Long-chain aliphatic polyesters are emerging sustainable
materials
that exhibit polyethylene-like properties while being amenable to
chemical recycling and biodegradation. However, varying polyester
chemical structures results in markedly different degradation rates,
which cannot be predicted from commonly correlated bulk polyester
properties, such as polymer melting temperature. To elucidate these
structure–degradability relationships, long-chain polyesters
varying in their monomer composition and crystallinity were subjected
to enzymatic hydrolysis, the rates of which were quantified via detection
of formed monomers. Copolymers with poorly water-soluble, long-chain
diol monomers (e.g., 1,18-octadecanediol) demonstrated strongly reduced
depolymerization rates compared to copolymers with shorter chain length
diol monomers. This was illustrated by, e.g., the 20× faster
hydrolysis of PE-4,18, consisting of 1,4-butanediol and 1,18-octadecanedicarboxylic
acid monomers, relative to PE-18,4. The insoluble long-chain diol
monomer released upon hydrolysis was proposed to remain attached to
the bulk polymer surface, decreasing the accessibility of the remaining
ester bonds to enzymes for further hydrolysis. Tuning of polyester
crystallinity via the introduction of branched monomers led to variable
hydrolysis rates, which increased by an order of magnitude when crystallinity
decreased from 72% to 45%. The results reported enables the informed
design of polyester structures with balanced material properties and
amenability to depolymerization.