Synthesis and characterization of liquid crystalline epoxy resins

Abstract

Abstract : Fiber reinforced polymer matrix composites (FRPs) have been developed for many decades and used in a wide variety of applications. However, the residual stresses caused by the mismatch in the coefficient of thermal expansion (CTE) between the polymer matrices and the fiber reinforcements during the processing of FRPs is a crucial factor affecting the performance of the composites, which can lead to a reduction of mechanical properties and loss of dimensional stability, thereby limiting the use of FRPs in high performance applications. Additionally, the relatively poor matrix properties is another factor affecting overall performance of the composites, including chemical resistance, moisture absorption, and long term durability of FRPs. A potential strategy to solve the problems mentioned above involves the development of novel polymer matrices with improved physical, thermal, and mechanical properties with low thermal expansion to ensure minimal mismatch in CTE with the fiber reinforcements, which can reduce the magnitude of residual stresses, facilitating the development of FRPs for advanced applications. Liquid crystalline epoxy resins (LCERs) are a unique class of thermosetting materials formed upon curing of low molecular weight, rigid rod epoxy monomers, resulting in the retention of a liquid crystalline (LC) phase by the three dimensional networks. LCERs exhibit a polydomain structure, thereby combining the outstanding properties of liquid crystals and thermosets. The rigid and ordered structure of LC domains is expected to reduce the CTE of the resins as well as improve the thermal and mechanical properties of the resins. In addition, liquid crystals possess properties that can be controlled by external fields, greatly improving the design flexibility. These attractive features make LCERs good candidates for polymer matrices in high performance composites.