Chapters 14 and 15

Question 1

What are polymers?

Answer 1

Large molecules composed of repeating structural units called monomers.

Most polymers are hydrocarbons, (carbon and hydrogen)

They are defined by three key characteristics: chemistry, size, and structure.

Question 2

What are the two types of hydrocarbons?

Answer 2

Saturated hydrocarbons: Carbon single bond to 4 other atoms

Unsaturated hydrocarbons: Double and triple bonds (unstable, more reactive)

Question 3

How are polymers made?

Answer 3

Synthesized through polymerization. 2 types of polymerization:

Addition: Monomers with double bonds open up to join other monomers

Step: Two reacting monomers form a new molecule. Repeat until long chain forms

Question 4

What is the degree of polymerization and why is it important?

Answer 4

DP is the number of repeating units (monomers) in a polymer chain.

Higher DP means stronger, more viscous material, which can be harder to process.

The DP influences the molecular weight of the polymer, which in turn affects its physical properties (polydisparity) such as melting temperature, viscosity, and strength.

Question 5

a) What is polydisparity and how does it affect polymers?

b) What is the polydisparity index and what does it indicate?

Answer 5

a) Polydispersity is the variation in molecular weight of polymer chains.

This is because:
Not all molecules in the chain have the same weight.
Therefore, not all chains are the same length

Polydispersity significantly affects the physical properties of polymers, including their processing characteristics.

b) Polydispersity index (PDI) measures the distribution of molecular mass.

PDI=1 indicates all chains have the same weight (rare)
PDI>1 indicates a broader distribution of weights (typical).

Question 6

What are the different type of polymer structures?

Answer 6

3 categories: stereo-regularity, branching arrangements, structure type

1) Stereo-regularity:
Spatial arrangement of atoms and groups in repeating polymer units
-isotactic (strongest)
-syndiotactic (strong)
-atactic (softest)

2) Branching arrangements:
-Linear (chain-like)
-Branched (chain-like with side branches)
-cross linked (network structure)

3) Structure types:
-Homopolymers (repeating unit of one type)
-Copolymers (repeating unit of two types)
-Terpolymers (repeating unit of three types)

Question 7

Compare the effects of branching vs. cross linking

Answer 7

Effects of branching:
higher entanglement = higher strength (solid) or higher viscosity (plastic, liquid)

Effects of cross linking:
permanent irreversible structure set
-Thermosets: high cross linking, hard and brittle
-Elastomers: Low cross linking, elastic

Question 8

Give examples for arrangement of copolymers

Answer 8

1) Alternating:
Repeats every other place

2) Random:
No pattern

3) Block:
Same type groups into one long segment

4) Graft:
One type attaches as branches

Question 9

What are the main types of polymers?

Answer 9

1) Thermoplastic polymers
Soft when heated, solid when cooled
Easy to reshape and recycle
2) Thermosetting polymers
Soft when heated, solid when cooled
Cannot remelt, hardens irreversibly due to cross linking
3) Elastomers
High elasticity, recovers original shape
Similar to 2, cannot remelt, hardens irreversibly due to cross linking

Question 10

Pros vs. Cons of Polymers

Answer 10

Pros:
Low density
Good strength-to-weight ratio
High corrosion resistance
Low conductivity
Good ductility when heated
Less processing and energy consumption
Cost-competitive with metals

Cons:
Low strength
Low stiffness
Limited service temperature
Degradation from sunlight
Cannot handle continuous loads

Question 11

What are the 7 types of plastics in the plastics identification code?

Answer 11

1) PET
2) HDPE
3) PVC
4) LDPE
5) PP
6) PS
7) Other

Question 12

Explain commercial applications for thermoplastics

Answer 12

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