Microstructural Organization of Three-Phase Polydimethylsiloxane-Based Segmented Polyurethanes

Abstract

Microphase separation is investigated for segmented polyurethane copolymers synthesized from 4,4′-methylenediphenyl diisocyanate and 1,4-butanediol as the hard segments and poly(hexamethylene oxide diol) and hydroxyl-terminated polydimethylsiloxane as soft segments. The neat PDMS-based diol exhibits two segmental relaxations corresponding to the principal repeating unit, Si(CH 3 ) 2 O, and to the hydroxyl end-group segments. When incorporated in the polyurethanes, the siloxane units form their own phase, while the end-group segments are mixed with the second macrodiol and some short hard segment sequences. This is demonstrated by the results of dynamic mechanical analysis and wide-angle X-ray diffraction experiments. The microdomain morphology was characterized principally by small-angle X-ray scattering, and the scattering data were analyzed with a pseudotwo-phase model as well as a modified three-phase core-shell model.

Microstructure-Property Relationship in Self-Crosslinked Non-Derivative Acetic Acid Lignin-Containing Polyurethane Membranes

“…There is a reduction in the storage modulus for LPUT3 after the α transition. For copolymers with the same soft segment composition, the storage modulus is strongly dependent on the hard segment [44]. This above results further supported the conclusion that over-crosslinking occurred for LPUT3 due to the fact that TMP content is too high, resulting in the decrease in strength properties.…”

The effect of some disiloxane chain extenders on the thermal and mechanical properties of cross-linked poly(siloxane-urethane)s

“…PSiU and silicone-urea segmented copolymers were investigated by numerous research groups to understand the relationship between their structure and thermal or mechanical behaviour [5][6][7][8][9][10]. It was found that the polysiloxane chains are phase separated from the hard segments (HS), consisting of mostly 4,4!-methylene diphenylene diisocyanate (MDI) and 1,4-butanediol (BDO), and also from the polyether soft segments (SS).…”

Synthesis and structure-property relationships of biodegradable polyurethanes

“…Considering the large difference in polarity between the urethane/urea hard segments and the siloxane soft segments, there are now two general approaches to the synthesis of PUS and PUUS copolymers. The first involves the presence of polyether or polyester segments as co-soft segments, in order to improve the miscibility of PDMS with the urethane or/and urea units [83][84][85]. Gunatillake et al [86,87] reported that thermoplastic PUs based on mixed PDMS and poly(hexamethylene oxide) (PHMO) as the soft segments exhibit excellent tensile strength (~ 28 MPa), elongation at break (~ 580 %) and Young's modulus (~ 33 MPa).…”

“…The second approach to the synthesis of PUS and PUUS copolymers is based on using end-functionalized PDMS as a single soft segment, whereby the terminal units attached to the ends of the siloxane oligomers act as a 'compatibilizer' between the highly polar urethane/urea hard segments and the non-polar siloxane soft segments [85]. Figure 4 shows the structures of some PDMS end-functionalized prepolymers for synthesis of segmented PUs.…”