Mechanical relaxations in a series of polyurethanes with varying hard to soft segment ratio
✍ Scribed by J. Ferguson; D.J. Hourston; R. Meredith; D. Patsavoudis
- Book ID
- 103072529
- Publisher
- Elsevier Science
- Year
- 1972
- Tongue
- English
- Weight
- 861 KB
- Volume
- 8
- Category
- Article
- ISSN
- 0014-3057
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✦ Synopsis
Abstraet--A series of nine polyurethanes with a systematically varying hard to soft segment ratio was prepared; their dynamic mechanical spectra were studied over a wide temperature range. These polyurethanes were prepared using Adiprene L-100 which contains polyether units (forming the soft segment material) and diphenylmethane-4,4'di-isocyanate which formed the bulk of the hard segments. The chain extender was 1,3-diaminopropane. The samples were studied at 2 per cent static strain and at a frequency of 110 Hz. They showed tan 8 maxima in three temperature regions, but each sample did not necessarily show all three transitions. In general, these transitions occurred at about --130 °, --20 ° and over a range from about 11 ° to over 225 °. These transitions were referred to as the a, fl and ~, transitions in order of decreasing temperature.
The transitions were interpreted in terms of molecular motion. The ~, transition was thought to arise through a Schatzki type mechanism while the fl transition for most samples represented the glass transition and was caused by miero-Brownian motion of the more flexible parts of the chain. The a transition, which only occurred when MDI was also present, exists in the 15-20 ° range for the samples with the higher soft segment concentrations; it was thought to be the result of phenyl group rotation. As the hard segment concentration was increased, spherulites were detected and the a transition shifted to considerably higher temperatures, but a shoulder remained at about 20 ° until hard segment concentration had reached a high level. The high temperature transition was the result of crystallite fusion.