Diacid chloride, organic solvents

As with polyesters, the amidation reaction of acid chlorides may be carried out in solution because of the enhanced reactivity of acid chlorides compared with carboxylic acids. A technique known as interfacial polymerization has been employed for the formation of polyamides and other step-growth polymers, including polyesters, polyurethanes, and polycarbonates. In this method the polymerization is carried out at the interface between two immiscible solutions, one of which contains one of the dissolved reactants, while the second monomer is dissolved in the other. Figure 5.7 shows a polyamide film forming at the interface between an aqueous solution of a diamine layered on a solution of a diacid chloride in an organic solvent. In this form interfacial polymerization is part of the standard repertoire of chemical demonstrations. It is sometimes called the nylon rope trick because of the filament of nylon produced by withdrawing the collapsed film. 

Because almost any diacid can be leaddy converted to the acid chloride, this reaction is quite versatile and several variations have been developed. In the interfacial polymerization method the reaction occurs at the boundary of two phases one contains a solution of the acid chloride in a water-immiscible solvent and the other is a solution of the diamine in water with an inorganic base and a surfactant (48). In the solution method, only one phase is present, which contains a solution of the diamine and diacid chloride. An organic base is added as an acceptor for the hydrogen chloride produced in the reaction (49). Following any of these methods of preparation, the polymer is exposed to water and the acid chloride end is converted to a carboxyhc acid end. However, it is very difficult to remove all traces of chloride from the polymer, even with repeated washings with a strong base. 

Organic solvents are most commonly used, and encapsulating polymers include ethylcellu-lose, NC, polvvinylidene chloride, polystyrene, polycarbonate, polymethylmethacrylate, polyvinyl acetate and others. Inter facial polymerization produces a polymer such as nylon at the interface between layered solns of two precursor materials such as (in the case of a nylon) a diamine and a diacid (Refs 3 11). If the particle or drop-... 

A second classical method for making capsules from emulsions is to form the shell polymer in situ using interfacial polymerization (Morgan and Kwolek 1959 Wittbecker and Morgan 1959). This method is similar to the nylon rope trick often used as a demonstration, where a solution of diacid chloride in organic solvent (such as adipoyl chloride in hexanes) is layered in a beaker with a diamine aqueous phase (such as 1,6-hexadiamine in water Friedli et al. 2005). Because the two monomers meet only at the interface of the two phases, the condensation polymerization to form the polyamide occurs only at the interface. 

This experiment is an example of a step-growth polymerization that takes place at the interface of two immiscible solutions. For this reaction, a diamine dissolved in water reacts with a diacid chloride that is dissolved in an organic solvent. Because neither of the monomers is soluble in the solvent containing the others reaction can occur only at die surface4 or interface between the two solutions. The product is a polyamide, either nylon-6,6 or nylon-6,10, depending upon the number of carbon atoms in the diacid chloride chosen. This activity works well either as a laboratory experiment or as a demonstration. 

You may have carried out the nylon rope trick in a practical class. The diacid chloride of adipic acid is dissolved in a layer of a heavy organic solvent such as CCI4 and a layer of aqueous hexane-1,6-diamine is carefully placed on top. With a pair of tweezers you can pick up the film of polymer that forms at the interface and draw it out to form a fibre. The reaction is a simple amide formation. 

In this experiment a diamine dissolved in water is carefully floated on top of a solution of a diacid chloride dissolved in an organic solvent. Where the two solutions come in contact (the interface), an 8 2 reaction occurs to form a film of a polyamide. The reaction stops there unless the polyamide is removed. In the case of nylon 6.10, the product of this reaction, the film is so strong that it can be picked up with a wire hook and continuously removed in the form of a rope. 

Polymerization conducted in aqueous interfaeial systems suffers from hydrolytic decomposition. The decomposition reaction can be minimized when contact with water is avoided. In the case of polymerization in nonaqueous interfacial environments, products with number average molecular weights up to 5000 can be obtained. Various aromatic polymers were prepared from the reaction of equimolar amounts of the acid dissolved in an aqueous base and the corresponding diacid chloride dissolved in an organic solvent. Reaction occurred between dibasic acid in one phase and an acid chloride in the other. Polar solvents for this reaction include dimethylformamide and 1,4-dicya-nobutane. 

The generation of homo- and copolymers prepared by Friedel-Crafts reactions of 2,7-bis [(2-ferroceneyl)methylene]cycloheptanone with various diacid chlorides has been reported.222 These polyketones were insoluble in most common organic solvents, but were quite soluble in concentrated H2S04. The homopolymers were thermally stable with two decompositions between 220 and 520°C, and the copolyketones showed decomposition at temperatures between 250 and 600°C. In both cases the first weight loss was determined to depend on the nature of the polymers and occurred at a faster rate than the second degradation. 

As we have seen so far, in tow temperature solution methods, the monomers are dissolved and reacted in a single solvent phase. Monomers can also be brought to react in an alternative way, e.g. at the interface of two pha. In the so-called interfacial polycondensation method, the two fast reacting intermediates are dissolved in a pair of immiscible liquids, one of which is preferably water. The water phase generally contains the diamine and usually an inorganic base to neutralise the by-product acid. The other phase contains tte diacid chloride in an organic solvent such as dichloromethane, toluene or hexane (Scheme 11). 

The reaction of diamines with diacid chlorides produces at least two types of polymerization. The first type is an interfacial polymerization in which the diamine is dissolved in water and the diacid chloride is in the organic phase. This reaction can be improved by the addition of an inorganic base to the aqueous solution or by the inclusion of a surfactant the reaction will take place in the interface. The second type is a polymerization in solution in which both diamine and diacid chloride are dissolved in an organic solvent. With this method, a high molecular weight polyamide can be prepared. 

Step-growth polymerizations can also be carried out with certain monomers at low temperature by a technique known as interfacial polymerization or interfacial polycondensation Tht reactions (applicable only to fast reactions) are conducted at the interface between two inuniscible liquids. Usually, one of the liquids is water and the other an organic solvent. An example may be a Schotten-Baumann polyamidation reaction. In such an interfacial polymerization, the diamine would be in the aqueous phase and the diacid chloride in the organic phase. The strong reactivity of acid chloride groups with amines allows the reaction to be carried out at room temperature ... 

The polyketones, possessing intrinsic viscosity 0.76-1.18 dL/g and badly dissolving in organic solvents, can be produced by Friedel-Crafts polycondensation of diarylidenecyclopentanone or diarylidenecyclohexanone, chlorides of aromatic or aliphatic diacids, or azodibenzoylchlorides. The temperature of 10% mass loss is 190-300 °C. The in polyketones have the absorption band at wavelength 240-350 nm in ultraviolet spectra (visible range) [357]. 

Similarly to suspension and emulsion polymerisation, the system used in interfacial polymerisation is heterogeneous, but polymerisation takes place at the interface between both phases. Such a system can be easily illustrated in a practical laboratory course by reaction of a diamine soluble in an aqueous alkaline medium present in the upper part of a beaker, with a diacid chloride soluble in a non-miscible organic solvent such as chloroform present in the... 

The two-phase process occurs between the reaction of diacid chlorides and diamines dissolved in water and water-immiscible solvent media of low polarity, and low-molecular-weight PAs are formed due to rapid precipitation. A base and a surfactant are usually added to the aqueous media. The reaction is extremely fast and occurs in the interphase on the organic solvent side. The mixture of immiscible solutions, on rapid stirring, gives rise to a polymer precipitate. Wholly or partially water-miscible solvents have been found suitable for the synthesis of aromatic PAs. The main drawback of this method is that the precipitation of the growing polymer chains usually forms polymers with broad molecular weight distribution, and they are considered to be unsuitable for fibers or filmforming materials. 

Another route for the preparation of the polyamides is the interfacial polymerization method. In this method the diamine is dissolved in water (which usually also contains a base such as potassium hydroxide for scavenging the HCl formed in the reaction). The diacid chloride is dissolved in an organic solvent such as dichloromethane or tetrachloroethylene. These two solutions are brought in contact with each other. The polymer is formed at the interface of the two immiscible solvent systems. An example of this polymerization is shown in Eq. 2.62. 

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