Polymers are studied in the fields of biophysics and macromolecular science, and polymer science (which includes polymer chemistry and polymer physics). Branched Polymer are those polymers in which one or more of the side chains are different, structurally or configurationally, from the main chain. In polymer chemistry, branching occurs by the replacement of a substituent. An elastomer is a polymer with viscoelasticity (colloquially "elasticity"), generally having low Young's modulus and high failure strain compared with other materials. The study of deformations in polymeric networks from the simplest models the phantom Gaussian network. The first theoretical molecular approach to the theory of rubber elasticity was done by Kuhn in late thirties.