Macrocyclic Ruthenium Ring Expansion Metathesis Polymerization Initiators Exhibit Tether Length-Dependent Behavior

Area of Science:

• Materials Science
• Polymer Chemistry
• Organometallic Chemistry

Background:

• Cyclic polymers possess enhanced mechanical durability due to their topology.
• Ring-expansion metathesis polymerization (REMP) is a growing method for synthesizing cyclic polymers.
• Understanding initiator structure-activity relationships is crucial for REMP.

Purpose of the Study:

• To synthesize and evaluate novel cyclic ruthenium-benzylidene initiators (CBX) for REMP.
• To investigate the impact of tether length on initiator activity and polymer properties.
• To elucidate the mechanistic differences between REMP and ROMP initiators.

Main Methods:

• Synthesis of CBX initiators (X=4-6).
• Mechanistic studies of REMP.
• Solid-state X-ray crystallography.
• Density Functional Theory (DFT) calculations.

Main Results:

• CBX initiators demonstrate controlled molar mass in REMP.
• Tether length significantly influences secondary metathesis, a key step in REMP.
• Structural and computational analyses reveal initiator-polymerization dynamics.

Conclusions:

• The CBX initiator series provides a platform for tunable cyclic polymer synthesis.
• Tether length is a critical parameter for controlling polymer molar mass in REMP.
• These findings advance the understanding of REMP mechanisms and initiator design.