The influence of phosphoric acid on the activity of Sb(III) catalyst was studied in the catalytic polycondensation of bis(2-hydroxyethyl) terephthalate (BHET). Although the rate of polycondensation in the initial stage was depressed by the addition of phosphoric acid to the Sb(III) catalyst, subsequent polycondensation was accelerated to give a higher-molecular-weight poly(ethylene terephthalate) as compared with that obtained in the absence of phosphoric acid. The yield of by-products in the polycondensation was also affected by the addition of phosphoric acid; the formation of acetaldehyde decreased, and that of the diethylene glycol unit increased. It was made clear from studies of 31 P NMR that the phosphoric acid was converted into phosphate (0= P(OC2H4 0R)3) in the early stage of the polycondensation by reaction with BHET or ethylene glycol which was generated in the polycondensation ofBHET. It is assumed that the modification of the polycondensation reaction caused by the addition of phosphoric acid is due to the complexation of Sb(III) catalyst with the phosphate. The mechanism for the polycondensation of BHET catalyzed by Sb(III) compounds in the presence of phosphoric acid was proposed on the basis of these findings. KEY WORDS Bis(2-hydroxyethyl) Terephthalate I Poly(ethylene !erephthalate) I Polycondensation I Sb(III) Catalyst I Phosphoric Acid I 31p NMR I

It has been confirmed that the reaction model proposed previously, which can express simultaneously the oligomer properties and the distillate properties under low esterification pressure, is applicable to a continuous direct esterification process in a practical plant. The experimental data of the first esterification reactor (RA‐1) was obtained under low reaction pressures (atomospheric or 1 kg/cm2G) with the pilot plant throughput based on poly(ethylene terephthalate) (PET) polymer production of about 50 kg/h. The Arrhenius' parameters, frequency factor, and apparent activation energy, were determined fitting the experimental data of the pilot plant by using the Simplex method as an optimization technique. The activation energy of diethylene glycol (DEG) formation, E7, is about twice as much as those of the esterifications, E1, E2, E3, and E4. The activation energies are E1, = 19640 cal/mol, E2 = 18140, E3 = 22310, E4 = 18380, E5 = 2810, E6 = 14960, and E7 = 42520 cal/mol. Good agreement was obtained between experimental data and calculated predictions for several oligomer and distillate properties. The vapor‐liquid equilibrium can be expressed by Raoult's law with little problem of practical use.

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

SYNOPSISSide reactions of isocyanate groups in N,N-dimethylacetamide ( DMAC ) were studied. Although 4,4'-diphenylmethane diisocyanate (MDI) in DMAC was stable and no changes occurred at 3"C, the isocyanate content decreased and a gel was finally formed a t 40°C. Using phenyl isocyanate ( P I ) as a model compound of MDI, the identification of PI sidereaction products in DMAC were studied. From these experiments, the following five products were identified; ( 1 ) 1,3-diphenylurea (DPU ), ( 2 ) 1,3-diphenyl-5-phenylcarbamyl-6-dimethylaminouracil ( P U R ) , (3) 1,3,5-triphenylbiuret ( T P B ) , ( 4 ) triphenyl-s-triazine-2,4,6-trione (TTT), and ( 5 ) l,l-dimethyl-3-phenylurea (DMPU) . Among these identified products, the novel side reaction product PUR, which was formed between P I and DMAC as solvent, was found along with T P B and TTT, which were already known to cause threedimensional network formation.

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