A Fundamental Study Of The Complex Structure-property-processing Relationships In Interpenetrating Polymer Networks (IPNs)
Published 2007 · Materials Science
Experimental studies were conducted to qualitatively define the relationships between dilution, temperature, and reaction sequence on the polymerization kinetics of neat monomers, diluted monomers and during interpenetrating polymer network (IPN) formation. The system studied was a thermally initiated cationic polymerization of a difunctional epoxy and the photoinitiated free radical polymerization of a difunctional acrylate. Both reactions are autoaccelerating and quickly become diffusion controlled. The effects of increasing temperature and dilution on the acrylate polymerization rate profiles are similar, leading to reduced polymerization rate and longer polymerization times. The dilution effect on the epoxy polymerization is similar to that of the acrylate. However, unlike the acrylate reaction the epoxy polymerization rate increases strongly with temperature. The pre-existence of one polymer has a significant effect on the polymerization of the second monomer. This effect is larger for the acrylate then for the epoxy polymerization. New kinetic models are needed to capture these complex behaviors. Samples of the same model system were prepared over the range of compositions and by varying the reaction sequence for physical property and morphology studies. The materials were evaluated by attenuated total reflectance Fourier transform infrared spectroscopy, photo differential scanning calorimetry and modulated differential scanning calorimetry for conversion. Initial and final sample glass transition temperature was estimated from modulated differential scanning calorimetry. Mechanical testing and rheology tests revealed information on the strength and hardness of the materials. Morphology and phase separation was explored via optical microscopy and scanning electron microscopy. As expected, all of the physical properties were dependant on composition. Some of the material properties and the morphology were also dependent on reaction sequence. Differences in glass transition temperatures as high as 75 °C were observed at the same composition but formed by different reaction sequence. Correlations can be made between the morphology and material properties with partially phase separated samples exhibiting maximum damping. The experiments indicate that the relationships between phase morphology and physical properties of IPNs are complex and not readily predictable a priori.