Chapter 14

Question 1

What is a polymer?

Answer 1

Many repeating units

Question 2

What are some naturally occurring polymers?

Answer 2

• Wood
• Cotton
• Rubber
• Wool
• Leather
• Silk

Question 3

What are hydrocarbons?

Answer 3

Polymers made up of H and C

Question 4

What are saturated hydrocarbons?

Answer 4

Each carbon atom is bonded to four other atoms

Question 5

What are unsaturated hydrocarbons?

Answer 5

• At least one double or triple Carbon Carbon bond
• Somewhat unstable

Question 6

What is an isomer?

Answer 6

Compounds with the same chemical formula but different structures and properties

Question 7

What is free radical polymerization?

Answer 7

A free radical/initiator is used to open up a double or triple bond and resulting monomers also have only single bonds

Question 8

What is a repeat unit?

Answer 8

The most fundamental structural unit in a polymer chain. A polymer molecule is composed of a large number of repeat units linked together.

Question 9

What is molecular weight M?

Answer 9

Mass of a mole of chains, but not all chains in a polymer at the same length

Question 10

How is number average molecular weight calculated?

Answer 10

Mn = total weight/total # of molecules
or number fraction of chains * mean weight

Question 11

How is weight average molecular weight calculated?

Answer 11

Mw = weight fraction of chains * mean weight

Question 12

What is the number fraction?

Answer 12

Number of chains within a range/total number of chains

Question 13

What is the weight fraction?

Answer 13

(Number of chains within a range * mean weight)/total w

Question 14

What is polymerization?

Answer 14

When monomers bond together to form polymer chains

Question 15

What is the degree of polymerization?

Answer 15

The average number of repeat units per polymer chain molecule

Question 16

What are the four types of polymer structures?

Answer 16

• Linear (High-density polyethylene)
• Branched (Low-density polyethylene)
• Cross-linked
• Network (3D shapes within a single polymer)
• Strength increases down the list

Question 17

How is molecular shape or conformation changed?

Answer 17

Changing the shape of a polymer by rotating carbon atoms about their bonds without breaking them

Question 18

How is configuration changed?

Answer 18

By breaking bonds

Question 19

What are stereoisomers?

Answer 19

Monomers that are mirrored and can’t be superimposed without breaking a bond

Question 20

What is tacticity?

Answer 20

The stereoregularity or spatial arrangement of R units along chain (atom or side group other than H) along chain

Question 21

What is isostatic?

Answer 21

All R groups are on the same side of the chain

Question 22

What is syndiotactic?

Answer 22

R groups alternate sides of the chain

Question 23

What is atactic?

Answer 23

R groups are randomly positioned along the chain

Question 24

What is a cis isomer?

Answer 24

Isomer that has a side group on the same side of the chain

Question 25

What is a trans isomer?

Answer 25

Isomer that has a side group on opposing sides of the chain

Question 26

What are copolymers?

Answer 26

Two or more monomers polymerized together

Question 27

What are the four types of copolymers?

Answer 27

- Random (randomly positioned along a chain) - Alternating (A and B alternate along a chain) - Block (Large blocks of A and B alternate) - Graft (chains of B units grafted onto A backbone)

Question 28

What is crystallinity in polymers?

Answer 28

Crystal structures in terms of unit cells

Question 29

What are some characteristics of crystalline regions?

Answer 29

- Thin platelets with chain folds at faces - Chain folded structure

Question 30

What are crystallites?

Answer 30

A region within a crystalline polymer in which all the molecular chains are ordered and aligned.

Question 31

What are some characteristics of crystallinity in polymers?

Answer 31

- Polymers are rarely 100% crystalline - Degree or % crystallinity can influence physical properties - Heat treating causes the crystalline region to grow and increase in % crystallinity - Slower cooling increases % crystallinity

Question 32

What does amorphous mean?

Answer 32

Without a clearly defined shape or form (noncrystalline)

Question 33

What is spherulite?

Answer 33

Chain-folded crystallites that radiate from a nucleation site and are separated by amorphous regions. Often caused by rapid growth rates

Question 34

How are single crystals formed?

Answer 34

Through slow and controlled growth rates