Precipitation,Separation,Purification and Ring-Opening Polymerization of Cyclic Ethylene Terephthalate Oligomers
Cyclic ethylene terephthalate(CET)can be prepared by the cyclo-depolymerization(CDP)of polyethylene terephthalate(PET)at low solution concentrations,but the composition of crude depolymerization product is complicated and needs further purification for high-valued application.Here,effects of precipitation temperature and type of precipitating agent on the yield of CET,thermal properties and ring-opening polymerization behavior of purified CET were investigated.The results showed that when ethanol was used as the precipitant,the content of linear oligomers and catalyst residues in the selectively precipitated CET decreased with the reduction of temperature,and at a precipitation temperature of 30℃,the content of linear oligomers and catalyst residues was relatively low.When saturated alkanes such as n-hexane were used as precipitants,CET free of linear oligomer components could be obtained at a precipitation temperature of 30℃,and the highest yield of CET(up to 72.69% )was achieved using n-hexane as the precipitant.Purified CET,without the addition of a catalyst and with the addition of 1% (mass fraction)antimony trioxide catalyst,could be ring-opening polymerized at 320℃ for 8 min to produce PET with intrinsic viscosities of 0.56 dL/g and 0.64 dL/g,respectively.
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