Alkyl side chains, polyesters

Although rigid-rod poly(p-phenyleneterephthalamide) analogues having alkyl side chains did not contain cyclic polymers, the polycondensation of silylated m-phenylenediamine and aliphatic dicarboxyhc acid chloride afforded cyclic polyamides predominantly (Scheme 49) [187]. Furthermore, cyclic polymers were also produced in polycondensations for polyesters, poly(ether ketone)s, polyimides, and polyurethanes [183]. These examples are the products in polycondensation of AB monomers or in A2 + B2 polycondensations, but cyclization of oligomer and polymer was also confirmed in polycondensation of AB2 monomers [ 188-195] and in A2 + B3 [ 196-202] and A2 + B4 polycondensations [203-206], which afford hyperbranched polymers. 

Oxidation of aromatic systems containing alkyl side-chains results in the formation of a carboxylic acid, irrespective of the length of the side-chain. The usual oxidizing agents are potassium permanganate [potassium manganate(VII)] or chromic acid [chromium(VI) acid]. For example, 1,4-dimethylbenzene is oxidized to benzene-1,4-dicarboxylic acid (tereph-thalic acid, 9), an important building block for polyesters. The oxidation of isopropylbenzene (cumene) to phenol is an important industrial process and is discussed in Chapter 4. 

Tetrasubstituted polyesters with long alkyl side chains on the hydroquinone moiety connected via ether or ester linkages have been reported [20 c] (Fig. 12). In these polyesters, the tetrasubstituted moiety can be considered as a discotic mesogen. The polyesters with Z = H are highly soluble and have low melting temperatures (T n < 100 °C) and low clearing temperatures in the range of 123-260°C. The type of mesophase formed is referred to as sanid-... 

The solution behavior has been significantly enhanced by the same structural modifications as reported previously for aromatic LC polyesters. For example poly-(p-phenylene terephthalamide) has been modified by bulky, stiff substituents [32], flexible alkyl side chains [33], the incorporation of kinked and double kinked comonomers, and comonomers of different lengths [34], as well as the use of noncoplanar bipheny-lene monomers [35]. To develop high performance materials, modifications that increase the solubility while maintaining the rod-like character, high glass transition temperatures, and the temperature stability are of particular interest. The solubility and the chain stiffness are critical factors in achieving lyotropic solutions. 

Three poly(n-alkyl acrylates) PA-H, PA-16, PA-18 and two poly-(vinyl alcohol aliphatic acid esters) PVA-1A and PVA-16 have been synthesized. They are white crystalline polymers at room temperature, characterized with IR, DSC, SALLS-photometer and polarizing microscope. Only PA-I4 and PVA-IZf are effective for 0/ diesel oil. The influences of molecular weight, molecular weight distribution and amount of addition of PA-1i+ and PVA-lif upon the pour-point depression of oil are very alike. These results reveal the length of n-alkyl side-chain of the polyesters plays the most important role in depressing the pour-point of petrolic oil and the order of linking in the ester group seems in no relation to this effect. 

All these facts reveal that the length of n-alkyl side-chain of the polyesters plays the most important role in depressing the pour-point of oil and the order of linking of the ester-group to the backbone seems in no relation to this effect. 

B-C polyesters(n the carbon number of the n-alkyl side chain) such as B-C6 indicated in Figure 7-2 have been used [13, 26],... 

Capillary and packed (GC) columns are of value in the analysis of complex mixtures of lipids. The best capillary column length will depend on the complexity of the material injected, however, 30-m columns are often employed. In packed columns, many types of stationary phases are available for lipid separation, and these include silicone and alkylated or cyanogenated derivatives, polyesters, polyglycol, and carboranes. It is also common to derivatize the fatty-acid side chains to the corresponding methyl esters by reaction in BF3/ methanol prior to chromatographic analysis to achieve more distinct and uniform separations. 

As flexible substituents, linear and branched alkyl, alkoxy, or thioalkyl side chains of different lengths have been utilized to modify para-linked aromatic polyesters. The main difference to the systems discussed above is the limited thermal stability caused by the substitution with alkyl chains. Also, the mechanical poperties are substantially lowered with increasing... 

PHAs are polyesters composed of several units of hydroxyalkanoate monomers linked to each other through ester linkages. Figure 12.1 represents PHA s general formula where n is the number of monomer units in each polymer chain, which varies between 100 and 30,000, Ri and R2 the side chain that includes alkyl groups with 1-13 carbons and x in the main chain which ranges from 1 to 4. 

Let us emphasize the main facts for alkyl-substituted stiff macromolecules. The conformation of the main chain is affected by side groups and depends critically on the chain length. For relatively short side chains hexagonal packing of macromolecules is possible, whereas for longer chains the boardlike shape of the molecules leads to formation of a highly ordered layered structure. In the crystal state the coplanar arrangement of the fully extended aromatic backbone for polyesters is possible. In the liquid crystalline state both a well-ordered layered structure and a nematic structure are observed. Because of the boardlike shape of the molecules, the nematic phase is biaxial. 

An ester is a compound whose structure may be derived by the replacement of the replaceable hydrogen of an acid by an alkyl, aryl, alicyclic or heterocyclic group. The most important esters are these derived from carboxylic acids the structural formula of these esters is R-CO—O—R For the purposes of this chapter, polyesters are defined as polymers containing recurring —CO—0— groups in the main chain. It may be noted that this definition excludes polymers of esters such as vinyl acetate and methyl methacrylate since in these polymers the ester groups occur in side-chains and not in the main chain. 

Unsubstituted rigid rod polymers typically have a high melting temperature (e.g., ca. 600° C for the polyester of Fig. 25a with a side-chain length n = 0). However, even a short alkyl tail of length 0 < n < 6 reduces substantially the melting temperature i.e., a... 

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