High-density polydicyclopentadiene

A method comprising contacting a membrane with a feed solution comprising a) a first component having a molecular weight in the range of from about 100 g mol−1 to about 600 g mol−1 and a critical area of less than about 0.40 nm2 and b) a second component having a molecular weight in the range of from about 100 to about 600 grams g mol−1 and a critical area of greater than about 0.50 nm2 so that the feed solution is fractionated into a permeate comprising the first component and a retentate enriched in the second component, wherein the membrane comprises a highly cross-linked polydicyclopentadiene matrix and wherein the critical area of the first component is the lowest rectangular cross-sectional area of the first component in its energy minimized conformation and the critical area of the second component is the lowest rectangular cross-sectional area of the second component in its energy minimized conformation.