"Brill Transition" Shown by Green Material Poly(octamethylene carbonate)

Area of Science:

• Polymer Science
• Materials Science
• Crystallography

Background:

• Poly(octamethylene carbonate) (POMC) is a biodegradable aliphatic polycarbonate.
• Aliphatic polycarbonates are a developing class of polymers with potential applications in sustainable materials.
• Brill transition is a well-studied phenomenon in polymers like nylon, involving reversible crystal-to-crystal transformations.

Purpose of the Study:

• To investigate the reversible crystal-crystal transition in Poly(octamethylene carbonate) (POMC).
• To characterize the crystalline structures of POMC below and above its transition temperature.
• To understand the molecular mechanisms driving the transition in POMC.

Main Methods:

• Differential Scanning Calorimetry (DSC) to identify transition temperatures.
• X-ray Diffraction (XRD) to analyze crystalline structures.
• Spectroscopic techniques to probe molecular conformation changes.

Main Results:

• POMC exhibits a reversible crystal-crystal transition at approximately 42 °C.
• The transition temperature of POMC is significantly lower than that of nylons due to weaker dipole-dipole interactions compared to hydrogen bonding.
• Two distinct crystalline structures were identified for POMC below and above the transition temperature.
• The transition is attributed to a reversible conformational change in the methylene sequences, shifting from trans-dominated to trans/gauche coexistence.

Conclusions:

• Poly(octamethylene carbonate) displays a unique Brill-type transition at a low temperature.
• The transition mechanism in POMC is linked to the conformational dynamics of its aliphatic chains.
• Understanding this transition is crucial for tailoring POMC's properties for various applications.