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Starlike poly (oxypropylene) molecules (M = 2630 resp. 710 g/tool), each with three OH-end-groups, are crosslinked with 4,4'-diphenylmethane diisocyanate in one stoichiometric and several nonstoichiometric reactions. Dynamic mechanical (frequency 10 -4 to 102 Hz) and also some dielectric (10 -2 to 106 Hz) measurements were made on these networks in a wide temperature range. The time-temperature-superposition principle was used to obtain master curves. Two large relaxation processes were detected (separated by many decades of frequency in some samples). The high frequency process seems to correspond to the glass-rubber transition in linear polymers, the low frequency process is probably due to the relaxation of "dangling chains".

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Using the theory of branching processes, structural parameters such as the molecular weights of elastically active network chains (EANCs), including dangling chains, backbone EANCs and dangling chains of networks built up by the alternating polyaddition of a bi-and trifunctional monomer, are characterized. The theory is compared with viscoelastic data on polyurethane networks prepared from poly(oxypropylene)triols and diisocyanate at various initial ratios of functional groups; in the calculation, the distribution of functionalities of the triols used and the possible incompleteness of the reaction is taken into account. The comparison reveals that both the length of the backbone EANC and the length of dangling chains contribute to the total width of the retardation spectrum.

No abstract