L9 - 11: Ring-Opening Polymerisation

Question 1

1 disadvantage of ring-opening polymerisation:

Answer 1

• Starting material requires its own synthesis

Question 2

Key advantage of ring opening polymerisation:

Answer 2

• Hydrolysis allows simple breakdown into lactic acid (however this does require industrial processes to do)

Question 3

How is degree of polymerisation calculated?

Answer 3

• DP = 1/(1-p)

Question 4

How is ROP typically terminated?

Answer 4

• Water to quench
• Other solvents

Question 5

Metals used for ROP:

Answer 5

• Must be an electron pair acceptor (lewis acid)
• Many can be used; typical examples include Al, Zn, Sn, Mg, Ca, Ln

Question 6

Characteristics of controlled ROP:

Answer 6

• No chain termination (block copolymerisation possible)
• Rate of initiation&raquo_space;> rate of propagation
• Predictable Mn for a given [I]/[M] ratio
• Linear relationship between % conversion of monomer and Mn
• Narrow PDI (1 - 1.1)
• Polymer chains end capped by initiating group

Question 7

How does chain transfer occur in ROP?

Answer 7

• Ester is retained in polymer
• Transesterification reactions occur
• See general mechanism

Question 8

Typical monomers for ROP:

Answer 8

• Lactide
• e-caprolactone
• B-butyrolactone
• d-valerolactone
• glycolide
• racemic mix or meso form of lactide

Question 9

What is an immortal polymerisation?

Answer 9

• Controlled chain transfer
• Alcohol etc added (in greater equiv. than catalyst) to exchange off polymer chain
• Generates new metal alkoxide group to undergo polymerisation
• Able to use much smaller amount of catalyst
• Amount of alcohol exerts control over length of polymers
• Much be growing at same rate i.e. rate of chain transfer is much greater than that of polymerisation -> Narrow Dispersity

Question 10

Why are alcohols good chain transfer agents?

Answer 10

• Alkoxide -> initiating group for polymerisation process

Question 11

Properties of stereoregular polyesters:

Answer 11

• High glass transition temperatures (higher than body temperature)

Question 12

What is sterocomplex PLA?

Answer 12

• Cocrystallisation of isotactic poly(S-lactide) and (R-lactide)
• Melting temperature far exceeds that of single enantiomers
• Brings about a different X-ray diffraction pattern (due to interfaces between RRRRR and SSSSSSSSSSSS domains