H-2 nuclear magnetic resonance (NMR) and small angle neutron scattering (SANS) data are reported for deuterated guest chains of polydiethysiloxane (PDES) in end-linked PDES networks as a function of the molecular weight of guest chains relative to that of the network elastic chains. We exploit the ability of PDES networks to form a strain-induced mesophase to demonstrate the tendency of longer guest chains to phase separate or partition selectively to the amorphous phase and the tendency of smaller guest chains to remain distributed between the mesophase and the amorphous phase. The segmental orientation of the guest chains measured via H-2 NMR peak splitting can be interpreted in terms of an enthalpic orientational coupling of the chain segments in the amorphous state. SANS results show that the radius of gyration of guest chains in the unstretched networks and in the networks stretched below the mesomorphic transition remains essentially unchanged from that in the melt state. The scattering intensity from SANS patterns for networks with guest chains of any size has a peak in the direction parallel to the stretch direction that reflects the domain spacing of the lamellae in the mesophase.