The molecular structure of thermoreversible gels made up of poly(vinyl chloride) (PVC) and chemically-modified PVCs in diethyl oxalate has been investigated by small-angle neutron scattering : The chemical modification, which chiefly takes place in the less-stereoregular sequences, consists of replacing a few-chlorine atoms by either hydrogen or benzothiolate groups. It is Shown that small modifications significantly alter the gel structure. At small q vectors the results are analyzed by considering cross-section polydispersed fibers characterized by a distribution function of the type w(r) similar to r(-1). Results at larger q vectors, which yield a q(-2) behavior, indicate that the fibers are no longer compact at short distances. This behavior is interpreted with a sheetlike structure, which is thought to arise from the formation of a polymer-solvent complex. Fiber associations, which occurs essentially through the weak links, is accounted for by an interdigitation mechanism of the sheetlike structures. All the results on the different samples are discussed In the light of the polymer-solvent complex and its sheetlike structure and the interdigitation mechanism.