Linear‐temperature programmed pyrolysis of thermoresistant polymers — mass and FTIR spectrometries, 2. Aromatic polyesters and copolyesters

Linear‐temperature controlled pyrolysis with subsequent analysis of the pyrolyzates (volatiles and residue) by 18 V electron‐impact mass spectrometry (EIMS) and FTIR spectrometry, respectively, yields optimal informations on the thermal degradation mechanisms of heat‐resistant polymers. In the present paper results with aromatic polyesters are reported. Poly(4‐oxybenzoyl) firstly (675 K) releases residual educt (acetoxybenzoic acid), solvent (hexahydroterphenyl), phenol and oligomers. In the temperature range of maximum decomposition (Tmax = 815 K) several consecutive processes take place. At 760 K, “monomer” (oxybenzoyl) and two series of oligomers with different endgroups are set free. At 815 K, formation of phenol, and at 845 K. formation of diphenyl ether are the dominating process. The maxima of CO2 and CO release are at 790 K and 825 K, respectively. In the residue, diaryl ketone, 9‐fluorenone and phenolic structures were observed. Mechanisms including Fries‐analogue rearrangements are discussed. A typical poly‐(4‐oxybenzoyl‐ran‐2‐oxy‐6‐naphthoyl) (“Vectra A 950”) with 73 mol‐% oxybenzoyl units produced, during the “evaporation phase” (640 K) and in addition to oxybenzoyl “monomer” and oligomers, oxynaphthoyl and a series of hetero‐fragments containing one oxynaphthoyl unit and one or two oxybenzoyl units. At 785 K (close to Tmax), the formation of phenol, CO2, CO and oxybenzoyl was predominant. In the residue, the formation of diaryl ketone, dibenzofuran and 9‐fluorenone structures was observed. Mechanisms are discussed in analogy to the degradation of poly(4‐oxybenzoyl).