytotoxicity
Processing of polyurethanes
Most thermoset some thermoplastic
Properties of polymers based on structure
- Structure determines properties (types of isocyanate and polyol)
- with long polyol chains with few crosslinks result in a highly elastic polymer
- short chains with high crosslinking result in a highly rigid polymer
- High crosslinking results in high molecular weight polymer results in one large single molecule with thermoset properties
What makes polyurethanes thermoplastic?
- Segmented structure of polyurethane
- Crosslinking between hard segments
- Crosslinks are broken by heat and reformed by cooling resulting in thermoplastic behavior
What makes up silicone elastomers?
Repeating Si-O bonds
What contributes to unique properties of silicones?
Presence of organic (C) groups attached to an inorganic (no C) backbone
