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MSE 2034 > Chapter 14 > Flashcards

Chapter 14 Flashcards

1
Q

What is a polymer?

A

Many repeating units

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2
Q

What are some naturally occurring polymers?

A
  • Wood
  • Cotton
  • Rubber
  • Wool
  • Leather
  • Silk
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3
Q

What are hydrocarbons?

A

Polymers made up of H and C

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4
Q

What are saturated hydrocarbons?

A

Each carbon atom is bonded to four other atoms

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5
Q

What are unsaturated hydrocarbons?

A
  • At least one double or triple Carbon Carbon bond
  • Somewhat unstable
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6
Q

What is an isomer?

A

Compounds with the same chemical formula but different structures and properties

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7
Q

What is free radical polymerization?

A

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

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8
Q

What is a repeat unit?

A

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

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9
Q

What is molecular weight M?

A

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

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10
Q

How is number average molecular weight calculated?

A

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

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11
Q

How is weight average molecular weight calculated?

A

Mw = weight fraction of chains * mean weight

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12
Q

What is the number fraction?

A

Number of chains within a range/total number of chains

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13
Q

What is the weight fraction?

A

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

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14
Q

What is polymerization?

A

When monomers bond together to form polymer chains

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15
Q

What is the degree of polymerization?

A

The average number of repeat units per polymer chain molecule

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16
Q

What are the four types of polymer structures?

A
  • Linear (High-density polyethylene)
  • Branched (Low-density polyethylene)
  • Cross-linked
  • Network (3D shapes within a single polymer)
  • Strength increases down the list
17
Q

How is molecular shape or conformation changed?

A

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

18
Q

How is configuration changed?

A

By breaking bonds

19
Q

What are stereoisomers?

A

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

20
Q

What is tacticity?

A

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

21
Q

What is isostatic?

A

All R groups are on the same side of the chain

22
Q

What is syndiotactic?

A

R groups alternate sides of the chain

23
Q

What is atactic?

A

R groups are randomly positioned along the chain

24
Q

What is a cis isomer?

A

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

25
Q

What is a trans isomer?

A

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

26
Q

What are copolymers?

A

Two or more monomers polymerized together

27
Q

What are the four types of copolymers?

A
  • 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)
28
Q

What is crystallinity in polymers?

A

Crystal structures in terms of unit cells

29
Q

What are some characteristics of crystalline regions?

A
  • Thin platelets with chain folds at faces
  • Chain folded structure
30
Q

What are crystallites?

A

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

31
Q

What are some characteristics of crystallinity in polymers?

A
  • 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
32
Q

What does amorphous mean?

A

Without a clearly defined shape or form (noncrystalline)

33
Q

What is spherulite?

A

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

34
Q

How are single crystals formed?

A

Through slow and controlled growth rates

MSE 2034 (15 decks)

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