The cumulative effects of molecular weight and concentration on the structural transitions in the electrospun polymer have been studied. Experiments have been conducted with water as the solvent for molecular weights of polyvinylalcohol (PVA) ranging from 9500 g/mol to 155,000 g/mol. The structural regimes for beads, beaded fibers, complete fibers and flat ribbons have been mapped. The development of a stable fiber structure generally corresponds to the onset of significant molecular entanglements. (c) 2006 Elsevier B.V. All rights reserved.