Journal
MACROMOLECULES
Volume 42, Issue 6, Pages 2041-2053Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ma8022052
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Funding
- US Army [DAAD-19-02-0002]
- National Science Foundation
- National Institutes of Health/National Institute of General Medical Sciences [DMR-0225180]
- US Department of Energy, Division of Materials Sciences and Division of Chemical Sciences [DE-AC02-98CH10886]
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The phase-segregated nature of polyurethanes allows meaningful connections to be made between morphological and physical properties. We have taken advantage of this behavior by synthesizing a series of polyurethanes with varying extents of crystallinity and Studying their morphologies in both the unstrained and deformed states, going from a completely amorphous soft segment to one with similar chemistry that displays a high extent of soft domain crystallization, thus enhancing phase segregation. The presence of dispersed semicrystalline regions within the continuous soft domain has been shown to provide a reinforcing effect when compared to that of a non-crystalline soft segment polyurethane. Incorporating a semicrystalline soft segment (PEO, 1000 g/mol) has been shown to improve overall sample toughness; however, if higher molecular weight PEO soft segments are employed (4600 g/mol), extensibility and, Consequently, toughness are adversely affected due to an increased continuous domain modulus. In-situ deformation experiments demonstrate two very different deformation responses. In the copolymer-containing polyurethane (PEO-PPO-PEO, 1900 g/mol), the hard domains retain a tilted configuration up to strains of similar to 450%, with only a small fraction of the hard segments undergoing reshuffling. The PEO 1000-containing polyurethane, on the other hand, begins to demonstrate meridional scattering at strains of 200%, with it being the dominant peak by a strain of 300%. These two deformation behaviors are indicative of the two primary responses to deformation, which are shear and tensile, respectively. Frequently, a tensile mechanism points to decreased polyurethane mechanical properties, though this phenomenon is not seen in the series of interest.
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