Preparation Of PET Cyclic Oligomers And Study Of Ring-opening Polymerization In High Viscosity Systems

Cyclic oligomer(COET)is a by-product produced in the polycondensation process of polyester(polyethylene terephthalate,PET),which will cause damage to the spinning and dyeing process of polyester fibers.The current industrial method of reducing the content of cyclic oligomers is mainly by adding stabilizers during polymerization to inhibit its formation,but this method cannot completely eliminate the formation of oligomers.If the cyclic oligomer can be converted into PET through ring-opening polymerization(ROP)in the existing catalytic system,the quality of PET will be effectively improved.For this reason,this article prepares COET by the suspension method and adds it to PET to study the ring-opening polymerization law of COET in PET high-viscosity melt.In order to eliminate the effect of PET and COET transesterification effect on COET ring-opening polymerization,this paper selects polystyrene(PS)melt to prepare a reference system,and compares and studies the ring-opening polymerization of COET in an inert environment.The polymerization mechanism in PET melt provides reference.The specific research content is as follows:(1)Using bis(2-hydroxyethyl)terephthalate as the raw material,n-hexadecane as the solvent,and isopropyl titanate as the catalyst,the suspension method is used to efficiently prepare COET in a short time and with COET as the monomer.Prepare PET by bulk ring-opening polymerization,and analyze the structure and performance of COET and its PET polymer products by characterization methods such as morphology,structure,and thermal properties.Infrared and nuclear magnetic resonance spectra show that COET was successfully prepared by the suspension method,and its molecular structure is the same as that of the cyclic oligomer contained in PET.The melting point of COET is 307 °C after differential scanning calorimetry test,which indicates that the COET is 307 °C.Predominantly shaped trimers.The microscopic morphology is hexagonal prism-like crystals.Studies have shown that the open loop temperature of pure COET is above 310 °C.(2)The COET/PET mixture was prepared by the solution method.After removing the solvent,using antimony trioxide as the catalyst,the polymerization reaction of COET in the PET melt in the temperature range of 260 °C-310 °C was studied.The results show that the melting point of the DSC heating curve of the product of COET/PET(50/50)reaction above 270 ? is near 255 °C,which is close to the melting point of pure PET,indicating that COET has a ring-opening reaction in the PET melt;In addition to the melting peak at 255 °C in the DSC curve of the reaction product at 260 °C,there is still a weak melting peak at 290 °C,indicating that the COET has not reacted completely.As the reaction temperature increased from 270°C to310°C,the intrinsic viscosity of the reaction product increased from 0.25 d L/g to 0.41 d L/g.(3)Prepare the COET/PS solution system with dichloromethane as the solvent.After removing the solvent,raise the COET/PS to the reaction temperature to cause the COET to polymerize in the PS melt,and use the solvent method to remove the PS component in the reaction product,conduct structure and performance analysis of COET polymerization products.The results show that the lowest temperature at which COET can undergo ring-opening polymerization in PS melt is 250 °C.The thermogravimetric analysis technique is used to analyze and test the products at different reaction temperatures.As the reaction time increases from 15 min to 75 min,the intrinsic viscosity of the reaction product increases from 0.26 d L/g to 0.41 d L/g.Under the same reaction conditions,compared with PET,COET can obtain products with higher intrinsic viscosity in PS melt.