High Thermal Conductivity and Recycling of Main-Chain Liquid Crystal Polyesters Based on π–π Stacking

The production of degradable polymer materials with high thermal conductivity is urgently needed to reduce plastic pollution from electronic waste. This research prepared a series of intrinsically thermally conductive polyesters (L-LCPs) by the melt polycondensation reaction of biphenyl diol with three different dicarboxylic acids, which are dl-tartaric acid, dl-malic acid, and diethanolic acid. The thermal conductivity and hydrolysis behavior of these were investigated. Biphenyl group π–π stacking enhances the interchain interactions and endows the polyester with high thermal conductivity. The thermal conductivity of L-LCP3 reaches 0.716 W/(m·K), showing a significant improvement of 168.8% compared to L-LCP1, which is 3.5 times higher than polyethylene terephthalate (PET). The differential scanning calorimetry (DSC) results of the cooling process and the polarizing optical microscopy (POM) pictures showed that all of the L-LCPs are bidirectional thermotropic liquid crystal polymers. Meanwhile, the L-LCPs were efficiently hydrolyzed to valuable raw materials by using the mixed solvents tetrahydrofuran (THF) and H2O. The notable merits of the solvent system are the fragmentation effect of tetrahydrofuran and the enhancement of the catalyst NaOH activity by H2O. The L-LCPs are transformed into oligomers or monomers as the hydrolysis reaction proceeds. The residue weights of L-LCP3 were reduced to 67.2% in the THF–H2O solvent system. The T5%, Tmax, and residual carbon of L-LCP3 were 375.1 °C, 430.4 °C, and 6.2% at 800 °C, respectively, indicating that it has good thermal stability.