Preparation and cure behavior of organoclay-modified allyl-functional benzoxazine resin and the properties of their nanocomposites

A new type of polybenzoxazine-clay nanocomposites were prepared by the in-situ polymerization of allyl functional benzoxazine monomer, bis(3-allyl-3,4-dihydro-2H-1,3-benzoxazinyl)isopropane (B-ala), in the presence of two different types of organoclay, allyldi-methylstearyl-ammonium-montmorillonite and propyldi-methyl-stearylammonium-montmorillonite. The organo clays were mixed with molten B-ala, followed by pouring into glass mold and then gradual curing up to 250 degrees C. DSC and IR were used to follow the cure behavior of B-ala in the presence of organoclay, indicating that organoclays catalyzed the ring opening of cyclic benzoxazine structure. The XRD of the nanocomposites showed featureless patterns, suggesting the exfoliation of the organoclay into the matrix. The visco-elastic properties of the hybrids showed that the glass transition temperatures (T-g) of the nanocomposites shifted to lower temperature in the presence of small amount of organoclay, but T-g started to increase with the increase of the organoclay content. This result suggests that, in the presence of organoclay, the curing reaction of ally and benzoxazine occurred in a different way, resulting in a different network structure. However, the presence of dispersed layered silicates into the matrix enhanced the thermal stability over the neat thermoset resin.