Synthesis of Polyamides and Polyimides

The azolide method has also been used for the synthesis of polyamides and polyimides. These can be obtained by several routes First by condensation of two dihomofunctional components (dicarboxylic acid diimidazolides and diamines), secondly by condensation of a heterodifunctional compound (amino carboxylic acid and CDI), or through reaction on a polymer (for example, polymeric carboxylic acid imidazolides and amines). 

Imai Y (1996) A new facile and rapid synthesis of polyamides and polyimides by microwave-assisted polycondensation. In Hedrick JL, Labadie JW (eds) Step-growth polymers for high-performance materials. Am Chem Soc Washington, p421... 

A New Facile and Rapid Synthesis of Polyamides and Polyimides by Microwave-Assisted Polycondensation... 

Kawakami Y, Yu SP, Abe T (1992) Synthesis and gas permeability of aromatic polyamide and polyimide having oligodimethylsiloxane in main chain or in side chain. Polym J (Tokyo) 24( 10) 1129... 

There are two main methods for synthesis of polyimides. In one, the dianhydride and diamine are separately dissolved in A,lV-dimethylacetamide or A-methylpyrrollidinone. The solutions are mixed for 24 h to afford poly(amic) acid. The mixture is then refluxed for a further 24 h, using an azeotroping solvent to distill off water. Alternatively, the diamine is mixed with the dianhydride as its ester-acid, and heated at 190 °C in the presence of o-dichlorobenzene as azeotroping solvent. There are reported improvements113. A useful intermediate used in the manufacture of polyamide and imide engineering plastics is 1,3-bis(3-aminophenoxybenzene). 

The author worked for many years at BP Research on the synthesis of LCPs and devised an empirical method called the Mesogenic Index, which employs functional group contributions on an additive score basis to predict whether a particular random copolymer is likely to exhibit a mesophase (subject to the polymer being soluble or fusible). This chapter explores the general features and theoretical aspects of the chemical structures of main chain LCPs and describes the Mesogenic Index and how it was successfully applied to polyesters, polyamides and polycarbonates. The final section describes the extension of the MI empirical method to the various types of LC polyimides reported in recent years. 

Within the extensive literature on this subject, there are many examples of the synthesis of thermotropic polyesters, polyesteramides, polycarbonates, polyethers, polyurethanes and polyester-imides. Until recently, the main omissions had been thermotropic polyamides and polyimides however, many examples of polyamides that show lyotropic behaviour have been known for a long time. 

Tetraamino-9,9 -spirobifluorene was taken for the synthesis of polyamide (PA) and polyimide (PI) networks having an intrinsic microporosity, because the crosslike spatial orientation of spirobifluorene units provides loose packing of polymeric chains in final networks [263]. By reacting the tetraamine with terephthalic acid or pyromellitic acid dianhydride dissolved in A/-methylpyrrolidone or o-cresol, respectively, microporous materials were obtained as depicted in the following scheme ... 

Another important group are the polyamide imides and polyimides. The substitution of tricarboxylic acid anhydride for dicarboxylic acids during synthesis results in thermally more stable polyamide imides. The polycondensation reaction proceeds in two steps, with the solution of the intermediate polycarboxylic acid used in applications where the final product can be generated by a thermal or baking process. Uses include heat-resistant wire and cable coatings. The basic synthesis of polyamide imides is as follows ... 

When resin acid ketone dimers [26] (bisdienes) were submitted to the Diels-Alder reaction with an aromatic bismaleimide [106], high molecular weight thermally stable polyimides were obtained (Fig. 4.20). Similar materials were also prepared using resin acid dimers and aliphatic bismaleimides, as well as bisacrilamides [107]. Acrylonitrile adducts with resin acid dimers were also used as intermediates for the synthesis of polyamides with... 

In the series of papers, synthesis of aliphatic polyamides and polyimides under microwave irradiation was described by Imai et al. [67-71]. The reactions were carried out in a modified domestic microwave oven with a small hole on the top of the oven so that nitrogen was introduced to a 30 ml wide-mouth vial adapted as a reaction vessel. In the case of polyamides synthesis, they were prepared of both CO-amino acids and nylon salt type monomers while polyimides were obtained from the salt form of monomers composed of aliphatic diamines and pyromellitic acid or its diethyl ester in the presence of a small amount of a polar organic medium (Fig. 11). 

As with Volume 1 in the series, this Chapter will deal specifically with polyesters, polycarbonates, polyamides, and polyimides. The four groups form a cohesive unit for a number of reasons the kinetics and techniques of synthesis are frequently similar, indeed the same difunctional reagents appear repeatedly as starting materials for synthesis, and their characteristic functional groups form an integral part of the polymer backbone. 

Step-Growth Polymerization Microwave-assisted step-growth polymerizations -that is, polycondensation and polyaddition reactions - have been studied extensively. According to a review by Wiesbrock et ol. [10], a plethora of reports has been devoted to the microwave-assisted synthesis of polyamides, polyimides, polyethers, and polyesters. For the majority of polymerizations, the reaction rates were significantly increased under microwave irradiation as compared to conventional heating, whilst in many cases the reaction times were shortened from hours, and sometimes days, to about 10 minutes. Moreover, the product purity was improved and the polymers exhibited superior properties, most likely due to a reduction in... 

Imai (1996a) developed a new facile method for the rapid synthesis of aliphatic polyamides and polyimides from polycondensation of ra-antino acids and nylon salts. The polymerization reactions were carried out in domestic nticrowave oven in the presence of a small amount of a polar organic medium. Suitable organic media for the polyamide synthesis are tetramethylenesulfone (TMS) amide-type solvents such as N-cyclohexyl-2-pyrrolidone (CHP), 1, 3-dimethyl-2-imidazoUdone (DMI), phenolic solvents like m-cresol and o-chlorophenol, etc. and for the polyimide synthesis amide-type solvents such as N-methyl-2-pyrrolidone (NMP), CHP and DMI. In polyamide synthesis, the polycondensation was almost complete within 5 min, producing a series of polyamides with inherent viscosities aroimd 0.5 dL/g, and the polyimides having the viscosity values above 0.5 dL/g were obtained within 2 min. 

Photosensitive functions are in many cases also heat sensitive, so the preparation of photosensitive polyimides needs smooth conditions for the condensations and imidization reactions. Some chemical reactants, which can be used for polyamide preparation, have been patented for the synthesis of polyimides and polyimide precursors. For example, chemical imidization takes place at room temperature by using phosphonic derivative of a thiabenzothiazoline.102 A mixture of N -hydroxybenzotriazole and dicyclohexylcarbodiimide allows the room temperature condensation of diacid di(photosensitive) ester with a diamine.103 Dimethyl-2-chloro-imidazolinium chloride (Fig. 5.25) has been patented for the cyclization of a maleamic acid in toluene at 90°C.104 The chemistry of imidazolide has been recently investigated for the synthesis of polyimide precursor.105 As shown in Fig. 5.26, a secondary amine reacts with a dianhydride giving meta- and para-diamide diacid. The carbonyldiimidazole... 

Much attention has been paid to the synthesis of fluorine-containing condensation polymers because of their unique properties (43) and different classes of polymers including polyethers, polyesters, polycarbonates, polyamides, polyurethanes, polyimides, polybenzimidazoles, and epoxy prepolymers containing pendent or backbone-incorporated bis-trifluoromethyl groups have been developed. These polymers exhibit promise as film formers, gas separation membranes, seals, soluble polymers, coatings, adhesives, and in other high temperature applications (103,104). Such polymers show increased solubility, glass-transition temperature, flame resistance, thermal stability, oxidation and environmental stability, decreased color, crystallinity, dielectric constant, and water absorption. 

In short, the microwave energy was successfully applied for the first time for the rapid synthesis of condensation polymers such as polyimides and polyamides from the salt monomers (and co-amino acids) by using a simple domestic microwave oven. The rapid polymer formation is caused by the efficient internal heating of the reactants. This compares favorably with the long reaction time required for the conventional thermal polycondensation with external heating. 

The most important method used in the preparation of polyamides is direct amidation, usually through the intermediate formation of a salt of the diamine and dicarboxylic acid, but without it in the case of aminoacids or for pairs of monomers that do not readily form a salt. Esters can react with diamines to form polyamides with liberation of alcohol or phenol. Diamines can be reacted with diamides yielding polyamides and freeing ammonia. Polyamides have been prepared by acidolysis of acyl derivatives of diamines (compare Section 5.4 for acidolysis in polyester preparation). Bis-anhydrides react with diamines to form polyamides and, if reacted further, polyimides. The low-temperature reaction of acid chlorides with diamines has been used, interfacially or as a solution technique, to prepare certain polyamides (compare Section 5.7 for related reactions in polyester synthesis). 

An empirical method for predicting the chemical compositions of random or partially ordered condensation copolymers which are capable of exhibiting mesophases (either in solution or in the melt) was devised by the author in 1989, while working on liquid crystal copolymer synthesis for BP Chemicals. A brief description of the method and its application to the chemical synthesis of amorphous thermotropic polyamides has been given in a previous paper [45] and a further more detailed description of the method is to be published shortly [46]. Subsequently, the method has been updated and applied to polycarbonates and polyimides. Thermotropic polyimides have also been synthesised by the author resulting from the use of the predictive method [43]. 

Commercial polymers based on the principle of synthesis of polyaromatic compounds include the previously discussed commercial polymers—aromatic polyamides, polyimides, polyfphenylene oxide), polysulfone, and polybenzimidazole (see Chapter 4). 

Metal-2,9,16,23-tetraaminophthalocyanines have been employed in the synthesis of polyimides and as curing agents for epoxy resins [133-135] Variables such as molar concentrations of the reagents, solvents and temperature were investigated to improve the conditions of the polycondensation. Solutions of the polyamide-acid copolymers can be used to fabricate films or fibers. The polyimide copolymers obtained in the second step of the reactions are insoluble. Excellent thermal stabilities up to 500 °C in air and 600 °C under vacuum were reported. 

S.H. Hasio, C.P. Yang, C.Y. Yang, Synthesis and properties of polyimides, polyamides and poly(amide-imide)s from ether diamine having the spirobichroman structure, J. Polym. Sci., Part A Polym. Chem. 35 (8) (1997) 1487-1497. 

PBO membranes prepared by the thermal rearrangement of the hydroxyl-containing polyimides or polyamides at elevated temperature were used for membrane-based gas separation. Lee s group has done considerable work on the thermally rearranged (TR) PBO membrane (TR-PBO) (Figure 5.38) for gas separation [67,80]. They had studied the effect of imidization methods on the properties of TR-PBO membranes. The final properties of the TR-PBO membranes depended on the synthetic methods to prepare polyimide precursors. There are three different routes for the synthesis of the polyimides (1) thermal, (2) chemical, and (3) solution thermal imidization using an azeotrope. They demonstrated the effect of these routes on the final properties of the PBOs. The precursor ort/jo-functional polyimides were synthesized from 4,4 -hexafiuoroisopropyli-dene diphthalic anhydrides and 2,2 -bis(3-amino-4-hydroxyphenyl)hexafiuoropropane. 

In this article, the synthesis, characterization, rheology, solution processing, and mechanical properties of novel molecular composites are discussed. These molecular composite are block copolymers composed of a liquid-crystalline polyamide and two amorphous polyimides. Also, the rheological properties of both isotorpic and anisotropic solutions of PBTA homopolymers and PBTA/PI block copolymers are... 

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