Aromatic polymers production procedure

Jackson and Walker [7] studied the applicability of pyrolysis combined with capillary column GC to the examination of phenyl polymers (e.g., styrene-isoprene copolymer) and phenyl ethers e.g., bis[w-(w-phenoxy phenoxy)phenyl]ether. In the procedure the polymer sample is dissolved in benzene. The pyrolysis Curie point temperature wire is dipped 6 mm into the polymer solution. The polymer-coated wires are then placed in a vacuum oven at 75-80 °C for 30 minutes to remove the solvent. Figure 6.2 shows a characteristic pyrogram of the copolymer (isoprene-styrene) resulting from a 10-second pyrolysis at 601 °C. When the polyisoprene is pyrolysed, C2, C3, C4, isoprene, and CjoHig dimers are produced. When PS is pyrolysed, styrene and aromatic hydrocarbons are the products. Figure 6.2 shows that the copolymer product distribution and relative area basis resemble the two individual polymer product distributions. 

Condensation ofDianhydrides with Diamines. The preparation of polyetherknides by the reaction of a diamine with a dianhydride has advantages over nitro-displacement polymerization sodium nitrite is not a by-product and thus does not have to be removed from the polymer, and a dipolar aprotic solvent is not required, which makes solvent-free melt polymerization a possibiUty. Aromatic dianhydride monomers (8) can be prepared from A/-substituted rutrophthalimides by a three-step sequence that utilizes the nitro-displacement reaction in the first step, followed by hydrolysis and then ring closure. For the 4-nitro compounds, the procedure is as follows. 

The procedure for getting the polymer-bound ligands is very easy to reproduce. Three jS-functionalized aromatic ketones were successfully reduced to the corresponding alcohols by heterogeneous asymmetric hydrogen transfer reaction with formic acid-triethylamine azeotrope as the hydrogen donor. One of the product alcohols (19c) is an intermediate for the synthesis of optically active fluoxetine. 

Considerable research effort has been devoted in recent years to the use of chloral derivatives for the synthesis of linear heterocyclic polymers. Of these, the most common are aromatic polyimides [1-12], Many of these polymers have been synthesised from compounds like 4,4 -diaminobenzophenone, and other diamines, which, as demonstrated in the previous chapter, can be obtained from chloral. Polyimides prepared from these diamines were largely synthesised by the conventional two-step procedure [11, 12] involving mild reaction of the diamines with the bis(phthalic)anhydrides, isolation of poly(o-carboxy)amide (PCA) prepolymers, and then processing into products followed by thermal or chemical imidisation [13—16] (Scheme 3.1). Some properties of polyimides prepared from 4,4 -diaminobenzophenone are provided in Table 3.1. 

Reverse osmosis was not commercially practical until techniques for increasing productivity were developed. The principal discovery (32) involved a casting procedure that results in asymmetric membranes having a thin dense layer of polymer, approximately 0.2)a thick, supported on a porous sublayer as Illustrated in Figure 8. These membranes are called Loeb membranes (33). Current commercial membranes of this type are made of cellulose acetate, aromatic polyamides, and certain composites that achieve water fluxes of the order of 1.0 m /m day with NaCl rejections of 99% or more (27). As seen in Equation 25, rejection increases with applied pressure. 

The c/s-dihydroxylation reaction catalyzed by these dioxygenases is typically highly enantioselective (often >98% ee) and, as a result, has proven particularly useful as a source of chiral synthetic intermediates (2,4). Chiral cis-dihydrodiols have been made available commercially and a practical laboratory procedure for the oxidation of chlorobenzene to IS, 2S)-3-chlorocyclohexa-3,5-diene-l,2-c diol by a mutant strain of Pseudomonas putida has been published (6). Transformation with whole cells can be achieved either by mutant strains that lack the second enzyme in the aromatic catabolic pathway, cw-dihydrodiol dehydrogenase (E.C. 1.3.1.19), or by recombinant strains expressing the cloned dioxygenase. This biocatalytic process is scalable, and has been used to synthesize polymer precursors such as 3-hydroxyphenylacetylene, an intermediate in the production of acetylene-terminated resins (7). A synthesis of polyphenylene was developed by ICI whereby ftie product of enzymatic benzene dioxygenation, c/s-cyclohexa-3,5-diene-1,2-diol, was acetylated and polymerized as shown in Scheme 2 (8). 

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