Preparation Of POSS Composite Polyimide Film And Simulation Calculation Of Its Thermal Properties

With the rapid development of microelectronics in recent decades,the common polymer substrate materials have single performance and limited function,which can not meet the needs of the development of science and technology in today's era.Polyimide,as a kind of polymer material with comprehensive properties,has been widely used in daily life.However,the traditional polyimide has high dielectric constant and thermal expansion coefficient,and it is easy to adsorb water molecules,which greatly limits its application in the field of electronics.Therefore,it is urgent to develop polyimide materials with low dielectric constant,high thermal stability and good hydrophobicity.In this paper,through the preparation of polyhedral oligomeric silsesquioxane(POSS),the simulation calculation of the properties of POSS doped polyimides,and the study of the thermal stability and hydrophobic properties of POSS doped polyimides,POSS doped Polyimides with high thermal stability and good hydrophobic properties were prepared.Firstly,the polyimide model was constructed by Materials Studio 6.0 software.The glass transition temperature(Tg)of polyimide modified by POSS with different doping methods and doping ratios was simulated by molecular dynamics method.The relationship between the density and temperature of the model is obtained,which reflects the Tg temperature of the material.The results show that the two kinds of POSS doping methods can improve the Tg of polyimide materials,and the physical doping method is better than the chemical doping method by changing the content of POSS.The mean square displacement and free volume fraction were used to observe the changes of chain mobility and free volume.The results show that the physical doping POSS can limit the movement of the molecular chain by occupying the free volume in the system,so as to improve the Tg of the material;However,chemically doped POSS can increase the Tg temperature by anchoring in the molecular chain and limiting the movement of the molecular chain.In this experiment,aminopropyl-phenyl bifunctional POSS was successfully synthesized by step hydrolysis and condensation at the ratio of 4:1.The polyimide films doped with phenyl POSS and aminopropyl-phenyl POSS were synthesized by a two-step method using diamine monomer 4,4'-diaminodiphenyl ether and dianhydride monomer pyromellitic anhydride.The results of differential scanning calorimetry show that the Tg temperature increases with the increase of the content of phenyl POSS,but it is not affected by the change of the content of aminopropyl-phenyl POSS.The experimental Tg values of the two POSS with different doping methods are close to the simulation trend.The static thermomechanical analysis also reflects the changes of free volume and chain stacking in polyimide system.With the increase of POSS content,the thermal expansion coefficient of polyimide decreases;the thermal expansion coefficient of chemically bonded polyimides decreases first and then increases.The results show that the polyimide system doped by physical blending has lower free volume and higher chain stacking with the increase of POSS content,while the polyimide system doped by chemical bonding has the opposite effect.The film modified by POSS also has good hydrophobicity.