Chapter 14 Flashcards
What is a polymer?
Many repeating units
What are some naturally occurring polymers?
- Wood
- Cotton
- Rubber
- Wool
- Leather
- Silk
What are hydrocarbons?
Polymers made up of H and C
What are saturated hydrocarbons?
Each carbon atom is bonded to four other atoms
What are unsaturated hydrocarbons?
- At least one double or triple Carbon Carbon bond
- Somewhat unstable
What is an isomer?
Compounds with the same chemical formula but different structures and properties
What is free radical polymerization?
A free radical/initiator is used to open up a double or triple bond and resulting monomers also have only single bonds
What is a repeat unit?
The most fundamental structural unit in a polymer chain. A polymer molecule is composed of a large number of repeat units linked together.
What is molecular weight M?
Mass of a mole of chains, but not all chains in a polymer at the same length
How is number average molecular weight calculated?
Mn = total weight/total # of molecules
or number fraction of chains * mean weight
How is weight average molecular weight calculated?
Mw = weight fraction of chains * mean weight
What is the number fraction?
Number of chains within a range/total number of chains
What is the weight fraction?
(Number of chains within a range * mean weight)/total w
What is polymerization?
When monomers bond together to form polymer chains
What is the degree of polymerization?
The average number of repeat units per polymer chain molecule
What are the four types of polymer structures?
- Linear (High-density polyethylene)
- Branched (Low-density polyethylene)
- Cross-linked
- Network (3D shapes within a single polymer)
- Strength increases down the list
How is molecular shape or conformation changed?
Changing the shape of a polymer by rotating carbon atoms about their bonds without breaking them
How is configuration changed?
By breaking bonds
What are stereoisomers?
Monomers that are mirrored and can’t be superimposed without breaking a bond
What is tacticity?
The stereoregularity or spatial arrangement of R units along chain (atom or side group other than H) along chain
What is isostatic?
All R groups are on the same side of the chain
What is syndiotactic?
R groups alternate sides of the chain
What is atactic?
R groups are randomly positioned along the chain
What is a cis isomer?
Isomer that has a side group on the same side of the chain
What is a trans isomer?
Isomer that has a side group on opposing sides of the chain
What are copolymers?
Two or more monomers polymerized together
What are the four types of copolymers?
- 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)
What is crystallinity in polymers?
Crystal structures in terms of unit cells
What are some characteristics of crystalline regions?
- Thin platelets with chain folds at faces
- Chain folded structure
What are crystallites?
A region within a crystalline polymer in which all the molecular chains are ordered and aligned.
What are some characteristics of crystallinity in polymers?
- 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
What does amorphous mean?
Without a clearly defined shape or form (noncrystalline)
What is spherulite?
Chain-folded crystallites that radiate from a nucleation site and are separated by amorphous regions. Often caused by rapid growth rates
How are single crystals formed?
Through slow and controlled growth rates
