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The present research was carried out in two stages. First, various nanoparticles (Closite30B and multiwalled carbon nanotubes [MWCNTs]) for reinforcement of the polymer matrix were prepared and characterized. Samples were prepared with a melt mixing technique. In the next step, the kinetics of phase separation of thermoplastic polyurethane with nanoparticle (Closite30B, MWCNTs) and preshear were investigated by linear viscoelastic experiments, including frequency sweep and time sweep tests, which were performed on TPU/Closite30B/MWCNT samples varying in nanoparticle content at rheological measurements. The kinetics of phase separation at high preshear and a lower percentage of nanoparticles increased, while they showed a decrease in higher compositions. The nucleation effect of nanoparticles and the effect of preshear with the orientation of the hard segment increases the kinetics of phase separation of the soft and hard segments. The differential scanning calorimetry (DSC) showed that multiple endothermic peaks of thermoplastic polyurethane were affected in the presence of nanoparticles. Dynamic mechanical tests showed that Closite30B has greater affinity with the soft segment and MWCNTs with the hard segment, according to the DSC and rheological experiments. Finally, it was observed that the shear flow and nanoparticles can accelerate phase separation kinetics, but the effect of preshear on the kinetics of phase separation was reduced in the presence of a strong nucleating agent like MWCNTs. POLYM. COMPOS., 39:4551–4559, 2018. © 2017 Society of Plastics Engineers

Polyurethanes (PUs) microstructure and characteristics is strongly affected by microphase separation that arises from the thermodynamic immiscibility between the hard and soft segments. The extent of phase separation as well as the morphology and size of the separated phase governs their mechanical, electrical, thermal, and functional properties. This review: (1) provides an insight into how phase separation affects PU properties, (2) explains methods used to study PU phase separation. We review approaches from the simplest one, that is, the transparency measurement, to the more advanced methods including the spectroscopic techniques (infrared, nuclear magnetic resonance spectroscopies and X-ray scattering), rheological instruments ( rheometrics mechanical spectrometer), and thermal analyses (differential scanning calorimetry). We also discuss the theoretical calculations and the molecular modeling used to study PU phase separation.

Thermoplastic polyurethane consists of hard and soft segments. The difference in glass transition temperature and thermodynamic incompatibility of these segments results in phase separation and shape memory behavior. In this study, the effect of molecular weight of polyol and the amount of nanoparticles on the phase separation and shape memory behavior of polyurethane nanocomposites were studied. Polyurethane was synthesized using poly(tetramethylene glycol) with molecular weights of 1000 and 2000 g/mol, hexamethylene diisocyanate, and 1,4‐butanediol by step polymerization. The nanocomposites were synthesized through in situ method containing 1 and 2 wt% of nanoparticle. Phase separation and shape memory behaviors were studied using attenuated total reflectance‐Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical thermal analysis, and atomic force microscopy analysis. The results indicated that higher molecular weight polyol with molecular weight of 2000 g mol−1 shows higher phase separation than the lower molecular weight sample. Also, the addition of nanoparticles results in an increased phase separation due to the halloysite nanotubes tendency to the hard segment. The shape fixity ratio (Rf) and shape recovery ratio (Rr) were in the range of 90% to 100% in all of the synthesized samples. By increasing the nanoparticles content, the shape fixity and shape recovery parameters were increased and decreased, respectively. The study of shape memory behavior also showed that the higher the polyol molecular weight, the better the nanocomposite shape memory behavior.