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The phosphorus-containing copolyesters were synthesized through poly-condensation of flame retardant with terephthalic acid (TPA) and ethylene glycol (EG). The products are suitable for flame retardible polyester fiber fabrication.
For the dosage time of flame retardible monomer OPGE, we designed two synthetic processes: in process Ⅰ, OPGE was dosed in the polycondensation stage; whereas in process Ⅱ, OPGE was dosed in the esterfication stage. We choosed one feed mole ratios (EG/TPA) of reaction to proceed 1.5. In the experiments, we used two kinds of catalyst: Ti(OBu)4 for esterfication catalyst; and Sb2O3, GeO2, Sb(CH3COO)4 for the polycondensation catalysts. The phosphorous containing copolyester was synthesized by proper reaction conditions, then the products were analyzed by FT-IR and 31P-NMR to judge the molecular structure, from the analysis, we knew that OPGE was reacted into the main chain of polymer. We could calculate the phosphrous containing of product by 1H-NMR, EA, and also used DSC adnd TGA to analyze thermal characteristics.
As experiment results showed, in batch reaction process, the catalyst Ti(OBu)4 was very favorable for whole reaction. Not only the EG/TPA feed mole ratio could be used as low ratio as 1.5. By the phosphorous containing of product, to change the OPGE dosage, we could synthesize different phosphorous containing copolyester. The intrisic viscosity of product was decreased by increasing phosphorous containing. The more OPGE ratio was added, the more complicated affect to the copolyester structure. Additionally, the thermal weight loss(290℃, N2, 30 minutes) could be kept below 0.7%, thereby indicating that phosphorous containg copolyesters had excellent thermal stability. The result shows that, the P-O bonding in the phosphonate unit would be more readily attacked. So increasing the flame retardant resulted in lower Tm and Td as well as slow crystallization of copolyesters.
As the experiment results were induced, we suggested the optimal process conditions to synthesize phosphorous containing copolyester as below: we used the feed mole ratio EG/TPA=1.5 in the esterfication section, at the same time added the esterfication catalyst (Ti(OBu)4+GeO2) and OPGE to precede esterfication reaction for obtaining BHET, then direct polymeization is followed, and proper conditions; by increasing temperature and decreasing pressure process, we could proceed polycondensation reactions to produce the products of phosphorous containing copolyester.
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