Metal-Based Catalysts for Controlled Ring-Opening
Polymerization of Macrolactones: High Molecular Weight and Well-Defined
Copolymer Architectures
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Abstract
This contribution describes our recent
results regarding the metal-catalyzed
ring-opening polymerization of pentadecalactone and its copolymerization
with ε-caprolactone involving single-site metal complexes based
on aluminum, zinc, and calcium. Under the right conditions (i.e.,
monomer concentration, catalyst type, catalyst/initiator ratio, reaction
time, etc.), high molecular weight polypentadecalactone with <i>M</i><sub>n</sub> up to 130 000 g mol<sup>–1</sup> could be obtained. The copolymerization of a mixture of ε-caprolactone
and pentadecalactone yielded random copolymers. Zinc and calcium-catalyzed
copolymerization using a sequential feed of pentadecalactone followed
by ε-caprolactone afforded perfect block copolymers. The blocky
structure was retained even for prolonged times at 100 °C after
full conversion of the monomers, indicating that transesterification
is negligible. On the other hand, in the presence of the aluminum
catalyst, the initially formed block copolymers gradually randomized
as a result of intra- and intermolecular transesterification reactions.
The formation of homopolymers and copolymers with different architectures
has been evidenced by HT-SEC chromatography, NMR, DSC and MALDI-ToF-MS