Controlled and Regioselective Ring-Opening Polymerization for Poly(disulfide)s by Anion-Binding Catalysis

Area of Science:

• Polymer Chemistry
• Materials Science
• Organic Synthesis

Background:

• Poly(disulfide)s are versatile sulfur-containing polymers with significant potential in medicine, energy, and functional materials.
• The dynamic covalent disulfide (S-S) bond in poly(disulfide)s is highly reactive towards sulfide (RS-) anions, hindering controlled polymerization.
• Existing methods struggle to manage the reactivity of the sulfide chain end, posing a challenge for synthesizing linear poly(disulfide)s.

Purpose of the Study:

• To develop a novel strategy for controlling the synthesis of linear poly(disulfide)s by addressing the reactivity of the sulfide anion.
• To achieve rapid, living ring-opening polymerization of 1,2-dithiolanes with high control over molecular weight distribution and regioselectivity.
• To elucidate the mechanism of polymerization and the role of the catalyst in controlling chain propagation and monomer addition.

Main Methods:

• Anion-binding approach utilizing a thiourea-base catalyst to complex with the sulfide chain end.
• Ring-opening polymerization of 1,2-dithiolanes.
• Mechanistic studies involving ternary complex formation and theoretical analyses of catalytic models.
• Characterization of polymer properties, including dispersity and regioselectivity.

Main Results:

• Successful control over poly(disulfide) synthesis via an anion-binding strategy, arresting the reactivity of the sulfide chain end.
• Achieved rapid, living ring-opening polymerization of 1,2-dithiolanes, yielding polymers with narrow dispersity (Mw/Mn ≈ 1.1) and high regioselectivity (Ps ≈ 0.85).
• Identified a thiourea-base-sulfide ternary complex as the active catalytic species, supported by mechanistic and theoretical studies.
• Demonstrated the catalytic system's compatibility with various functional groups and its ability to produce semicrystalline polymers from lipoic acid derivatives.

Conclusions:

• The developed anion-binding approach effectively controls the polymerization of poly(disulfide)s by managing sulfide anion reactivity.
• The synergistic catalytic model involving a ternary complex provides a new paradigm for achieving high regioselectivity and controlled polymerization.
• This methodology opens avenues for synthesizing advanced poly(disulfide) materials with tailored properties for diverse applications.