Branching analysis

To get an insight into the branched structure of PEs it is important to analyze them for their content and distribution in the macromolecules. The branching analysis of PEs have been reviewed by many workers [13,20,21]. 

Our latest efforts have been to concentrate on investigating the architecture of the DIB core. As discussed before, the average number of branches per molecule (B) determined by selective link destmction and equilibrium swelling showed good agreement with the kinetic B (Equation 7.2). However, branching analysis by SEC proved to be a challenge. 

Various PIB architectures with aromatic finks are ideal model polymers for branching analysis, since they can be disassembled by selective link destmction (see Figure 7.7). For example, a monodisperse star would yield linear PIB arms of nearly equal MW, while polydisperse stars will yield linear arms with a polydispersity similar to the original star. Both a monodisperse and polydisperse randomly branched stmcture would yield linear PIB with the most-probable distribution of M jM = 2, provided the branches have the most-probable distribution. Indeed, this is what we found after selective link destruction of various DlBs with narrow and broad distribution. Recently we synthesized various PIB architectures for branching analysis. 

Two analytical methods, size exclusion chromatography and rheology, provide a long chain branching index. The application of size exclusion chromatography to long chain branching analysis was described in Section 5.2.3.1. 

It should be pointed out that this method for ring analysis and branching analysis is based exclusively on reliable data of n, d, M and a of pure individual hydrocarbons, and holds, within the limits of accuracy of the determination, for widely differing types of branched as well as non-branched saturated hydrocarbon mixtures. It is particularly recommended for the structural analysis of saturated polymers, where other statistical methods (w- -M-method, v-n-d-method, etc.) fail because they have been developed for mineral oils, and are based on correlations of physical data of mineral oil fractions that always show approximately the same small degree of branching 1-2 branchings per molecular weight = 100. 

BRANCHING ANALYSIS OF HYDROGENATED PLATFORMING PRODUCTS OBTAINED BY HYDROISOMERIZATION OF PARAFFIN WAX... 

If charges are neutralized at the center of a junction containing short branches, analysis reveals that counterions are released not near sites of neutralization, but from the entire molecule [74], Furthermore, counterion release is enhanced for junctions with larger branches [74], A basic conclusion of this study is that a protein recognizes a tertiary structure in part through an increase of the associated counterions [74]... 

Block copolymers made from monomers A and B contain long sequences of A units connected to long sequences of B units. To understand the block polymerization mechanism, it is useful to measure the number of structures at block junctions. The issues associated with the study of block copolymers are similar to those discussed earlier in relation to chain-end and branching analysis the resonances from block junctions are small compared with those of the main chain peaks. 

It is unlikely that this branching analysis can be reliably applied to graft or to block copolymers because chain dimensions—from which branching indices are determined—are influenced by polymer-polymer and polymer-solvent interactions. The magnitude of the problem is indicated by published data that indicate that graft copolymers can exhibit an intrinsic viscosity, for the same molecular weight, which is not even intermediate between the two homopolymers [6, 7]. A fortuitous match of cohesive energy densities... 

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