The Study On Synthesis And Modification Of Hyperbranched Polyurethane

Polyurethane(PU)possessed unique structure and excellent performance as well as widespread applications.Nevertheless,its application in the field of high temperature had been limited on account of poor mechanical properties and thermal stability.In addition,the UV resistance property of PU was not good.Especially aromatic PU,when it was vulnerable to UV,it yellowed easily and then degraded,which affected seriously its performance.Therefore,it was an urgent problem in the PU field that the thermal stability and UV resistance property of PU was improved.Polyimide(PI)was one of the best comprehensive polymer materials with excellent heat resistance,mechanical and radiation resistance property.It was an valid way to introduce imide structure into chain segment of PU,which not only improved heat resistance of PU but also enhanced mechanical property.The natural melanin existed widely in organisms in nature was a kind of polymer with high UV absorption capacity,which contained a number of hydroxyl(-OH)and carboxyl(-COOH)active groups.Modified PU using the natural melanin was an appropriate way for improving UV resistance property.In present work,imide-containing glycol(HEPMI)was synthesized firstly by using pyromellitic dianhydride(PMDA)and ethano lamine(EA).Hyperbranched poly(urethane-imide)s(HBPUI)were then synthesized via A2+B2+B3 approache used isophorone diisocyanate(IPDI),polycarbonate diol(PCDL),butanediol(BD),HEPMI,triethanolamine as raw materials,which needed to adjust the ratio of BD and HEPMI.Due to the successful introduction of the imide ring structure,the heat resistance and mechanical properties of PU were significantly improved.The 10%thermal decomposition temperature reached 289?300?,and the tensile strength reached 19 MPa.At the same time,the so-prepared HBPUI had good solubility in aprotic polar solventand water resistance.In order to improve UV resistance of PU,a seires of hyperbranched poly(urethane-imide)s/natural melanin composites(HBPUI/M)were prepared by complexing as-prepared HBPUI with natural melanin.Through the photocatalytic degradation test of methylene blue solution(MB),it was found that the UV resistance of HBPUI/M was obviously improved,and when the melanin content was 2%,the degradation of MB was only 22%.Meanwhile,DSC and mechanical properties tests showed that the heat resistance and mechanical properties of HBPUI/M were also significantly improved,the glass transition temperature(Tg)was increased optimally by 18.3 ? and the tensile strength was enhanced by 20.8MPa.