This work focused in its first part on the preparation and characterization of novel elastomers based on poly(tetrahydrofuran) (PTHF) networks. Elastomers were prepared by a hydrolysis-condensation reaction which has been followed up by FTIR spectroscopic techniques. The elastomers thus obtained were studied with regard to their equilibrium swelling in toluene at 25 °C, and their stress-strain isotherms in elongation. For some of the samples, high elongations seemed to bring about highly desirable strain-induced crystallization, as evidenced by upturns in the modulus. Swelling of these samples with increasing amounts of the non-volatile diluent dibutyl phthalate caused the upturns to gradually disappear.
The second part of this work was focused on diversifying the newly developed sound wave propagation technique to characterize elastomeric polymer networks. The technique was applied to characterize polybutadiene (PBD) networks. The speed of wave propagation in PBD networks was found to be strongly dependent on the network structural parameters such as average molecular weight of chain between crosslinks and entanglement molecular weight. Also, for the swollen networks, pulse speeds decreased with increase in degree of swelling. Upturns due to strain-induced crystallization at higher elongations were clearly evidenced in the pulse speeds.
The third part of this work presented improvements in the mechanical properties of thermoplastic biodegradable poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (Nodax™) using a pre-orientation technique. This simple approach involved heating the polymer film to a temperature above its glass transition temperature, stretching it to the desired extension (%), and then quenching it to room temperature while in the stretched state. As expected, pre-orientation resulted in substantial improvements in the mechanical properties of the films. The pre-oriented films had higher values of the modulus, toughness, yield stress, and tensile strength. Attributing these changes in mechanical properties to changes in crystallinity was supported by x-ray diffraction measurements.
The fourth part focused on the preparation and characterization of Nodax™/clay nanocomposites which were prepared by exfoliation-adsorption technique using chloroform as a solvent. X-ray diffraction measurements showed a transition in the nanocomposite structure from exfoliated to intercalated depending on organoclay content. Improved thermal stability and increased modulus were observed for the nanocomposites by increase in clay content.