Molecular Design,Preparation And Properties Of Degradable Isosorbide-based Thermosetting Resins

Under the condition of the increasingly exhausted petroleum resources and the increasingly serious environmental pollution,synthsis and preparation of bio-based degradable thermosetting resins,through using biomass renewable resources as raw materials and introducing degradable groups,is an effective way to reduce the dependence of thermosetting materials on petrochemical resources and effectively reduce environmental pollution,and it also has became a current research hotspot.In order to endow thermosetting materials with the characteristics of sustainable development and recovery,the structure of biomass isosorbide and acid-sensitive hexahydrotriazine(HT)ring were used to design and prepare three types of degradable thermosetting resins,including polyhexahydrotriazine,polyimide and poly(estersulfide).The research work was carried out and the main results were as follows:(1)Bis(4-aminophenoxy)isosorbide(DPAI)was synthesized by two-step method,and the poly(hexahydrotriazine)(PHT)was prepared by polycondensation of DPAI with paraformaldehyde and the high-temperature curing process.The properties of PHT films cured at different temperatures were tested.It was found that the HT crosslinked structure of PHT resin was more complete when the curing temperature was up to180 ℃.Therefore,this PHT resin exhibited good comprehensive properties,such as high mechanical strength(tensile strength = 58.2 Mpa,Young’s modulus = 2.89 GPa),and the better hydrophobicity and chemical stability.At the same time,PHT resin had good degradation performance,which can be quickly degraded in 2 mol/L phosphoric acid solution,and the raw material DPAI with 85% yield can be recovered.(3)Bio-based crosslinked polyimide(PI)resins containing isosorbide and HT ring structures were preparation by the solution copolymerization of bis(1,2,4-phthalic anhydride)isosorbide(BPTI),DPAI and 1,3,5-tri(4-propionyl thioether aniline)hexahydro-1,3,5-triazine(PTHT)and high-temperature imidization process.The effects of the contents of two kinds of aromatic amine units on the thermal,mechanical,dielectric and degradability of the PI materials were investigated.The results shown that when the molar ratio of amino group from PTHT was up to 10%,PI had relatively balanced comprehensive properties,the glass transition temperature,5% weight loss temperature and the linear expansion coefficient of PI were 218.6 ℃,351.7 ℃ and42.68 ppm/ ℃,respectively,and the tensile strength and dielectric constant of PI were separately 104.7 MPa and 2.89.While continuing to increase the the molar ratio of amino group from PTHT,the imidization degree and rigidity of PI structure decreased,which resulted in the deterioration of heat resistance,mechanical strength and dielectric property of PI.In addition,because of the the high content of ester and amide in the structure of cross-linked PI,PI had a better degradation effect in 3 mol/L NaOH solution than in acidic solution.(4)Bio-based cross-linked poly(ester-sulfide)(PET)resins containing isosorbide and HT ring structure were prepared by mixing of self-made diallyl ether isosorbitol(DEI),1,3,5-triacrylamide-hexahydro-1,3,5-triazine(TAT)and trimethylolpropane tri(3-mercaptopropionate)(TMPTMPT)and various initiation polymerization methods.Through testing and comparing the thermal properties,gel yield and morphology of PET films obtained by different polymerization methods,it was found that the best polymerization method of PET was: AIBN initiated polymerization of DEI and TMPTMP to get oligomer firstly,and then the Michael addition polymerization between hydrogen-sulfur bonds at the end of the oligomer and TAT under catalyzing by triethylamine was carried out.A series of PET resins with different TAT content were prepared by optimum polymerization method.The effects of TAT content on gel ratio,thermal properties,tensile properties and degradability of PET resins were investigated.The results shown that with the increase of ratio of TAT in copolymerization,although the tensile strength and modulus of PET resin increased,the decrease of gel point resulted in the decrease of the degree of group reaction and the increase of side reactions such as thiol coupling,as a result,the gel ratio and thermal properties of the material decreased.In terms of degradability,PET resin shown a good degradability,it can be quickly oxidized and degraded into aliphatic chain,carboxylic acid and alcohols in 3mol/L nitric acid solution.The three kinds of bio-based thermosetting resins prepared in this research work have good comprehensive performance and degradability,and are expected to be used as substitutes for some petroleum-based thermosetting resins.At the same time,this work provides some theoretical basis and experimental experience for the preparation of degradable thermosetting resins based on biomass and the regulation of their structure and properties.