Salt monomer method

Nevertheless, further detailed information was unavailable on the polyimide synthesis from nylon-salt-type monomers that is referred to as salt monomer method , and this method was not really recognized as a simple synthetic method of both aromatic and aliphatic polyimides. In addition, many polyimide investigations have mainly been concentrated on aromatic polyimides, and little information is available about aliphatic polyimides [13-18] that are also potential candidates for engineering plastics. 

Quite recently we have found that the salt monomers were extremely reactive, producing directly polyimides in a very short reaction time (Eq. 5) [19]. In this connection, we have also found that the salt monomer method coupled with... 

Thus, we have recovered the lost salt monomer method for a facile and versatile synthetic method for polyimides. This chapter reviews our recent findings on the rapid synthesis of a series of polyimides by the salt monomer method. This also includes the properties of newly synthesized aliphatic polyimides, and the application of the salt monomer method as well. 

In a brief summary, we have developed a facile and versatile asalt monomer method for the rapid synthesis of both aliphatic and aromatic polyimides. The salt monomer method has the following advantages over the conventional two-step method. First, the aliphatic-aromatic salt monomers as well as all aromatic, composed of diamines (both aliphatic and aromatic) and aromatic tetracarbox-ylic acids (or their half diesters) are highly reactive and rapidly produce polyimides with high molecular weights in one step by the solid-state thermal poly-... 

Quite recently, we have investigated systematically the high-pressure polycondensation leading to the formation of a variety of polyimides, and polyben-zoxazoles as well [19,33]. Here we applied the salt monomer method to the high-pressure synthesis of aliphatic polyimides. 

Here we have combined the salt monomer method with microwave-induced polycondensation for the synthesis of aliphatic polyimides P-XPM from salt monomers XPMA and XPME (see Eq. 5, X=6-12, Ar=PM, and R=H and ethyl) [28]. When DMI or CHP was used as the solvent, the polycondensation of both salt monomers proceeded quite rapidly, and only 2 min of microwave irradiation readily afforded the aliphatic polyimides with inherent viscosities around 0.7 dL/g or above. Under these microwave irradiation conditions, salt monomers XPME were found to be more reactive than salts XPMA, judging from the attained inherent viscosity values. 

The salt monomer method was successfully applied to the preparation of the electrically-conducting polyimide-carbon black composites [62]. The composites are prepared as follows An aqueous solution of salt monomer 9PMA was mixed with carbon black, giving a suspension. This was evaporated to dryness under reduced pressure to afford a homogeneously-mixed powder composed of the salt monomer and carbon black. The powder was subjected to solid-state thermal polycondensation in the form of a pellet at 240 °C for 1 h under atmospheric pressure. The semiconducting aliphatic polyimides (P-9PM, Tm=315 °C) having electric conductivity of about 10"6 S/cm was readily obtained by mixing only 1 wt% of carbon black based on the polyimide. 

Contrary to the high-pressure polycondensation, when the polycondensation of the salt monomers was conducted in a molten state under atmospheric or reduced pressure for the preparation of the polyimides having Tm below 300°C, this often led to the formation of crosslinked aliphatic polyimides that were insoluble even in concentrated sulfuric acid. Therefore, the high-pressure polycondensation process provides a simple and effective method for the synthesis of the linear polyimides with well-defined structures that caused high crystallinity, compared with the other synthetic methods. 

The high-pressure polyimide synthesis from salt monomers was extended to the development of a new approach for hybrid materials composed of aliphatic polyimides and silica, wherein this method was combined with the sol-gel process [63,64]. The preparation process is outlined in Scheme 2, where aliphatic polyimide P-9PM was used as the polyimide component. 

Scheme 8 shows the synthetic routes of the oxadiazole unit containing phospho-nium salt monomers and Scheme 9 outlines the preparation of Jt-conjugated polymers composed of oxadiazole units [67]. The synthetic pathways to the para-linked salt monomer (A) and meta-linked salt monomer (B) are of multisteps, but the synthetic method for each step is not difficult and the product yields of intermediate compounds are very high (75-95%). Treatment of bis(4-methylphenyl)hydrazine with POCl3 results in the formation of the 2,5-bis(4-methylphenyl)-1,3,4-oxadiazole. 

Poly(p-phenylene vinylene) (PPV) is a conjugated polymer, which becomes conductive by the addition of electron donors or acceptors [114, 115], Several methods have been reported for the synthesis of PPV [3, 4, 6], Direct chemical polymerization, which was used in the first attempt of synthesizing PPV, gave a product in the form of an insoluble powder that limited the use of the polymer in many applications [116], The most popular method for the preparation of PPV is base-induced polymerization of sul-fonium salt monomer in aqueous solution [114-118], In this method, PPV films are obtained from the precursor polymer after thermal elimination of the sulfonium groups. PPV has also been prepared electrochemically by reducing p-xylene-bis-(triphenylphosphonium). Two approaches are generally used for the synthesis of PPVs the Wessling... 

Precursor polymers, (I) and (II) of PPV and (in) of PDPV were synthesized by the method of Karasz - et al. This involves the polymerization of a bis-sulphonium salt monomer to a water-soluble sulphonium salt polyelectrolyte precursor polymer which can subsequently easily be converted to PPV or PDPV by thermal elimination. In their work, metal-like conductivities were observed when these polymers were doped with AsFs. Compared to PPV, PDPV has improved stability and can be doped under milder conditions. 

These salt monomers have been prepared as white crystalline solids by dissolving an equimolar amount of each individual diamine and tetracarboxylic acid half diester in hot ethanol (or methanol), and subsequently cooling the resultant solution. The author has been found that imidization (polycondensation) of salt run to polylmide for 10 min at 250 °C. The high-pressure polycondensation of the salt monomer has been applied. The pressure affect on the temperature and reaction time that directly afforded high molecular-weight polyimide. This method is useful for the s)mthesis of the polyimides having well defined structures, compared with the other S3mthetic methods [4]. 

A new facile method for the rapid synthesis of aliphatic polyamides and polyimides was developed by using a domestic microwave oven to facilitate the polycondensation of both w-amino acids and nylon salts as well as of the salt monomers composed of aliphatic diamines and pyromellitic acid or its diethyl ester in the presence of a small amount of a polar organic medium. Suitable organic media for the polyamide synthesis were tetramethylene sulfone, amide-type solvents such as A -cyclohexyl-2-pyrrolidone (CHP) and 13-dimethyl-2-imidazolidone (DMI), and phenolic solvents like m-cresol and c)-chlorophenol, and for the polyimide synthesis amide-type solvents such as A-methyl-2-pyrrolidone, CHP, and DMI. In the case of the polyamide synthesis, the polycondensation was almost complete within 5 min, producing a series of polyamides with inherent viscosities around 0.5 dL/g, whereas the polyimides having the viscosity values above 0.5 dL/g were obtained quite rapidly by the microwave-assisted polycondensation for only 2 min. 

Emulsion Polymerization. In this method, polymerization is initiated by a water-soluble catalyst, eg, a persulfate or a redox system, within the micelles formed by an emulsifying agent (11). The choice of the emulsifier is important because acrylates are readily hydrolyzed under basic conditions (11). As a consequence, the commonly used salts of fatty acids (soaps) are preferably substituted by salts of long-chain sulfonic acids, since they operate well under neutral and acid conditions (12). After polymerization is complete the excess monomer is steam-stripped, and the polymer is coagulated with a salt solution the cmmbs are washed, dried, and finally baled. 

Radical copolymerization is used in the manufacturing of random copolymers of acrylamide with vinyl monomers. Anionic copolymers are obtained by copolymerization of acrylamide with acrylic, methacrylic, maleic, fu-maric, styrenesulfonic, 2-acrylamide-2-methylpro-panesulfonic acids and its salts, etc., as well as by hydrolysis and sulfomethylation of polyacrylamide Cationic copolymers are obtained by copolymerization of acrylamide with jV-dialkylaminoalkyl acrylates and methacrylates, l,2-dimethyl-5-vinylpyridinum sulfate, etc. or by postreactions of polyacrylamide (the Mannich reaction and Hofmann degradation). Nonionic copolymers are obtained by copolymerization of acrylamide with acrylates, methacrylates, styrene derivatives, acrylonitrile, etc. Copolymerization methods are the same as the polymerization of acrylamide. 

Trimerization to isocyanurates (Scheme 4.14) is commonly used as a method for modifying the physical properties of both raw materials and polymeric products. For example, trimerization of aliphatic isocyanates is used to increase monomer functionality and reduce volatility (Section 4.2.2). This is especially important in raw materials for coatings applications where higher functionality is needed for crosslinking and decreased volatility is essential to reduce VOCs. Another application is rigid isocyanurate foams for insulation and structural support (Section 4.1.1) where trimerization is utilized to increase thermal stability and reduce combustibility and smoke formation. Effective trimer catalysts include potassium salts of carboxylic acids and quaternary ammonium salts for aliphatic isocyanates and Mannich bases for aromatic isocyanates. 

Ionic polymers are a special class of polymeric materials having a hydrocarbon backbone containing pendant acid groups. These are then neutralized partially or fully to form salts. lonomeric TPEs are a class of ionic polymers in which properties of vulcanized rubber are combined with the ease of processing of thermoplastics. These polymers contain up to 10 mol% of ionic group. These ionomeric TPEs are typically prepared by copolymerization of a functionalized monomer with an olefinic unsamrated monomer or direct functionalization of a preformed polymer [68-71]. The methods of preparation of various ionomeric TPEs are discussed below. 

T. M. Sopko and R. E. Lorentz. Method of using polymers of amido-sulfonic acid containing monomers and salts as drilling additive. Patent US 5039433, 1991. 

My last kinetic work was aimed at determining the kp+ of a range of monomers by what I believed to be a reliable method. For kinetic and electrochemical reasons I chose nitrobenzene as the solvent, and I chose carbenium and carboxonium salts as initiators so as to achieve a clean and fast initiation. The rate-constants were adequately reproducible, but it turned out that they were not the kp+. The project was flawed because I had been unaware of the reversible cationation of the solvent by the carbenium ions. A careful analysis of the kinetic, analytical and thermochemical results gave a new insight into the reaction mechanisms in nitrobenzene, but the main objective had eluded me. 

The initiation of the cationic polymerisation of alkenes is examined in detail by means of simple thermodynamic concepts. From a consideration of the kinetic requirements it is shown that the ideal initiator will yield a stable, singly charged anion and a cation with a high reactivity towards the monomer by simple, well defined reactions. It must also be adequately soluble in the solvent of choice and for the experimental method to be used. The calculations are applied to carbocation salts as initiators and a method of predicting their relative solubilities is described. From established and predicted data for a variety of carbocation salts the position of their ion molecule equilibria and their reactivity towards alkenes are examined by means of Born-Haber cycles. This treatment established the relative stabilities of a number of anions and the reason for dityl, but not trityl salts initiating the polymerisation of isobutene. 

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