Fiber formation by electrospinning is investigated for polymer solutions capable of physical gelation. It is shown that close to the gelation threshold, the combination of thermoreversible junctions and chain entanglements help to stabilize the liquid jet and overcome capillary forces thus giving micro/nano fibers. The effect of cooling time and dissolution temperature besides polymer concentration and molecular weight is clearly demonstrated for polyvinyl alcohol/water and polyvinyl chloride/THF solutions. Finally, the relationship between solvent quality, chain entanglements and poly(vinyl chloride) fiber formation is unequivocally illustrated. (c) 2005 Elsevier Ltd. All rights reserved.