New polymeric materials have been prepared from the cationic copolymerization of fish oil ethyl ester (NFO), conjugated fish oil ethyl ester (CFO) or triglyceride fish oil (TFO) with styrene and divinylbenzene initiated by boron trifluoride diethyl etherate (BF3. OEt2). These materials are typical thermosetting polymers with crosslink densities ranging from 1.1 X 10(2) to 2.5 X 10(3) mol/m(3). The thermogravimetric analysis of the new fish oil polymers exhibits three distinct decomposition stages at 200-340, 340-500 and > 500 degreesC, respectively, with the maximum weight loss rate at approximately 450 degreesC. Single glass-transition temperatures of T-g = 30-109 degreesC have been obtained for the fish oil polymers. As expected, these new polymeric materials exhibit tensile stress-strain behavior ranging from soft rubbers through ductile to relatively brittle plastics. The Young's modulus (E) of these materials varies from 2 to 870 MPa, the ultimate tensile strength (Ob) varies from 0.4 to 42.6 MPa, and the percent elongation at break (Eb) varies from 2 to 160%. The failure topography indicates typical fracture mechanisms of rigid thermosets, and the unique fibrillation on the fracture surface gives rise to relatively high mechanical properties for the corresponding NFO polymer. The new fish oil polymers not only exhibit thermophysical and mechanical properties comparable to petroleum-based rubbery materials and conventional plastics, but also possess more valuable properties, such as good damping and shape memory behavior, which most petroleum-based polymers do not possess, suggesting numerous, more promising applications of these novel fish oil-based polymeric materials.