Synthesis And Charaterization Of A Low Thermal Expansion Coefficient Copolymerization Polyimide

The paper mainly used the method of copolymrization by polycondensation in solution and got polyamide acid. After procedural heat treatment, the polyamide acid trasfer to amination polyimide films. We choosed 3,3',3,4'-biphenyl tetracarboxylic acid dianhydride(s-BPDA), 2,3',3,4'- biphenyl tetracarboxylic acid dianhydride(a-BPDA), pyromellitic dianhydride(PDA) and 4,4'-diamino ether(ODA), para-phenylene diamine(PDA) as reaction raw materials, with N,N-dimethyl acetamide(DMAc). We first disscussed the optimal formula of virious materials of the synthesis of polyamide acid. According to the optimal formula, we further determine the optimun condition for synthesis of polyamide acid. After determining the optimal formula and optimal conditions of synthesis polyamide acid, the further discussion of procedural heat treatment to the influence of the stucture and properties of the final polyimide film.Under the condition of this paper, when the molar ratio of the dianhydride and diamine was 1:1. Through adjusting the molar ratio, we synthesised the polyamide acid and after heating processsing wo got polyimide film. By observing the film-forming ability and its appearance, we confirmed that the molar ratio of the raw material for synthesis of polyamide acid was 0.2:0.8:0.9:0.1.Based on the optimum proportion of the synthesis of polyamide acid, we discuss the synthesis condition of polyamide acid, such as reaction temperature, reaction time, silid content and the way of adding material. These condition have influence on the structure and performance properties of the final polyimide and the structure and properties were tested and characterized. After comparative analysis of the structure and the properties of the polyimide films, we found that the reaction temperature at 0 ?, the time at 48 h, the 20% solid content and dropwise add dianhydride was superior to other condit ions. Under the above condition, we synthesied a polyimide film which had high degree of crystallinity, high heat resistance, low thermal expansion coefficient is 18.3×10-6/K and its surface topography was homogeneous and neat.Under the optimum synthesis condition, we discussed the heating curing process on the structure and properties of the polyimide film. It is concluded that when the heating rate was 5 ?/min, the film showed best film-forming ability and best film properties.