21. Polymers II: Bulk Properties

Question 1

For the same compostion and MW, increased cystalinity means _____ density because….

Answer 1

increased density

better packing in crystalline versus amorphous

Question 2

Name 4 factorrs that inhibit crystal formation in polymer

Answer 2

1. Bulky side groups
2. Branching
3. Atacticity (random distribution of sidechain locations)
4. Random arrangement of mers in copolymers

Question 3

Crystallinity means greater degree of secondary bonds which means increased…. (name 5 things)

Answer 3

1. Melting temperature
2. Strength
3. Stiffness
4. Density (ie. Greater packing of polymer chains)
5. Resistance to softening (polymer can be used at higher temperatures)

Question 4

Increased strain rate (deformation rate) means ____ elastic modulus, ____ ductility, ____ ultimate tensile strength

Answer 4

increased elastic modulus
decreased ductility
increased ultimate tensile strength

Question 5

_____ decompose upon heating and do not become softer

Answer 5

thermoset

Question 6

_____ become more pliable and moldable upon heating

Answer 6

thermoplastics

Question 7

______ can withstand large elastic strains at ambient temperatures

Answer 7

elastomers

Question 8

Name 3 characteristics of thermosets

Answer 8

1. strong and stiff
2. better at high temps than thermoplastics (until it decomposes)
3. more chemically inert than thermo plastics

Question 9

Name 3 characteristis of thermoplastics

Answer 9

1. less strong and stiff than thermosets
2. cannot be used at high temperature (it melts)
3. can be formed using injection moulding, vacuum forming, or extrusion

Question 10

In thermoset polymer chains are held together by _____

Answer 10

crosslinking

Question 11

In thermoplastics, polymer chains are held together by _____

Answer 11

weak secondary bonds