Drafting Orientation And Shape Memory Properties Of Polyimide Films

Polyimide(PI)has excellent properties that distinguish it from other polymers due to its unique imide ring(-CO-N-CO-)structure in its molecular chain.As a special engineering material,it is high-tech industries such as the electronics industry,aerospace,and smart materials have a wide range of applications.With the rapid iterative iteration of science and technology,higher requirements are put forward for the performance of PI film.Drafting is a crucial link in the PI film forming process.It adjusts the condensed structure of the PI film to control its performance.It is an important factor that affects the mechanical properties,dimensional stability,and heat recovery characteristics of the film.Therefore,the study of the draft orientation behavior of PI film is of great significance to its performance control and application research.In order to better study the effect of drafting on the performance of PI film,in this paper,the PI film that is almost completely imidized is used for drawing experiment to eliminate the influence of the imidization reaction in the traditional drawing process of polyamic acid(PAA)film.Drafting can make the molecular chains of the PI film aligned in the direction of the external force,improve the in-plane orientation,and effectively reduce the free volume of the PI film,so as to obtain a PI film with high modulus and low coefficient of thermal expansion(CTE).In addition,the introduction of flexible groups can make the molecular chains of the PI film more likely to be entangled and physically cross-linked,and obtain a PI film with excellent thermal drawing recovery,that is shape memory performance.Based on the above research ideas,main work of this paper is as follows.First,PMDA,ODA and PDA were used as monomers to prepare three systems PMDA-ODA,PMDA-ODA/PDA-73,PMDA-ODA/PDA-55 PI film,and further draw experiments on the PI film of the three systems,and discuss the effect of the draft ratio on its mechanical properties and CTE.The longitudinal comparison results show that the PI films of the three systems have internal orientation behavior after being drawn.The CTE decreases due to the decrease of free volume.And the modulus increases with the increase of the draw ratio,which has excellent mechanical properties.The horizontal comparison results show that the PI film of the more rigid system is more affected by the draft due to the relatively straight molecular chain conformation,and the reduction of CTE is more obvious.Furthermore,6FDA and ODPA were used as two dianhydrides to copolymerize with ODA to prepare 6FDA/ODPA-ODA system PI film,and its shape memory properties were studied,and the influence of different copolymerization components on the mechanical properties,shape memory properties and other properties of PI films was discussed.The research results show that the addition of ODPA increases the physical crosslinking density of the PI film and significantly improves the shape recovery rate.At the same time,the presence of 6FDA also enables the PI film to quickly fix the shape at low temperatures,with a high shape fixation rate,and success a PI film with both shape recovery rate and shape fixation rate was prepared.