Self-polycondensation reactions

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. 

The self-polycondensation of molecules bearing two antagonist functions at their chain ends (denoted as AB) is more interesting since at any stage of the reaction, the polymer molecules always bear one A and one B function at the chain end. If one of these functions can be reacted subsequently with an unsaturated compound, the synthesis of macromonomers becomes possible. 

Self-polycondensation would be expected to compete with the reaction with the core, but it has been found that it is possible to drive the reaction to achieve the high degree of branching required. The resulting polymer has predominantly -OH terminal groups. 

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... 

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... 

A large number of inorganic polycondensation reactions are also known. However, here again, only a few reactions have become really important for example, the poly condensation of dimethyl dichlorosilanes with water (Section 33.3.2) or the self-condensation of phosphoric acid (Section 33.3.3). 

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. 

Then we directly carried out click reaction between 40-fold excess of alkyne-PS and alkyne-(PlBA-N3)2 to result in PS-PfBA-PS triblock while 5-fold excess is not enough to suppress the self-polycondensation of alkyne-(PiBA-N3)2 chains (Fig. 4.16a). However, one problem to deal with is how to remove the excess of alkyne-PS chains from the mixtures of reaction products. Further TFA de-protection of tertiary butyl group into carboxyl group leads to the corresponding HB-(PAA) -g-(PS)n+i and PS-PAA-PS, which would facilitate the removal of excess alkyne-PS chains. In the precipitation-purification step, we repeated dissolution-precipitation cycle three times to remove excess alkyne-PS, where cyclohexane was used as precipitant, which is a good solvent for short PS, but a very poor solvent for HB-(PAA) -g-(PS) +i and PS-PAA-PS copolymers. Finally, purified white-powder of amphiphilic copolymer HB-(PAA)io-g-(PS)n = 6.30 x 10 g/mol), HB-(PAA)47- -(PS)48 (Afw = 2.60 X 10 g/mol) and their linear triblock analogues PS-PAA-PS (Afw = 7.50 X 10 g/mol) were obtained. 

Figure 4.26 shows that the two elution curves respectively from the RI and MALLS detectors are very different, which has been explained before. Figure 4.26b shows the reaction time dependent SEC curves of HB-(S-S-PS) during the self-polycondensation. As the reaction proceeds, the macromonomer peak becomes smaller while the hyperbranched polymer peaks emerged after a few hours. Gradually, DP increases to 28 and its polydis-persity index (M /Mn) changes from 1.14 to 4.90 (Fig. 4.27) when most of the... 

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