Distribution of end-groups

If a uniform distribution of end groups were present throughout the dendrimer, we would see the same Rg for both the labeled and the whole dendrimer. This is demonstrated by the illustration in Figure 11.11, where the end groups have different locations. Instead, we see a clear difference between the Rg values for the labeled units and the unlabeled dendrimers. The distribution of den-... 

Vogtle, F. Lindner, P. Distribution of end groups within a dendritic structure a SANS study including contrast variation. Macromolecules 2002, 35, 8098-8105. 

Chemical Structure and Properties. Homopolymer consists exclusively of repeating oxymethylene units. The copolymer contains alkyhdene units (eg, ethyUdene —CH2—CH2—) randomly distributed along the chain. A variety of end groups may be present in the polymers. Both homopolymer and copolymer may have alkoxy, especially methoxy (CH3 O—), or formate (HCOO—) end groups. Copolymer made with ethylene oxide has 2-hydroxyethoxy end groups. Homopolymer generally has acetate end groups. 

The starburst point occurs at a well-defined limit for each dendrimer system, and its occurrence is dependent mainly on (a) the functionality of the core, (b) the multiplicity of the branches and (c) the branch length. However, the volume of the core itself, and the length of the monomer branches also have an influence. The end groups may occupy the outer surface of the dendrimer, or the branches may fold inwards, thus distributing the end-groups within the dendrimer. The factors that control this behaviour of the branches are not fully understood, but include the nature of the solvent and the detailed chemistry of the dendrimer branches. 

MALDI-ToF-MS is a powerful technique capable of obtaining information on molecular weight, molecular weight distribution and end-group analysis [18-19], see also Chapters 5 and 6. This technique has not only become a workhorse in the... 

What we require now in order to consolidate our understanding is more work with a variety of monomers and solvents, with the simplest possible initiator systems, aimed at obtaining the maximum amount of information on the polymerisations (rates, equilibria, conductivities, constituents of the reaction mixtures before and after neutralisation) and on the polymers (existence, nature and concentration of end-groups, DP distributions). There are unfortunately still too many who think they can base a valid theory on the determination of only one or two features of a polymerisation system. 

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