Low-temperature polycondensation

Recently we have also extended these low temperature polycondensation synthetic techniques to the preparation of borazine containing polyureas as precursors for BN/G C ceramics.- ... 

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. 

Even higher viscosities are typical for polyimides based on tetranuclear diamines, e.g., 4,4 -di-(p-aminophenoxy)-benzophenone and l,l-dichloro-2,2 di(/ -aminophenoxy)-ethylene. Polyimides were prepared according to the method for the synthesis of PCA by low-temperature polycondensation in NMP. Polyimides were prepared by catalytic cyclodehydration of PCA directly in the reaction solutions using the catalytic system pyridine-acetic acid anhydride (1 1) [22] (Scheme 3.5). 

Syntheses. Interfacial Polycondensation. Morgan has discussed low temperature polycondensations involving room temperature reactions of fast-reacting intermediates under interfacial conditions (II). In his many papers (9) concerning this method of polymer preparation, in the published work of Conix (I, 2, 3), and in our own patent (6), the application of interfacial polycondensation to polyphthalate and to polysulfonate preparation is well described. Hence, we dwell only briefly on the interfacial method to make available our observations particularly with regard to scaleup problems. 

Preparation of Bis(pyrrolidinyl)silanes. The low-temperature polycondensation reaction of l,4-bis(hydroxydimethylsilyl)benzene (II) with eight different bis(ureido)silanes (Va-Vh) in chlorobenzene was carried out to prepare the high-molecular-weight polymers la-Ih. The bis(pyr-rolidinyl)silanes, IVa-IVh, were prepared by modification of published procedures (JO) by the reaction of dichlorosilanes with pyrrolidine in hexane solution, as shown in equation 2. 

The change from one chemical class to another, as in Table I, will produce changes in polymer properties such as solubility and melting point. The same type of change within a polymer class can be produced by varying the structures connecting the functional groups. Low-temperature polycondensation procedures are especially applicable to the formation of polymers with wide property differences, as indicated in Table II. 

Table II. Variation in Physical Properties and Order in Polymers from Low-Temperature Polycondensation Processes...

Low-temperature polycondensation processes provide polymer chemists with a broadly applicable and fast laboratory tool, with which rapid surveys of a large number of polymer structures are possible. Semiworks-scale preparations are easy and even plant-scale operations are feasible. Already one such operation has been started. On a large scale, solvent recovery and waste disposal present some economic problems. 

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... 

The high temperature melt polycondensation method involving a diamine and a diacid has been successfully used in the synthesis of aliphatic polyamides, especially in the fabrication of nylon [le, f]. Neverthele this method is not applicaUe to the preparation of wholly aromatic polyamides because the potential polyamides either do not melt or melt at high temperature with decomposition. Many aromatic diacids will decarboxylate and the aromatic diamines are readily oxidized and have a tendency to sublime [Id]. Scientists from the Du Pont company then developed low temperature polycondensation methods either in solution or at the interface of two solvents. Solution polycondensation involves a diamine and a diacid chloride reacting in an amide solvent such as N-methylpyrrolidone (NMP), hexamethylphosphoramide (HMPA), or dimethylacetamide (DMAc) (Scheme 1) [3]. 

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. 

MOL Molodtsova, E.D., Pavlova, S.A., Timofeeva, G.I., Vygodskii, Ya.S., Vinogradova, S.V., and Korshak, V.V., Molecular weight characteristics of cardo poly(amido esters) produced by the low temperature polycondensation (Russ.), Vysokomol. Soedin., Ser. A, 16, 2183, 1974. 

Various organic solvents were used as reactionary medium at nonequilibrium polycondensation in solution realization [96]. The solvent type influence on the synthesis reaction main characteristics (conversion degree Q and molecular weight MM) is well known and is explained usually by solvent various characteristics (dielectric constant, solubility parameter, heat of dissolution and so on) [96]. However, up to now the indicated effects general theoretical explanation is not obtained. Besides, at the solvent type influence analysis its correlation with polycondensation process quantitative characteristics (the same Q and MM) is usually considered, but any changes of polymer structure or reaction mechanism are not assumed, although the possibility of side reactions is noted repeatedly [96]. The authors [71, 127] studied the solvent influence on the enumerated above characteristics on die example of the rules of chloranhydride of terephthalic acid and phenolfthaleine low-temperature polycondensation (polyarylate F-2), performed in 8 different solvents [128]. 

Kozlov, G. V. Temitaev, K. B. Ovchatenko, E. N. Lipatov, Yu.S. The description of low-temperature polycondensation process within the framework of irreversible aggregation models. Reports of National Academy of Sciences of Ukraine, 1999, 12, 136-140. 

Kozlov, G. V. Temiraev, K. B. Kaloev, N. I. Influence of solvent nature on structure and formation mechanism of polyarylate in conditions of low-temperature polycondensation. Reports of Academy of Sciences, 1998,362(4), 489-492. 

Kozlov, G. V. Burya, A. 1. Shustov, G. B. The influence of solvent nature on low-temperature polycondensation the fractal analysis. Bulletin of Academy of Sciences of Kazakhstan, Engineering Sciences, 2007, (5-6), 23-32. 

Korshak, V. V. Vinogradova, S. V Vasnev, V. A. The smdy of solvent nature influence on low-temperature polycondensation. High-Molecular Compounds. A, 1968, 10(6), 1329-1335. 

J. Ding, Y. Qi, M. Day, J. Jiang, and C. L. Callender. A low temperature polycondensation for the preparation of highly fluorinated poly(aryl-ene ether sulfone)s containing crosslinkable pentafluorostyrene moieties. Macromol. Chem. Phys., 206 2396-2407, 2005. 

The Eq. (22) gives one more possible mode of value estimation. The estimations according to the Eqs. (4) and (22) showed, that different solvents used in low-temperature polycondensation process resulted to various D, values (Table 1). 

For fractal description of low-temperature polycondensation process the authors [33] made use of the relationship, connecting accessible for reaction active sites number, which is supposed proportional to Q, and Devalue [40] ... 

The typical for poly condensation this type value t = 60 min was chosen for all solvents, the value c is also the same for all solvents and therefore is included in the Eq. (26) constant coefficient and the parameter estimation method should be specially described. In paper [34] the values Q and for low-temperature polycondensation realization two conditions are adduced—with stirring (200 rpm) and without reactive mass Stirling. In the first case it is supposed, that stirring levels distinctions in rig value and then the simplest relationship was used for Q estimation [33] ... 

Hence, the stated above results demonstrated the possibility of quantitative description of solvent nature on polyarylate Ph-2 formation process by low-temperature polycondensation. The proposed within the frameworks of modem... 

The authors [118, 119] fulfilled description of the low-temperature polycondensation process of polyaiylate Ph-2 in 8 different solvents (N,N-di-meth-ylformamide, nitrobenzene, acetone, 1,2-dichloroethane, chloroform, 1,2,4-tri-chlorobenzene, benzene and 1,4-dioxane) within the framewoiks of irreversible aggregation cluster-cluster model [120]. 

In the end the conclusion can be made, that reaction cessation in low-temperature polycondensation process is limited by pnrely physical factor, namely, by macromolecular coil density reaching of reactive medium density (mixture monomer — polymer solution) [121], that is possible for fractal objects only. Such conclusion follows from the simple analysis, adduced below. As it is known [122], the fractal object density pfr can be calculated according to the Eq. (73) ... 

Kozlov, G. V Burya, A. I. Temiraev, K. B. Mikitaev, A. K. Chigvintseva, O. P. The description of low-temperature polycondensation kinetics within the frameworks of irreversible aggregation models and fractal analysis. Problems of Chemistry and Chemical Technology, 1998, (3), 26-29. 

Shogenov, V. N. Temiraev, K. B. Kozlov, G. V. The reagents relation influence on low-temperature polycondensation process. In collection Physics and Chemistry of Perspective Materials. Nal chik, KBSU, 1997, 80-84. 

The simple polyesterketone containing lateral side cyano-groups, possessing the glass transition temperature in range 161-179 °C, has been produced [379] by low-temperature polycondensation of mix 2,6-phenoxy-benzonitrile and 4,4 -bisphenoxybenzophenone with terephthaloylchloride in 1,2-dichloroethane. 

Terpolymers on the basis of 4,4 -bisphenoxybisphenylsulfone, 4,4 -bi-sphenoxybenzophenone and terephthaloylchloride were produced in Ref [383] by low-temperature polycondensation. The reaction was lead in... 

The statistical copol5miers of polyarylesterketones, involving naphdia-lene cycle in the main ehain, ean be produeed [388] by low-temperature polycondensation of bisphenyloxide, 4,4 - -bis(P-naphtoxy)benzophe-none with chloranhydrides of aromatic bicarbonic acids - terephthaloyl-chloride and isophthaloylchloride (I) in the presence of catalytical system AlCl3/N-methylpirrolydone/ClCH2CH2Cl (copolymers are characterized by improved thermo- and chemical stabiUty), and also by the reaction of hydroquinone with l,4-bis(4,4 -flourobenzoyl)naphthalene (II) in the presence of sodium and potassium carbonates in bisphenylsulfone [389],... 

Zhang Shanjy, Zheng Yubin, Ke Yangchuan, Wu Zhongwen. (1996). Synthesis of Aromatic Polyesterketones by Means of Low-Temperature Polycondensation Acta Sci. Nature. Univ. Jibimensis, I, 85-88. 

An interesting example of block copolymers is work by de Ruijter et al. [348], who prepared a series of block copolymers that contain rigid liquid crystal forming blocks of poly(p-phenylene terephthalamide) and flexible blocks of hexamethylene adipamide. The polymers have been prepared in a one-pot procedure by a low-temperature polycondensation reaction in A-methyl-2-pyrrolidone. 

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