Network structure and properties of dimethacrylate-styrene matrix materials

One of the major classes of polymer matrix resins under consideration for structural composite applications in the infrastructure and construction industries is the so-called "vinyl esters." These are comprised of low molecular weight poly(hydroxyether) oligomers with methacrylate endgroups diluted with styrene monomer. The methacrylate oligomeric endgroups co-cure with the styrene in free radical copolymerization to yield thermoset networks. Selected properties of such resins and resultant networks where the molecular weights of the poly(hydroxyether) oligomers have been varied from 700 to 1200 g/mole and the concentration of styrene has been systematically changed are presented. In general, both the glass transition temperatures and fracture toughness of the fully cured networks increased as the styrene was decreased in each oligomer series with different molecular weights. As expected, the volume contraction upon cure also decreased significantly as styrene was decreased, and thus residual cure stresses may be reduced in fiber reinforced composites. The resistance to crack propagation was significantly improved for networks prepared with the 1200 M-n dimethacrylate oligomer relative to those from the 700 g/mole material. Crosslink densities were estimated from measurements of the rubbery moduli at T-g + 40 degrees C and relationships between network density, chemical composition and properties are discussed.