Definite Indefiniteness of 'Molecular Weight' as a Claim Term for Polymer-Related Patents

The molecular weight of a polymer is not just a number for a single molecule. In fact, molecular weight measurement is based on a large volume of molecules of the same polymer. Due to the non-uniformity of molecular weights, there are several methods to measure an “average molecular weight” of a polymer. Unfortunately, the Federal Circuit in Teva Pharms. USA, Inc. v. Sandoz, Inc., 789 F.3d 1335 (Fed. Cir. 2015), held that the term “molecular weight” in several polymer claims was indefinite, because the term could mean either peak average molecular weight, number average molecular weight, or weight average molecular weight. This paper analyzes the claim construction and indefiniteness determination in Teva to illustrate the flaws of the patentee's specification. This paper also proposes practical solutions for patent drafting to avoid indefiniteness issues