The following thesis describes the synthesis of block polymers comprising
polycarbonates (derived from carbon dioxide) and polyesters, and their evaluation as
functional materials and possible renewable alternatives to current petrochemical-based
plastics. The preparation of the polymers utilises efficient and sequence-controlled
polymerisation catalysis, combining lactone ring-opening polymerisation (ROP) and
epoxide/CO2 ring-opening copolymerisation (ROCOP) cycles through a single catalyst.
Chapter 2 evaluates heterodinuclear zinc(II)/magnesium(II) catalysts for the
switchable polymerisation catalysis of lactone and epoxide/CO2. The heterodinuclear
catalyst, [LZnMg(OBzNMe2)2] where L = macrocyclic ancillary ligand, OBzNMe2 = parasubstituted benzoate, is initially assessed for the preparation of ABA-type triblock polymers,
but because of poor end-group fidelity the development of a new organometallic catalyst,
[LZnMg(C6F5)2] is undertaken. The organometallic catalyst shows strong performance with
equivalent high activity for epoxide/CO2 ROCOP and enhanced activity for lactone ROP
compared with the benzoate variant. Importantly, it delivers higher molar mass ABA triblock
polymers (Mn > 20 kg mol-1
) with block sequence-selectivity and with excellent end-group
fidelity.
Chapter 3 further explores the application of the organometallic Zn(II)/Mg(II) catalyst
in switchable polymerisation catalysis. High molar mass ABA triblock polymers
(38 n -1) with varying degrees of CO2 utilisation (6 – 23 wt %) are prepared by
controlling the starting monomer stoichiometry, with the final materials comprising hard
polycarbonate “A” blocks and a soft polyester “B” block. The effects of varying the relative
block ratio on the thermal and mechanical characteristics of the polymers are analysed, and
their performance as toughened plastics, elastomers, and pressure-sensitive adhesives is
evaluated.
Chapter 4 investigates the synthesis and thermal/mechanical effects of changing the
polymer architecture by varying the initiating alcohol groups, from linear to stars. A range of
tri-, tetra-, and hexafunctional star block polymers are synthesised from vinyl-cyclohexene
oxide (vCHO), CO2, and ε-decalactone (ε-DL). It also investigates the selective postpolymerisation modification of the polycarbonate block at fixed relative block composition.
Multi-arm star-like polymers are fashioned using a “core-first” approach by employing chaintransfer agents with varying numbers of hydroxyl groups. Trends in thermomechanical and
morphological characteristics for both the non-modified and modified polymers are analysed
in relation to molar mass (overall and individual arm) and number of star ‘arms’, and a
preliminary assessment of particular advantages/disadvantages for star vs. linear
architectures in these polymers is presented.</p
