Erythritol Dicarbonate as Intermediate for Solvent-and Isocyanate-Free Tailoring of Bio-Based Polyhydroxyurethane Thermoplastics and Thermoplastic Elastomers

The highly reactive [4,4'-bi(1,3-dioxolane)]2,2'-dione (BDC), also being referred to as erythritol dicarbonate and butadiene dicarbonate, enables the facile isocyanate-free tailoring and melt-processing of bio-based polyhydroxyurethane (PHU) materials. Both the direct carbonation of erythritol and the chemical fixation of CO2 with 2,2'-bioxirane, obtained by epoxidation of bioethanol-derived butadiene, afford high purity BDC in high yields. According to the FTIR spectroscopic model study BDC reacts with primary alkylamines at room temperature even in the absence of catalysts. High BDC reactivity is essential for producing high molar mass linear PHU thermoplastics via melt-phase polyaddtition with aliphatic diamines. Opposite to conventional isoycanate-mediated polyurethane syntheses erythritol units are incorporated into the polyurethane backbone without requiring the use of protective groups. As a function of the diamine structures and copolymer compositions the PHU properties vary from hard to soft and elastomeric. Typically isophorone diamine (IPDA) and trimethylhexamethylenediamine (TMHMDA) serve as building blocks for hard segments whereas highly flexible diamines such dimer fatty acid-derived diamidoamines render PHU soft and elastomeric. This study elucidates how copolymer composition and reaction parameters such as temperature, catalyst, and stabilizer addition influences PHU molar masses as well as mechanical and thermal properties. For the first time, owing to extraodinary BDC reactivity, melt-phase BDC polyaddition with diamines is competitive with conventional reactive processing of polyurethane thermoplastics using isocyanates. Moreover this versatile isocyanate-free synthetic route offers a great variety of options for fabricating unconventional bio-based PHUs and carbohydrate urethanes unparalleled by conventional polyurethanes.