Dynamic Memory Effects in the Mechanochemistry of Cyclic Polymers

Area of Science:

• Polymer Chemistry
• Mechanochemistry
• Materials Science

Background:

• Cyclic polymers offer unique properties but their mechanochemical behavior is less understood than linear counterparts.
• Gem-dichlorocyclopropane (gDCC) units serve as effective mechanophores, enabling polymer chain scission under mechanical stress.

Purpose of the Study:

• To investigate and compare the mechanochemical behavior of cyclic polymers containing gDCC mechanophores with their linear analogs.
• To determine the efficiency of mechanophore activation (Φ) during chain fragmentation in cyclic polymers.

Main Methods:

• Synthesis of cyclic polymers with multiple gDCC mechanophores via ring expansion metathesis polymerization.
• Investigation of polymer mechanochemistry using pulsed ultrasonication.
• Analysis of mechanochemical products via ozonolysis to assess activation zones.

Main Results:

• Cyclic polymers exhibited a lower fraction of activated gDCC mechanophores per chain halving event (Φ = 0.38) compared to linear analogs (Φ = 0.62).
• Ozonolysis revealed a less continuous mechanochemical activation zone in cyclic polymers versus linear ones.
• The fragmentation of cyclic polymers proceeds through linear intermediates that undergo further scission within the same event.

Conclusions:

• The reduced mechanophore activation in cyclic polymers suggests that the linear intermediate formed during fragmentation retains a memory of its cyclic conformation.
• This 'memory effect' influences subsequent scission events, leading to a less continuous activation pattern compared to initially linear polymers.