Copolymers

Question 1

What are copolymers?

Answer 1

they employ multiple monomer subunits in the same chain with complementary properties

• similar but different than polymer blends

Question 2

What is a classic example of copolymers?

Answer 2

Lego (ABS - acroylonitrile, butadiene, styrene subunits)

Question 3

How doe the properties of copolymers change?

Answer 3

the overall property depends on the relative fraction of each subunit

Question 4

How do we form black vs random vs alternating sequences for copolymers?

Answer 4

• depends on the probability for any one reaction to occur. These probabilities are based on the reaction kinetics for M1 or M2 to attach to a chain ending with M1 or M2 (4 possible combinations)

r1 = Kp11/Kp12
r2 = Kp22/Kp21
*rate constants of 1 reaction or another for species i

Can use probability distribution to determine how how long N will be before changing from adding M1 to M2

Question 5

What are the 4 cases relating to reaction rate for copolymer formation?

Answer 5

1. R1 «1 ; R2 «1
   - more likely to change which polymer is added - get alternating structure
2. R1 = 1; R2 = 1
   - get random, no preference for what chain is added next
3. R1R2 = 1
   - statistical copolymer (get statistical distribution of copolymer along chain with the probability of R1 and R2 determining the frequency of each
4. R1&raquo_space; 1; R2&raquo_space;1
   - favour same polymer, thus get block formation (low chance of switch then long sequence of same monomer)

Question 6

What changes the properties of a copolymer?

Answer 6

1. nature of its co-monomer subunits
2. the relative proportion of each co-monomer
3. the type of copolymer architecture
   - significantly large blocks can be seen to migrate (phase separation), creating interesting structures at the nanoscale

Question 7

How does phase separation occur for block copolymers?

Answer 7

• when blocks are sufficiently large, they can undergo phase separation processes where blocks will organize themselves to minimize surface energy
• these parameters can be tuned to provide structural control at the nanoscale and used to design function materials
• this thermodynamically driven ordering process is known as self-assembly

Question 8

What controls the structure of the copolymer?

Answer 8

• proportion of copolymers
• interfacial tension between copolymers

Get different structure depending on the volume fraction and how much copolymer likes to mix together (chiN) - can get lamellar, hexagonal, cubic, gyroid, or amorphous (disorder)

Question 9

What are some applications of copolymers?

Answer 9

block copolymers:
- conductive polymers: order of construction impacts properties
- thermoplastic elastomers (combines hard crystalline segments with soft segments through physical crosslinks)