Chapter 14 Flashcards
What are 6 examples of natural polymers?
wood, cotton, leather, rubber, wool, silk
What are most polymers made up of? What is this called?
made up of H and C
Hydrocarbons
What are the intramolecular bonds of hydrocarbons?
covalent
What is a saturated hydrocarbon? What is an example?
Each carbon is singly bonded to four other atoms
C2H6S
What are unsaturated molecules?
Molecules that have double and triple covalent bonds
What are saturated molecules?
Molecules where all bonds are single ones, and no new atoms may be joined without the removal of others that are already bonded
What is a Paraffin compound chemical formula?
What are the first four molecules of the Paraffin family?
Methane, ethane, propane, butane
What is the composition, structure, and boiling point of the first four paraffin compounds?
What kind of bonds do unsaturated hydrocarbons have? Give examples for each.
Double and triple bonds that are somewhat unstable
Double bond: ethylene or ethene- C2H4
Tripple bond: acetylene or ethyne- C2H2
What is isomerism? What’s are two examples?
When two compounds have the same chemical formula but have different structures/atomic arrangements
C8H18: normal-octane and 2,4-dimethylhexane
butane and isobutane
How big are polymer molecules in comparison to hydrocarbon molecules? What are they often called?
molecules in polymers are MUCH bigger. They are called macromoledules.
What are the two steps of free radical polymerization?
Initiation and propagation
What happens during initiation in free radical polymerization?
a free radical “R” is added to a monomer (ex: ethylene)
What happens during propagation in free radical polymerization?
the R+monomer i added to another repeat unit, creating a dimer, which eventually creates a polymer
What is an initiator? Give an example.
A substance that starts the polymerization reaction by generating free radicals
Benzoyl peroxide
What is polyethylene? Give an example.
A long-chain hydrocarbon
Paraffin wax for candles is short-chain polyethylene
What are the repeat units for the first 4/10 polymeric materials?
1) polyethylene (PE)
2) poly (vinyl chloride) (PVC)
3) polytetrafluoroethylene (PTFE)
4) polypropylene (PP)
What are the repeat units for 5-7/10 polymeric materials?
5) polystyrene (PS)
6) poly (methyl methacrylate) (PMMA)
7) phenol-formaldehyde (Backelite)
What are the repeat units for 8-10/10 polymeric materials?
8) poly (hexamethylene adipamide) (nylon 6,6)
9) poly (ethylene terepthalate) (PET, a polyester)
10) polycarbonate (PC)
What is molecular weight?
M
The mass of a mole of chains
What is a homopolymer?
When all of the repeating units along a chain are of the same type
What is a copolymer?
A polymer the chain has two or more different repeat units
Why are not all chains in a polymer the same length?
There’s a distribution of molecular weights
What type of bonding is in a linear polymer structure?
secondary bonding
What are copolymers?
Two or more monomers polymerized together
What are the four categories of copolymers?
1) random
2) alternating
3) block
4) graft
What does a random copolymer look like?
A and B are randomly positioned along chain
What does an alternating copolymer look like?
A and B alternate in polymer chains
What does a block copolymer look like?
large blocks of A units alternate with large blocks of B units
What does a graft copolymer look like?
chains of B units grafted onto A backbone
How do you identify crystallinity in polymers? How do you define a crystal structure? What’s an example?
Ordered atomic arrangements involving molecular chains
Crystal structures are in terms of unit cells
Polyethylene
What are crystalline regions? What is their structue?
Thin platelets with chain folds at faces
Chain folded structure
Are polymers ever 100% crystalline? Why?
No they’re rarely 100% crystalline
It’s difficult for all regions of all chains to become aligned
What is degree of crystallinity usually expressed as?
% crystallinity
What do physical properties of polymers usually depend on? What can change this?
Properties depend on % crystallinity
Heat treating causes crystalline regions to grow and % crystallinity to increase
How do polymer single crystals form? What do they look like under electron micrographs?
Single crystals only occur for slow and carefully controlled growth rates
They look like multilayered single crystals (chain-folded layers) of polyethylene
What structure do some semicrystalline polymers form?
Spherulite structures
What does spherulite structure look like?
Alternating (lamellar) chain-folded crystallites and amorphous regions
They begin at the nucleation site
Regions are divided by interspherulitic boundary
What is the growth rate for spherulite structure?
Relatively rapid
What happens when a cross-polarized light is used to photomicrograph spherulites in polyethylene?
a maltese cross appears in each spherulite
What are some polymers that form with linear structures?
1) polyethylene
2) poly (vinyl chloride)
3) nylon
4) fluorocarbons
