2,2'-Bipyridine-terminated poly(dimethylsiloxane)s (bpyPDMS) with number average molecular weights, M, of 3300, 6100, 26 200, and 50 000 g mol were synthesized. When mixed with Fe(BF) at low concentrations, red solutions formed with UV-vis spectra that match those of iron(ii) tris(2,2'-bipyridine) (Fe(bpy)). Upon solvent evaporation, Fe(bpy) crosslinked PDMS networks (bpyPDMS/Fe(ii)) formed, and were studied using oscillating shear rheometry. The shear storage moduli (0.084 to 2.6 MPa) were found to be inversely proportional to the M of the PDMS, though the storage moduli at low molecular weights greatly exceeded the storage moduli of comparable covalently crosslinked PDMS networks. The shear storage moduli exhibited the characteristic rubbery plateau up to ∼135 °C. Films of bpyPDMS/Fe(ii) coated onto electrodes were found to be electrochemically active, especially so when the PDMS M is low. The Fe(bpy) crosslinks can be reversibly oxidized over ∼500 nm away from the electrode surface in the presence of a suitable electrolyte.
Well-controlled ring-opening metathesis
polymerization (ROMP) of
δ-pinene is reported. The monomer is produced through a facile,
metal-free, three-step synthesis from highly abundant and sustainable
α-pinene. Using Grubbs third-generation catalyst, δ-pinene
undergoes ROMP to high conversion (>95%) with molar mass up to
70
kg mol–1 and narrow dispersity (<1.2). A highly
regioregular propagation mechanism was concluded by NMR spectroscopic
analysis that revealed a head-to-tail (HT, >95%) microstructure
and
high trans content (>98%). Successful ROMP is
corroborated
with density functional theory calculations on δ-pinene’s
ring strain energy (∼35 kJ mol–1). Poly(δ-pinene)
has a high glass transition temperature (∼104 °C) and
a unique chiral microstructure bearing gem-dimethylcyclobutane
rings. Controlled ROMP also allowed the synthesis of block copolymers
containing segments of poly(δ-pinene) and polynorbornene which
are discussed. Finally, bulk polymerization of δ-pinene is possible,
indicating a greener approach to these materials, albeit with some
loss of control.
Mandelic acid (MA) was utilized as a chiral biomass-based precursor to synthesize methacrylic monomers suitable for radical polymerization. A series of polymers were made that incorporated varying feeds of monomer stereopurity and the properties of these materials were investigated. High molar masses (>90 kg/mol) were achieved and the chirality in each polymer closely reflected the stereopurity of the monomer feeds. It was discovered that stereochemical effects had very little influence on the thermal and viscoelastic properties of the polymers produced, however, the steric bulk of the chiral pendants resulted in glassy, amorphous, and thermally stable materials with very low degrees of entanglement. The synthesis, thermal, and viscoelastic properties are discussed.
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