Free-radical chain generation of ketene during the synthesis of liquid crystalline aromatic polyesters

At the high temperatures used for the preparation of liquid crystalline aromatic polyesters (LCPs), ketene cleavage occurred from acetoxyarenes. Ketene is known to oligomerize to colored oligomers which may be responsible for an undesirable yellow color in LCPs. Thermolysis of the model compound p-acetoxybenzoate gave ketene oligomers and methyl p-hydroxybenzoate, which oligomerized. A free-radical chain reaction mechanism for ketene formation was demonstrated by the reaction of tributyltin hydride with haloacetoxyarenes.