Rheological Behavior of POSS/Polyurethane−Urea Nanocomposite Films Prepared by Homogeneous Solution Polymerization in Aqueous Dispersions

Abstract

Reinforced polyurethane−urea nanocomposite with reactive polyhedral oligomeric silsesquioxanes (POSS) has been prepared via environmentally friendly aqueous dispersion with no organic solvent. Rheological behavior of this important class of materials has been investigated as a function of POSS concentration over a wide range of shear frequency and temperature (−100 to 230 °C). The functionalized diamino-POSS was reacted initially with isophorone diisocyanate (the urethane hard segments) before adding the polyester diol (the soft segments). The complete reaction of diamino-POSS with urethane segments was confirmed rheologically and morphologically (TEM). The molecular relaxations of the hard and soft segments of PU/POSS nanocomposites were investigated using the rectangular torsional mode in the glassy and rubbery states. It was found that the storage elastic modulus increased systematically only in the high-temperature range (i.e., the range of the T g of the urethane segments) while the modulus did not significantly change at low temperatures corresponding to the range of the T g of the polyester soft segments. In addition, the rheological behavior of the pure PU in the melt confirmed the existence of microphase separation of the hard and soft segments at 140 °C. The value of the microphase separation temperature (T MPS) was found to be concentration independent when the POSS concentration is ≤6 wt %. For 10 wt % POSS the T MPS shifted by 20 °C to a higher temperature. The viscoelastic material functions (G‘, G‘ ‘, and η* ) for pure PU film and samples with POSS ≤6 wt % were found to be well described by the time−temperature superposition (or WLF) principle in the low-temperature range studied (i.e., T < T MPS (140 °C)); at higher temperatures the superposition principle failed to describe the experimental data. For 10 wt % POSS film, the validity of WLF principle was extended up to 160 °C due to the shift of T MPS to higher temperature. The incorporation of POSS to the hard segments of PU produced a more homogeneous structure for the 10 wt % POSS as confirmed by TEM. In addition, the viscosity and activation energy of flow were increased dramatically by adding POSS to PU. The thermal stability of PU under a nitrogen atmosphere did not improve by adding POSS, but it improved slightly when tested in an oxygen atmosphere.

On a novel method to synthesize POSS-based hybrids: An example of the preparation of TPU based system

“…However, the presence of POSS turns out to modify the microphase morphology, as neat TPU surface shows a finer structure compare to TPU/POSS-OH(5). Indeed, the dimension of domains seems to increase in the POSS-based TPU, evidencing that the silsesquioxane is capable of modifying the polymer microphase morphology, as previously reported in the literature [41]. On the basis of the results obtained, it is possible to hypothesize that the reaction between the polymer functional groups, formed during the melt blending, and POSS functionalities follows the mechanism shown in Figure 6.…”

POSS/Polyurethane Hybrids and Nanocomposites: A Review on Preparation, Structure and Performance

“…Madboul et al 41 used rheological measurements, TEM, thermal gravity analysis (TGA) to show that the incorporation of diamino-POSS to the hard segments of PU enhanced miscibility of PU, producing a more homogeneous composite. For samples, containing POSS ≤ 6 wt.%, the microphase separation temperature remained constant at 140°C regard- less of the concentration of POSS.…”

Thermal stability and flammability of polyurethane foams chemically reinforced with POSS

“…These siliceous cages have sizes of 1-3 nm and can be considered as the smallest possible particles of silica. Reactive POSS moieties can be bonded with macromolecules during the polymerization reaction or by a reactive blending approach [19]. POSS moieties were found to strongly influence mechanical, thermal and barrier properties of polymer matrices.…”