LONGEST RELAXATION-TIME OF LINEAR POLYBUTADIENE CHAINS TRAPPED IN RUBBER NETWORKS

We have used dynamic-mechanical measurements to probe the long-time dy namics of linear, almost monodisperse polybutadiene chains in two medi a: a) their own melts and b) as trapped in our recently prepared elast omeric networks. The results are compared with the classical reptation -in-a-tube model of de Gennes and Doi and Edwards. Within experimental accuracy, the obtained experimental scaling of the longest relaxation time tau(L) relative to the chain mass M (up to 9.10(5) g/mol) is the same in both media: tau(M) similar to M-x with x = 3.33 +/- 0.10 as a gainst x = 3 predicted by the ''pure'' reptation-in-a-tube model. Howe ver, the network data are well described in the range of molar masses 3.4.10(4)-5.5.10(5) g/mol, after correcting the reptation model for ch ain-end effects (in the form of contour length fluctuations). The tau( L) for the chains trapped in a network were found to be 1.9-3.2 times longer than the tau(L) of the respective melts. We present data on ten polybutadienes confined in two kinds of networks and covering the ran ge of weight average molar masses 3.4.10(4)-1.5.10(6) g/mol.