Solution polycondensation

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. 

Synthesis of polyanhydrides is carried out through generalized methods such as melt polycondensation, solution polymerization, use of coupling agents, and ring-opening polymerization. 

Thermally labile products are achieved through solution polycondensation. In a proper solution polycondensation, solutions of 20% are used. Water can be removed from the reaction mixture, for example, by azeotropic distillation, if a carrier such as benzene or CCU is used. In another method, water is removed by continuous thin-layer evaporation. The solution of the initial components is added at the top of a packed column and the evolved water is removed by a CO2 countercurrent. This method produces very light-colored products, since it is not possible for local overheating to occur. 

Synthetic Fiber and Plastics Industries. In the synthetic fibers and plastics industries, the substrate itself serves as the solvent, and the whitener is not appHed from solutions as in textiles. Table 6 Hsts the types of FWAs used in the synthetic fibers and plastic industries. In the case of synthetic fibers, such as polyamide and polyester produced by the melt-spinning process, FWAs can be added at the start or during the course of polymerization or polycondensation. However, FWAs can also be powdered onto the polymer chips prior to spinning. The above types of appHcation place severe thermal and chemical demands on FWAs. They must not interfere with the polymerization reaction and must remain stable under spinning conditions. 

Lower alkanes such as methane and ethane have been polycondensed ia superacid solutions at 50°C, yielding higher Hquid alkanes (73). The proposed mechanism for the oligocondensation of methane requires the involvement of protonated alkanes (pentacoordinated carbonium ions) and oxidative removal of hydrogen by the superacid system. 

Aromatic PODs containing amide and imide groups have been synthesized by the solution polycondensation method (52). 

Phosgene addition is continued until all the phenoHc groups are converted to carbonate functionahties. Some hydrolysis of phosgene to sodium carbonate occurs incidentally. When the reaction is complete, the methylene chloride solution of polymer is washed first with acid to remove residual base and amine, then with water. To complete the process, the aqueous sodium chloride stream can be reclaimed in a chlor-alkah plant, ultimately regenerating phosgene. Many variations of this polycarbonate process have been patented, including use of many different types of catalysts, continuous or semicontinuous processes, methods which rely on formation of bischloroformate oligomers followed by polycondensation, etc. 

The hydrolysis and polycondensation reactions initiate at numerous sites within the TMOS/H2O solution as mixing occurs. When sufficient intercoimected Si—O—Si bonds are formed in a region, the material responds cooperatively as colloidal (submicrometer) particles or a sol. The size of the sol particles and the cross-linking within the particles, ie, the density, depends on the pH and R ratio, where R = [H2 0]/[Si(0R)4]. 

Polytitanosiloxane (PTS) polymers containing Si—O—Ti linkages have also been synthesized through hydrolysis—polycondensation or hydrolysis—polycondensation—pyrolysis reactions involving clear precursor sol solutions consisting of monomeric silanes, TYZOR TET, methanol, water, and hydrochloric acid (Fig. 2). These PTS polymers could be used to form excellent corrosion protection coatings on aluminum substrates (171). 

Titanium-containing polyethers have been prepared by the reaction of dicyclopentadienyltitanium dichloride with aromatic and ahphatic diols via an interfacial and/or aqueous solution polycondensation technique (273). 

Polyphosphonates are well-known flame-retardant materials [110] and are generally prepared by melt [111,112], interfacial [113-115] and solution polycondensation methods [116]. A typical example of synthesis is the polycondensation of bifunctional organophosphorus compounds, such as dichlorophenylphosphine oxide, with bisphenols [117,118]. 

Polyphosphates are also an important class of organophosphorus polymers. In addition to their flame-retardant characteristics, they possess attractive plasticizing properties and can be used as polymeric additives to other polymers [123-128]. In general, polyphosphates can be prepared by interfacial [119,129], melt [130], or solution polycondensation [131,132a,b]. Kricheldorf and Koziel [133] prepared polyphosphates from silylated bisphenols. 

The first polyimine was reported by Adams and coworkers [182] from terephthalaldehyde and benzidine and dianisidine. Between 1950 and 1959 Marval and coworkers [174-176] reported a number of polyimines. Suematsu and coworkers [170] reported the first successful synthesis of high molecular weight fully aromatic polyimines by solution polycondensation method using w-cresol as reaction medium. 

A general step ahead in polycondensation was achieved by the application of the active ester method by DeTar et al.19) and Kovacs et al.291 Very soon, the nitrophenyl ester, the pentachlorophenyl ester, or the hydroxysucdnimido ester were used exclusively. The esters of the protected tripeptides could be purified by crystallization, then the N-protecting group was split off and the free peptide esters were purified again. Addition of base starts the polycondensation, resulting quickly in the formation of a viscous solution at low temperature. 

Activating agents, such as trifluoroacetic anhydride 1,1 -carbonyldiimidazolc carbodiimides sulfonyl, tosyl, and picryl chlorides and a range of phosphorus derivatives can promote direct solution reactions between dicarboxylic acids and diols or diphenols in mild conditions. The activating agents are consumed during the reaction and, therefore, do not act as catalysts. These so-called direct polycondensation or activation polycondensation reactions proceed via the in situ transformation of one of the reactants, generally the carboxylic acid, into a more... 

Polyesters have been obtained in organic medium by polyesterification of hydroxy acids,328,329 hydroxy esters,330 stoichiometric mixtures of diols and diacids,331-333 diols and diesters,334-339 and diols and cyclic anhydrides.340 Lipases have also been reported to catalyze ester-ester interchanges in solution or in die bulk at moderate temperature.341 Since lipases obviously catalyze the reverse reaction (i.e., hydrolysis or alcoholysis of polyester), lipase-catalyzed polyesterifications can be regarded as equilibrium polycondensations taking place in mild conditions (Scheme 2.35). 

The main polymerization method is by hydrolytic polymerization or a combination of ring opening as in (3.11) and hydrolytic polymerization as in (3.12).5,7 9 11 28 The reaction of a carboxylic group with an amino group can be noncatalyzed and acid catalyzed. This is illustrated in the reaction scheme shown in Fig. 3.13. The kinetics of the hydrolytic polyamidation-type reaction has die form shown in (3.13). In aqueous solutions, die polycondensation can be described by second-order kinetics.29 Equation (3.13) can also be expressed as (3.14) in which B is die temperature-independent equilibrium constant and AHa the endialpy change of die reaction5 6 812 28 29 ... 

Solution Table 13.1 shows results calculated using Equation (13.4). The stoichiometric requirement for a binary polycondensation is very demanding. High-molecular-weight pol5Tner, say li > 100, requires a weighing accuracy that is difficult to achieve in a flow system. 

Wang and coworkers first reported the use of these monomers as a novel elastomeric material for potential application in soft tissue engineering in 2002. The molar ratio of glycerol to sebacic acid they used was 1 1. The equimolar amounts of the two monomers were synthesized by polycondensation at 120°C for three days. The reaction scheme is shown in Scheme 8.1. To obtain the elastomers, they first synthesized a prepolymer and then poured an anhydrous 1,3-dioxolane solution of the prepolymer into a mold for curing and shaping under a high vacuum. 

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