Rosin resin is constituted by rosin acids, in particular, abietic acid, which is an inexpensive substance. This paper concerns the study of the molecular interactions between a bifunctional monomer of abietic acid with isocyanate to form polyurethane. Polyurethane is a varnish that can be applied to any timber surface protecting it from chemical and environmental factors. Furthermore, the polar groups (OH´s) of the diol have a direction along the molecular axis thus, increasing their intermolecular interactions with the isocyanate groups. The varnish named as (PAR), was synthesized in the laboratory and applied to a timber surface whereby its functionality was evaluated. Morphological and spectroscopic studies were carried out on the diol obtained and the polyurethane. Likewise, we behaved several of physical and chemical analyses of vanish. The comparative SEM showed a homogeneous phase on the PAR surface and FTIR between the diphenylmethane, 4-4, diisocyanate (MDI) and the varnish from hydroxylated rosin resin (HAA) showed that the reaction was carried out in its entirety, exhausting the limiting reagent (MDI). The obtained varnish which was labelled as PAR has very suitable characteristics for indoor use. It has a transparent and bright appearance, a solids percentage of 44-45%, a drying time for application between layers and layers of 15-20 minutes.