Biobased materials developed from triglycerides contain a large variety of structures, which makes it difficult to predict their properties. In this study, we used a structure property relation to design biobased materials, both theoretically and experimentally. A general equation to predict the crosslink density in terms of the level of chemical functionalities of the triglycerides was derived and used as a design rule for high-crosslinked polymer materials. The twinkling fractal theory and the Clausius-Mossotti equation were used to guide two approaches of synthesis to improve the properties of the biobased thermosets: the biobased resin acrylated epoxidized soybean oil (AESO) was either crosslinked with divinylbenzene (DVB) or chemically modified by phthalic anhydride. The DVB-crosslinked resins had a 14-24 degrees C increase in their glass-transition temperatures (T-g's) which was dependent on the crosslink densities. T-g increased linearly as the crosslink density increased. Phthalated acrylated epoxidized soybean oil (PAESO) had an 18-30% improvement in the modulus. The dielectric constants and loss tangents of both DVB-crosslinked AESO and PAESO were lower than conventional dielectrics used for printed circuit boards (PCBs). These results suggest that the new biobased resins with lower carbon dioxide footprint are potential replacements for commercial petroleum-based dielectric materials for PCBs. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 3274-3283, 2010