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Chieh, Kuo Ming
There are a number of studies that have correlated the significant impact of hard segment chain-length with the mechanical performance of polyurethane-urea. In the meantime, the same effect also has been implicated in the phase segregation phenomenon of PU. In more recent studies, introduction of multiple hydrogen-bonding functional groups at the terminals of molecules has been shown to the formation of supra-polymers of enhanced mechanical properties. This supra-molecular synthetic approach was identified to be one of the approaches in making thermal reversible polymers. Since there are few cases in the literature showing the preparation of hard-segment group with well-defined structures, this study has been carried out to synthesize those molecules in an effort to make a series of new thermal reversible PU polymers with possible phase-segregation phenomenon. We have utilized a MDI based derivative with two functional groups of different reactivity as our key building block. This intermediate possesses a highly reactive isocyanate group in one side of the molecule and an azetindine-2,4-dione in the other. This allows us to carry out the sequential step-wise additions of selective substractes to the molecule in manners similar to “Cascade”synthesis. Three generations of urea-malonic derivertives has been prepared as our hard-segment compounds. These derivertives also have been attached to the both ends of PTMEG based soft segment PU prepolymers in formation of linear tri-block type supra-polymers. The capability of controlling the chain-length of hard segments has been achieved in this work. However the purity of hard-segment composition appears to decrease with increasing generation. After PU triblocked polymer were prepared with these hard segments, the results showed that the thermal stabilities and TgH were found to increase with increasing of the chain-length. On measurement of polymer's physical properties, there is also a strong influence of the chain-length of hard segments. Especially thermal properties, mechanical properties and the degree of segregation all are remarkably enhance with increasing chain length. Finally, the measurements from variable temperature IR and DSC between 30℃-200℃ the exsiting of revealed that the thermal reversibility due to the formation and destruction of hydrogen-bondings between the hard-segment chains.
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