Effects of nanostructure on the deformation behavior of polymeric networks

The work involves three main parts: network synthesis, apparatus development and network deformation. Reactive polytetrahydrofuran polymers and clusters were synthesized from tetrahydrofuran. The networks with unimodal, bimodal and clustered topologies in the order of increasing inhomogeneities and controlled crosslink densities were designed and synthesized by selectively endlinking telechelic polymers and reactive clusters.; A real-time simultaneous birefringence measurement and static light scattering analysis apparatus with constant temperature control was developed. The GUI was programmed via LabVIEW software to control measurement and data acquisition processes. The precision of the apparatus and the accuracy of the measurement were evaluated in accordance with ISO 5725. The apparatus was accurate, fast and convenient for real time rheo-optical studies of solid polymer materials under a wide range of deformation rates.; Stress-optical behaviors of the topologically different model networks were investigated at four temperatures. The stress optical coefficient of the networks was found independent of crosslink densities and inhomogeneities, while strain optical coefficient was dependent on them. The ultimate properties and segmental orientation of the networks increased with inhomogeneities in the order of unimodal < bimodal < clustered topologies if their crosslink densities are equal. Specific effects of dispersion in crosslink distributions were related with length and volume fraction of the chains in the bimodal networks, and size and crosslink densities of the clusters in the clustered networks. The network topologies also affect their stress induced crystallization behaviors: The true stresses at the onset of crystallization increase in the order of unimodal long chain < bimodal < clustered < unimodal middle chain topologies, with equal network crosslink densities for the latter three topologies.; In summary, the inhomogeneities in the crosslink density of the networks affect orientation of chains though strain reapportionment. Increase in dispersion of the crosslink distribution causes higher percentage of the chains to orient and to reach their finite extensibilities, and the ultimate properties of the networks are thus increased.