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Polyureas have been widely applied in many fields, such as coatings, fibers, foams and dielectric materials. Traditionally, polyureas are prepared from isocyanates, which are highly toxic and harmful to humans and the environment. Synthesis of polyureas via non-isocyanate routes is green, environmentally friendly and sustainable. However, the application of non-isocyanate polyureas is quite restrained due to their brittleness as the result of the lack of a soft segment in their molecular blocks. To address this issue, we have prepared polyester polyureas via an isocyanate-free route and introduced polyester-based soft segments to improve their toughness and endow high impact resistance to the polyureas. In this paper, the soft segments of polyureas were synthesized by the esterification and polycondensation of dodecanedioic acid and 1,4-butanediol. Hard segments of polyureas were synthesized by melt polycondensation of urea and 1,10-diaminodecane without a catalyst or high pressure. A series of polyester polyureas were synthesized by the polycondensation of the soft and hard segments. These synthesized polyester-type polyureas exhibit excellent mechanical and thermal properties. Therefore, they have high potential to substitute traditional polyureas. [ABSTRACT FROM AUTHOR]

Developing green composite with high biomass content is one crucial way to realize the strategy of 'carbon reduction'. The type of polyurethane prepolymer and its soft segment's structure have an important influence on the structure and properties of composite materials. This work focused on preparing different kinds of wood powder-polyurethane prepolymer (WCLPU) composite with high biomass content to study the effects of the molecular weight of the soft segment of the polyurethane prepolymer (PCLPU) on the structure and properties of the composites. The results showed that the composite materials with 70 wt% wood content exhibited high strength and good bending performance. Specifically, with decreasing molecular weight of the PCLPU soft segment, the bending strength and bending modulus of the modified WCLPU composite also increased. This work has laid a foundation for studying the effects of the molecular weight of the PCLPU soft segment on the structure and properties of composite materials. [ABSTRACT FROM AUTHOR]

Developing biodegradable polyurethane (PU) materials as an alternative to non-degradable petroleum-based PU is a crucial and challenging task. This study utilized lactide as the starting material to synthesize polylactide polyols (PLA-OH). PLA-based polyurethanes (PLA-PUs) were successfully synthesized by introducing PLA-OH into the PU molecular chain. A higher content of PLA-OH in the soft segments resulted in a substantial improvement in the mechanical attributes of the PLA-PUs. This study found that the addition of PLA-OH content significantly improved the tensile stress of the PU from 5.35 MPa to 37.15 MPa and increased the maximum elongation to 820.8%. Additionally, the modulus and toughness of the resulting PLA-PU were also significantly improved with increasing PLA-OH content. Specifically, the PLA-PU with 40% PLA-OH exhibited a high modulus of 33.45 MPa and a toughness of 147.18 MJ m−3. PLA-PU films can be degraded to carbon dioxide and water after 6 months in the soil. This highlights the potential of synthesizing PLA-PU using biomass-renewable polylactide, which is important in green and sustainable chemistry.

Polyureas have been widely applied in many fields, such as coatings, fibers, foams and dielectric materials. Traditionally, polyureas are prepared from isocyanates, which are highly toxic and harmful to humans and the environment. Synthesis of polyureas via non-isocyanate routes is green, environmentally friendly and sustainable. However, the application of non-isocyanate polyureas is quite restrained due to their brittleness as the result of the lack of a soft segment in their molecular blocks. To address this issue, we have prepared polyester polyureas via an isocyanate-free route and introduced polyester-based soft segments to improve their toughness and endow high impact resistance to the polyureas. In this paper, the soft segments of polyureas were synthesized by the esterification and polycondensation of dodecanedioic acid and 1,4-butanediol. Hard segments of polyureas were synthesized by melt polycondensation of urea and 1,10-diaminodecane without a catalyst or high pressure. A series of polyester polyureas were synthesized by the polycondensation of the soft and hard segments. These synthesized polyester-type polyureas exhibit excellent mechanical and thermal properties. Therefore, they have high potential to substitute traditional polyureas.

The flexible polymers have an outstanding impact-resistant performance because of the improved stiffness upon a high speed loading. At the aspect of microstructure, the soft segments make an important contribution. In this article, molecular dynamics simulation is carried out to reveal the dynamic mechanical behavior of a mono helical soft segment. The tensile loadings at various strain rates are conducted. The stress–strain relations and strain rate dependencies of mechanical properties are derived. The evolution of potential energy with straining accompanied by the disentanglement of molecular chain is characterized. The characteristic molecular chain of dynamic mechanical response is determined. The intrinsic physical origins of straightening of characteristic molecular chain and bond angle expansion are explored. New parameters are defined to quantitatively analyze the micro mechanisms and their rate dependencies, which are linked to the dynamic mechanical properties. This work is full of interest to fill a knowledge gap of the physical origins of dynamic mechanical behavior of flexible polymers.

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. [ABSTRACT FROM AUTHOR]

Polyurethanes (PUs) have been versatilely applied in various fields because of their preferable properties with both elasticity and hardness. Due to the thermodynamic incompatibility of hard segments and soft segments, the PUs generally have the microphase-separated structures, which could dramatically affect their chemical and mechanical properties. In this review, the characterization methods of microphase-separated structures in PU polymers, such as fourier transformed infrared spectroscopy (FTIR), atomic force microscopy (AFM), differential scanning calorimetry (DSC), and small-angle X-ray scattering (SAXS) are summarized and illustrated. The relationship between microphase-separated structures and PU properties is also discussed. This review will lay the theoretical foundation for the improvement on the application performance of PUs. [ABSTRACT FROM AUTHOR]

Developing biodegradable polyurethane (PU) materials as an alternative to non-degradable petroleum-based PU is a crucial and challenging task. This study utilized lactide as the starting material to synthesize polylactide polyols (PLA-OH). PLA-based polyurethanes (PLA-PUs) were successfully synthesized by introducing PLA-OH into the PU molecular chain. A higher content of PLA-OH in the soft segments resulted in a substantial improvement in the mechanical attributes of the PLA-PUs. This study found that the addition of PLA-OH content significantly improved the tensile stress of the PU from 5.35 MPa to 37.15 MPa and increased the maximum elongation to 820.8%. Additionally, the modulus and toughness of the resulting PLA-PU were also significantly improved with increasing PLA-OH content. Specifically, the PLA-PU with 40% PLA-OH exhibited a high modulus of 33.45 MPa and a toughness of 147.18 MJ m -3 . PLA-PU films can be degraded to carbon dioxide and water after 6 months in the soil. This highlights the potential of synthesizing PLA-PU using biomass-renewable polylactide, which is important in green and sustainable chemistry.

The molecular structure of the polyurethane soft segment has significant influence on the performance of polyurethane modified asphalt (PUMA). To investigate the effect of soft segment length on the performance of PUMA, three kinds of polytetramethylene ether glycol (PTMEG) with different molar masses were selected to synthesize three polyurethane prepolymers (PUP) with various soft segment lengths. As a result, modifying asphalt with these PUPs lead to three PUMAs. Research showed that the initial decomposition temperature of the PUP rised with the increment of soft segment length and eventually above the base asphalt. The high and low temperature properties of PUMA were enhanced with increasing the soft segment length. However, the dispersion of modifier in the asphalt became worse with higher soft segment length. It should be attributed to the interaction between PUP and asphalt molecules and the crystallization of soft segments. This study provides a good reference for the selection of materials for PUMA. [ABSTRACT FROM AUTHOR]

Two well-defined comb-like polyester diols (GS) with C-18 side chains were synthesized by reacting glyceryl monostearate (GMS) with succinic anhydride. NCO-terminated polyurethane prepolymers (PUGS) with C-18 side chains in soft segment structure were synthesized from diphenylmethane diisocyanate (MDI), 1,4-butanediol (BDO) and GS. Then polyurethane hybrid materials (PUGS-Ti) were further prepared by mixing with nano-TiO2. The structures of GS and PUGS were characterized by 1H-NMR and FT-IR. The crystallization behavior, surface morphology and surface contact angle of the prepared PUGS and its hybrid material were characterized by DSC, WAXD, SEM, AFM and water contact angle measurements. The effects of alkyl side chain content and the amount of TiO2 on the surface properties of PUGS and its hybrid material were investigated. Results showed that the introduction of non-polar alkyl side chains into the polyurethane could significantly reduce the surface energy and improve the contact angles of water on the surface. In PUGS-Ti, the surface energy of the materials could be effectively adjusted to achieve superhydrophobicity of the surface by adjusting the content of soft segments (the number of alkyl side chains) and the amount of TiO2 in the structure. [ABSTRACT FROM AUTHOR]

A series of polyurethane membranes were synthesized through poly-addition polymerization for reverse osmosis application. Poly (ethylene glycol) with different molecular weights was used as a soft segment and structural and performance properties of membranes were investigated. FTIR spectra of membranes verified the presence of incorporated monomers and the development of urethane linkages. The water content and surface roughness of the membranes were increased progressively with an increase in the size of the soft segment. The surface hydrophilicity and development of porous structure of membranes increased water flux with compromised salt rejection as size of the soft segment was increased. The permeation properties of the membranes including salt rejection and water flux were recorded by a dead-end reverse osmosis unit. PU-3PEG membrane showed the highest salt rejection (88%) whereas the PU-15PEG membrane exhibited the highest water flux (20.7 L/h m2) at effective pressure of 60 bar. The gel content of PU membranes was decreased with increase in the molecular weight of soft segment (PEG). The antibacterial property of PU membranes was validated by the successful inhibition of the gram negative bacterium "Escherichia coli". These results proved to be influential in interpreting the structure–property relationship of polyurethane membranes for RO process. [ABSTRACT FROM AUTHOR]

• Stable WPUDs with variation in size of soft segment were prepared. • Tear strength of cotton fabric was improved with application of WPUDs. • WPUDs showed antimicrobial activity. • Antimicrobial effect was diminishing with increase in size of soft segment. The waterborne polyurethane dispersions (WPUDs) have substituted solvent borne systems due to strong environmental concerns. In this study, a series of WPUDs synthesized to evaluate the impact of size of soft segment (Polyethylene glycol; PEG) on their properties. The Fourier Transform Infrared spectroscopy (FTIR), dynamic light scattering, rheometer and gravimetric determination of total solid content were used to assess the physicochemical properties of dispersions. The appearance of characteristic NH and C O urethane bands in FTIR spectra demonstrated the proposed synthesis of WPUDs. An increase in the molecular weight of hydrophilic soft segment ensued a decrease in average particle size of dispersions along with a parallel increase in viscosity and total solid content of dispersions. The textile testing and SEM analyses supported the finishing of cotton fabric with slight improvement in tear strength. However, no significant correlation was observed between tear strength and size of soft segment. Furthermore, the dispersions showed antimicrobial activity against gram −ve and +ve bacteria though the effect was diminishing with increase in the molecular weight of soft segment. [ABSTRACT FROM AUTHOR]

Stimuli-responsive biocompatible polymer blends with adjustable properties are highly desirable for biomedical applications. It is crucial to meticulously consider the chemical structure and composition of each polymer to prepare a melt-miscible blend system that possesses desirable shape memory and cytocompatibility performance. Herein, we developed thermo-responsive SMPs by melt-blending Polycaprolactone (PCL) with two different Thermoplastic polyurethanes (TPU) composed of the same hard segment, but different soft segments derived from adipic acid polyester and polycaprolactone diols and the critical role of TPU chemical structure on the thermomechanical properties and biocompatibility of TPU-based SMPs were investigated and uncovered. Cyclic thermomechanical tests show that compared with adipic acid-based TPU/PCL blends, PCL diol-based TPU/PCL blends exhibit remarkable shape memory properties (R f and R r >90%) with the ability to start recovery at lower temperatures (∼45 °C), while the cytotoxicity and wettability studies implied higher biocompatibility and hydrophilicity of adipic acid-based TPU/PCL blends making them more favorable substrates for cell proliferation. [Display omitted] • The chemical structure of TPU has a significant impact on the miscibility, shape memory behavior, and cytocompatibility of TPU/PCL SMPs. • PCL diol-based SMPs exhibited lower transition temperature and higher shape fixity/recovery ratios compared to adipic acid-based blends. • The hydrophobic nature of PCL diol-based TPU/PCL had a negative impact on the proliferation of fibroblast cells on PCL-based substrates. • MTS study implied higher biocompatibility of adipic acid-based TPU/PCL blends and substrates with higher PCL content in the blend. [ABSTRACT FROM AUTHOR]

Abstract: Oligomeric bi‐soft segment isocyanate‐terminated polyurethanes (ITPUs) are semi‐finished materials crucial for the synthesis of various PU products like foams, thermoplastic parts, dispersions or elastomers. Incompatibilities and thus phase separation phenomena play an essential role in tailoring the properties of the final products. Therefore, a detailed knowledge of these phenomena is mandatory in order to design products with properties meeting the requirements of a given application. In this study the reaction‐induced phase separation during the formation of ITPUs by application of two partially miscible soft segments is presented. The physicochemical basics of this process as well as the extent of the resulting phase separation are discussed on the basis of the initial phase diagram of the reactants. Reaction monitoring by NCO content titration and UV–visible spectroscopy reveals a dependency between the onset of phase separation and conversion. It is found that an increase of the initial content of hexamethylene diisocyanate delays the onset of phase separation. Differential scanning calorimetry reveals further that the phase separation is a direct consequence of the incompatibility of the soft segments. Overall, the findings support the hypothesis that the mechanism and the extent of phase separation are closely related to the ternary phase diagram of the reactants. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]