Branch chain polymers

At the liquid nitrogen temperature, a lower molecular weight branched-chain polymer is obtained, which is believed to be produced in an additive ion-molecule chain reaction of the type... 

The integral intensities of signals of polysaccharides, obtained with a modem spectrometer under the usual operating conditions, are proportional or quasi-proportional, to the number of 13C nuclei present. This has been observed, in particular, in the case of linear hexo-pyranan structures containing one type,11,47,51,55,56 58-61 or two equal types, of linkage,62 or branched-chain polymers having two linkage types,53,58 where the resonances are readily resolved. In such cases, the T values would be low, 0.2 s or less, and the n.O.e. values would be approximately equal. However, few actual determinations of these values have been made, and extrapolation of such assumptions to more-complex polysaccharide structures is not recommended, as outlined in Section V,2,... 

Within the temperature range from 10 to 40°C, both PAMAM dendrimers in EDA [5] and PPI dendrimers in water [22] showed a linear relationship between In r and /T, in good agreement with the kinetic rate theory of flow [46]. The apparent activation energies of flow (En) were constant and independent of temperature, and it was shown for PAMAM/EDA systems that the dependence of En on solution concentration was linear for all generations examined [5]. This was considerably different from the typical relationships for the solutions of linear and/or randomly branched chain polymers, where a break in the slope of... 

Branched chain polymers such as low density polythene. 

Which of the following is a branched chain polymer (a) HDPE, (b) iPP, (c) LDPE, or (d) amylose starch ... 

Stockmeyer, W.H. 1943. Theory of molecular size distribution and gel formation in branched-chain polymers. J. Chem. Phys. 11 45-55. 

Stockmayer 25 subsequently developed equations relating to branched-chain polymer size distributions and gel formation, whereby branch connectors were of unspecified length and branch functionality was undefined. An equation was derived for the determination of the extent of reaction where a three-dimensional, network ( gel ) forms this relation was similar to Flory s, although it was derived using another procedure. Stockmayer likened gel formation to that of a phase transition and noted the need to consider (a) intramolecular reactions, and (b) unequal reactivity of differing functional groups. This work substantially corroborated Flory s earlier studies. 

Starch molecules are polymers of anhydroglucose and occur in both linear and branched form. The degree of polymerization and, accordingly, the molecular weight of the naturally occurring starch molecules vary radically. Furthermore, they vary in the ratio of branched-chain polymers (amylopectin) to linear-chain polymers (amylose), both within a given type of starch and from one type to another. These factors, in addition to any type of chemical modification used, affect the viscosity, texture, and stability of the starch sols significantly. 

Starch is the major energy storage polysaccharide of cereal crops. It is a natural polymer of dextrose. Starch has two naturally-occurring forms one is amylose, a polymer with long linear chains the other is amylo-pectin which is a branched chain polymer. The length of the amylose chain varies between different plants but common values are between 200... 

Phosphorous is a five-valent element, and its natural oxide is P2O5, phosphorous pentoxide. It is a highly hygroscopic powder and readily reacts with water to form phosphoric acid (H3PO4). This acid when reacted with various aUcaline compounds forms phosphates. These and other modified compounds are linear or chain, cyclic or ring, and branch chain polymers. Because these compounds are polymeric, phosphates can provide a continuous structure and, hence, form good ceramics. The reader is referred to Topics in Phosphorus Chemistry by Westman [1] for details. Because of the variety of polymeric compounds formed by phosphorous, a systematic nomenclature is used in phosphate chemistry. 

Gaskell (20,21) theoretically calculated the entropies of mixing for SiOj—CaO, SiOj—FeO and SiOj—MnO slags on the basis of Guggenheim s expresaon for the configuration entropy of a system of linear and branched chain polymer molecule. The value he derived deviated fiom the experimental values (20,21). He attributed the... 

Branched-chain polymers exhibit more tangled arrangements they are less likely to form crystalline regions and tend to be weaker, less dense materials. 

The branched-chain polymer occurs in amylopectin and glycogen. Branched-polyglucose-chain glycosidic bonds are a(1 6) at branched points, but all glycosidic bonds along the chain are a(1 4). 

FIGURE 16.16 Linear and branched-chain polymers of OrD-glucose. 

Molecules of high polymers can consist of chain structures (linear or branched) or are cross-linked. In linear chains, the monomer units are linked consecutively by primary chemical forces. In branched chains, shorter or longer side chains are bonded also by primary chemical connections. Both linear and branched-chain polymers can be molten and frozen repeatedly by alternating heating and cooling processes. They are soluble in some organic solvents. 

The interrelationships described above provide a basis for evaluating the possibility that chemotherapeutic or metabolic manipulation can be used to produce drastic alterations in ceU functions. We have shown that one mechanism of cell death, which we have called Type 1 or the Suicide mechanism, is mediated by activation of poly(ADP-ribose) polymerase and the consequent depletion of cellular energy metabolites (1,2). This enzyme is activated by DNA strand breaks to cleave NAD at the glycosylic bond between the nicotinamide and adenosine diphosphoribose moieties (3). The latter are joined by the same enzyme into linear or branched chain polymers of ADP-ribose (3). Poly(ADP-ribose) polymerase activity and utilization of its substrate, NAD, are proportional to the number and duration of DNA strand breaks (4, 5). As shown in Fig. 2, DNA damage can sufficiently... 

Notice, in each case, that a small molecule, water, is eliminated as a product of the reaction. Several other condensation polymers are listed in Table 2. Linear (or branched) chain polymers, as well as cross-linked polymers, are produced in condensation reactions. 

The result of this movement is a more branched-chain polymer. This can... 

The result is that diffusion in branched-chain polymers is much slower than in linear chains. For rings, diffusion is even more sluggish, because the ring is forced to collapse into a quasihnear conformation in order to have center-of-mass motion. Since many commercial polymers are branched or star-shaped, the self-diffusion of the polymer is correspondingly decreased, and the melt viscosity increased. 

Curve I is for a linear to branched-chain polymer with methylene or dimethylene ether linkages. In curves II, III, and IV the linking unit is methylene, and the cross-linking is greatest in IV. Curve V is for a linear polymer series with hexahydrotriazine linkages. The condensation of hexa-methylolmelamine has been interpreted in a similar fashion [51]. 

Glycogen A branched-chain polymer of glucose, linked by al—>4 links, with branch points provided by CCl—>6 links. The storage carbohydrate of mammalian liver and muscle. 

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