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SynopsisThe polymerization of p-cresyl glycidyl ether catalyzed by imidazoles has been investigated as a model reaction for the polymerization of technical epoxy resins. The dependence of oligomer yield on time, temperature, and imidazole concentration, the distribution of the polymerization degrees, and the influence of isopropanol have been studied. The reaction rate and the average degree of polymerization are affected by the presence or absence of a secondary nitrogen on the imidazole, i.e., different results are obtained when %ethyl, Cmethyl imidazole (EMI) or 1-methyl imidazole (1-MIA) are used. 1-MIA seems to be a "precursor" of the catalyst rather than a catalyst by itself. The comparisons of CGE polymerizations catalyzed by 1-MIA in the absence and presence of isopropanol show only quantitative differences: The polymerization in the presence of isopropanol is faster, and the average degree of polymerization is shifted to higher values. The activation energies of CGE polymerizations catalyzed by different imidazoles have been determined.

Network structures and physical properties of products obtained either by crosslinking polyepoxides with polyphenols, and by dicyanodiamide or by catalytic polymerization are discussed and compared with those obtained by amine or anhydride curing. The highest crosslinking density is achieved by the polymerization of epoxy compounds. In polymerization, the glass transition temperature may rise by more than ATgv = 100 K. Amine and phenol curing result in similarly structured networks with mobile aliphatic segments and comparatively low crosslinking densities. Impact resistance based on dissipation of mechanical energy increases as network density decreases, a maximum being achieved with a medium chain length of 25 -35 atom intervals between crosslinking points. The mechanical stability of polymers is limited by the cohesive strength KF. This latter corresponds to the maximum shear strength of bonds TKF,,, which was measured within the temperature range of 77 K to 450 K, in accordance with the equation T K F , , = K F = B -C . T ; T < T gThis equation was derived from Eyring's model of viscosity, correlating B and C with activation volume, activation energy, Tg, and strain rate. B equals the cohesive strength at 0 K. It is determined by intermolecular forces but does not depend on the density of crosslinking. An increase of Tg due to crosslinks or bulky segments causes a decrease of C and therefore a reduction of the temperature dependence of KF. Hence, cohesive strength at room temperature is improved.*) Systematischer IUPAC Name: 1,3,5-Tris(2,3-epoxypropyl)-l,3,5-perhydrotriazin-2,4,6-trion.

ZUSAMMENFASSUNG :Am Beispiel des Epoxidpolyadditionssystems werden einige grundlegende Zusammenhlinge zwischen chemischer Struktur und den physikalischen Eigenschaften vernetzter Makromolekule untersucht. Es zeigt sich, dalj nicht nur die Segmente zwischen den Verzweigungsstellen, sondern auch die wahrend der Polyadditionsreaktion gebildeten Vernetzungsfragmente die Morphologie der Polymeren in charakteristischer Weise beeinflussen. So resultieren bei der Reaktion Jon Epoxidharzen mit Aminen im Gegensatz zu Anhydriden Polymere mit ausgeprligten j3-Relaxationen, die sich in erhohter Zahigkeit und Flexibilitiit sowie erhohten Glasumwandlungstemperaturen der Endprodukte auswirken. lihnliche Systeme konnen aus epoxidierten Cycloolefinen und aliphatischen Polycarbonsauren als ,,Harter" gewonnen werden.Mit spezifischen HarzlHarter-Kombinationen wird die Bedeutung der Segmentstrukturen zwischen den Vernetzungsstellen demonstriert. Einflusse des Netzwerkauf baues auf die physikalischen Eigenschaften werden anhand von Aushlirtungsgrad, Vernetzungsdichte, Symmetrie der Bausteine sowie Nah-und Fernorientierungen gezeigt. SUMMARY:With the epoxy polyaddition system some fundamental relations between chemical structure and physical properties of crosslinked materials are shown. It became evident, that the morphology of the polymers is characteristically inRuenced not only by the segments between the crosslinks but also by the crosslinking fragments formed during the polyaddition reaction. Amine cured epoxy-systerns show distinct j3-relaxations causing higher toughness and flexibility as well as higher glass transition temperatures than the anhydride cured polymers. Similar systems result by crosslinking epoxidised cycloolefines with aliphatic polycarboxylic acids. The importance of the structure of the segments in positions between the crosslinks is shown by 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, crosslinking density, structural symmetry of the agents used, the molecular orientation and cristallization.