The Microphase-separated Structure of Polyurethane Bulk and Thin Films

Abstract

The microphase-separated structure of polyurethane bulk and thin films were investigated using atomic force microscopy (AFM). The polyurethane (PUs) were synthesized with poly(oxytetramethylene) glycol (PTMG), 4,4 0 -diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BD) by a prepolymer method. The hard segment contents were 34 and 45 wt %. Polarized optical microscopy (POM) revealed that the 34 wt % PUE is homogeneous at a macroscopic level, while the 45 wt % one is macrophase-separated into two phases. One phase forms spherulites of ca. 2-5 mm in diameter. AFM observation for the 34 wt % PUE showed the microphase-separated structure, consisting of hard segment domains and a soft segment matrix. In contrast, for the 45 wt % PUE, a lot of the hard segment domains were observed in the spherulite region, indicating that spherulites include much amount of hard segment component, in contrast, outside of spherulite exhibited similar structure to that of 34 wt % one. For the PU bulk, the different microphase-separated structure in the inside and outside of spherulite was successfully observed for the first time. Also, the microphase-separated structure of PU films was investigated as a function of the film thickness. The PU films exhibited similar microphase-separated structure. For the thicker film ($200 nm), the interdomain spacing almost corresponded to bulk one. On the other hand, that for the film thickness below 7 nm dramatically decreased. This seems to be simply related to a decreasing space. We obtained the experimental data, which the phase-separated domain size of multiblock copolymer decreased with decreasing film thickness.KEY WORDS: Polyurethane / Microphase-separated Structure / Atomic Force Microscopy / Thin Film / A microphase-separated structure formed in polymers plays a quite important role for their properties, such as electric, adsorption, mechanical properties. To form the microphaseseparated structure in polymers, they need to possess block structures, which are chemically connected each other. It is well-known that the polyurethane elastomers (PUEs), which possess the multiblock structure, show the microphase-separated structure, 1-6 resulting in giving some unique properties, such as mechanical and adhesive properties [6][7][8][9][10][11][12][13][14][15][16] and biocompatibility.17

Atomic force microscopy visualization of hard segment alignment in stretched polyurethane nanofibers prepared by electrospinning

“…The high phase angle shift (light color in the phase image) represents the ‘harder’ region. Therefore, the observed phase exhibiting spherical and cylindrical features with lateral dimensions of approximately 20–30 nm is considered to be made up of the hard segments, which is consistent with previous studies [24–29]. We attribute the light areas to the hard segment domains and the dark areas to the soft domains.…”

Soft polyurethanes treated by plasma immersion ion implantation: Structural and mechanical properties of the surface‐modified layer

“…There was a relation between the wave structure and the polymer. For PU1, which was harder than PU2, the values were shifted to short λs and low A s. The untreated surface was not ideally flat and had some height oscillations, which were related to certain more or less periodic domain structures of the hard and soft regions . The corresponding PSD had weak local maxima, which were reflected in low values of A .…”

“…For example, some chemical processes initiated by PIII could have also been part of the wrinkling mechanism. The inhomogeneous domain structure of polyurethane also could have also been the reason …”

Reactive Blending of Nitrile Butadiene Rubber and In situ Synthesized Thermoplastic Polyurethane‐Urea: Novel Preparation Method and Characterization

“…The extensively investigated thermoplastic polyurethanes and their analog thermoplastic polyurethane‐urea (PUU) are important engineering material with excellent tensile, abrasion, and tear strength profile owing to their unique and diverse structural chemistry. The physical characteristics of polyurethanes arise also from their structural morphology originating from constituting components, preparation procedure, synthesis conditions, and intermolecular interactions . The superior property profile of polyurethanes has been exploited by blending with other polymers to get materials with new application possibilities.…”