Trefoil polymers from a knotted synthon

Area of Science:

• Polymer Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Synthesizing polymers with controlled topology, particularly knots, is a significant challenge.
• Theoretical studies suggest polymer topology profoundly impacts material properties and function.
• Existing methods lack precise control over knot formation and placement.

Purpose of the Study:

• To develop a high-yielding synthetic strategy for creating trefoiled (three-lobed) closed-loop polymers.
• To enable direct examination of topology-property relationships by preparing linear, cyclic, and trefoiled polymer topoisomers.
• To demonstrate the versatility of the synthetic approach across different polymer backbones.

Main Methods:

• A topological synthon approach involving extension and macrocyclization of an overhand knot.
• Preparation of linear, cyclic, and trefoiled topoisomers from identical building blocks.
• Low-temperature ultrahigh-vacuum scanning tunneling microscopy (UHV-STM) for conformer analysis.
• Coarse-grained Langevin dynamics simulations for modeling conformer stability.

Main Results:

• Achieved high-yielding synthesis of closed-loop trefoiled polymers with narrow polydispersity.
• Resolved three distinct conformers of trefoiled polystyrene (high-, medium-, and low-symmetry) using UHV-STM.
• Simulations confirmed that bending energy and conformational entropy dictate conformer stability.
• Demonstrated the approach's generality by synthesizing trefoiled poly(ethylene glycol) and block copolymers.

Conclusions:

• The topological synthon approach provides precise control over polymer knot synthesis.
• The method allows for the creation of polymers with tunable topological parameters.
• Understanding polymer knot conformers is crucial for relating structure to function.
• This strategy is applicable to various polymer types, advancing polymer topology research.