Post condensation processes

Miyamoto, M., N. Onuma, and H. Takeda (1979). Wollastonite whiskers in the Allende meteorite and their bearing on a possible post condensation process. Geochem. J. 13 1-5. 

Again, the C-MeT PCR primers were used to obtain a gene probe from gDNA, which was then used to isolated a fused iterative Type I PKS / NRPS from B. bassiana which spears to be involved in tenellin biosynthesis (preliminary evidence from knockout experiments). The PKS/NRPS (hereafter called TENS) is highly homologous to FUSS, but appears to have a functional ER domain. In this synthase the PKS extends 4 times. It methylates and fully reduces after the first condensation, methylates but does not enoyl-reduce after the second condensation, does not methylate or enoyl reduce after the third condensation and does no post-condensation processing at all after the final condensation. Here, evidence from feeding experiments shows that the selected amino acid is tyrosine or phenylalanine (24). 

Table 10.5 Emission and consumption data of post condensation processes...

Figure 4.17 Schematic view of the chemical healing process in semi-crystalline linear polycondensates TR, transreactions AC, additional (post)condensation D, diffusion [87]. From Fakirov, S., J. Polym. Sci., Polym. Phys. Ed., 22,2095-2104 (1984), Copyright John Wiley Sons, Inc., 1984. Reprinted by permission of John Wiley Sons, Inc...

The amide derived from the carboxylic acid in Ugi adducts is in most cases tertiary, and therefore it cannot serve as nucleophilic partner in post-condensation transformations, unless a post-Ugi rearrangement converts it into a free amine [52, 54]. An exception is represented by Ugi adducts derived from ammonia, which give rise to two secondary amides, each of them potentially involved, as nucleophile, in nucleophilic substitution processes. Four competitive pathways are in principle possible (N- or 0-alkylations of the two amides), and the reaction is mainly driven by the stability of the formed rings. In the example shown in Fig. 12, 0-alkylation of the carboxylic-derived amide is favoured as it generates a 5-membered ring (oxazoline 62), while the alternative cyclization modes would have formed 3- or 4-membered rings [49]. When R C02H is phthalic acid, however, acylaziridines are formed instead via Walkylation [49]. In both cases, the intramolecular 8 2 reactions takes place directly under the Ugi conditions. 

The table shows that the process can eliminate volatile compounds much more efficiently than non-volatile substances. Volatiles, like toluene and chlorobenzene, are already efficiently removed by step (ii) alone. Toluene was no longer measurable at a detection limit of 0.4 ppm. The other volatile, chlorobenzene, was recovered at 5.5 % of the initial concentration after the extrusion step. After the post-condensation step, the amount of toluene in the final product was likely to be far below the limit of detection since the detection limit was already determined after the extrusion step. Chlorobenzene also could not be found above the limit of detection. These results show very impressively that a conventional recycling process (consisting of steps (i) and (ii)) for post-consumer PET removes volatile real-life contaminants very efficiently, for example solvents and fuel. An additional vacuum treatment during solid-phase post-condensation further decreases any level of volatile compounds in the final product. 

Figure 14, PET solid state post-condensation, continuous processing...

Method of synthesis polyamide-4,6 Is a product of polycondensation oftetrameth-ylene-dlamlne and adipic acid. Due to the very high melting temperature the production of polyamide-4,6 was very difficult. As late as 1985 a process was invented to produce polyam-ide-4,6 on a commercially attractive scale in two step process Including precondensation and solid-state post-condensation ... 

Increasing the temperature in inert atmosphere ieads to higher moiecuiar weight, i.e., post-condensation is more pronounced at eievated temperatures. At 310 °C, the measured values no longer differ as strongiy for the various processing conditions, because mechanicai degradation is reduced due to lower melt viscosity. 

Polymerization in Hquid monomer was pioneered by RexaH Dmg and Chemical and Phillips Petroleum (United States). In the RexaH process, Hquid propylene is polymerized in a stirred reactor to form a polymer slurry. This suspension is transferred to a cyclone to separate the polymer from gaseous monomer under atmospheric pressure. The gaseous monomer is then compressed, condensed, and recycled to the polymerizer (123). In the Phillips process, polymerization occurs in loop reactors, increasing the ratio of available heat-transfer surface to reactor volume (124). In both of these processes, high catalyst residues necessitate post-reactor treatment of the polymer. 

Gas-phase polymerization of propylene was pioneered by BASF, who developed the Novolen process which uses stirred-bed reactors (Fig. 8) (125). Unreacted monomer is condensed and recycled to the polymerizer, providing additional removal of the heat of reaction. As in the early Hquid-phase systems, post-reactor treatment of the polymer is required to remove catalyst residues (126). The high content of atactic polymer in the final product limits its usefiilness in many markets. 

Within any particular facility, steam is expected to be delivered to various points of use safely and at controlled temperatures and pressures through relatively long-lasting distribution networks. Where the steam is not excessively contaminated or directly consumed in a process as live steam, it should be condensed, collected, and returned to the boiler for reuse. Thus, the post-boiler section of a boiler plant essentially relates to the systems concerned with steam distribution and condensate return (CR). 

Synthetic resins are extremely widely used, both pre-boiler and postboiler. Pre-boiler, they are employed for basic MU water treatment (e.g., softening) and various higher quality purification processes (e.g. dealkalization and demineralization). Post-boiler applications are for condensate polishing. 

The Ugi reaction is the four-component condensation of an amine, aldehyde or ketone, carboxylic acid and isocyanide to give an o -acylamino amide [22-24], Although this process has the potential to introduce considerable diversity, the products themselves are not heterocycles but through appropriate choice of substrates, latent functionality in one of the precursors can intercept either an intermediate or further derivatize the acylamino amide Ugi product through post-modification. Thus variants of the Ugi reaction have been investigated under microwave-assisted conditions for the synthesis of diverse heterocyclic libraries [16,19-24],... 

Process Activation Large binding system Binding sites Condensation Elongation and movement Termination Post-synthetic modifications... 

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