The transformation of carbon dioxide (CO2) and epoxides to cyclic carbonates has gained much interest due to its low cost, abundance, low toxicity, and renewability. Therefore, novel constrained aluminum chloride...
The ring-opening
copolymerization (ROCOP) of epoxides and cyclic
anhydrides is a promising method for the synthesis of new polyesters
with various polymer properties. Among previously reported metal catalysts
for ROCOP, the Schiff-base complexes have gained significant attention
because of their ease of synthesis and modification. In this work,
zinc and magnesium complexes containing Schiff-base ligands with different
alkoxy side arms [−(CH2)2O– and
−(CH2)3O−] were synthesized and
shown to have a cubane metal core by X-ray crystal structures. All
complexes were studied in the ROCOP of cyclohexene oxide (CHO) and
succinic anhydride (SA) in toluene at 110 °C. The zinc complex
having a shorter side arm is the most active catalyst for copolymerization,
giving poly(CHO-alt-SA) with narrow dispersity and
negligible ether linkage. On the other hand, magnesium complexes were
not active because of the formation of stable carboxylate species.
The detailed analysis of polyester obtained from zinc complexes unexpectedly
revealed three different types of polymer structures occurring at
different polymerization times. Cyclic polymer was generated at the
beginning by intramolecular transesterification of the alkoxy side
arm, giving a low-molecular-weight polyester. At higher conversion,
cyclization diminished, giving just a linear polyester but with minor
competitive formation of higher-molecular-weight polyester having
cyclohexanediol as an end group. On the basis of a thorough understanding
of the polymerization mechanism, the desired cyclic poly(CHO-alt-SA) was successfully synthesized using a low monomer/catalyst
ratio.
Seven constrained aluminum inden complexes having different
substituents
and diamine backbones were developed for the ring-opening copolymerization
(ROCOP) of epoxides and bulky cyclic anhydrides giving alternating
polyesters with T
g ranging from 49 to
226 °C. Among several catalyst/cocatalyst screenings, the aluminum
inden complex having a rigid phenylene backbone coupled with 4-dimethylaminopyridine
showed the best performance giving linear polyesters. In the case
of cyclohexene oxide (CHO) and succinic anhydride (SA), the linear
poly(CHO-alt-SA) could be transformed to cyclic polymer
when the polymerization was left under prolonged reaction time to
induce intramolecular transesterification. The kinetic studies of
the ROCOP revealed a zeroth-order dependence on cyclic anhydride and
a first-order dependence on epoxide and the catalyst. The catalysts
can be extended efficiently to the one-pot CHO/PA/l-lactide
terpolymerization giving uncommon tapered copolymers of poly(CHO-alt-PA) and PLA via switchable polymerization.
Novel bifunctional zinc and magnesium Schiff-base complexes containing quaternary ammonium halide side-arm were developed. The zinc complex 1Et-I (0.02 mol%) having iodide anion has shown the highest TOF for propylene...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.