Synthesis of oxazolidinones - a structural motif for high-performance polymers

Breuer, Timo; Müller, Thomas Ernst (Thesis advisor); Klankermayer, Jürgen (Thesis advisor)

Aachen : RWTH Aachen University (2022, 2023)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2022


This thesis concerns itself with the synthesis of oxazolidinones and polyoxazolidinones from the corresponding epoxides and isocyanates. The oxazolidinone moiety is applied widely as constituent of antibiotics and auxiliaries in enantioselective organic synthesis. Because of the readily available raw materials, the oxazolidinone building block is likewise of interest for the synthesis of polyoxazolidinone-based high-performance thermoplastics. As will be shown in this thesis, the oxazolidinone moiety is obtained readily by conversion of epoxide and isocyanate, when a suitable catalyst is applied. For application in the polymerization reaction, the catalyst not only had to provide excellent activity, but also outstanding selectivity. The approach described in this thesis is divided into two parts. The first part (Chapter II) deals with the identification of a suitable catalyst. Catalysts were assessed in a model system comprising a monofunctional epoxide and isocyanate. The focus was placed on organic Lewis acid-base catalysts, as the catalyst needed to be metal-free. Literature-known tertiary ammonium salts were the starting point. Azaspiro and imidazolium salts proved to be selective catalysts, but their activity was not adequate for industrial application. Comparing tetrabutyl ammonium with tetrabutyl phosphonium bromide salts, we found that phosphonium catalysts not only were more active, but also provided similar or enhanced selectivity. The effect of the chemical groups attached to the phosphonium center were explored in detail. Substitution of alkyl by aryl groups led to drastic increase in activity, while the high selectivity was preserved. The activity was optimized further by amending the aryl group with adequate substituents. The catalysts developed this way were then applied to the polymerization reaction of difunctional epoxides with diisocyanates. As the polyoxazolidinone synthesis was subject to the formation of various side products, the selectivity of the catalyst was a central aspect. A suitable reactor system and appropriate reaction parameters had to be defined. Successfully, we synthesized polyoxazolidinones that performed as high-performance thermoplastics. The second part of this thesis (Chapter III) focuses on the chemical and thermophysical properties of the thermoplastics that were obtained. The polyoxazolidinones were thermally highly stable with glass transition temperatures of 170-180°C and decomposition temperatures up to 400°C. First tests showed that antioxidants have a beneficial effect on the thermal stability of polyoxazolidinones at elevated temperatures. Last but not least, the application aspects were explored by spinning polymer samples into fibers.