Conformational characteristics and conformation-dependent properties of poly(ε-caprolactone)

Area of Science:

• Polymer Science
• Computational Chemistry
• Materials Science

Background:

• Poly(ε-caprolactone) (PCL) is a biodegradable polyester with significant industrial applications.
• Understanding PCL's molecular structure and properties is crucial for optimizing its performance and biodegradability.

Purpose of the Study:

• To investigate the conformational preferences of isolated and crystalline poly(ε-caprolactone) (PCL) chains.
• To determine the mechanical properties, specifically Young's moduli, of crystalline PCL.
• To correlate PCL's conformational and surface characteristics with its enzymatic selectivity.

Main Methods:

• Ab initio molecular orbital (MO) calculations on methyl 6-acetoxyhexanoate (MAH) as a PCL model.
• Rotational isomeric state (RIS) calculations for PCL chain conformations.
• Periodic density functional theory (DFT) calculations for crystalline PCL structures and moduli.
• Analysis of 1H and 13C NMR data for bond conformation validation.

Main Results:

• MO calculations revealed gauche preferences for C-C bonds near the ester group in MAH due to intramolecular C-H⋯O attractions.
• RIS calculations yielded characteristic ratios for PCL chains consistent with experimental data.
• DFT calculations determined PCL's Young's moduli along a-, b-, and c-axes, with a fiber-axis modulus of 252 GPa.
• The three-dimensionally averaged Young's modulus of PCL was found to be the lowest among representative polymers studied.

Conclusions:

• The study elucidates the conformational behavior and mechanical properties of PCL at a molecular level.
• PCL's conformational characteristics and enzyme surface interactions are key factors in its enzymatic degradation.
• Findings provide insights into the structure-property relationships of PCL, relevant for biodegradable polymer design.