Highly Efficient Approach to High-Molecular Weight Polyhydroxyurethanes

Area of Science:

• Polymer Chemistry
• Materials Science
• Organic Synthesis

Background:

• Conventional thermoplastic polyurethanes (TPUs) synthesis involves hazardous isocyanates and tin catalysts.
• Nonisocyanate polyurethanes (NIPUs) offer a safer alternative but are limited by low molecular weights (typically <70 kg/mol).
• Existing NIPU synthesis often requires oligomeric monomers or postmodification, hindering industrial application.

Purpose of the Study:

• To develop a direct polyaddition strategy for synthesizing high-molecular-weight poly-(hydroxyurethane)-s (PHUs), a subclass of NIPUs.
• To overcome the molecular weight limitations of previously reported NIPUs.
• To achieve NIPU synthesis without catalysts, oligomers, or postmodification steps.

Main Methods:

• Designed novel activated aromatic bis-(cyclic carbonate) monomers with enhanced reactivity.
• Investigated the influence of steric and electronic effects of secondary amines on the polyaddition reaction.
• Employed a direct polyaddition of activated bis-(cyclic carbonate) monomers with alicyclic secondary diamines under mild, catalyst-free conditions.

Main Results:

• Achieved nearly quantitative monomer conversion under mild conditions (50 °C) without catalysts.
• Synthesized linear PHUs with a record-high degree of polymerization (DPn) up to 220 and number-average molecular weight (Mn) of 105 kg/mol.
• Successfully extended the strategy to another aromatic cyclic carbonate, yielding PHUs with Mn up to 100 kg/mol.

Conclusions:

• Demonstrated a viable direct polyaddition strategy for high-molecular-weight NIPU synthesis from low-mass monomers.
• The rational design of monomers and selection of alicyclic diamines are crucial for achieving high molecular weights.
• This catalyst-free approach offers a sustainable and efficient route for producing advanced NIPUs.