Oligomer synthesis

1. High Tg ester based liquid crystal thermosets: synthesis and characterization PhD Candidate: Martino Marchetti Department: ASM Section: Novel Aerospace Materials Supervisor: Prof. Theo Dingemans Promoter: Prof. Theo Dingemans Start date: 01-01-2013 Thermal stability Introduction Liquid crystal thermosets are a unique sub-set of high-performance polymers that combine desirable processing characteristics with outstanding thermo-mechanical properties after cure. LCTs are prepared via the so called reactive oligomer approach, where the oligomer backbone is terminated with latent end-groups that can react in a successive thermal post treatment step to form a network structure. In this work we have explored the most rigid, high Tg (~ 400 oC) LCT formulation known to data, i.e. based on 4-hydroxybenzoic acid (HBA), terephthalic acid (TA) and 4,4’-biphenol (BP). Herein we will discuss the thermo mechanical performance of these new polymers. Oligomer synthesis Thermal stability of the HBA/BP/TA(20)-9K cured thermosets, measured from room temperature to 600 ºC, under nitrogen atmosphere (red) and air atmosphere (blue), using a heating rate of 10 ºC/min. A B Thermo-mechanical behavior Synthesis of the all-aromatic ester-based reactive liquid crystalline oligomers end-capped with phenylethynyl reactive end-groups.1 Aerospace Engineering Melt behavior of the oligomers Representative DMTA scan for HBA/BP/TA(35)-5K. The experiment was performed under a N2 atmosphere using a heating rate of 2 ºC/min and a frequency of 1 Hz. Tg data were obtained from DMTA experiments and defined by the maximum of the E’’ peak. DMTA data showing HBA/BP/TA(35)-5K film (red) and a commercial available polyether-ketoneketone (PEKK) sample (black). DSC signals of the 5K oligomers series. First heat using a heating rate of 20 ºC/min. Phase behavior Series 9000 g/mol- HBA/TA/BP • 60%/20%/20% • 50%/25%/25% • 40%/30%/30% • 30%/35%/35% • Series 5000 g/mol- HBA/TA/BP • 60%/20%/20% • 50%/25%/25% • 40%/30%/30% • 30%/35%/35% Conclusions and future Work • The reactive oligomer approach is an excellent method towards novel processable all-aromatic liquid crystalline polyesters based on all-para-substituted monomers (HBA/BP/TA). • High Tg (> 350 oC) and high thermal stability (Td5% (N2) > 475 oC) make this class of polymers promising for demanding high-performance applications. • All cured polymers show excellent storage moduli (E’) as function of temperature and easily out performs PEKK. • Melt and cure rheology analyses are in progress. • One or two reactive oligomers will be selected and used as matrix in carbon fiber reinforced composites. Nematic textures of HBA/BP/TA(25)-9K observed by polarized microscopy. A– Low viscous sample at 370 ºC during cure. B– Crosslinked sample at 550 ºC after the complete cure. 1. Mazhar Iqbal, Theo J. Dingemans, European Polymer Journal, 2010, 46, 2174–2180.