In the reported experiments stress relaxation in uniaxial extension and dynamic shear moduli G prime and G double prime have been studied in networks of vinyl-terminated poly(dimethyl siloxane) (PDMS) of five different molecular weights (M OVER BAR //n from 1800 to 29,200) crosslinked with cis-dichlorobis(diethyl sulfide) platinum (II) and containing 10 and 15 wt% of two samples of high-molecular-weight unattached linear hydroxyl-terminated PDMS (M OVER BAR //w 700,000 and 950,000). After multiplication by (1 minus upsilon //2**2)** minus **1G//N**0 /G//e, where upsilon //2 is the volume fraction of network G//N**0 is the plateau modulus of the uncrosslinked polymer, and G//e is the equilibrium modulus of the network containing unattached molecules, G//1(t) was compared with G//1//1(t), the relaxation modulus in the homologous environment, for each linear polymer. The relaxation was slower in the networks than in the uncrosslinked polymer by 1 to 2 orders of magnitude, and it increased gradually with increasing G//e, which is a measure of total topological obstacles represented by crosslinks plus trapped entanglements. It appears that, in these systems where the topology of the obstacles is fixed, the reputation is severely restricted or else alternative modes of configurational rearrangement which contribute to relaxation in the uncrosslinked polymer are suppressed.
|Original language||English (US)|
|Number of pages||13|
|Journal||Journal of polymer science. Part A-2, Polymer physics|
|State||Published - 1981|