Technical advancement: A simple but effective method for synthesis and preparation of epoxy resin based organic composites with controllable negative thermal expansion was developed. We synthesized polyamide with eight-membered carbon ring structure and introduced it into epoxy resin crosslinking network by solvent-assisted method to modify epoxy resin. It makes up for the defects of high thermal expansion coefficient and brittleness of traditional epoxy resin, and overcomes the problems of weak interfacial connectivity and low degree of crosslinking existing in inorganic NTE materials. Nano TiO2 ultrasonic dispersion plus modified epoxy resin composite can realize the comprehensive improvement of thermal stability and mechanical properties of composite materials, and solve the problem of positive expansion of materials at low temperature caused by low polyamide content.

The synthesis of eight-membered cyclic polyamide was characterized by nuclear magnetic resonance carbon spectrum, hydrogen spectrum, infrared spectrum, mass spectrum. The surface and section morphology of modified epoxy materials were studied by scanning electron microscopy (SEM). By molecular dynamics simulation, polymer crosslinking and total energy of the system were calculated, and swelling equilibrium method was used to study the swelling rate of the composites. The thermal and mechanical properties of the composites were evaluated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and electronic universal testing machine. The results show that with the increase of polyamide proportion, the characteristic peak does not change, the crack order gradually becomes worse, the flexibility is enhanced, the swelling rate of NMP is increased, and the thermal stability is improved.

The thermal expansion (shrinkage) behavior of epoxy resin matrix composites was tested by thermomechanical analyzer. The composite films exhibit excellent negative thermal expansion characteristics, with negative thermal expansion coefficient of −492.6 ppm/K in the temperature range of 80-104℃. With the best comprehensive performance, the negative thermal expansion coefficient α_T can reach −364.3ppm/K(20-54°C), the elastic modulus can reach 63.72MPa, and the compression modulus can reach 967.31MPa. This study provides a way for the preparation of organic composites with controllable negative thermal expansion properties, provides a solution to eliminate the problem of thermal expansion of traditional materials, and promotes the further application of negative thermal expansion materials in precision instruments, electronics industry, biomedicine, aerospace and other fields.

Maturity: The synthesis method and preparation process are mature and complete; the mechanism research needs to be strengthened; and the results need to be further improved according to the actual production.

Intellectual property rights: A preparation method of negative thermal expansion epoxy resin and polyurethane (invention patent)