The double bonds of the rosin acid can be reacted to form rosin dimer as shown in Figure 1. While it is theoretically possible to continue this reaction to form a rosin polymer, in practice this does not occur due to the steric hindrance of the bulky rosin acid molecule. Once the dimer is formed it is not possible to bring another rosin molecule into close enough proximity for a reaction to occur. The effect of dimerization on rosin increases its molecular weight and softening point and improves stability since the number of double bonds in the rosin is decreased. The reaction is controllable so varying levels of dimerization are possible.
Figure 1: The Dimerization of Rosin Resins
Poly-Pale™ partially dimerized rosin is the partially dimerized rosin product offered by Eastman Chemical Company.
Dymerex™ polymerized rosin is the most completely dimerized rosin available from Eastman. Since it is not possible to produce a completely dimerized rosin resin these products will contain a mixture of rosin acid and rosin dimer. The dimerization process does not affect the carboxylic acid groups of the rosin molecule so it is possible to esterify rosin dimer to produce secondary derivatives. The full line of dimerized rosin resins available can be found in publication
Eastman Rosin Products for Adhesives and Sealants. The dimerized rosin products are made in China and distributed globally.