Effect of long-term and short-term dynamic mechanical evaluation of networks based on urethane and soybean oil

Abstract

The intermixing between urethane acrylate (UA) prepolymer and acrylated epoxidized soybean oil (AESO) by thermal polymerization results in a product with promising properties for biomedical application. The results of dynamic mechanical analysis (DMA) performed on the polymerized UA, in a limited range of frequencies (0.5-10 Hz), have raised questions related to the origin of relaxations. Whether a molecular motion can be associated with a relaxation process was ascertained by performing experiments in a much larger frequency range, in a step-scan DMA experiment. The particularities of this experiment made possible to evidence unequivocally the α-relaxations for the urethane domains, organized in a hydrogen bond physical network, and to register the transformations associated with the breaking of hydrogen bonds. Incorporation of AESO has gradually loosened the physical network and transformed it into a mixed urethane-AESO chemical network. The properties of urethane-AESO networks are ruled by the double function of AESO: plasticizer and crosslinker. The evolution of secondary relaxations reflected also the changes that occur in the urethane-AESO samples. During the step-scan procedure supplementary changes were induced in the samples with high AESO content, at high temperature. The morphology of the networks was investigated by electronic microscopy studies.