-The dynamics of polymer melts is well reflected in the complex shear compliance J*(o,T,M) measured in wide ranges of frequency and temperature and f o r various molecular weights. In the frame of the meander model all typical features of J * ( U ,T,M) are quantitatively described:(1) J&N is due to intra-meander shear, and decreases by incorporating pairs of chain ends within the superstructure folds, i.e. with decreasing M. (2) This shear motion is guaranteed by a certain amount of edge-dislocations (with Burgers vector b equal to the chain distance d -for some polymers equal to d/2). The glass relaxation and its activation diagram are understood by asking f o r the probability for just this amount of dislocation segments to be present. The dielectric relaxation strengths and those of the thermal properties support the chosen segment lengths. Neglecting flow,the stress-strain curves of uncrosslinked high molecular weight polymer melts can be derived by taking into account intra-and inter-meander shear deformation. INTRODUCTIONIn this paper experimental data shall be summarized which characterize the two main relaxations in uncrosslinked amorphous polymers, the glass process and the viscoelastic flow relaxation. These data (among others) should be explained by any molecular model of the levels of order in amorphous polymers to establish its availability for an understanding of more complex macroscopic properties. Here a quantitative interpretation will be given in the frame of the meander model, the suppositions and derivation of which are discussed elsewhere ( 1 , Z ) . The main topic will be the linear viscoelastic behavior in shear of polymer melts, which is best represented by the complex shear compliance J* (w,T,M) in the range between the glassy state (higho or low T) and the viscous flow region ( l o w w or high T). In fig. 1 -3

Mechanical relaxation processes in polymer melts and networks are discussed. This is performed by decomposing master curves of the dynamic shear compliance into i) glass relaxation with its plateau compliance JeN; ii) shearband process with its relaxation strength AJB, which is reciprocal to the total crosslink density pc; and iii) flow relaxation AJF and viscous flow (for uncrosslinked melts only). Plateau compliance JeN is exponentially reduced only by effective crosslinks (pc ~-pd30). This behavior is understood on the level of a meander superstructure, which includes shearbands.The observed saturation inleN at higher dicumylperoxide (DCUP) crosslinking-which doesn't appear with radiation -can be explained by the lack of chemically induced effective crosslinks across the interfaces among meander cubes. This lack may be a consequence of DCUP molecules concentrating at the interfaces and thereby preventing the contact and radical recombination between chains at adjacent meander faces.Crosslink densities Pc (per monomer), determined from the reduction of shearb and relaxation strength, vary linearly with the crosslinking agent and read: pc ~ 2,4-10 -z Dose/MGy and Pc ~ 0.97 9 10 -z DCUP/phr for radiation and DCUP crosslinking, respectively. This implies, e. g., that a dose of 0.4 MGy (40 Mrad) is equivalent to 1 part DCUP phr in a crosslinking polyisoprene. From activation-curve analysis it follows that 3 rid stays constant, and esr (flee energy of formation of a segment-dislocation) and Qr -Qyo (activation energy for segmental jumps) vary with the square of pc, as does the glass temperatur Tg -Tgo from DSC measurements.

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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