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With the epoxy polyaddition system some fundamental relations between chemical structure and physical properties of cross-linked materials are shown. It became evident, that the morphology of the polymers is characteristically influenced not only by the segments between the cross-links but also by the cross-linking fragments formed during the polyaddition reaction. Amine-cured epoxy systems show distinct Beta-relaxations causing higher toughness and flexibility as well as higher glass transition temperatures than the anhydridecured polymers. Similar systems result by cross-linking epoxidised cycloolefins with aliphatic polycarboxylic acids. The importance of the structure of the segments in positions between the cross-links is shown by the specific resin/hardener compositions. The influence of the network structure on the physical properties of the cured specimen is demonstrated by the degree of curing, cross-linking density, structural 9symmetry of the agents used, the molecular orientation and crystallization. (Author)