Preparation And Properties Of Fluorenyl Cardo Polyurea Composites Modified By PEI/TAC

Polyurea（PU）is a new type of green pollution-free and environment-friendly material with excellent mechanical properties,thermal properties,corrosion resistance and electrical properties.It has broad application prospects in microelectronic devices,aerospace,military,construction and other fields.However,with the rapid development of polymer materials and the continuous improvement of national standards,the use of traditional PU materials in the field of high temperature and high strength is limited.Therefore,in this thesis,fluorenyl Cardo polyurea was synthesized by molecular design,and used as a substrate.Using polyetherimide（PEI）and triallyl cyanate（TAC）as modifiers,a series of fluorenyl Cardo polyurea composites with high strength and excellent thermal properties were prepared by physical blending,tape casting,and thermal crosslinking methods.The research content of this paper mainly includes the following three parts:（1）A series of fluorenyl Cardo polyurea films were prepared by using4,4’-diaminodiphenyl ether（ODA）,9,9-bis（4-aminophenyl）fluorene（FDA）and4,4’-methylenebis（phenyl isocyanate）（MDI）as monomers to adjust the ratio of ODA and FDA.The results showd that the introduction of fluorenyl can effectively improve the mechanical and thermal properties of PU film.The tensile strength of PU-30（FDA content of 30%）was 111.61 MPa,which is 47.7%higher than that of PU film,and T_d5%（297.6℃）and T_g（224.4℃）were better than PU film.PU-30 film had high electrical breakdown strength（241.67 k V/mm）,and showd excellent solubility and chemical stability.（2）In order to further improve the comprehensive performance of PU-30,a series of PU-30/PEI composite films were prepared by introducing PEI with high temperature resistance and excellent mechanical properties as the modifier,and the influence of PEI content on the properties of the composite films was explored.The results showed that the tensile strength of PU-30/PEI-40 composite film（PEI content was 40 wt%）was 137.27 MPa,the elongation at break was 155.94%,and the electrical breakdown strength was 307.94 k V/mm,which were 23.0%,85.8%and27.4%higher than that of PU-30 matrix film,respectively.The T_d5%（315.1℃）and T_g（241.1℃）of PU-30/PEI-50 composite film（PEI content of 50 wt%）increased by17.5℃and 16.7℃,respectively,compared with PU-30.PU-30/PEI composite films had low water absorption and can be used for a long time in acidic and neutral environments.（3）In the second work,it was found that when the PEI content was high,the compatibility between PU-30 and PEI was poor,and there was phase separation,which had certain limitations on the performance improvement of PU-30.Based on this,a series of PU-30/TAC composite films with semi-interpenetrating network structure were prepared by introducing a trifunctional triazine monomer—TAC that can undergo thermal crosslinking（self-polymerization）reaction to form a network polymer under high temperature conditions,and the effects of TAC content and thermal crosslinking time on the properties of the composite films were explored.The results showed that when the TAC content was 15 wt%and the thermal crosslinking was 6 h,the tensile strength of the composite film was 160.40 MPa,which was 43.7%higher than that of PU-30.The maximum T_gof PU-30/TAC composite films was243.2℃,which was 18.8℃higher than PU-30,and had excellent corrosion resistance.