Synthesis And Properties Of Functional All-aromatic Thermosetting Liquid Crystalline Polyesters With High Thermal Resistance

All-aromatic liquid crystalline polyesters have become basic materials for manufacturing equipments such as cables and aerospace composite components,etc.,due to their excellent thermal resistance,remarkable mechanical properties,outstanding dimensional stability and chemical stability.However,their high melt viscosity and high crystal-to-nematic transition temperature make existing study on all-aromatic liquid crystalline polyesters basically focused on discussing their thermal properties,mechanical properties and processability.Therefore,it remains a subject with important academic significance and application value to develop functional all-aromatic liquid crystalline polyesters with high thermal resistance through designing and synthesizing new all-aromatic liquid crystalline polyesters as well as studying the functions(flame retardancy,the feasibility of 3D printing,reprocessability,shape memory behavior).This article focuses on this subject,of which the specific content is divided into the following two parts.Firstly,designing and synthesizing a new phenylethynyl-terminated reactive all-aromatic liquid crystalline polyester oligomer(LCP-ro)with good processability,and then an intrinsic flame retarding thermosetting liquid crystalline foam(LCTF)was fabricated without adding additional flame retardant and foaming agent through curing and foaming processes,the structure and integrated performance of LCTF were studied systematically.Results show that LCTF simultaneously has outstanding flame retardancy(UL94-V0 grade,36.4%of limit oxygen index),excellent smoke suppression and high thermal stability,these integrated performance is the best value among intrinsic flame retarding polymer foams reported so far.The morphological structure of LCTF was investigated with the aid of three-dimensional reconstruction of morphology,and the discussion on the flame retardant mechanism reveals that the roles from gas phase and condensed phase are proved to be responsible for the unique flame retardancy of LCTF,these roles include high initial thermal decomposition temperature(454?),large char yield with high graphitization degree and free radical scavenging.In addition,the feasibility of 3D printing of LCP-ro and the application potential of LCTF in thermal insulation were also evaluated.Secondly,based on the synthesis of LCP-ro,a multi-block all-aromatic liquid crystalline polyester(amide)oligomer with good processability was synthesized by using 4,4'-diacetamido-diphenyl sulfide as a new reactant and utilizing the different reactivities of amide and ester bonds in the transesterification reaction,and then a thermosetting liquid crystalline polymer(RLCP-Cured)with high thermal resistance and multi-functions was fabricated through curing.RLCP-Cured simultaneously exhibits reprocessability,triple shape memory behaviour and high thermal resistance.Because of the stable rigid molecular chain structure of all-aromatic RLCP-Cured,its initial thermal decomposition temperature(457.1?)and glass transition temperature(240?,340?)are the highest values among reprocessable thermosetting polymers containing S-S bonds reported so far.The reversible dynamic exchange of S-S bonds and double glass transition behaviour are the key reasons that endow RLCP-Cured with reprocessability and triple shape memory behavior.