Authors Voit, B. ; Scheel, A. ; Komber, H. ; Maier, G. ; Zech, C. ; Hawker, C.J.
Title Potential of Cycloaddition Reactions in the Synthesis of Hyperbranched Polymers of Different Degree of Branching
Date 13.12.2004
Number 12319
Abstract Dendritic polymers are often distinguished into perfect dendrimers and hyperbranched polymers according to their degree of branching, which is below 100% for the hyperbranched molecules. Both dendrimers and hyperbranched polymers gained high interest in the last years' and the discussion arose whether the more easily available hyperbranched polymers can substitute the synthetically demanding dendrimers. It was found that there are several similarities in the properties, e.g. low viscosity and high functionality. Nevertheless the hyperbranched polymers are a class of their own and their uncontrolled structure and broad molar mass distribution clearly distinguish them from perfect dendrimers. Unlike dendrimers, hyperbranched polymers possess linear units distributed throughout the polymer structure. Thus, an exact description of one molecule is impossible, since even molecules with an identical number of repeating units can exist as thousands or millions of different isomers. If the existence of linear units in hyperbranched polymers can be excluded or strongly reduced, one might come closer to perfect dendrimers in terms of degree of branching. In general, the ratio of dendritic and terminal units to all units, including the linear ones, defines the degree of branching2 which does not, however, give information on the symmetry of the molecule. Therefore, one can not distinguish between dendritic molecules prepared step by step with exactly defined structure, molar mass and symmetry, and those which simply lack linear units but are prepared in a one-step synthesis from ABx molecules. Specific cycloaddition reactions have recently been used very successfully to prepare new perfectly branched dendrimers in a step wise manner under mild conditions and in very good yields4. We would now like to show, that also typical hyperbranched polymers with a DB of about 50% can be prepared using a similar chemistry. A specific type of cycloaddition, the criss-cross cycloaddition, offers also the possibility to prepare hyperbranched products without any linear units.
Publisher Polymeric Materials: Science and Engineering
Citation Polymeric Materials: Science and Engineering 91 (2004) 258-259
Tags dendrimers alkynes cycloaddition molecular structure symmetry chain branching isomers

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