Title page for ETD etd-72698-13572
|Type of Document
|Author's Email Address
||polydimethylsiloxane modification of segmented thermoplastic polyurethanes and polyureas
|McGrath, James E.
|Anderson, Mark R.
|Dillard, John G.
|McGrath, James E.
|Riffle, Judy S.
|Shultz, Allan R.
- fire resistancy
- segmented copolymer
|Date of Defense
This thesis addresses the systematic modification of poly(tetramethylene oxide)
(PTMO), polyether based segmented thermoplastic polyurethane with a secondary
aminoalkyl functional polydimethylsiloxane (PDMS), which was intended to improve the
fire resistance of polyurethane systems. The PDMS oligomer was successfully
incorporated into the polyurethane backbone via one step solution polymerization. The
effect of PDMS content on thermal stability, morphology, surface composition,
mechanical properties, and fire resistance of polyurethane was investigated. These
polymers displayed a complex two phase morphology and composition-dependant
mechanical properties. The PDMS segment microphase separated from other
polyurethane segments and varying microphase separation morphologies were observed
with differing PDMS content. Spherical dispersed complex phases and co-continuous
phases occurred when the PDMS content was 15wt% and 55wt%, respectively. Similar
thermal stability was observed for both the polyurethane control and the PDMS modified
polyurethanes, but the later displayed increased char yield in air with increased PDMS
concentration. Quantitative measurements of the fire resistance of the modified
polyurethanes by cone calorimetry showed that the peak heat release rate of the 15wt%
siloxane modified samples dropped 67wt%, compared with the polyurethane control.
However, the peak heat release rate did not further change with increasing siloxane
content. Excellent mechanical properties, in terms of tensile strength and elongation,
were found for the modified polyurethane with 15wt% of PDMS. Higher PDMS levels
did reduce tensile strength, probably because of the reduction in strain crystallizing PTMO content. The PDMS modification, which resulted in improved fire resistance and
excellent mechanical properties, is attributed to the low surface energy of the PDMS
segment that tended to migrate to the surface of the polymer. It could be oxidized into a
partially silicate-like material upon heating in air.
In addition, the syntheses of primary and secondary aminoalkyl functional PDMS
based segmented polyureas are described herein. Two-phase morphology was observed
for all the polyurea samples, even when the hard segment concentration was as low as
6wt%. All these polyureas formed clear transparent films that exhibited good mechanical
properties even with very high PDMS content, up to 94wt%. They also demonstrated
similar thermal stability, independent of the PDMS end group. However, the nature of
the end group, i.e. primary or secondary aminoalkyl, had a dramatic effect on mechanical
and morphological properties of these PDMS based polyureas, which was interpreted in
terms of the level of hydrogen bonding.
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