Monomers, self-polycondensation reaction

Hyperbranched polyimides can result due to the self-polycondensation reactions of AB2-, A2- and Bs-types. The preparation of hyperbranched polyimides involves chemical imidization of polyamic acid ester synthesized from AB2-monomers, which are carboxylic dianhydrides containing an ether bond and a diamine [6,19,76]. Polyamic acid in combination with a condensation agent is used because it is difficult to separate the synthesized polymer from AB2-type monomers. 

Equation 20.17 puts the kinetic expression entirely in terms of the initial concentration of monomer, Cq, and is in the form useful for following the rates of linear (only bifunctional monomers) self-catalyzed polycondensations. If 1/p is plotted against t one gets a straight line. Under self-catalyzed conditions, the reaction is third order, and the degree of polymerization (DP, or Xn) is approximately proportional to t. This third-order dependency of the rate of self-catalyzed polycondensations also means that the rate of increase in the molecular weight (degree of polymerization) slows down quite rapidly as the reaction proceeds. 

By incorporating unsaturated dicarboxylic acids (e.g. maleic acid), besides phthalic acid, into the polycondensation reaction, unsaturated polyesters are formed. These are then cross-linked with a low-molecular unsaturated monomer, usually styrene, in the presence of a peroxide catalyst and a cobalt compound as accelerator. Unsaturated polyesters are applied as cast resins or glass fibre-reinforced composites. The latter product was the first large-scale plastic material in the self-extinguishing category for the building industry... 

The reaction of excess amounts of methyl acrylate and the self-metathesis products of monounsaturated fatty acids like methyl ester of oleic acid with ethylene, produces valuable monomers for polycondensation polymers, as well as precursors for detergents in the presence of a suitable metathesis catalyst. In oleochemistry, azaleic and pelargonic acid were obtained industrially by ozonolysis of oleic acid. Non-linear fatty acid derivatives with two double bonds, (ricinoleic acid maleate) and one double bond (ricinoleic acid succinate) were produced from ricinoleic acid by esterification with maleic and succinic anhydride, respectively. Hydrogenation of this ricinoleic acid succinate yielded 12-hydroxystearic acid succinate which is a monomer for vegetable oil-based polyester. 

Other examples of self-polycondensation of an AB2-type monomer containing an imide-ring via etherification reactions can be found in the literature [7,10,77]. The selfpolycondensation can be performed though nucleophilic etherification of silylated phenol and aryl fluoride in diphenylsulfone at 240 °C under the presence of caesium fluoride... 

With polycondensation polymerization, two monomers join to produce dimers, trimers, tetramers, and higher ohgomers and finally polymers, plus a by-product which is usually H2O. HCl, NaCl, CH3OH, and other byproducts can be formed instead of water. When a single monomer is used instead of two monomers, the reaction is self-polycondensation polymerization. Stoichiometry is monitored and controlled when two different monomers are polymerized, but stoichiometry is ensured with selfpolycondensation. Most engineering thermoplastics can be produced by polycondensation polymerization ABS, PET, PBT, polyamides (nylons), polycarbonate, PAI, LCP, TPI, PEI, PPS, PPE, PSU, and PAEK. 

This reaction is reported to be much more difficult to perform than it appears. According to Rajan et al. 72) the mechanism is not typical of polycondensations, since appreciable amounts of high polymer are present at low conversions and unreacted monomer is found at high conversions. Numerous other synthetic routes have been described. According to Cleary 71) the only other process which has been unequivocally demonstrated to give the required polymer is the self condensation of alkali metal salts of 4-halothiophenols, as described by Lenz et al. 73). 

The application of Heck coupling polycondensation is not limited to the synthesis of poly(arylene vinylene)s via the alkenylation of haloarenes in simple monomer systems but includes a variety of self- and cross-coupling reactions involving reactants with various functionalities. For instance, the polycondensation of diiodoarene with bis(acrylamido)arene by the Pd(OOCCH3)2—P (o-C6H4—CH3)3 catalyst yields respective aromatic polycinnamamide [106] ... 

The formation of racemic mixtures of homochiral oligopeptides is not confined to racemates undergoing spontaneous segregation into enantiomor-phous domains it can also be extended to racemic 2-D crystallites, provided the reaction pathway takes place preferentially between homochiral molecules related by translation symmetry, as in the case of the thioethylester of N -slearoyl-lysinc (Cis-TE-Lys) [193]. It has been experimentally proven by GIXD that racemic Cis-TE-Lys self-assemble into racemic 2-D crystallites, Fig. 15. Moreover, MALDI-TOF MS analyses of oligopeptide samples obtained from the polycondensation of deuterium enantiolabeled monomers have revealed a clear trend toward enhanced formation of di- to hexa-peptides with homochiral sequences, in agreement with a reaction pathway between homochiral monomer molecules related by translation symmetry [193,195]. 

Hyperbranched polymers can be prepared by a variety of techniques, including the polycondensation of AB monomers as originally described by Flory [113], the reaction of A2 + B3 monomers, and self-condensing vinyl polymerization [139-141]. The first report [142] of using click chemistry in the synthesis of hyperbranched materials appeared at about the same time as the initial report for dendrimers prepared using CuAAC however, but much fewer examples have been reported that describe hyperbranched materials involving click chemistry. Nevertheless, these polymers represent an important class of materials, and both CuAAC [142-147] and thiol-ene [148] chemistry have found their way into the hyperbranched hterature. 

A special form of condensation polymerization occurs when the monomer can react with itself Conceptually, the monomer has the form AMB. The initial stoichiometry is perfect so there is no inherent limitation on molecular weight. Typically, however, there is an equilibrium limitation caused by the condensation by-product. Self-condensing polymerizations can be regarded as a special case of binary polycondensations, as discussed above, that start with the dimer, AMNB. This view is a bit misleading with respect to the actual chemistry. The final reaction step in the manufacture of polyethylene terephthalate is... 

The use of metathesis reactions as a versatile tool in fatty acid-based monomer synthesis was studied in detail by Meier s group (Rybak et al, 2008 Meier, 2009) (Figure 11.11). A comparative study of dimerization of methyl 10-undecenoate via self-metathesis (Djigoud and Meier, 2009) and subsequent polycondensation with different diamines was reported by Mutlu and Meier in 2009. 

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