Terminal carboxyl content

In oxidized cellulose, part of the terminal primary alcohol groups of the glucose residues are converted to carboxyl groups. The product should contain no less than 16% and no more than 24% carboxyl groups. Products with low carboxyl content have better technical properties. Oxidized cellulose is a fibrous white powder prepared from cotton wool and posesses a slight acid odor. 

As the viscosity of the reaction system increases, it becomes more difficult for ethylene glycol to diffuse through the reaction system and be eliminated from it. Thermal decomposition also occurs under melt polycondensation conditions, resulting in an increase of terminal carboxyl content and a decrease of hydroxyl ends that lower the apparent polycondensation rate even further. 

The effect of the chain extenders in increasing the polycondensation rate and in decreasing terminal carboxyl content is explained by several reaction mechanisms. 

Reaction 22 will decrease terminal carboxyl content and intermediate IV will accelerate the polycondensation Reaction 7. 

The reaction of a diepoxide with a carboxylic acid-terminated polymer will, therefore, result in a coupling of two chains. This method has been proposed in a patent as early as 1971. In the late 1990s, a comparative study of chain extension of PET by means of several commercial diepoxides has been reported. The reactions were carried out at 270 °C for different periods of time. The diepoxides 1 and 2 of Figure 1, comprising aliphatic cyclohexyl moieties, gave chain extension reaction as evidenced by the increase in intrinsic viscosities and substantial decrease of carboxyl content of the end products. With the diglycidyl ether types (3, 4, and 5), however, decreased viscosity values, increased carboxyl content, and lower melting points were observed. 

Hirano et al. [150, 151] immobilized several peptides, RGDS, on ethylene-acrylic acid copolymer (EAA, acrylic acid content 20 wt%) film by reacting the amino-terminal of the peptide with the carboxylic acid of the copolymer with the aid of a water-soluble carbodiimide, to form EAA-co-NH-RGDX. Their objective was to examine effect of the fourth residue, X, on the cell-attachment activity of the tetrapeptide, RGDX, where X is S, V and T. They also examined the activity of RGD, YIGSR and YIGSR-NH2 for comparison. The cell lines used were ovary CHO-K1 cell (Chinese hamster), kidney NRK cell... 

As a model experiment to see the effect of orthoesters in reducing the content of terminal carboxyl, aliphatic long-chain dicarboxylic acid and a large excess of various additives reacted in biphenyl at 250°C, and the rate constants of the pseudo-first-order reaction were compared. The reaction rate constant decreases in the order of tetraphenyl... 

As was pointed out previously, clostridial ferredoxins are closely related in spectral properties, iron, and inorganic sulfide content, and amino acid composition. The recent work of Tanaka et al. (100) shows that this similarity applies also to the amino acid sequence of these proteins. Preliminary results indicated that C. butyricum ferredoxin, like C. pasteurianum, contains 55 amino acid residues (3 in addition to those in Table 6), the same glutaminyl-glutamic acid carboxyl-terminal sequence, and the same aminoterminal amino acid, alanine. Their results show also the isomorphic replacement of certain amino acids, such as phenylalanine for tyrosine. 

In the case of a low content of a comonomer in a copolymer, the peak characteristics for fragment molecules generated from the comonomer or comonomer sequences can be very small. Since most pyrograms are very complex, with hundreds of small components, it is in many instances difficult to assign a particular compound to a low level comonomer. This is, for example, the case of the pyrolysis of the terpolymer poly acrylonitrile-co-butadiene-co-acrylic acid) dicarboxy terminated 18 wt % acrylonitrile, 2.4 carboxyl/molecule, CAS 68891-50-9. No peaks characteristic for the acrylic acid are seen in the pyrogram. 

Poly(NIPAM-co-MAA) with MAA content above 5 mol% is soluble under both physiological pH (7.4) and temperature (37°C), when its carboxylic functions are ionized. However, when the pH is decreased to the pH of late endosomes and lysosomes ( pH = 5-5.5) (1), MAA protonation triggers dehydration of the polymer chains. If the polymer is anchored to a phospholipid membrane through randomly or terminally incorporated alkyl chains, transition, to a globule conformation induces reorganization of the bilayer that leads to massive content leakage (3). 

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