Study On Preparation And Performance Of A New Type Of Bisphenol Ternary Liquid Crystal Copolyester

Thermotropic liquid crystal polymers(TLCPs)are a class of organic polymer materials whose main chain are generally composed of rigid rodshaped molecules which can exhibit a liquid crystal phase after heating.Due to their excellent comprehensive performances in terms of heat,electricity,machinery,and chemistry,TLCPs have high application value in the fields of electronics,electrical,aerospace,and 5G communications.In this thesis,we obtain the synthetic routes of two model TLCPs based on the process parameters optimization of these two model copolymers with simple structures.Furthermore,we prepare four new ternary liquid crystal copolyesters by introducing different bisphenol monomers through molecular design.And the main research contents are listed as follows:1.Study on synthesis process of TLCP based on model copolymerThe model copolymers MP1 and MP2 are synthesized by a one-pot method.By improving the control conditions of the two-step reaction of acetylation and high-temperature melt polycondensation,the appearance and coloring of the model copolymer can be effectively improved and their thermal performances can also be optimized.Through experimental research,it is determined that the optimal holding time for the acetylation process is 90 minutes,and the duration of the high-temperature vacuum stage should be 60 minutes.Finally,thermotropic liquid crystal polyester MP1-Ⅴ and thermotropic liquid crystal polyester amide MP2-Ⅲ with high glass transition temperature,high melting point,and good thermal stability are prepared.2.Synthesis of modified TLCP based on bisphenol monomersBased on the technological exploration for the preparation of TLCP by the one-pot method,four new ternary liquid crystal copolyesters are prepared from the perspective of molecular design,in which bisphenol monomers including 4,4’-dihydroxy diphenyl ketone(DHBP),4,4’-dihydroxy diphenyl sulfone(SDP),4,4’-dihydroxy diphenyl ether(ODP),and 4,4’-dihydroxy diphenyl sulfide(TDP)are introduced into the copolymer molecules,respectively.As"kink groups",the introduction of four kinds of bisphenol monomers disrupt the crystallization ability of the copolyester to a certain extent,but the characterization of polarizing optical microscope confirmes that all new copolyesters have good liquid crystallinity.The characterization of thermogravimetric analysis shows that the four new ternary liquid crystal copolyesters have good thermal stability,their maximum weight loss rate temperature is greater than 500℃,and the final char formation rate at 800℃exceeds 40%.Among them,the modified polyester TLCP-SDP has the highest melting point,which is as high as 297℃,but its high viscosity is not conducive to processing and molding.The initial storage modulus of TLCP-ODP,TLCPDHBP,and TLCP-TDP copolyester films at room temperature are 0.85 GPa,1.2 GPa,and 1.5 GPa,respectively,showing good tensile strength.In addition,it also exhibits low dielectric strength at high frequencies,and the dielectric loss factor is relatively stable at high frequencies,about 0.01.While TLCP-DHBP has a high melting point of 290 ℃,it also has good melt fluidity and excellent processing performance.It is expected that these new TLCPs can be well applied in the fields of electronics,electrical,and 5G substrates.TLCP-TDP can still maintain a high storage modulus at a high temperature above 250℃ and has a certain application prospect in a high-temperature environment.In summary,this work explores the synthesis process of TLCP based on a model copolymer with a simple structure and uses this synthesis process to prepare four new ternary thermotropic liquid crystal copolyester with good liquid crystal properties and thermal properties.This work provides a new route for designing and synthesizing aromatic polyesters with outstanding performances.