Synthesis And Degradation Recovery Of Diglycidyl Terephthalate

In this paper,diglycidyl terephthalate(DGT)was synthesized from terephthalic acid and epichlorohydrin,and the thermal,mechanical,solvent resistance and degradation properties of DGT/amine cured products were investigated.It was found that there are two mechanisms in the first step of the esterification reaction in the "two-step synthesis" of DGT,namely,nucleophilic substitution of C-Cl(SN1)and ring opening of epoxy groups(SN2).In this paper,this mechanism was verified by infrared spectroscopy,and experiments were designed for this phenomenon,and the effects of five esterification conditions on the reactions of SN1 and SN2 were discussed.It was also found that the second step of the closed-loop reaction conditions had a large effect on the yield and epoxy value of the products.The effect of different closed-loop reaction conditions on the yield and epoxy value of the products was discussed in this paper,and the reaction conditions for the closed-loop reaction were optimized.The basic properties of DGT/amine cures were measured,and the degradation and recovery of epoxy resin cures were discussed,and the study showed that:(1)In the first step of the esterification reaction,the high ratio of(epoxy chloropropane)ECH is favorable to the SN1 reaction,and the reaction rate has a significant effect;the optimal temperature of the SN1 reaction is 100℃,and the increase in temperature is favorable to the SN2 reaction;extending a certain reaction time is favorable to the SN1reaction;increasing the catalyst content is favorable to the SN1 reaction and the reaction is accelerated;the catalyst tetrabutylammonium chloride has a When the SN1 reaction was carried out to a greater extent,the closed-loop products had higher epoxy values and yields.(2)In the second step of the closed-loop reaction,the reaction time was controlled at1.5～2.0 h.The short closed-loop reaction time resulted in low yield and epoxy value,while the long time resulted in a significant decrease in yield;the temperature of the reaction was controlled at about 35℃,too low was not conducive to the reaction,too high was likely to cause hydrolysis side reactions;the amount of alkali should be controlled at 2.0～2.2 times of PTA.The amount of alkali should be controlled at 2.0～2.2 times of terephthalic acid,the reaction is incomplete if the amount is too low,and the yield and epoxy value are significantly decreased if the amount is too high;the higher the concentration of alkali,the higher the epoxy value,but the solid alkali is not conducive to the reaction,and the yield increases and then decreases with the increase of alkali concentration;the slower the drop acceleration rate of alkali,the higher the epoxy value and yield,and the appropriate extension of the drop addition time is beneficial to the closed-loop reaction.(3)After curing the synthesized DGT and polyetheramine,the mechanical properties were higher in tensile strength,higher in modulus,higher in elongation at break,slightly lower in glass transition temperature than E-51,and excellent in acid/base and solvent resistance compared with E-51.The cured material can be degraded rapidly at 160℃ in EG/DMSO solvent,and the swelling effect of organic solvent can accelerate the degradation rate.The optimal ratio of EG/ DMSO is 60/40,and the degradation rate is accelerated with the increase in temperature.When the degraded material is reused with a 10% addition,the new resin can still maintain good mechanical properties and degrade faster.