**1. Introduction**

The wide introduction of polymer materials in various fields of production is due to their special mechanical and physicochemical characteristics, such as elasticity, low brittleness,

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

directional changes in structure and properties under physicochemical effects. To reduce the cost of material and give it special properties, various fillers are actively used.

a polymer basis [2, 3]. Polymer nanocomposites are extensively studied for a potentially wide range of applications due to their ease of processing, low production costs, good adhesion to the substrate, and unique physicochemical properties. Dispersing of inorganic materials in a polyimide matrix is a complex task and a key factor affecting the final properties of hybrid materials. The addition of a cross-linking agent is a solution to overcome the difficulties associated with dispersing. By adding a cross-linking agent, organic and inorganic materials can be covalently bonded and compatibility between these two phases can be improved [4, 5].

Nanocomposite Polyimide Materials http://dx.doi.org/10.5772/intechopen.79889 87

The transition to nanofillers has significantly improved the performance of composites and

With the development of industries, an increase in the operating temperature range occurs, as

Polyimides are one of the most interesting polymers, which have increased heat resistance and are widely used in the manufacture of high-temperature plastics, adhesives, dielectrics,

Currently, polyimide resins are used as matrices to create reinforced composites based on lightweight carbon fibers, as a replacement for metal parts in the aerospace industry and airframe, due to their outstanding thermal and mechanical resistance, as well as resistance to the action of ionizing radiation. Polyimide resins are widely used in such areas as microelectronics, aerospace, gas separation, and the production of fuel cells. They are used in the cable industry for the production of electrical insulating varnishes and enamels, which have high

As is known, polyimides (PI) can be aliphatic, alicyclic, or aromatic, depending on the chemical structure. Depending on the structure of the chain, polyimides can be linear or three-dimensional [6]. There are polyimides with aliphatic links in the main chain of the macromolecule and purely aromatic polyimides. The first are solid, readily crystallizable substances of white or yellow color. Polypyromellitimides based on aliphatic diamines containing less than seven carbon atoms in the molecule have high melting points that are higher than the temperatures of their onset of decomposition (above 350°C) and do not dissolve in known organic solvents. Polypyromellitimides based on aliphatic diamines containing, in the chain, more than seven carbon atoms or having a branched hydrocarbon chain (at least seven carbon atoms), as well as polyimides of other aromatic tetracarboxylic acids and various aliphatic diamines, soften

Aromatic polyimides are characterized by high heat resistance, and the most heat-resistant polyimides based on pyromellitic acid (**Figure 1**) and 1,4,5,8-naphthalenetetracarboxylic (**Figure 2**) acids, practically not softening before the onset of thermal decomposition, have a

The heat resistance of other polyimides is well regulated by varying the nature of the monomers and is usually 300–430°C [7]. Most aromatic polyimides, especially high-heat-resistant,

achieved new properties unattainable with the use of traditional fillers and modifiers.

a result of which the requirements for materials increase.

heat resistance, elasticity, and good dielectric properties.

and other materials.

at temperatures of 300°C.

glass transition temperature of 500°C.

**2. Polyimides: the structure of polyimide matrices**

Most of the composite materials are developed for the aerospace industry, which has always been and still is the most high-tech branch of modern production. At the same time, these materials and technologies for their production are also innovative drivers in many other sectors, such as construction, engineering, energy, instrumentation, medicine.

To produce materials with increased rigidity, impact, and tribological properties, during the last decade a lot of research has been devoted to the modification of polymers by nanoparticles. These composites exhibit unique properties that combine the advantages of inorganic fillers, such as stiffness, high thermal stability, and mechanical properties with processability, flexibility, and plasticity of organic polymers. Due to the influence of nanosized fillers on the bulk properties of polymer nanocomposites, it is possible to achieve such unique properties by adding small amounts of nanofillers to the polymer matrix.

Polymeric nanocomposites representing a new class of materials have unique barrier properties, electrical conductivity, thermal conductivity, increased strength, heat resistance, and thermal stability, as well as reduced combustibility. It is known that the addition of nanodispersed layered silicates and various forms of carbon nanofillers to polymeric matrices can significantly affect the mechanisms of thermal and thermooxidative destruction and burning of nanocomposites.

One of the most important issues facing nanotechnology is how to get molecules to group themselves in a certain way, to organize themselves, in order to eventually obtain new materials or devices capable of long-term preservation of their performance properties under the action of high and very low temperatures, chemical agents, increased radiation, and other factors. One of the main ways to solve this problem is the creation of composite materials based on a polyimide (PI) matrix. Adding different amounts of nanoparticles at different stages of polymerization of the matrix, increasing the number of available monomers (dianhydrides acid), and reversibility of the imidization reaction (the second stage of the synthesis reaction) will allow to vary the molecular and molecular mass characteristics and, as a consequence, their thermal resistance and solubility to processing, deformation-strength, and other properties of future composites.

In the world literature, examples of nanocomposite materials based on polyimide matrix filled with carbon nanotubes (CNTs), carbon fibers, and nanostructured silicon carbide (SiC) are known, and their thermal and deformation strength and other properties have been measured. Expanding the diversity of polyimide matrices and varying the content of nanostructured materials allow us to obtain a huge variety of composite materials.

Thus, creation of new composite materials with high performance characteristics and technology for their production is a very urgent and important task.

During the last decade, a lot of research has been devoted to the combination of polymers with nanoparticles to produce materials with increased rigidity, impact, and tribological properties [1]. The growing demand for nanomaterials is due to the fact that new chemical and physical properties are achievable with the addition of nanosized fillers to the polymer matrix, even if the same material without a nanofiller does not have such advantages. This is due to the influence of the unique nature of the nanosized filler on the bulk properties of nanocomposites on a polymer basis [2, 3]. Polymer nanocomposites are extensively studied for a potentially wide range of applications due to their ease of processing, low production costs, good adhesion to the substrate, and unique physicochemical properties. Dispersing of inorganic materials in a polyimide matrix is a complex task and a key factor affecting the final properties of hybrid materials. The addition of a cross-linking agent is a solution to overcome the difficulties associated with dispersing. By adding a cross-linking agent, organic and inorganic materials can be covalently bonded and compatibility between these two phases can be improved [4, 5].

The transition to nanofillers has significantly improved the performance of composites and achieved new properties unattainable with the use of traditional fillers and modifiers.

With the development of industries, an increase in the operating temperature range occurs, as a result of which the requirements for materials increase.
