J. Phys. II France
Volume 2, Numéro 7, July 1992
Page(s) 1453 - 1463
DOI: 10.1051/jp2:1992212
J. Phys. II France 2 (1992) 1453-1463

Critical behavior of anhydride cured epoxies

V. Trappe, W. Richtering and W. Burchard

Institute of Macromolecular Chemistry, University of Freiburg, 78000 Freiburg, Germany

(Received 17 February 1992, accepted 8 April 1992)

Critical behavior was studied with a crosslinking system obtained by living anionic polymerization, where the primary chain length was kept constant and the crosslinking density was varied. Gelation was found at a critical ratio of crosslinker per chain $X_{\rm c}=0.884\pm 0.004$. Different samples from the pre gel region were studied by dynamic and static light scattering in dilute solution and oscillatory rheology in melt. The exponents $\gamma = 1.75\pm 0.38$ and $\nu = 0.98\pm 0.19$, determined from $M_{\rm w}$ and $R_{\rm g}$ dependence on ( $X_{\rm c}-X$), are in accordance with three dimensional percolation theory. The distribution of diffusion coefficients obtained by inverse Laplace transformation of the time correlation function shows power law behavior in a limited interval, from which an exponent $\tau = 2.17\pm 0.03$ is derived. Rheological measurements show a systematic change of $G^{\prime}(\omega)$ and $G''(\omega)$ from typical liquid to the critical gel behavior, where tan  $\delta~= G''(\omega)/G^{\prime}(\omega)$ becomes frequency independent.


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