The Hidden Isodimorphic Crystallization of Poly(ε-Caprolactone-Ran-ω-Pentadecalactone) Copolymers

Area of Science:

• Polymer Chemistry
• Materials Science
• Crystallography

Background:

• Poly(ε-caprolactone) (PCL) and poly(ω-pentadecalactone) (PPDL) are biodegradable polyesters.
• Understanding copolymer crystallization is crucial for material properties and applications.
• Previous studies suggested PCL-PPDL copolymers might be isomorphic.

Purpose of the Study:

• Synthesize PCL-PPDL copolymers with varying compositions.
• Investigate their crystallization behavior and determine if they are isomorphic or isodimorphic.
• Clarify the comonomer inclusion/exclusion balance under different crystallization conditions.

Main Methods:

• Ring-opening polymerization using Candida antarctica lipase B.
• Differential scanning calorimetry (DSC).
• Polarized light optical microscopy (PLOM).
• In situ wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS).
• Fourier-transform infrared spectroscopy (FTIR).
• Self-nucleation tests.

Main Results:

• Copolymers exhibited pseudoeutectic behavior across all compositions.
• Crystallization occurred in either PPDL-type or PCL-type unit cells and conformations, irrespective of conditions.
• Self-nucleation data indicated a decrease in Domain II width with increasing comonomer content.
• A pseudoeutectic point was identified at PCL contents above 83%.

Conclusions:

• PCL-PPDL copolymers are isodimorphic, not isomorphic as previously reported.
• The isodimorphic nature is maintained across various compositions and crystallization conditions.
• The identified pseudoeutectic point explains the previously unrecognized isodimorphic character.