Study On Preparation Of Polyimide Molding Powder Based On Isocyanate

In this study,a series of polyimide(PI)molding powders of different molecular structures were prepared with isocyanate,binary anhydride and diamine as the basic raw materials.The research contents are as follows:(1)Four types of polyimide(PI)molding powders were prepared with biphenyl tetracarboxylic dianhydride(BPDA),4,4'-diphenylmethane diisocyanate(MDI),pyromellitic dianhydride(PMDA)and 2,4-toluene diisocyanate(TDI)as raw materials,through chemical synthesis and followed high-temperature processing.The chemical structure of the PI molding powder was confirmed by FT-IR analysis.Thermal stability and glass transition temperature(Tg)of the samples were characterized by TGA and DMA measurements,respectively.The particle size distribution of the powders was analyzed via laser granulometer,and the PI powders was molded using plate vulcanization machine.The results showed that the PI powder prepared with BPDA and MDI owned the best thermal stability,and the temperature corresponding to 5%weight loss appeared at 526?.The PI powder prepared with PMDA,MDI and TDI owned the highest Tg,the value of that was 419?.Double peaks existed in the range of particle size distribution of the PI powders.The principle factors impacting on the property and appearance of the products were the molding temperature and heating moding in the process of molding.(2)Three types of PI molding powders were prepared via isocyanate-amide acid method using 3,3',4,4'-biphenyltetracarboxylic dianhydride(BPDA),4,4'-diphenylmethane diisocyanate(MDI)and 4,4'-oxydianiline(ODA)as raw materials.The chemical structure of the PI molding powders was confirmed by FT-IR analysis.Thermal stability of PI powders was characterized by TGA analysis.Tg and melt temperature of the PI powders were analyzed using DMA and DSC measurements,respectively.The results showed that the temperature of 5%weight loss for the three types of PI powders all appeared above 530?.The Tg decreased as the content of ODA increasing,and the lowest Tg was 276?.The melting temperatures of the samples all occurred approximately at 430?.(3)Three types of polyureaimide(PIU)molding powders were synthesized through changing the mixture ratio and feeding sequence using 3,3',4,4'-biphenyl tetracarboxylic dianhydride(BPDA),4,4'-diphenylmethane diisocyanate(MDI)and 4,4'-oxydianiline(ODA)as raw materials.The chemical structure of the PIU molding powders was confirmed by FT-IR analysis.Thermal stability of the PIU powders was characterized by TGA analysis.Tg and melt temperature of the samples were analyzed using DMA and DSC measurements,respectively.The results showed that the highest and lowest temperatures of 5%weight loss for the samples appeared at 376? and 318 ?,respectively.The highest and lowest values of char yield at 800? were 59.1%and 45.9%,respectively.The samples showed two glass transition temperatures,Tgi and Tg2.Tgis all appeared approximately at 253? and the highest and lowest Tg2 were 330? and 299?,respectively.The melting temperatures of the molding powders all were about 450?.