Ring-Opening Metathesis Polymerization of δ-Pinene: Well-Defined Polyolefins from Pine Sap

Area of Science:

• Polymer Chemistry
• Organic Synthesis
• Materials Science

Background:

• Alpha-pinene is an abundant and sustainable feedstock.
• Ring-opening metathesis polymerization (ROMP) is a versatile polymerization technique.
• Developing controlled polymerization methods for novel monomers is crucial for advanced materials.

Purpose of the Study:

• To achieve well-controlled ROMP of delta-pinene.
• To synthesize poly(delta-pinene) with defined properties.
• To explore the potential of poly(delta-pinene) in block copolymers and bulk polymerization.

Main Methods:

• Three-step, metal-free synthesis of delta-pinene monomer from alpha-pinene.
• ROMP of delta-pinene using a third-generation Grubbs catalyst.
• Characterization of polymer microstructure and properties using NMR spectroscopy and DSC.
• Density functional theory (DFT) calculations to determine ring strain energy.

Main Results:

• High conversion ROMP (>95%) of delta-pinene achieved.
• Polymerization yielded high molar mass (up to 70 kg mol-1) with narrow dispersity (<1.2).
• NMR analysis confirmed a highly regioregular head-to-tail microstructure (>95%) and high trans content (>98%).
• Poly(delta-pinene) exhibited a high glass transition temperature (approx. 104 °C) and a unique chiral microstructure.
• Successful synthesis of poly(delta-pinene)/polynorbornene block copolymers.
• Feasibility of bulk polymerization demonstrated, indicating a greener approach.

Conclusions:

• Well-controlled ROMP of delta-pinene is achievable, producing polymers with desirable characteristics.
• The sustainable monomer synthesis and controlled polymerization offer a promising route to novel polymeric materials.
• Poly(delta-pinene) possesses unique properties making it suitable for advanced applications and copolymer synthesis.