Microphase Separation and Rheological Properties of Polyurethane Melts. 2. Effect of Block Incompatibility on the Microstructure

Abstract

This second paper in this series regarding the relationship between structure and viscoelastic properties of multiblock polyurethane elastomers presents the results of varying segmental incompatibility at fixed segment length and composition. Three series of amorphous polyurethanes with pendant trimethylammonium groups were synthesized. Quaternization of these groups with iodomethane caused segmental incompatibility to increase in a controlled fashion without significantly affecting the block length, composition, or molecular weight. This gave three series of polyurethanes with varying incompatibility; their microstructures have been characterized in this paper and their viscoelastic properties, in the accompanying paper. DSC experiments showed that increasing incompatibility caused microphase separation and that the polyurethanes ranged from almost homogeneous to highly microphaseseparated. All polyurethanes showed a peak in their SAXS data. The peak intensity was independent of temperature for all materials studied except one, which showed a decrease in intensity with increasing temperature. This was found to be in accordance with a mean-field-like approach to a spinodal temperature that was well below room temperature, although this polyurethane showed strong microphase separation even at room temperature. In accordance with past research on polyurethanes, there was no evidence for long-range lamellar order in the microphase-separated structure for any polyurethane studied. This paper demonstrates that in such a situation rigorously distinguishing between the homogeneous and the microphase-separated states is a difficult task, and the concept of a binodal separating these two states is highly ambiguous.

Specific interactions, structure and properties in segmented polyurethane elastomers

“…Their molecular structure is determined by the components used in the polymerization reaction and on stoichiometry, and they phase separate during the reaction forming a supermolecular structure [6][7][8][9][10]. Phase separation has been the subject of many studies [11,12].…”

Dynamics of hydrated polyurethane biomaterials: Surface microphase restructuring, protein activity and platelet adhesion

“…Microphase separation in segmented PUs is affected by block lengths, chemical composition and associated thermodynamic miscibility between hard and soft segments [7][8][9][10]. For a fixed PU co-polymer, however, the structure is also significantly influenced by the environmental conditions during their application.…”

Miscibility and properties of semi‐interpenetrating polymer networks based on polyurethane and nitroguar gum

“…The concentration fluctuation of the PU molecular chain and the restriction of PU molecular motion due to the interaction between two polymers were responsible for the obvious microphase separation between the soft and hard segments of PU. 32 Figure 4 SEM images of surface sections of the PU, PUNG films, and NGG.…”