Entropy-Driven Design of Depolymerizable Polyolefins from Strained Bridged Bicyclic Monomers

Area of Science:

• Polymer Chemistry
• Materials Science
• Organic Chemistry

Background:

• Ring-opening metathesis polymerization (ROMP) of strained cyclic olefins yields polymers difficult to depolymerize due to favorable thermodynamics.
• Current methods for depolymerizable ROMP polymers involve low-strain monomers, limiting polymerizability.
• Polymerization thermodynamics involves both enthalpy and entropy, offering alternative design strategies.

Purpose of the Study:

• To develop depolymerizable polymers from highly strained cyclic olefin monomers.
• To investigate the role of entropic penalty in facilitating polymer depolymerization.
• To expand the scope of monomers usable for creating chemically recyclable polymers.

Main Methods:

• Design and synthesis of strained bicyclo[3.2.1] monomers.
• Investigation of polymerization thermodynamics, including enthalpic and entropic contributions.
• Evaluation of depolymerization efficiency and monomer recovery using ring-closing metathesis.

Main Results:

• A novel depolymerizable polymer system was created using strained bicyclo[3.2.1] monomers.
• These monomers exhibit a substantial enthalpic driving force (-6 to -11 kcal/mol) and a significant entropic penalty (-15 to -24 cal/mol/K).
• The entropy-driven strategy achieved high monomer recovery (74-99%) while maintaining efficient polymerization and block copolymer synthesis.

Conclusions:

• A large entropic penalty, arising from a rigid polymer backbone, effectively lowers the ceiling temperature and enables depolymerization.
• This approach allows the use of highly strained monomers, traditionally unsuitable for depolymerizable polymers.
• The entropy-driven strategy offers a new pathway for designing chemically recyclable polymers with a broader monomer selection.