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Microstructure and deformation mechanism of thermoplastic elastomers
Abstract
Molecular simulation technique together with spectroscopic methods were utilized to study the phase separation behavior of thermoplastic elastomers. Several kinds of systems were investigated, which included diacetylene-containing polyurethane elastomers, polyurethane elastomers with monodisperse hard segments, and a bio-degradable polyester elastomer. For the semi-rigid segmented polyurethane elastomers, we found that the chain rigidity of hard segment is the dominating factor responsible for their phase separation behavior. Chemical immiscibility, crystallization, and presence of hydrogen bonding are not necessary to drive phase separation even though they can promote it. The phase diagrams for semi-rigid polyurethane elastomers associated with different lengths in hard/soft segments were explicitly calculated using molecular simulation technique based on rod-coil model. It was found that longer hard segment or shorter soft segments have higher degree of phase separation than their counterparts. This result was verified by vibrational spectroscopy. It was also shown that DSC is not appropriate to evaluate the phase composition of polyurethane elastomers. The phase separation kinetics and the ultimate degree of phase separation for ultra-thin films of polyurethane elastomers are different from their bulk forms. Hard segments will also show preferential orientation onto the substrate surface. These are the direct consequence of hard segment chain rigidity effect. All the experimental results were successfully reproduced by Monte Carlo simulation based on rod-coil model. Finally, the phase transformation process and mechanical deformation process of a bio-degradable thermoplastic elastomer, PHO, was investigated by FT-Raman spectroscopy and normal coordinate analysis. The long side-chains of PHO will form more extended conformations when PHO undergoes crystallization. It was also found that the strain-induced crystallization and crystalline break-up are not significant for deformed sample. We proposed that the high permanent tensile set associated with PHO comes from the amorphous part rather than from the crystalline part of the system.
Subject Area
Polymers|Materials science|Plastics
Recommended Citation
Tao, Hun-Jan, "Microstructure and deformation mechanism of thermoplastic elastomers" (1994). Doctoral Dissertations Available from Proquest. AAI9434538.
https://scholarworks.umass.edu/dissertations/AAI9434538