How Does Microstructural Design Affect the Dynamics and Rheology of Segmented Polyurethanes?

Abstract

To molecularly investigate the role of the microstructure in controlling the dynamics of segmented polyurethanes (PUs), a series of them were systematically designed, synthesized, and experimentally scrutinized. Broadband dielectric spectroscopy and rheometry along with small-angle X-ray scattering and differential scanning calorimetry were applied to provide insights into molecular origins, particularly the role of transitional friction coefficients (ζ), affecting dynamics and rheology of the various microstructures of PUs. In this way, first, the effective ζs of model PUs were extracted from their rheological data using the Bueche−Ferry procedure. Second, the experienced ζ by the hard and soft segments (SS and HS) in pure components and resultant PUs were calculated using BDS data and were applied in a Rouse model based methodology to estimate the effective ζ. Finally, the obtained effective ζ from rheometry (ζ eff ) and BDS (ζ eff Rouse ) were compared at the same temperatures. For highly microphase-mixed system with liquid-like terminal behavior, ζ eff Rouse was consistent with ζ eff . For microphase-separated PUs with their nonterminal behavior, however, a fairly large difference between ζ eff and ζ eff Rouse was found. A universal curve was also prepared to illustrate the relationship between the dynamics and microstructural features of model PUs. According to these results and the SAXS data analyses, the frictional forces acting at the interfaces between SS-rich and HS-rich phases were suggested as a main origin for the deviation from terminal Rouse-like dynamics in the microphase-separated PUs, while bare friction coefficients in their pure components play an insignificant role in the dynamics of these systems.

Recent advances on the structure–properties relationship of multiblock copolymers

“…On top of this, the emergence of the normal mode (), arising from long PPG SSs diffusion is another proof of the growing phases incompatibility. By combining these results with DSC, SAXS and rheology experiments in two papers, 40,41 Heydarnezhad et al provide a deep understanding of the structure–properties of their amorphous TPUs and corresponding nanocomposites that one could be very much tempted to reproduce from other MBCs. The task seems, however, more intricate for semicrystalline MBCs because of the lack of mobility of the hard phase.…”

“…[33][34][35][36] In this case, the word "ordered" is sometimes used to substitute "crystalline", 37 revealing the uncertainty regarding the molecular arrangement of these complex molecules. [38][39][40][41] Lastly, polystyrene (PS) forming amorphous spherical domains in soft PB or PI is used for several decades, [2][3][4][5][6][7][8] and until recently, in association with soft poly(phenylene sulfide sulfone). 42 Note that beyond their chemical nature, their length and their number density, the HSs polymolecularity, their position in the chain and the architecture of the molecule (e.g., comb, stars …) strongly impact the phase diagram of MBCs.…”

“…Besides, thermoplastic polyurethanes (TPUs), based on diisocyanate HSs, are appreciated for their great chemical tunability, involving either crystalline or amorphous hard domains 33–36 . In this case, the word “ordered” is sometimes used to substitute “crystalline”, 37 revealing the uncertainty regarding the molecular arrangement of these complex molecules 38–41 . Lastly, polystyrene (PS) forming amorphous spherical domains in soft PB or PI is used for several decades, 2–8 and until recently, in association with soft poly(phenylene sulfide sulfone) 42 .…”

Bio-based Thermoplastic Polyhydroxyurethanes Synthesized from the Terpolymerization of a Dicarbonate and Two Diamines: Design, Rheology, and Application in Melt Blending

“…However, blending more than one diamine draws a question about the nanophase separation and the rheological behavior of the final TPHUs. Like conventional thermoplastic polyurethanes (TPUs), the reaction between the hard segments (dicarbonates) and the soft segments (diamines) produces segmented di/triblock copolymer TPHUs whose microstructure and rheology might deviate from those of standard homopolymers. − Beniah et al and Leitsch et al explored in depth the formation of nanophase separation in their segmented PHUs, notably in those prepared from poly­(tetramethylene oxide)-based diamines. In their studies, the authors investigated the effects that the choice of the dicarbonates, diamines, and chain extenders as well as the functionalization of the hydroxyl groups has on tuning the nanophase separations of their TPHUs. − Nevertheless, there have been limited findings on the rheological behavior of such systems and their compliance to previously established models used for conventional polymers.…”

Interplay of Structural Factors in Formation of Microphase-Separated or Microphase-Mixed Structures of Polyurethanes Revealed by Solid-State NMR and Dielectric Spectroscopy

“…All these parameters are connected to molecular mobility, which determines a number of polymer properties, including mechanical and thermoplastic characteristics. With so many variables to consider, investigation of the morphological behavior of PUs and interpretation of their structure-morphology-property behavior has been a very active but also a very challenging field of research [8].…”