Polyamides from interfacial polycondensation

Fully aromatic polyamides are synthesized by interfacial polycondensation of diamines and dicarboxylic acid dichlorides or by solution condensation at low temperature. For the synthesis of poly(p-benzamide)s the low-temperature polycondensation of 4-aminobenzoyl chloride hydrochloride is applicable in a mixture of N-methylpyrrolidone and calcium chloride as solvent. The rate of the reaction and molecular weight are influenced by many factors, like the purity of monomers and solvents, the mode of monomer addition, temperature, stirring velocity, and chain terminators. Also, the type and amount of the neutralization agents which react with the hydrochloric acid from the condensation reaction, play an important role. Suitable are, e.g., calcium hydroxide or calcium oxide. 

In interfacial polycondensation, the two components are separately dissolved in two immiscible solvents. The polycondensation can now take place only at the interface of the two liquids, whereby the practically instantaneously formed thin polyamide film prevents further diffusion of the two reactants. The polycondensation can only continue when this film is pulled carefully away from the interface the process can thus be run continuously in a simple way (Fig. 4.1). 

Preparation of Polyamide-6,10 from Hexamethylenediamine and Sebacoyl Dichloride in Soiution and by Interfacial Polycondensation... 

The preparation of polyamides having metallocenes incorporated into the backbone can be achieved by the use of bifunctional ferrocene derivatives, such as diacid chlorides or diamines. In the following, a few examples of such reactions are presented. In the early 1960s Knobloch and Rauscher reported the preparation of polyamides and polyesters by the reaction of 1,1 ferrocenyldicarbonyl chloride 14 with several diamines and diols by interfacial polycondensation.80 The synthesis of elastomeric polyamides 54a, Mn = 10,000-18,000) in high yields was reported by Rausch and co-workers from 1,1 -bis((3-aminoethyl)ferrocene 53 and diacid chlorides (Scheme 12.11). The reaction with bis-isocyanates allows the formation of ferrocene-containing polyureas 54b. 

J/n < 6,000). Often, no analytical data or structural characterization was provided. Room-temperature interfacial polycondensation methods were also investigated as a convenient alternative to classical polycondensations. Such methods were first reported for the preparation of polyamides and polyesters from the reaction of l,l -ferrocenyldi-carbonyl chloride with several diamines and diols. The synthesis of polyurethanes using this technique was also reported and involved the condensation of l,T-ferrocenedimethanol and l,T-bis(dihydroxyethyl)ferrocene with diisocyanates. Once again, however, these polymers possessed low molecular weights.The early research in these areas has been summarized and critically reviewed and will not be discussed further here. ... 

With the interfacial method, high molecular weight polymers can be obtained, but the molecular weight distribution, unlike that from polymers from solution polycondensation, is rather broad and this method is not suitable for the preparation of polymers for fibres and films [Ic]. The solution method also has other advantages over the interfacial method. For example, it yields a solution of polymer amenable for direct fabrication of certain aromatic polyamides some polyamides are soluble as made in solution by low temperature polycondensation but they often cannot be redissolved in solvents other than H2SO4 once they have been dried. 

Besides the synthesis of bulk polymers, microreactor technology is also used for more specialized polymerization applications such as the formation of polymer membranes or particles [119, 141-146] Bouqey et al. [142] synthesized monodisperse and size-controlled polymer particles from emulsions polymerization under UV irradiation in a microfluidic system. By incorporating a functional comonomer, polymer microparticles bearing reactive groups on their surface were obtained, which could be linked together to form polymer beads necklaces. The ability to confine and position the boundary between immiscible liquids inside microchannels was utilized by Beebe and coworkers [145] and Kitamori and coworkers [146] for the fabrication of semipermeable polyamide membranes in a microfluidic chip via interfacial polycondensation. 

Interfacial and solution polycondensations are commercially important. For example, an unstirred interfacial poly condensation reaction is utilized in the production of polyamide fibers. Another important application of interfacial polycondensation is the enhancement of shrink resistance of wool. The wool is immersed first in a solution containing one of the reactants and subsequently in another solution containing the other reactant. The polymer resulting from the interfacial reaction coats the wool and improves its surface properties. 

Aromatic polyamide fibers, better known as aramid fibers, have been defined as a long chain synthetic polyamide in which at least 85% of the amide linkages are attached directly to two aromatic rings [42] The first significant material of this type was introduced in 1961 by Du Pont as Nomex. It is poly(m-phenyleneisophthalamide), prepared from m-phenylenediamine and isophthaloyl chloride by interfacial polycondensation. 

Improvement of Water Permeability (UTC-70L) In our past experiments of various polyamide composite membranes, introduction of end acids is preferable to obtain better water permeability and decrease of end amines is preferable to obtain better tolerance to chloride. From the view point, we tried to improve water permeability of UTC-70. Our strategy for introduction of end acids and decrease of end amines is an improvement of acid chlorides reactivity by using catalyst for in-situ interfacial polycondensation. Thus, we found common catalysts for acylation worked effectively as we had expected, and water permeability of UTC-70 were increased without severe decrease of membrane selectivity. This type of membrane are commercialized as "UTC-70L", and membrane performance is shown Figure 7. 

Interfacial polycondensation is an interesting procedure that is often used in demonstrations in polymer chemistry courses. Polyamides are prepared rapidly, in fiont of the class, from diacid chlorides and diamines. The products are removed quickly as they form, by pulling them out as a string from the interface." Polyesters can also be prepared from diacid chlorides and bisphenols. On the other hand, preparation of polyesters from glycols and diacid chlorides is usually unsuccessful due to low reactivity of the dialcohols. The diacid chlorides tend to undergo hydrolysis instead. Commercially, this procedure is so far confined mainly to preparations of polycarbonates (discussed further in this chapter). 

With a few exceptions, interfacial polycondensation has remained a laboratory method for the synthesis of polymers, since diacyl chlorides are too expensive for commercial production. The exceptions include the polycondensation of bisphenols with phosgene (see Section 26.5.1) and the synthesis of aromatic polyamides, from m-phenylene diamine, isophthaloyl chloride, and terephthaloyl chloride (Section 28.2.4). The method is also used to give wool a fluff-free finish by producing a polycondensate from sebacoyl chloride and hexamethylene diamine on the wool fiber. 

The synthesis of 1,6-diamino-l,6-dideoxy-2,3,4,5-tetra-0-methyl-D-mannitol and its L-iditol analogue from D-mannitol has been described [100], These diamines, containing a two-fold axis, gave stereoregular AABB polyamides on polycondensation with terephthaloyl dichloride and dipentachlorophenyl esters, or dichlorides of aliphatic dicarboxylic acids, in solution or under interfacial polycondensation conditions [99, 109]. In spite of the regioregularity present in the polymeric chains, these optically active polyamides could not be crystallized. 

An aromatic polyamide is produced by the interfacial polycondensation method from isophthalyl dichloride (in cyclohexanone) and m-phenyl-ene diamine dihydrochloride with trimethyl amine hydrochloride added as catalyst and NaOH to absorb the HCl. The polymer has a very high melting point of over 375°C and is also of poor solubility. It can be spun out of a boiling dimethyl acetamide solution with the addition of 3% CaCl2. Textiles and fibers cannot be dyed and are used in industry, for example, to reinforce elastomers and as filter cloths for hot gases. Papers are manufactured from fibers that have been cut and then sintered together they have a thickness of 2-30 mil (1 mil = 0.0025 cm) and are used for electrical insulation. 

Scheme 24 summarizes the preparation of polyamides (99) and polyureas (101) from the reaction of l,r- is (P-aminoethyl)feiTocene (97) with diisocyanates (98) and diacid chlorides (100). These polymers were prepared via solution or interfacial polycondensation reactions to yield polymers with intrinsic viscosities ranging from 0.1 to LSdr/g. ... 

The interest of such OA polyamides based on derivatives of a-aminoacids has prompted Crescenzi et al. [39] to investigate the preparation and characterization of polymers obtained from the interfacial polycondensation of bifunctional diketopiperazines of ol-1-aminoacids with diacid chlorides and diamines with good yield (68%). The poly(/-lysine diketopiperazine) adipamide has the following structural unit (XVI) ... 

A series of simple OA polyamides is described by Hamoud et al [42]. These polymers were obtained in our laboratory by interfacial polycondensation of (+)-, and diaminopropane with succinyl, adipyl and sebacyl dichloride. With ClCO(CH2) COCl when the number of methylene residues n increased from 4 to 6 and 8, the yield of polymer increased from 2% to 40% and 95%. The anomalous chiroptical properties in the presence of various divalent salts have been investigated by Le Bris et al [43] they are further detailed by Dr Vert in his Chapter. 

Polyamides derived from o-glucose and o-glucosamine by interfacial and solution polycondensations of the sugar diamino derivatives with aromatic and aliphatic acyl chlorides have also been described [83]. 

If one were to choose more reactive monomers, it would be possible to carry out polycondensations at considerably lower temperatures in solution. For example, consider the reaction of a diamine and a diacid to make a polyamide (nylon), a polymerization that requires relatively high temperatures (see Equation 9). A much faster reaction would occur between the diamine and a corresponding diacid chloride (see Equation 10). Both reactions would produce the same polymer, although the reaction conditions would be much different, and the byproduct HC1 from the acid chloride reaction would have to be carefully trapped. One technique for performing a polymerization such as that in Equation 10 is to dissolve the monomers in different, immiscible solvents, forcing the polymerization to occur only at the interface of the two solvents, a process called interfacial polymerization. Because of the high reactivity of an acid chloride, these reactions can be carried out at very low temperatures. This polymerization can be carried out rather dramatically in a beaker and is known as the nylon rope trick (see Section 4). 

Reaction of Acid Chlorides. Low-temperature polycondensation of diamines and diacid chlorides is an important route for preparing high-melting polyamides such as aromatic polyamides, which decompose or cross-link if prepared by high-temperature melt routes. The reaction may involve an interfacial reaction between the diacid chloride in a water-immiscible solvent with an aqueous diamine solution, or the reaction may be carried out in a homogeneous solution. The presence of a base is usually needed to remove HCl so that polymerization is complete. With weakly basic aromatic diamines, an acid acceptor is not always needed because HCl can be evaporated from the reaction mixture. The general reaction is given by... 

Polyamides derived from D-glucose and D-glucosamine by interfacial and solution polycondensations of the sugar diamino derivatives with aromatic and aliphatic acyl chlorides have also been described [107]. The presence of an anomeric benzyl group did not decrease the reactivity of the 2-amino function. Similar chiral polyamides were synthesized from the 1,7-diamino derivative, which was prepared from D-glucal. 

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