Elastomers

Question 1

Which of the following is not true regarding elastomers?
Material capable of reversible change
Rubbery Compound
Referred to as memory
Generally semi-crystalline thermoplastic

Answer 1

Generally semi-crystalline thermoplastic

Question 2

True or false: Amorphous thermosets have temporary crosslinks.

Answer 2

False

Question 3

True or false: When a force is removed, the elastomer will return to the exact same orientation as before the force was applied.

Answer 3

False

Question 4

What makes thermoplastic elastomers different from thermoset polymers?
No Crosslinking
More recyclable
Can be remelted and reshaped by heating
All of the above

Answer 4

All of the above

Question 5

Neoprene is an example of what type of elastomer?
Polyurethane
Silicone
Natural and Synthetic Rubber
Natural Protein

Answer 5

Natural and Synthetic Rubber

Question 6

What is the general formula for polyisocyanates?
R-(N=C=O)n, n=2-4
R-(N=C)n, n=4-6
R-(N=C=Si)n, n=2-4
R-(N=C=P)n, n=4-6

Answer 6

R-(N=C=O)n, n=2-4

Question 7

True or false: PEO is most commonly used as elastomers because of its flexibility

Answer 7

False

Question 8

True or false: Polyols with short chains give higher cross-linking and result in a rigid polyurethane foam.

Answer 8

True

Question 9

Elastomer examples

Answer 9

gaskets, wetsuits, sealant, gloves, flexible tubing, soft-touch components

Question 10

Elastomers

Answer 10

materials capable of reversible change in length at operating temperatures, that is, once a load is removed the material returns to its original dimensions, rubbery compound, generally amorphous thermosets

Question 11

Glass transition temperature (Tg)

Answer 11

temperature at which transition from a brittle, glass-like state to a rubbery, flexible state
Below Tg, frozen, stiff polymer chains
Above Tg, chains gain mobility and can move more freely
must be below room temp for material to exhibit rubber-like behavior

Question 12

Elastomer, amorphous thermosets

Answer 12

Amorphous thermosets maintain a random arrangement of polymer chains but have permanent crosslinks. This cross-linking is essential for maintaining elasticity while preventing flow or deformation at elevated temperatures. disordered molecular structure

Question 13

Entropy

Answer 13

Measure of randomness
When the force is removed, the chains spontaneously return to their disordered, random coil state, which maximizes entropy.
low entropy: aligned, more ordered, thermodynamically unfavorable
elasticity in elastomers is entropy-driven

Question 14

Thermoset elastomers

Answer 14

• irreversible curing process
• permanent chemical crosslinks between polymer chains (provide elasticity, resistance to deformation, and durability)
• cannot be remelted or reshaped by heating
• less recyclable

Question 15

Thermoset elastomer applications

Answer 15

high heat resistance, mechanical stability, long-term durability
ex: neoprene, rubber

Question 16

Important reactions of isocyanates

Answer 16

formation of carbamic acid redirected by the addition of components with an acidic H-atom across the C=N double bond
OH group-containing compounds are the most important reactants for isocyanates.

Question 17

Synthesis of polyurethanes

Answer 17

Two-component system, generate polyurethanes with different structures depending on the component used

Question 18

Polyols

Answer 18

bring different properties to the table, allowing polyurethane materials to be tailored for specific applications.

Question 19

PTMO and PPG (polyols)

Answer 19

more commonly used in elastomers and foams for their flexibility.

Question 20

PEO (polyols)

Answer 20

favored for its biocompatibility.

Question 21

PXS (polyol)

Answer 21

used for applications requiring chemical and thermal stability.

Question 22

Three-component system

Answer 22

diisocyantes, diols, chain extenders

Question 23

Polyurethanes (PUs)

Answer 23

can be either thermoplastic or irreversibly thermoset. use of diisocyanate and a bi-functional polyol results in thermoplastics without crosslinking, whereas the use of components with more than two functional groups (e.g., triisocyanate or a multi-hydroxyl polyol) will yield PUs with three-dimensional crosslinking.

Question 24

Polyol with short chains and high functionality…

Answer 24

gives high cross-linking and rigid PU foam

Question 25

Polyol with long chains and low functionality…

Answer 25

gives lower cross-linking and flexible PU foam

Question 26

Silicone

Answer 26

polysiloxanes

Question 27

neoprene

Answer 27

natural and synthetic polymer