Poly(lactic acid), PLA, is a viable replacement to petroleum derived polymers due to its
renewable feedstock, biodegradability and bioassimilability, yet improvements in its
physical, thermal and mechanical properties are required before it can fully enter all
commodity markets. This thesis investigates olefin cross-metathesis (CM) as a synthetic
strategy to modify the properties of PLA. The use of novel lanthanide and actinide
catalysts on the microstructure control of PLA are also explored.
The Tebbe reagent was used in a new synthetic strategy to produce a novel olefin
derivative of lactide (MML). Olefin CM of MML with hex-1-ene was successful but
polymerisation pre- and post-CM was unsuccessful due to monomer instability. CM of
another olefin derivative of lactide, 3-methylenated lactide (3-ML) was successful with
aliphatic alkenes; hex-1-ene to dodec-1-ene. To overcome competing alcoholysis of the
functionalised monomers, which prevented polymerisation, hydrogenation was used to
remove the olefin entity followed by successful ring-opening polymerisation (ROP) to
produce polymers of low glass-transition temperatures (Tg).
Post-polymerisation CM on an olefin containing polymer P(β-heptenolactone) P(β-HL),
with methyl acrylate and an epoxide, generated functionalised homopolymers with
increased Tg’s. Co-polymerisation of lactide with β-HL generated novel gradient-copolymers.
Olefin CM with 15 different cross-partners produced functionalised copolymers
with different thermal properties. Based on this route a new methodology was
created to introduce two unique functionalities into the polymer backbone by
manipulation of the olefin reactivities.
Finally, in a collaborative project, uranium and cerium catalysts, Me3SiOU(OArP)3 and
Me3SiOCe(OArP)3 - designed out-with the group- were tested and compared as ROP
catalysts for lactide. Both catalysts were active in living polymerisations of L-lactide and
under immortal conditions the activity and rates of the catalysts were switched, accounted
for by a change in the coordination sphere due to ligand displacement. ROP of rac-lactide
using the uranium analogue produced heterotactic-biased PLA with a Pr = 0.79