Study On Viscosity Regulator Based On Hyperbranched Polyimides

With the development of aerospace, mechanical and electrical manufacturing,cutting-edge technology, military and even during our lives, the needs of high strength,high modulus, light weight and high temperature resistant material needs more andmore urgent and bigger. Polyimide is a super performance engineering plastic withexcellent mechanical performance and thermal stability. There are some rigidstructures, such as benzene and imine, in the polyimide macromolecules. For itsprocessing, except injection molding, those polyimides that require highertemperature can only prepared through hot pressing or even more special, morecomplex molding method that would limit its wider application. At present, the studyof hyperbranched polymers attracts more and more attentions, which mainly due to:firstly, the special physical and chemical properties of hyperbranched polymer, e.g.,ellipsoidal molecular structure, good flowability, low chain entanglement, highsolubility, low melt viscosity and versatility, etc.; secondly, the periphery of the threedimensional structure exists a large number of terminal groups. A huge number ofhyperbranched polymer terminal groups can provide reaction sites forfurther-chemical modification and functionalization reaction; thirdly, the synthesis ofhyperbranched polymer is easier and lower cost compared with the linear polymer.Based on these advantages, the researchers made a thorough research on itsapplication, the use of hyperbranched polymer viscosity regulator to improve theprocessing performance of the linear polymer is one of the important applications.During the first part, based on previous work of our group, this paper selecttriamines and dianhydride monomers containing ether bond and bulky group,end-capped by the three kinds of end capping agent, hyperbranched polyimides (HBPIs) with different end groups obtained by polycondensation reaction. These fivekinds of hyperbranched polymers were characterized by FT-IR,1H NMR, GPC andEA. The degree of branching of the HBPI is0.453calculated from NMR data. Thepolymers containing alkynyl group through high temperature treatment to give curedHBPIs. The solvents commonly used during experiments are used for testing thesolubility of the polymer, and these five kinds of HBPIs have good solubility instrongly polar solvents, such as DMSO, DMAc, DMF, NMP. Two crosslinkedhyperbranched polymers are insoluble in any of above solvents. Thermal performancetest results show that all the polymers have excellent thermal stability, and5%weightloss temperatures were above542oC. After cured5%weight loss temperature is up to600oC. Due to the influence of the terminal groups, HBPIs’ glass transitiontemperature changes between166-193oC. Hyperbranched polyimides with anhydride,amino and phenyl end groups have high melt viscosity. The lowest melt viscositywere2165Pa s (315oC),2277Pa s (283oC) and2086Pa s (329oC), respectively. Thehyperbranched polymers terminated with alkynyl exhibit low melt viscosity, and thelowest melt viscosity were13.3Pa s (309oC),12.6Pa s (319oC), respectively. Thisdiscrepancy is related to the free volume of the end groups judging from the literatureand comparative analysis.During the second part, this part mainly discusses the performance ofphenylethynyl phthalic anhydride terminated hyperbranched polyimide (PE-HBPI) asa viscosity modifier, and compare with phthalic anhydride terminated hyperbranchedpolyimide (OPA-HBPI). After sufficiently blending, we analyze the thermal propertiesof the blend, and these two series blends were found have excellent thermal stability.After curing the5%weight loss temperature of the blend is further improved reach tosurpass540oC. These two series of blends have only one glass transition temperature,indicating that the blend was homogeneous. With the increasing amount of PE-HBPI,the glass transition temperature moved to a lower temperature. The addition ofhyperbranched polyimide make the melt viscosity of linear polyimide decreased, however, the effect of adding PE-HBPI is better. And with the increasing of thecontent of PE-HBPI, the temperature of minimum melt viscosity is reduced, therebyreducing the temperature of the process window, reducing energy and costs. Tensileproperties of these two series of blends were tested. After curing, blends added with3%PE-HBPI exhibit good tensile properties. A tensile modulus of1803MPa, a tensilestrength of86.1MPa, compared to pure linear polyimides, the mechanical propertiesof the blend has not only no decreased but also increased slightly.In general, through selecting the polymerizable monomers and capping agentsproperly, we synthesized hyperbranched polyimide with low viscosity. The blendprepared by PE-HBPI with linear polyimide not only the melt viscosity reduced whichimprove the processing performance, but also the thermal stability and mechanicalproperties also increased slightly after cured.