Formation of Aromatic Compounds as Side Reactions in the Polycondensation of Bis(2-hydroxyethyl) Terephthalate

Abstract

ABSTRACT:Studies on the side reactions in the polycondensation of bis(2-hydroxyethyl) terephthalate were performed in the presence of catalysts (Mn, Co, Zn, W). 4,4'-Biphenyldicarboxylic acid, l,2-bis(4-carboxyphenyl)ethane, and 2,4',5-biphenyltricarboxylic acid were found as major aromatic by-products in the reaction. The yield of these by-products was very poor in the absence of these catalysts, and remarkably increased in the presence of catalysts in the following order: Mn< Co< Zn <1; W. This order was in accord with that of the activity of catalysts for polycondensation of bis(2-hydroxyethyl) terephthalate. The side reactions were suppressed with the addition of radical inhibitor, indicating that the side reactions occurred with a radical mechanism; this was supported from ESR studies. The side reactio'ls are probably initiated by the alkyl radical ( -C6 H4 COOC2H4 ·) obtained from the reaction ofbis(2-hydroxyethyl) terephthalate with the metal of catalysts.KEY WORDS Bis(2-hydroxyethyl) Terephthalate / Poly(ethylene terephthalate) / Polycondensation / 4,4'-Biphenyldicarboxylic Acid / l,2-Bis(4-carboxyphenyl)ethane / 2,4',5-Biphenyltricarboxylic Acid / ESR / Free EXPERIMENT A-L MaterialsSeveral side reactions such as etherification 1 · 2 and thermal degradation 3 -6 have been observed in the polycondensation of bis(2-hydroxyethyl) terephthalate (BHET) or its oligomer. We found that 4,4'-biphenyldicarboxylic acid, 2,4' ,5-biphenyltricarboxylic acid, and 1,2-bis( 4-carboxyphenyl)ethane were obtained as by.products in the polycondensation of BHET. The side reactions sometimes lead to the deterioration of the physical and chemical properties of the poly(ethylene terephthalate) (PET) obtained. 2 · 3 · 7 In order to manufacture PET of high quality, details of the side reactions in the polycondensation must be investigated.BHET was prepared by the reaction of terephthalic acid with ethylene oxide. 9One of the present authors previously identified the mechanism of the polycondensation of BHET in the presence of catalysts (Co, Mn, Zn). 8 In this research, aromatic compounds formed by the side reactions in the polycondensation of BHET were determined quantitatively in the presence of a catalyst (Mn, Co, Zn, W); the mechanisms for the side reactions are discussed here.Catalysts (commercially available guaranteed grade) and a radical inhibitor, 1,3,4, Shell Fine Chemicals), were used without further prufication. Polycondensation of BHETPolycondensation ofBHET (1.5 mol) was carried out in a 1.0 dm 3 autoclave in the presence of a catalyst (0.3 mmol) at 273°C under reduced pressure. 8 Samples for the study of by-products were taken out of the autoclave at regular time intervals 8 and were subjected to methanolysis. Thermooxidative Degradation of PETThe polymer containing a polycondensation catalyst was powdered and heated for I h in an oven at 300°C under an air stream 4 -6 and was subjected to 787

Nucleation of crystallization of polyester by catalyst remnants—a review

“…Others are Zn, Pb, Cd, Mg, Ca, Ce, Co, and Sn. Certain metals among this group are not chosen for industrial processes due to their propensity to catalyze the thermal pyrolysis of PET during the polycondensation step (10,11). The widely used Mn is "deactivated" by complexing it with a phosphorus additive, such as phosphoric acid or triphenyl phosphate.…”

“…The polycondensation step is catalyzed by Sb. Antimony is the industrial catalyst of choice due to its relatively high activity toward catalysis of polycondensation with low activity toward thermal pyrolysis (10,11,13). It has been shown that in the polycondensation melt, there is a potential for Sb to be complexed by phosphoric acid (14).…”

Effect of Reaction Time on Poly(ethylene terephthalate) Properties

“…The formation of high molecular weight byproducts, specifically 4,4'-dicarboxybiphenyl (DCBI), 2,4',5-tricarboxybiphenyl (TCBI), and l,2-bis(4-carboxyphenyl)ethane (BCPE) (Figure 14), has been shown to occur both during thermooxidative degradation and polycondensation (Nealy and Adams, 1971;Spanninger, 1974;Kamatani and Kuze, 1979). The compounds were identified as their methyl ester derivatives by gas chromatographic analysis of products from high-temperature methanolysis of PET.…”

“…The compounds were identified as their methyl ester derivatives by gas chromatographic analysis of products from high-temperature methanolysis of PET. In the most comprehensive of these studies, the data obtained by Kamatani and Kuze (1979) indicated the following: (1) yields of byproducts increased with polycondensation time; (2) although the same byproducts were formed, the mechanism of formation during thermal degradation was apparently different than during polycondensation; (3) byproduct formation rates increased as the catalyst activity increased; therefore, byproducts were formed by metal catalysis; and (4) the metal-catalyzed polycondensation reaction was ionic, while metal-catalyzed byproduct-forming reactions involved free radicals.…”

Poly(Ethylene Terephthalate) Polymerization – Mechanism, Catalysis, Kinetics, Mass Transfer and Reactor Design

“…Free radical mechanisms have been proposed for this reaction [61,72], and 4,4 -biphenyldicarboxylic acid, 2,4 ,5-biphenyltricarboxylic acid, and 1,2-bis(4carboxyphenyl)ethane have been detected as side products [72]. Free radical mechanisms have been proposed for this reaction [61,72], and 4,4 -biphenyldicarboxylic acid, 2,4 ,5-biphenyltricarboxylic acid, and 1,2-bis(4carboxyphenyl)ethane have been detected as side products [72].…”