Branching characteristics

Although carbohydrates/polysaccharides exist in such huge amounts, their industrial processing is expensive due to enormous quality fluctuations of succeeding raw material batches. The reason for these fluctuations is a high variability on the molecular level, particularly in the degree of polymerization distribution, in branching characteristics, and in complex interactive properties. 

FIGURE 16.7 Native starch ( ) and fractions of native starch differing in their branching characteristics (nb/lcb amylose -type fraction scb amylopectin -t/pe fraction ) separated on semipreparative... 

For illustration consider SEC chromatograms obtained for two polymers on the same chromatographic system. One sample is a linear homopolymer while the other is a branched polymer with the same chemical composition. In the latter sample assume that the polymer components of different molecular weight have uniform branching characteristics so that all have similar molecular size/weight relationships. 

Apart from differences in molecular weight, 14 of the 16 samples show little variation in branching characteristics the constituent chains contain 10 -14 D-glucose residues per end-group, and 41-51 % of these are removed, as maltose, by /3-amylase. The average interior and exterior chain-lengths are, therefore, approximately 3 and 8 n-glucose residues, respectively. 

The procedure of fractal set construction can be shown using the Cayley tree so that each fractal set has its own Cayley tree [25,26]. We show a Cayley tree with branch characteristic j = 4. 

The smart response capability of polysaccharides upon application of stress allows polar and apolar domains to easily form or disintegrate due to variation of the order/disorder ratio at the molecular level. This finally results in variation of specific crystallinity index or crystalline/amorphous ratio at the macroscopic level. Significant variation of interactive properties may even be achieved by minor variation of branching characteristics, which changes surface/volume ratio and, hence, preferences for inter- or intramolecular stabilization. Additionally, a rather effective response option is variation of relative percentages of molar and mass fractions by limited degradation/ reorganization or precipitation/dissolution transition. 

Heterogeneity is a generic quality of polysaccharides All characteristics occur as distributions and may be handled as distributions of molar fractions, referring to the number of distributed components, or distributions of mass fractions, referring to mass contributions of distributed components. In particular, for broad distributions, the difference between mass and molar distribution becomes significant and sometimes crucial. Molar mass distribution is a central piece in this puzzle of correlating molecular characteristics with polysaccharide performance. Additionally, optional branching characteristics, substitution patterns, and responses of aqueous polysaccharide systems to different kinds of applied stress need to be determined. 

Branching enzyme is responsible in glycogen biosynthesis for making the many 1,6 branches characteristic of the glycogen molecules. 

M. Schlamowitz, The nature of rabbit liver glycogen. I. Branching characteristics, J. Biol Chem., 188 (1951) 145-153. 

AF4 coupled with static and DLS detectors enables comprehensive information about structural and branching characteristics of biopolymers (e.g., starches), synthetic polymers, proteins, etc. [25, 26]. Especially in case of branched polymer stractures like dendronized glycopolymers, the separation and characterization with AF4-LS lead to comprehensive information and understanding in molecular structures and aggregation behavior [27]. Furthermore, studies of uptake studies of dendritic glycopolymers and dye molecules were performed for the first time by AF4-LS (see Fig. 4.12). Here, a good correlation was obtained between the increase of molar mass and the quantified amount of dye molecules, which were encapsulated by the glycopolymers [28]. 

Z.J. Fan, M.C. Williams, P. Choi, A molecular study of the effects of branching characteristics of LDPE on its miscibility with HDPE. Polymer 43, 1497-1502 (2002)... 

Polyethylene is a thermoplastic material which varies from type to type according to the particular molecular structure of each type. Actually, several products can be made by varying the molecular weight (i.e., the chain length), the crystallinity (i.e., the chain orientation), and the branching characteristics (i.e., chemical bonds between adjacent chains). Polyethylene can be prepared in four commercial grades ... 

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