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LCP aromatic polyesters by esterolysis melt polymerization

Polyarylates have previously been synthesized from acetate esters via esterolysis (loss of methyl acetate). This polycondensation can be extended top-substituted aromatic monomers for liquid crystal polyesters (LCPs). For AB-type polymers, methyl p-acetoxybenzoate and methyl 6-acetoxynaphthoate were copolymerized to an LCP with reasonable molecular weights. Benzoate esters, methyl 4-benzoyloxybenzoate (MBB) and methyl 6-benzoyloxy-2-naphthoate (MBN), are also investigated. Several tin and antimony oxide catalysts were effective. The rate of esterolysis polymerization of MBB and MBN is slower than that of the corresponding acidolysis melt polymerization, but fast enough to give relatively high-molecular-weight polymers and similar thermal stability as commercial LCP prepared by acidolysis. Using these alternative benzoyloxy groups significantly reduced the color problem, because ketene loss cannot occur. Esterolysis melt polymerizations leading to AB/AABB-type LCPs were performed using either dimethyl 2,6-naphthalene dicarboxylate (DMND) or dimethyl terephthalate (DMT) with methyl 4-acetoxybenzoate and phenylhydroquinone diacetate with tin and antimony catalysts. DMT-based monomer compositions show much faster polymerization than DMND-based compositions using antimony oxide catalyst. All these LCPs show a T g in the 140-170 °C range as a result of the inclusion of the naphthalene and/or phenyl hydroquinone units in the polymer chain. Compositions completely off-balanced on either side still lead to relatively high-molecular-weight copolyesters because either excess monomer can be removed during polymerization.