High Performance Liquid Crystalline Polymers from 2,5- furandicarboxylic acid; Synthesis, Characterization and Properties

Thermotropic polyesters are an important class of materials for high performance applications.Their low melt viscosities, low thermal expansion coefficients, high use temperatures, and ease in processing allow for the production of high strength and high modulus fibers, films, or compressionmolded articles. In this work we explore the synthesis, melt extrusion, fiber spinning, and performance of thermotropic liquid-crystalline polyesters from renewable resources. Special focus is on the application of the bio-based co-monomers 2,5-furandicarboxylic acid and vanillic acid and on their effect of the material properties. Using a high-temperature acidolysis melt-polycondensation reaction at temperatures up to 360 °C, fully aromatic bio-based thermotropic polyesters with melting temperature around 300 °C have successfully synthesized. [1] Unfortunately, processing at these high temperatures causes degradation of the monomers during the polymerization, resulting in discoloured and low molecular weight material (Mn of 8,000 g/mol). Instead, synthesis at mild temperatures (< 260 °C) and the inclusion of aliphatic dicarboxylic acids to suppress the melting temperature yields materials with molecular weight (Mn) above 20,000 g/mol [2]. Using various characterization tools, we demonstrate that a judicious selection of the aromatic and aliphatic monomers gives excellent control over the glass transition temperatures, melting temperatures, overall crystallinity, and the degree of segmental block formation inside the polymeric chains. As anticipated, the thermotropic characteristics of the polymer melt eases the melt-processing, yielding highly oriented fibers after melt-drawing. Preliminary fibre spinning experiments yield single-filament fibres with a high orientation parameter (<P2n(cosφ)> up to 0.9), a tensile modulus of 10 GPa, and a tensile strength in the range of 150 – 200 MPa. [3] Although these values are promising, they are not comparable to performance of commercial liquid crystalline fibers. This is likely resulting from the large percentage of aliphatic content, which is generally 30 mole%. Despite the moderate performance of the pure thermotropic fibres, we demonstrate that the developed materials are efficient fillers in polyester blends: Detailed Tunnelling Electron Microscopy, differential scanning calirometry, small angle X-ray diffraction, and tensile testing studies indicate that these bio-based thermotropic liquid crystalline polyesters both reinforcing and provide surface for nucleation for the polyester matrix. [4] The resulting enhancement in interfacial interaction between the matrix and filler allows for the development of fibres from renewable polyester blends with enhanced tensile modulus and tensile strength, without mitigating on the strain at break (> 600 %). References [1] Wilsens, C.H.R.M.; Noordover, B.A.J.; Rastogi, S.; Polymer, 55, 2014, 2432 [2] Wilsens, C.H.R.M.; Verhoeven, J.M.G.A.; Noordover, B.A.J.; Hansen, M.R.; Auhl, D.; Rastogi, S.; Macromolecules, 47, 2014, 3306. [3] Wilsens, C.H.R.M.; Deshmukh, Y.S.; Liu, W.; Noordover, B.A.J.; Yao, Y.; Meijer, H.E.H.; Rastogi, S.; Polymer, 60, 2015, 198. [4] Wilsens, C.H.R.M.; Pepels, M.P.F.; Spoelstra, A.B.; Portale, G.; Auhl, D.; Deshmukh, Y.S.; Harings, J.A.W.; Macromolecules, 49, 2016, 2228.