2,3-Butanediol has emerged as a promising bio sourced
monomer for
polyester synthesis. However, it has received limited attention as
monomer for semicrystalline polyesters, due to the lower reactivity
of secondary alcohols often resulting in low molecular weight polymers.
Furthermore, the methyl branches of 2,3-butanediol reduce the crystallinity
of resulting polyesters, leading to lowered melting temperatures.
We report the synthesis of semicrystalline polyesters from 2,3-butanediol
with long-chain aliphatic dicarboxylate monomers ranging in chain
length from C10 to C48. With appropriate reaction
conditions, high molecular weights up to 59,000 g mol–1 were obtained. Polyester-b4.48 (b4 = 2,3-butanediol-based repeat
units) features a high melting point of 103 °C and orthorhombic
polyethylene-like crystal structure, while shorter dicarboxylate-based
polyesters have different crystal structures and polyester-b4.10 is
amorphous. Tensile tests of polyester-b4.18 reveal a modulus of elasticity
of 290 MPa and elongation at break of 430%. The combination of b4/C10 noncrystallizing repeat units with the well-crystallizable
C48 repeat units provides 2,3-butanediol-based thermoplastic
elastomers. Faster enzyme-catalyzed hydrolysis rates were measured
for polyester-b4.18 compared to the linear polyester-4.18, indicating
an increase in biodegradability with decreasing polymer melting points
and crystallinities.