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Positron annihilation lifetime spectroscopy and large molecule diffusion into a polyurethane matrix

Ward, S. A. and Pethrick, R. A. (2011) Positron annihilation lifetime spectroscopy and large molecule diffusion into a polyurethane matrix. Macromolecules, 44 (21). pp. 8479-8486. ISSN 0024-9297

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Abstract

Positron annihilation lifetime spectroscopy (PALS) measurements are reported on a three polyurethane (PU) materials created by the reaction of polymeric toluene diisocyanate with either ethylene glycol, 1,10-decanediol, or a silicone containing diol. Dynamical mechanical analysis indicated that the glass transition temperature of the PU’s were respectively 118, 95, and −40 °C. Whereas the ethylene glycol and 1,10-decanediol materials exhibited a glass–rubber transition, the silicone containing PU showed rubber characteristics over the temperature 0–180 °C. The PALS measurements on the silicone-based PU’s showed significantly larger voids dimensions than the other PU’s. Void collapse is observed to occur on the time scale of the oPs measurements. The permeation of dioctyl phthalate, 2-ethylhexylbenzyl phthalate, nonylphenol ethoxylate, isopropyl myristate, and oleic acid into a polyurethane matrix was measured gravimetrically. The silicone containing material at low temperatures exhibits relative simple permeation behavior however deviations from simple Fickian-type behavior are observed at higher temperature. Surprisingly, the ethylene glycol and 1,10-decanediol exhibited no significant absorption over a period of 5 months with the exception being nonylphenol ethoxylate. A comparison of the void sizes with the molecular dimensions for the lowest energy conformations of the permeants obtained using theoretical calculations indicate that for the silicone-based material the diffusion cross section for the permeants is larger than the available void size. The permeation process is considered to occur by a reptation type of motion of the permeants into channels created by the phase segregation of the flexible segments.