Chemistry and properties of addition polyimides

Abstract

Recent years have seen a rapid development in the area of temperatureresistant thermosets. Polyimides in particular are gaining wide acceptance by the industry because they combine a number of unique features. These include excellent physical property retention at elevated temperatures and in wet environments, almost constant electrical properties over a wide range of temperatures and non-flammability properti<!s. Their commercial success is based on the fact that the raw materials, such as aromatic diamines and tetracarboxylic acid dianhydrides, are relatively cheap and the chemical synthesis is, in most instances, straightforward. In addition, chemists and users are supported by a constantly growing data base on structure-property and structure-processing relationships.Polyimides still carry the image of being difficult to process. Considerable effort continues to be devoted to improving the process ability without sacrificing thermal stability. The major application for thermosetting polyimides is as matrices in advanced composites. Consequently, processing via hot melt prepregging, wet-and towpreg filament winding and resin transfer moulding is mandatory. These different processing techniques, however, require specific rheological properties and cure kinetics. These can be tailored into the thermosetting polyimide resin by controlling the molecular weight and the chemistry of the backbone structure between the reactive crosslinking terminations.Before discussing structure-property-processing interrelations in thermosetting poJyimides more specifically a definition of this resin family is appropriate.Thermosetting polyimides are best defined as low molecular weight, at least difunctional monomers or prepolymers, or mixtures thereof, which carry imide moieties in their backbone structure (Figure 4.1). Such materials are terminated by reactive groups which undergo homo-and/or copolymerisation by thermal or catalytic means.The classical thermosetting resins, such as epoxies or unsaturated polyesters, crosslink via polymerisation (styrene solutions of unsaturated

Mechanical, Dielectric, and Thermal Attributes of Polyimides Stemmed Out of 4, 4’–Diaminodiphenyl Ether

“…Crystals 2020, 10, x FOR PEER REVIEW 2 of 9 of different diamine and dianhydride have been reported [15][16][17][18]. However, for the structurally different PIs, their properties are different, as well.…”

“…The typical Kapton PI was obtained from pyromellitic dianhydride (PMDA), along with 4,4'-diaminodiphenyl ether (ODA). Moreover, ever since the commercialization of the Kapton type PI began the usage in the early 1960s, a series of PIs composed of different diamine and dianhydride have been reported [15][16][17][18]. However, for the structurally different PIs, their properties are different, as well.…”

Methylnadimide End-Capped Polyimides for Use in High Temperature Composites—A New Approach to Their Synthesis

“…When these polyimides are cured under pressure it is believed that most of the evolved methylcyclopentadiene re-reacts to build up a complex cure structure [15,16]. Further reaction involving the end-cap is evidenced by the occurrence of a broad exotherm corresponding, in the DDS model, to 57 kJ mol −1 of the end-cap.…”

Modern advances in bismaleimide resin technology: A 21st century perspective on the chemistry of addition polyimides

“…The outpouring of work during the 1980s encompassed an extremely dynamic period of synthetic chemistry and culminated in a series of excellent reviews by Stenzenberger [14,33], who concisely summarised the early progress in the area. These reviews outlined a number of fundamental aspects on which future chemists and technologists would need to focus if BMIs were to develop and become a commercially acceptable standard.…”

“…For example, in 1990, Stenzenberger listed some thirty or more experimental monomer systems with representative physical properties [14] Representative examples of the most commonly researched monomers are given in Table 3 with selected properties of interest. The simplest strategy, which was pursued in many studies during the 1980s [15][16][17], involved increasing the distance between the maleimide rings (often in the form of 1,4-disubstituted aromatic rings bridged with ether, sulphonyl or isopropylidene moieties) in order to decrease the crosslink density with the aim of increasing rotational freedom.…”