Polycondensation procedure

The polymerization methods to PPV and PPV derivatives described in the previous section involve 1,6-polymerization of an immediately formed 1,4-xylyl-ene derivative. Aside frome this polymerization approach, a broad spectrum of polycondensation procedures (step-growth methods) to PPV and PPV derivatives has been developed. The methods can be classified as follows ... 

Polycondensation Procedure. This method is essentially the controlled polymerization of tetraethoxysilane (TES). In the first step, TES is partially hydrolyzed in a viscous liquid, which then is emulsified in the mixture of ethanol and water and then undergoes further hydrolytic polycondensation when catalyzed. The formed solid beads of hydrogel are washed and dried into porous siUca. This procedure allows synthesis of highly pure silica particles, which is essential for HPLC. 

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 IV. Important Variables in Interfacial Polycondensation Procedures...

This method, developed by Cadotte and coworkers of Film Tech in the 1970s, is currently most widely used to prepare high-performance reverse osmosis and nanofiltration membranes.A thin selective layer is deposited on top of a porous substrate membrane by interfacial in situ polycondensation. There are a number of modifications of this method primarily based on the choice of the monomers.However, for the sake of simplicity, the polycondensation procedure is described by a pair of diamine and diacid chloride monomers. 

The synthesis of high-molar-mass PLA and PGA by two-step polycondensations of lactic and glycolic acids, respectively, has recently been reported.374,375 It involves the formation of a low-molar-mass oligomer followed by a polycondensation step either in the solid state374 or in the melt under vacuum.375 The procedures are detailed in Section 2.4.1.5.2. 

Maleic anhydride, 98 g (1.0 mol), 148 g (1.0 mol) of phthalic anhydride, and 160 g (2.1 mol) of 1,2-propanediol are poly condensed in a three-necked flask equipped with a mechanical stirrer, a nitrogen inlet, and a distillation head connected to a condenser and a receiver flask. The flask is placed in a salt bath preheated at 160°C. Water begins to distill and the temperature is then raised gradually to 190°C. The polycondensation is stopped (after about 15 h) when the reaction mixture has an acid number of 50 (see Section 2.3.8.4.1) (Scheme 2.54). A slightly different procedure is described in ref. 423. 

This aliphatic hyperbranched polyester is prepared by the bulk polycondensation of 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) as AB2 monomer and 1,1,1-tris(hydroxymethyl)propane (TMP) as B3 core molecule, according to a procedure... 

A variety of synthetic procedures have been described based on the ringopening polymerization processes of (NPCl2)3 to (NPCl2)n followed by the nucleophilic replacement of the reactive chlorines with carefully selected nucleophiles, and on polycondensation reaction processes of new monomers and of substituted phosphoranimines. 

Poly(para-phenylenevinylene)s (PPVs) represent one of the most intensively investigated classes of rr-conjugated materials. Many synthetic procedures to generate unsubstituted and substituted PPVs have been developed. They include 1,6-polymerizations of 1,4-xylylene intermediates as well as several polycondensation methods. Parallel to the polymer syntheses, several series of PPV oligomers (OPVs) have been synthesized and characterized. Such model oligomers of different molecular size allow for a study of the dependence of electronic and optical properties on the length of the conjugated Ti-system. 

Amino acids containing nucleobases like uracil and adenine, as well as imidazole, such as / -(uraciM-yl)-a-alanine, j5-(adenin-9-yl)-a-alanine, and j8-(imidazol-l-yl)-a-alanine, can also be polycondensed by CDI in aqueous imidazole buffer solution at pH 6.8 at 0 °C. The polycondensation leads to low conversion (yields of polymer 1% after four days), but pure polypeptides resulted from the reaction. Thus, compared to other alternative procedures for polycondensation, that using CDI proved to be the most effective 503... 

Interfacial or solution polycondensation, with or without stirring, was the general procedure utilized for the preparation of the polyamides and polyureas.l a Details are given in Table I. An important point to be noted is that, in the unstirred interfacial condensation polymerization of 1 with sebacoyl chloride or tere-phthaloyl chloride in the organic phase and triethylamine as the proton acceptor, immediate film formation took place at the interface. The polyamide films were removed after 1 h, dried, and utilized for taking electron micrographs. 

The second step is the thermal conversion of borylaminoborazine into poly(borylaminoborazine). Continuous elimination of parent alkylamine is the main by-product dining the thermal polycondensation of 2,4,6-trialkylaminoborazine (see earlier). We expected the continuous elimination of the starting 5-alkylam i noborane during the thermal polycondensation of borylborazine. However, the alkylami noborane is a liquid, which requires that the thermal polycondensation must be performed in vacuo to continuously remove the evolving B(NHR)3 from the reaction mixture. This procedure also precludes any competing polycondensation reaction from B(NHR)3. 

Orthosilicic acid, Si(OH)4, could be an appropriate precursor, but it cannot be stored in monomeric form at reasonable concentrations in aqueous solutions. It enters easily into polycondensation reactions (1) that result in its polymerization. As a monomer, the orthosilicic add exists in aqueous solutions at a concentration of less than 100 ppm [18]. This is too small to fabricate sol-gel derived materials, although diatoms and sponges have the property of concentrating silica from seawater containing only a few mg per liter [60]. Sol-gel processing in the laboratory can be performed with a rather concentrated solution of orthosilicic add. This requires freshly prepared add the procedure is time consuming which restrids its widespread use. 

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