Backbone polymers simple structures

CARBOHYDRATES ARE IMPORTANT, naturally occurring organic compounds. They include simple sugars, or monosaccharides, such as glucose and fructose, and polysaccharides, such as starch and cellulose, which are more complex compounds composed of a number of sugar units. Carbohydrates are one of the initial products of photosynthesis. As such, they serve as the molecules that store the sun s energy for later use in metabolism. In addition, carbohydrate polymers are structural materials used by plants and animals. Even our genetic material, DNA, contains carbohydrate units as part of its polymeric backbone. 

Poly(imines) are polymers that contain in their backbone amino nitrogens connected by single bonds to carbon atoms. Some of these polymers have a simple structure like poly(ethylene imine) or [-CH2-CH2-NH-]n. The polymer is obtained from the polymerization of aziridine, typically generating a mix of linear and branched macromolecules with about 25% primary amine groups, 50% secondary amine groups, and 25% tertiary amine groups. The polymer is used in paper industry and for various other purposes that make use of its anionic character [1]. 

Another system of interest is substituted polyacetylene, first because the backbone is simple and close to the ethylene structure, second because numerous soluble polyacetylenes with either long alkyl chains or bulky substituents are available, so that a systematic study can be performed. Due to the structure of the backbone and the great variety of linear polymers, a direct comparison with a similar saturated polymer was thu.s possible, providing additional information on the actual effect of the conjugated backbone. 

This paper describes novel approaches to the exploitation of both furan monomers and a specific facet of furan reactivity in order to synthesize either conjugated oligomers incorporating the heterocycle in their backbone, or polymeric structures which can be crosslinked and returned to linear structures through the reversible chemistry of the Diels-Alder reaction. The first family of compounds showed interesting features in terms of conductivity, luminescence, mesogenic character and photoactivity. The second class of materials owes its interest to the possibility of recycling otherwise intractable polymers, e.g. tires, thanks to a simple thermal process. 

Detection, resolution and identification of the weak chain-end resonances in the presence of the much larger signals from the polymer backbone, using simple ID- ( H, and and 2D- (HMQC and HMBC) NMR experiments, was a problem. To surmount this problem, they took advantage of the unique NMR characteristics of the phosphorus-containing chain-end structure when compared with the hydrocarbon-based structure of the rest of the polymer. The atoms on the chain end, exhibit / coupling to which has 100% natural abundance and nuclear spin I = 1/2. These couplings can be used to produce a variety of multidimensional triple-resonance 2D- and 3D-NMR... 

The changes in structure of denatured nuclease as a function of urea concentration (Fig. 3) suggest that, as hydrophobic interactions are weakened and the backbone becomes more highly solvated, the chain expands gradually. The data presented by Millet et al. in this volume suggest that this expansion does not continue asymptotically as predicted by simple polymer physical chemistry. This is the behavior expected for a polypeptide chain trapped in a small region of conformation space. Most, perhaps all, of the conformations accessible in the expanded denatured state may have a native-like topology. 

We have reported that ESR and ENDOR (52) examination of degassed, irradiated samples of a number of polymers (PDHS, PDBS, poly(di-a-tetra-decylsilane) (PDTDS), poly(di-n-octylsilane (PDOS), poly(di-n-decylsilane) (PDDS) and poly(di-4-methylpentylsilane) (PDMPS) shows the formation of radical species which are persistent for hours and even days. The radical spectra (see Figure 4) are, however, clearly not consistent with those expected from the simple cleavage of the polymer backbone as described by Equation [2]. The structure of these radicals... 

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