The specification discloses a method for making DCPD based resins that have relatively narrow molecular weight distributions. The method comprises thermally polymerizing dicyclopentadiene monomer in the presence of one or more strong acids, preferably with an olefinic modifier, to provide a dicyclopentadiene oligomer. Optionally, an organic sulfur species can also be used to further effect molecular weight control. For end-use performance in inks, adhesives, coatings and other related areas, the invention provides dicyclopentadiene oligomer resins having weight average molecular weights less than 1000 and relatively narrow molecular weight distributions, as measured by a polydispersity index, of less than about 2.3. Among the strong acids that are effective for controlling molecular weight, hypophosphorous acid is preferred because it gives light colored resins.
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