Carboxyl-terminated oligomers

Perez-Vilar J., Eckhardt, A.E. and Hill R.L. (1996). Porcine submaxillary mucin forms disulfide- b onded dimers between its carboxyl-terminal domains. J Biol Chem. 271, 9845-9850 Perez-Vilar J. and Hill R.L. (1997). Norrie disease protein (norrin) forms disulfide-linked oligomers associated with the extracellular matrix. J Biol Chem 272, 33410-33415 Perez-Vilar J., Eckhardt, A.E., DeLuca A. and Hill R.L. (1998). Porcine submaxillary mucin forms disulfide-linked multimers through its amino-terminal D domains. J Biol Chem. 273, 14442-14449... 

Terminally functionalized PIB oligomers have been used in a thermomor-phic heptane/JV,N-dimethylacetamide mixture as supports for thermally stable SCS-Pd(II) Heck catalyst precursors. A PIB-supported SCS-Pd(II) Heck catalyst was prepared from the carboxyl-terminated PIB oligomer by the sequence of reactions shown in Eq. 61. The PIB-bound SCS-Pd(II) species 125 so ormed was then used to carry out Heck chemistry (Eq. 62). As was true for SCS-Pd(II) species on other polymers [154,155,162], this catalyst was only effective for aryl iodides or activated aryl bromides. However, the catalyst could be used through... 

Ariga (45) disclosed developments with CTBN-modified epoxy acrylates which when prepared with other lower molecular weight dicarboxylic acids and select carboxyl-terminated oligopolyesters serve as novel oligomers for photocurable coatings. These systems have low uncured viscosity. In the cured state they possess excellent scratch and crosshatch adhesion, good direct and reverse impacts (duPont impact tester) and pass bending diameters of 2 mm. 

Thiolated polymers, also termed thiomers, are conventional mucoadhesive polymers chemically modified to contain a cysteine residue in the polymer chain and thus establish covalent disulfide bonds with mucin." They can be manufactured to be either cationic (mostly thiolated chitosans) or anionic (carboxylic acid-containing polymers) however, their mucoadhesive extent will mostly be determined by their capacity to covalently bind to mucin. The polypeptide backbone of mucin can be divided into three major subunits tandem repeat array, carboxyl-, and amino-terminal domains. While the amino-terminal domain contains some of the cysteine residues, the carboxyl-terminal domain contains more than 10% of the cysteine residues. These cysteine-rich regions are responsible for forming the large mucin oligomers and ultimately, the groups that allow for the covalent mucoadhesive bond formation with oral mucosal systems." ... 

Conversely, the brittleness of cured epoxy resins can be ameliorated by copolymeiizing with flexible curing agents. The two most popular types are carboxyl-terminated nitrile rubber and mercaptan-terminated polysnlflde rnbber oligomers (Fig. 3.35). 

To the vinylester resins, thixotropic agents are added, for example silica fume (silicon dioxide in microspheres, which is a by-product of the glass industry), to obtain a behaviour adequate to their use also in open moulds. In addition, to improve their toughness, CTBN polymers (carboxyl-terminated copolymers of butadiene and acrylonitrile) are widely employed as reactive modifiers. This occurs since the CTBN-modified vinylester oligomers act as compatibilizers for blending additional butadiene copolymer (Burchill and Pearce, 1996). 

Li et al. [5] used a combination of 2D-NMR methods to study a similar perflu-oropolyether. They examined carboxyl-terminated low MW oligomers of PHFPO which served as a model for Dupont s Krytox fluoropolymers. They used spectra from selective one- and two-bond Fj C HSQC experiments, similar to the data shown in Figure 24.8, to identify the atomic connectivities within each polyether unit. Note that the correlations to F resonances A3 and Aj occur at slightly different chemical shifts in the one-bond experiment (top spectra) compared to those in the two-bond spectra (bottom spectra). This is due to a one-bond C isotope effect which shifts resonances of attached fluorines up-field by approximately 0.1 ppm compared to the resonances of fluorines attached to C. The two-bond isotope effect is 10-fold smaller and is too small to notice in these 2D-NMR spectra. Similar sets of correlations were observed for each monomer unit in the structure. 

Lipid autoxidation is generally believed to involve a free- radical chain mechanism (1) initiation steps that lead to free radicals (R ), (2) propagation of the free radicals (R -I-O2 —> ROO, ROO -1-RH — ROOH-I-R ), and (3) termination steps R -H R R—R, R- ROO- ROOR, ROO ROO O 2 ROOR (or alcohol and carbonyl compound). The oxidation of lipids results in peroxides as primary oxidation products, which in turn degrade further to secondary oxidation products, including aldehydes, ketones, epoxides, hydroxy compounds, carboxylic acids, oligomers, and polymers. 

For these oligomers, it is preferred that n have a value of about 1 to 6. Modified block copolymers have been synthesized by coupling the above products with difunctional isocyanates (193) and with cycloaliphatic diepoxides (194). They were also used to synthesize radiation-curable diacrylates by means of a condensation reaction with acrylic acid (195). Other modifications of the oligomeric compounds include end capping with anhydrides to form acid-terminated oligomers (196) and reaction with polyols, anhydrides, and carboxylic acids to form low-viscosity, oil-free alkyds that are useful as coating intermediates (197). 

FIGURE 8.37 Synthesis of poly(arylene ether sulfone)-f>-PBI (BPS-PBI) multiblock copolymers (a) synthesis of the PBI oligomer, (b) synthesis of the carboxyl-terminated polyfethyl sulfone) oligomer (BPS), and (c) block copolymerization. (Reprinted with modification from Lee, H.-S. et al.. Polymer, 49, 5387, 2008. With permission.)... 

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