Introductory Chapter: Polyimides - Importance and Its Applications

1. Part A: introduction

Polyimides (PIs) are engineered polymers that resisted with high-temperature; these are exceptionally thermo stable with the combination of other ligands, observed mechanical toughness and chemical resistance. PIs exhibit excellent properties of dielectric and low coefficient the increasing condition of temperature. These are aromatic in nature belongs to the class of polymers and in the combination of ligands exhibit various properties. The major advantages of PIs are physical properties and mechanical characteristics in the higher scale of cryogenic temperatures (250–300°C) and heat resistance (400–450°C), factors that influence the set of properties with the presence of conjugated hetero aromatic compounds, also exhibit potent molecular interaction and strong chain bonds. Several methods are developed for the synthesis of PIs and all are familiar. The most familiar method for the synthesis of PIs is the two-stage and one-stage under thermo stable conditions using complex mixture of diamines and aromatic tetracarboxylic acids dianhydrides. The structures of these polymers (PIs) are exhibited as thermo labile plastic and provide very good chemical resistance, electrical, mechanical, and thermal properties. The application of PIs brings the following benefits to the medical tubing such as flexibility, high tensile strength, biocompatibility, low friction, transparency, tight tolerances, thin walls, smooth surface, push ability, and column strength. Polyimide was first developed at DuPont and reported in the year 1950s. In the last few years, PIs gained a lot of interest due to their huge applications as semi-conductor in electronic appliances. The superior properties of thermal, mechanical, and electrical PIs have made it possible use and various applications. PIs exhibit very lower amount of electrical leakage in applied surfaces. They act as inter layer, good dielectric insulators and also provide fine coverage in the fabrication stepwise in the multi layer form in IC structures. They are highly resisted with solvents and can be use it as sprayer, spun-on, traditional photo imaging as lithography and also engineered in etch process. PIs are a poly merofimide monomers belongs to the class of high performance synthetic plastics. Due to their high heat-resistance, they possess various applications and roles as harsh organic materials, like high temperature fuel cells, displays and unique features. A Kapton is a typical polyimide, which was synthesized by condensation reaction using pyromellitic dianhydride and 4,4′-oxydianiline materials [1]. The report of first polyimide discovery was made in 1908 by Bogart and Renshaw [2]. They found initially 4-amino phthalic anhydride which exhibit high heat along with water evaporation during the formation of polyimide which shows a high molecular weight. After that, the semi aliphatic polyimide was discovered by Edward and Robinson by the method of fusion using diamines and tetra acid as base materials [3]. The polyimide application was reported as commercially important as Kaptonin in the year 1950s by the workers at Dupont and they developed route for synthesis with the involvement of soluble polymer as a precursor. Till today similar method was used to synthesize as primary route to produce polyimides compounds. PIs have been started with this method for mass production in 1955. The fields, applications, types, composite mixtures, etc. of polyimides were extensively worked on and reported in many books, research articles [4, 5, 6], and review articles [7, 8]. Also found is literature on biobased polymers, to protect the environment, because petroleum-based materials are not eco-friendly, hence it is a matter of need of hour in the current societies [9]. Currently, many renewable resources are there such as proteins, carbohydrates and fats, these are employed to produce it as biodegradable material and alternative to the synthetic polyimides [10, 11]. In this context, packaging materials in industries mainly focused on the production of eco-friendly and work smartly, which includes antimicrobial protection, hydrophobicity, extension of shelf life, meet the demands of consumer and maximizing benefits [12]. These characteristics are significantly achieved by assisted techniques by using nanofillers, which act as supporting agents and nano carrier materials as antimicrobial substances [13]. Poly(L-lactic acid) (PLLA) and DL-lactide are produced on large scale in biological approach using of agricultural by-products in a microbial fermentation [14, 15, 16, 17]. Owing to its beneficial features, exhibit very good mechanical properties, transparency, bio-degradability and bio-compatibility, hence it is considered best product industrial fields to produce it for wide range of application. It has been classified as a safe material by the Food and Drug Administration (FDA), due to that currently using in industries of food packaging applications [18]. As advanced methods PIs bounded with nanoparticles with different structures to develop more efficient and eco-friendly packaging materials to obtain excellent results. In the Santa Barbara Amorphous (SBA-15) and meso porous cellular foam (MCF) material as nanoparticles with 2D hexagonal shape along with cylindrical pores and 3D porous system in spherical structure were used to develop the PIs, respectively [19, 20, 21] and also they were act as nanocarriers for enhancing the chemical properties as preservatives to develop it into polymeric matrices with antimicrobial applications [22, 23, 24]. The advanced step as eco-friendly materials would be the greater extent to incorporation of natural key elements which exhibit useful properties by using essential oils [25, 26, 27, 28]. However, their volatile nature may vary in the reaction, and it needs further characterization and optimization of the protocol [29, 30].

2. Part B: properties and applications

Thermo stable polyimides are familiar for thermal stability, strong chemical resistance, excellent mechanical support and its characteristic in orange/yellow color. Polyimides compounds affinity with graphite or glass fiber reinforcements have more flexural strengths measuring up to 340 MPa (49,000 psi) and flexural moduli of 21,000 MPa (3,000,000 psi). These properties makes them strong matrix of polyimides to exhibit low creep with extended tensile strength. Such properties are very vital when continuously use it to in higher temperatures like 232°C with minimizing excursions, even with the high temperature like 704°C. Molded products of polyimides and their laminates have a very good heat resistance. Normal conditions of such products and laminates range exhibit cryogenic properties in which exceeding temperature at 260°C. Polyimides are naturally resistant against to flame combustion, they do not react it easily and usually exhibit as flame retardants. Generally polyimides are yellow color in nature. The polyimides which are synthesized and purified as aromatic dianhydrides are heavily colored. In the similar process, distilled and sublimed, m-and p-phenylenediamine are colorless crystalline solid materials, which exposed to air or in the liquid state, they produce colored characters, due to its oxidation reaction. Polyimides are radiant or opaque, the specific gravity of polyimides compounds are in the range of 1.1–1.5. Even though when polyimide compounds burn, they exhibit the inherent property of self-extinguishable to develop in to as surface charmaterial which smoothers the flame characters, hence it is preferred in the transportation sector and construction industries.