Degree Of Microphase Separation Research Articles

A microphase-separated structure of polystyrene-b-polyisoprene-b-polystyrene triblock copolymers prepared via shear-press and injection molding methods during uniaxial deformation

The influence of the preparation method on the initial structure and deformation behavior of polystyrene (PS) - polyisoprene (PI) - PS (SIS) triblock copolymer elastomers was investigated using small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD). Shear pressing (SP) and injection molding (IM) were used as the preparation methods. The samples exhibited a microphase-separated structure, in which the PS cylinders were packed in a hexagonal lattice for the entire sample. SP-SIS possessed a higher degree of microphase separation (DMPS) and an ordering of a microphase-separated structure (OMPSS), and lower degree of the PS cylinder orientation (DCO) than IM-SIS. Uniaxial tensile testing was performed along the parallel (//) and perpendicular (–|) directions to the PS cylinder orientation combining in situ SAXS/WAXD measurements. Young’s modulus and tensile strength of IM-SIS were lager and smaller than those of SP-SIS. A change in the PS cylinder orientation, which occurs for –| stretching, of IM-SIS occurred at larger strain than SP-SIS, indicating that the orientation of highly ordered PS cylinders are difficult to be changed due to their larger domains. It was found that the DCO relates to Young's modulus, yielding, and change in the PS cylinder orientation, while the OMPSS and DMPS relate to tensile strength.

Synthesis and characterization of linear hybrid aliphatic/aromatic copolyurea via one‐step feeding method

AbstractThe combination of aromatic and aliphatic structures can endow polyurea with distinct performance advantages. A one‐step feeding method is used to synthesize linear hybrid aliphatic/aromatic copolyureas by varying the ratio of m‐phenylenediamine (MPD) and polyoxypropylenediamine (D2000) reacting with 4,4′‐diphenylmethane diisocyanate (MDI). Real‐time Fourier‐transform infrared spectrometer monitoring reveals that D2000 exhibits higher reactivity than MPD. Consequently, in the MDI/MPD/D2000 system, D2000 initially reacts with MDI to form an isocyanate‐terminated prepolymer, which subsequently reacts with MPD. Compared with the two‐step feeding method, this approach successfully eliminates biuret formation and enhances tensile strength. Additionally, decreasing the molar ratio of D2000 to MPD (λm) reduces the size and degree of microphase separation in the polyurea by increasing the ordered hydrogen bonding and benzene conjugation, leading to an increase in tensile strength. Specifically, as λm decreases from 70 mol% to 30 mol%, the degree of microphase separation decreases from 0.47 to 0.2, causing the tensile strength to rise from 28 to 48 MPa. Further reducing λm to 30 mol% decreases the degree of microphase separation to 0.16, resulting in an increase in tensile strength to 78 MPa.

Controllable Design and Synthesis of Polyurethane Elastomers Containing Polar Dangling Chains with High Mechanical Properties and Wide Damping Temperature Range.

Vibration and noise severely affect the operation of mechanical equipment and is also detrimental to human health. Therefore, the development of high performance damping materials is crucial. However, current methods to improve damping properties often come at the expense of mechanical properties, resulting in inferior mechanical performance of materials. In order to address the issue of imbalance between damping properties and mechanical properties in polyurethane damping elastomers. In this study, polyester dangling chains containing polar groups are synthesized and introduced into polyurethane. The obtained polyurethane exhibited an effective damping temperature range of 154 °C (-54 °C to 100 °C) and a tensile strength of 15.82 MPa. Furthermore, dynamic mechanical analysis and broadband dielectric relaxation spectroscopy are combined to investigate the influence of polar dangling chains on the structure and properties of polyurethane. The degree of microphase separation increases after the introduction of polar dangling chains, indicating enhances intermolecular interaction forces, facilitating the formation of hydrogen bond between the main chain and dangling chains, thereby increasing molecular chain friction and energy dissipation. This work overcomes the challenge of balancing the damping and mechanical properties of polyurethane, providing a new strategy for designing high performance polyurethane damping elastomers.

Investigating the Effect of Chain Extender on the Phase Separation and Mechanical Properties of Polybutadiene-Based Polyurethane.

The thermodynamic incompatibility between the soft and hard segments of thermoplastic polyurethane (TPU) results in a microphase-separated behavior and excellent mechanical properties. However, the effect of the chain extender on the degree of microphase separation (DMS) and the resultant mechanical properties of TPU have not been well studied because of the complex interactions between the soft and hard segments. Herein, hydroxyl-terminated polybutadiene-based TPUs(HTPB-TPUs) without hydrogen bonding between the soft and hard segments are synthesized using hydroxyl-terminated polybutadiene, toluene diisocyanate, and four different chain extenders, and the effect of the chain extender structure on DMS is analyzed experimentally using a combination of analytical techniques. Furthermore, the solubility parameters of the soft and hard segments, glass transition temperatures, and hydrogen-bond density of the HTPB-TPUs, are computed using all-atom molecular dynamics simulations. The results clearly reveal that the chain extender significantly affects the DMS and thus the mechanical properties of HTPB-TPUs. This study paves the way for studying the relationship between the structure and properties of TPU.

Structure, morphology, and properties of aliphatic polyurethane elastomers from bio‐based 1,3‐propanediol

AbstractThe utilization of biomass resources in the production of bio‐based or bio‐recycled polyurethanes (PUs) enhances the sustainable development and eco‐friendliness of PU. Herein, a series of new bio‐based aliphatic poly(propylene dicarboxylate) diols were synthesized using bio‐based 1,3‐propanediol (bio‐PDO) and aliphatic dicarboxylic acids with different chain lengths. These bio‐based polyester diols and 1,4‐butanediol (BDO) reacted with 4,4′‐dicyclohexylmethane diisocyanate to produce aliphatic PU elastomers (PUEs). The study aimed to evaluate the impact of the structure of poly(propylene dicarboxylate) diols on the architecture, morphology, mechanical properties, and degradation of PUEs, thereby expanding the application of bio‐PDO. The results indicate a strong correlation between the degree of microphase separation, tensile properties, and degradation behavior of the synthesized PUEs and the number of methylene groups in the repeating unit of the poly(propylene dicarboxylate) diols. Notably, the PUE derived from poly(propylene pimelate) diol demonstrates the highest level of microphase separation and superior elasticity properties because of the high flexibility of the polyester. On the other hand, PUE prepared from poly(propylene succinate) diol exhibits the fastest degradation performance due to its high density of ester groups. Bio‐PDO based polyester diols show significant potential as raw materials for PUEs with biodegradable and adjustable mechanical properties.Highlights Poly(propylene dicarboxylate) diols were prepared from bio‐based 1,3‐propanediol. The poly(propylene dicarboxylate) diols based polyurethane elastomers (PUEs) have high tensile strength (>22 MPa) and elongation at break (>920%). The morphology, mechanical properties and degradation of PUEs are highly related to the structure of the poly(propylene dicarboxylate) diols. The increasing repeating unit length of the poly(propylene dicarboxylate) diols increases elastic recovery of PUEs.

Completely Methylene-Free Side Chain Enables Significant Microphase Separation at Medium IECs for Fuel-Cell Anion Exchange Membranes.

The introduction of hydrophobic side chain structures in anion exchange membranes (AEMs) to facilitate ion transport has been widely studied; however, low or moderate hydrophobic hydrocarbon and semifluorinated side chains are insufficient to induce a high degree of microphase separation. Herein, we design and prepare poly(aryl piperidinium) AEMs with completely methylene-free perfluorinated side chains, which can maximize the thermodynamic incompatibility between main- and side chains, thus enhancing microphase separation at medium ion exchange capacities (IECs). According to the molecular dynamics study, the methylene-free perfluorinated side chain leads to better hydration of cations. The hydroxide conductivity of the methylene-free perfluorinated side chain-grafted PAP-pF-1 membrane reaches 124.9 mS cm-1 at 80 °C, and the PAP-sF-1 with semifluorinated side chains and PAP-CH-1 with hydrocarbon side chains show lower conductivity (116.8 and 104.0 mS cm-1). The H2/O2 fuel cell using the PAP-pF-1 membrane demonstrates a remarkable peak power density (1651 mW cm-2 at 80 °C) and durability (greater than 300 h). This work provides a novel insight into enhancing microphase separation in AEMs; it opens up new possibilities for developing high-performance AEMs.

Acoustically transparent polybutadiene-based polyurethane encapsulants for deep-sea and transducers

Copolyether polyurethane (PUR), as a typical encapsulation material, is widely used for underwater acoustic transducers. Two novel types of polybutadiene-based PURs were prepared using a one-step method and compared with copolyether PURs. The polybutadiene-based PUR exhibited excellent mechanical properties. Epoxidized hydroxyl-terminated polybutadiene (EHTPB)–based PUR exhibited tensile strength and hardness of up to 17.3 MPa and Shore A95, respectively, which were 76.5% and 13.3% higher than those of copolyether PURs. The molecular chain of hydroxyl-terminated polybutadiene (HTPB)-based PUR exhibited good flexibility, a soft segment glass transition temperature (Tg) (approximately -52 °C), and complete microphase separation. Compared with HTPB-based PUR, EHTPB-based PUR exhibited a higher molecular chain rigidity and a lower degree of microphase separation. The insertion losses of HTPB-based PUR at 350 and 700 kHz were 69.8 dB/m and 204.6 dB/m, respectively, which were 57.4% and 47.1% lower than those of copolymer PUR. The water absorption and water vapor transmission coefficient of HTPB-based PUR were an order of magnitude lower than those of copolymer PUR. EHTPB-based and copolymer PURs exhibited similar insertion losses at 350 kHz. EHTPB-based PUR exhibited the lowest water vapor transmission coefficient of 7.2 × 10−14 g·cm/cm2·s·Pa, which was approximately 1/15th of that of copolyether PUR.

Gas transport properties of poly(ether-b-amide) segmented copolymers: The role of the degree of microphase separation in amorphous regions

Polyether-based crystalline multiblock copolymers have been employed as membrane materials for the removal of CO2 from light gases due to their excellent gas permeability and selectivity. However, the influence of the nature of the crystalline and amorphous regions on gas permeability needs to be deeply explored. In this work, the effect of the phase structure, especially the degree of microphase separation (DPS) in the amorphous regions, on the gas transport properties of poly(ether-b-amide) (PEBA) segmented copolymers has been studied. It was found that the amorphous domain consists of two partially mixed phases enriched either with poly(tetramethylene oxide) (PTMO) or with polyamide 1012 (PA1012). The effect of annealing on the microphase structure in the crystalline and amorphous regions was investigated by X-ray scattering techniques. The DPS was found to be inversely correlated with the crystallinity of the hard segments. Gas permeability measurements confirmed that for PEBA membranes with lower crystallinity, weak microphase separation favors gas permeability. All these findings provide a simple method to modulate the degree of microphase separation by varying the crystallinity of the hard segments. Additionally, this work shed light on the synergistic effects of these factors on gas permeability, providing valuable guidance to enhance the performance of gas separation membranes.

Improvement for the mechanical performance of boroxine‐based self‐healing polyurethane by quadruple hydrogen bonds

AbstractThe self‐prepared boroxine‐based polyurethane has excellent self‐healing property, but its mechanical strength is poor, so a functional monomer 5‐(2‐hydroxyethyl)‐6‐methyl‐2‐aminouracil containing UPy motif (HMA) as non‐covalent dynamic reversible bond was introduced into the polyurethane matrix to prepare HMA reinforced boroxine‐based self‐healing polyurethane (HmBPU). The results showed that when the dosage of HMA was 4 mmoL, the tensile strength of H4BPU film was the best which increased to 3.64 MPa from 2.05 MPa, while the self‐healing efficiency increased to 70.81% from 60.06%, which indicated that the introduction of HMA had positive effect to the self‐healing and mechanical strength. In addition, the recovery efficiency and mechanical strength of H4BPU still reached to 89.29% and 3.25 MPa after three cycles, which indicated that H4BPU had good recycling performance. Compared with H0BPU, the water contact angle of H4BPU increased by 16°, which indicated that the water resistance of H4BPU was improved. Atomic force microscope (AFM) images showed that the degree of microphase separation of H4BPU was reduced. It is beneficial for the mixed version of double dynamic reversible covalent bonds and non‐covalent bonds to improve the strength of self‐healing polyurethane. Meantime, it provides a reference for the balance of the mechanical strength and self‐healing performance.

Effect of fillers on the microphase separation in polyurethane composites: A review

AbstractThe microphase separation behavior of polyurethane (PU) strongly affects its mechanical, thermal, electrical, and other functional properties. Adding fillers to change the degree of microphase separation (DPS) in PU is a convenient and efficient method. Although many scholars have tried to regulate the microphase separation of PU by adding fillers, there are still many controversies about the effect. In this review, we classify commonly used fillers into three categories according to their morphology: spherical fillers, fibrous fillers, and layered fillers, and summarize their effects on the microphase separation behavior of PU. We explore the similarities and differences in the mechanisms by which different fillers affect the microphase separation of PU, and find that the polarity, morphology, size of fillers, and preparation method have a significant impact on the degree of microphase separation in PU. The impact of microphase separation on the mechanical properties of PU has also been summarized to illustrate their close relationship. We hope that these summaries will provide some guidance for the development of new high‐strength and multifunctional PU composites.Highlights Summarized recent research progress on effect of common fillers on DPS of PU. Common fillers are classified into three categories based on their morphology. Common laws of the fillers impact on the DPS are classified and discussed. The close relationship between DPS and mechanical properties is reviewed. Provided information for high‐strength and multifunctional PU development.

Quantification Characterization of Hierarchical Structure of Polyurethane by Advanced AFM and X-ray Techniques.

Polyurethane (PU) with microphase separation has garnered significant attention due to its highly designable molecular structure and a wide range of adjustable properties. However, there is currently a lack of systematic approaches for quantifying PU's microphase separation. To address this research gap, we utilized an atomic force microscopy (AFM) nanomechanical mapping technique along with Gaussian fitting to recolor and quantitatively analyze the evolution of PU's microphase separation. By varying the ratios of the chain extender to cross-linking agent, we observed the changes in the hydrogen bonding between the soft and hard segments. As the ratio of the chain extender to cross-linking agent decreases, the strength of the hydrogen bonding weakens, resulting in a reduction in the quantity and phase percentage of hard segment (HS) domains. Consequently, the degree of microphase separation between the soft and hard segments decreases, leading to specific alterations in the material's mechanical properties and dynamic viscoelasticity. To further investigate the hierarchical structure of PU, we employed various techniques, such as X-ray analysis, transmission electron microscopy (TEM), and AFM-based infrared spectroscopy (AFM-IR). Our findings reveal a spherulite pattern composed of lamellae within the HS domains, with the cross-linking density gradually increasing from the center to the periphery. Overall, our comprehensive characterization of PU provides valuable insights into its hierarchical structure and establishes a quantitative framework to explore the intricate relationship between the structure and properties.

The Influence of Soft Segment Structure on the Properties of Polyurethanes.

A series of polyurethanes (PU) were synthesised via one-step polymerisation without a chain extender, using toluene diisocyanate as well as a variety of soft segments composed of different macrodiols. Poly(D,L-lactide) (PDLLA) and polycaprolactone diol (PCL) were synthesised as a polyester type polyols to obtain soft segments. The process of varying the molar ratio of newly synthesised PDLLA in soft segments has been confirmed as a powerful tool for fine-tuning the final properties of PU. Fourier-transformed infrared spectroscopy was used for evaluation of molecular structures of synthesised PDLLA polyol and final PU. Nuclear magnetic resonance spectrometry was used to confirm the presumed structure of PU. The influence of soft segment composition on polyurethane thermal characteristics was examined using thermogravimetric analysis and differential scanning calorimetry. The composition of soft segments had little impact on the thermal stability of PU materials, which is explained by the comparable structures of both polyester polyols. Wide-angle X-ray scattering was utilised to evaluate the effect of amorphous PDLLA on the degree of crystallinity of PCL in soft PU segments. It was discovered that not only did the PDLLA ratio in the soft segment have a substantial influence on the degree of microphase separation in the soft and hard segments, but it also influenced the crystallisation behaviour of the materials. Furthermore, the restriction of crystallisation of the PCL soft segment has been verified to be dependent on the hard segment concentration and the ratio of PDLLA/PCL polyols. The sample with pure PCL as the polyol component achieved the highest degree of crystallinity (34.8%). The results demonstrated that the composition of soft segments directly affected the properties of obtained polyurethane films. These results can be utilised to easily achieve a desirable set of properties required for application in biomaterials.

Influence of microphase separation and crosslinking density on dynamic viscoelastic properties of nano‐Fe3O4 modified polyurethane

AbstractAlthough there have been some studies on the preparation and characteristics of nano‐Fe3O4‐filled polyurethane (PU) composites, research focusing on the quantitative influence of the degree of microphase separation (DPS) and the crosslinking density (CLD) on dynamic viscoelastic properties is rare. In this paper, PU composites are synthesized by incorporating nano‐Fe3O4 as fillers. The dynamic mechanical properties under alternating loads are investigated using dynamic mechanical analysis. The influences of the DPS and the CLD on the dynamic hysteresis loss are analyzed. The experimental results show that the DPS and CLD of PU nanocomposites increase and then decrease with the increase of nano‐Fe3O4 addition and reached a maximum at the addition amount of 1.0 wt%. The quantitative relationships between DPS, CLD and the dynamic hysteresis loss of PU nanocomposites at different filler ratios are obtained. With a 1.0 wt% nano‐Fe3O4 content, the strain energy density (SED) and hysteresis energy density (HED) are increased by 416% and 354%, respectively. The hysteretic loss H indexes of all composites are kept lower than that of pure PU. These characteristics make nano‐Fe3O4‐filled PU a promising material for reducing the rolling resistance and increasing the service life of fuel‐saving tire materials.

Tailored Dynamic Viscoelasticity of Polyurethanes Based on Different Diols.

The development of damping and tire materials has led to a growing need to customize the dynamic viscoelasticity of polymers. In the case of polyurethane (PU), which possesses a designable molecular structure, the desired dynamic viscoelasticity can be achieved by carefully selecting flexible soft segments and employing chain extenders with diverse chemical structures. This process involves fine-tuning the molecular structure and optimizing the degree of micro-phase separation. It is worth noting that the temperature at which the loss peak occurs increases as the soft segment structure becomes more rigid. By incorporating soft segments with varying degrees of flexibility, the loss peak temperature can be adjusted within a broad range, from -50 °C to 14 °C. Furthermore, when the molecular structure of the chain extender becomes more regular, it enhances interaction between the soft and hard segments, leading to a higher degree of micro-phase separation. This phenomenon is evident from the increased percentage of hydrogen-bonding carbonyl, a lower loss peak temperature, and a higher modulus. By modifying the molecular weight of the chain extender, we can achieve precise control over the loss peak temperature, allowing us to regulate it within the range of -1 °C and 13 °C. To summarize, our research presents a novel approach for tailoring the dynamic viscoelasticity of PU materials and thus offers a new avenue for further exploration in this field.

A Transparent, and Self-Healable Strain-Sensor E-Skin Based on Polyurethane Membrane with Silver Nanowires

Electronic skin (E-skin) is increasingly utilized in modern society, yet current E-skin technology suffers from issues, such as opacity, hardness, and fragility. To address these challenges, a novel E-skin was developed using polyurethane (PU) as the matrix material and silver nanowires (AgNWs) as the sensing material. By leveraging the small degree of microphase separation and lack of crystallization in the PU, combined with the appropriate length–diameter ratio of the AgNWs, the resulting E-skin exhibited a visible light transmittance of 75%. The E-skin also showed excellent self-healing properties (83.63% efficiency in the third repair) and mechanical properties (with almost no degradation after 60 tensile cycles) due to the reversible dynamic cross-linking network within the PU. The synergistic effect of PU and AgNWs resulted in exceptional sensing performance for the E-skin, with a gauge factor of 46 (when ε = 10%). Moreover, the E-skin demonstrated signal stability during human joint motion monitoring and successfully identified different movement states, highlighting its potential for diverse applications. This research presents a simple yet effective approach for producing transparent, durable, and stable E-skin.

Polyurethane coatings modified by OH-PDMS for anti-cavitation, antifouling and anticorrosion applications

Cavitation, biofouling, and seawater corrosion are important factors that reduce the service life of propellers and other overcurrent components of ship. Herein, OH-PDMS was introduced into polyurethane and a series of hydrophobic polyurethane coatings (SiPU-X) with anti-cavitation, antifouling and anticorrosion functions were synthesized by a simple addition reaction. The chemical composition and microstructure of the prepared coatings were analyzed by means of FT-IR, SEM, and EDS, and it was found that the addition of OH-PDMS enhanced the degree of microphase separation of SiPU-X. The addition of OH-PDMS resulted in a large number of island structures of OH-PDMS on the coating surface. The SiPU-15 with the optimal microphase separation had better tensile strength of 12.33 MPa, excellent hydrophobicity (with a contact angle of 105.3°), hydrolysis resistance (with a hydrolysis rate of 0.26 %), and water repellency (with a water absorption of 2.21 %). More importantly, the weight loss (7.1 mg) of SiPU-15 was much lower than that of SiPU-0 (10.0 mg) under 60 h cavitation owing to the suitable microphase structure on the surface. In addition, SiPU-15 exhibited excellent fouling release properties and could remain in the ocean for 60 days without microbial adhesion. The |Z|0.01Hz of SiPU-15 can maintain 3.33 × 107 Ω·cm2 after immersion in 3.5 wt% NaCl for 10 days. This work provides a heuristic perspective on the design of polymer materials with cavitation, fouling, and corrosion resistance performance.

The Role of Diisocyanate Structure to Modify Properties of Segmented Polyurethanes

Segmented thermoplastic polyurethanes (PU) were synthetized using a polycarbonatediol macrodiol as a flexible or soft segment with a molar mass of 2000 g/mol, and different diisocyanate molecules and 1,4-butanediol as a rigid or hard segment. The diisocyanate molecules employed are 3,3'-Dimethyl-4,4'-biphenyl diisocyanate (TODI), 4,4'-diphenylmethane diisocyanate (MDI), 4,4'-Methylenebis(phenyl isocyanate) 1-isocyanato-4-[(4-phenylisocyanate)methyl]benzene and 1-isocyanate-4-[(2-phenylisocyanate) methyl]benzene (ratio 1:1) (MDIi), isophorone diisocyanate (IPDI), and hexamethylene diisocyanate (HDI). The polyurethanes obtained reveal a wide variation of microphase separation degree that is correlated with mechanical properties. Different techniques, such as DSC, DMA, and FTIR, have been used to determine flexible-rigid segment phase behavior. Mechanical properties, such as tensile properties, Shore D hardness, and "compression set", have been determined. This work reveals that the structure of the hard segment is crucial to determine the degree of phase miscibility which affects the resulting mechanical properties, such as tensile properties, hardness, and "compression set".

Microstructure construction design and damping properties of polyurethane microporous elastomer modified by suspension chain extender via end-controlling oriented synthesis

Broadening the damping temperature range of viscoelastic microporous polyurethane elastomers (MPUE) is a challenge to break the limits of practical applications in damping field. Based on the molecular reaction kinetics and the molecular structure design of MPUE, different molecular weight suspension chain extenders were synthesized from polyethylene glycol monomethyl ether (MPEG), isophorone diisocyanate (IPDI) and 2-amino-1,3-propanediol via end-controlling oriented synthesis. The effect of molecular weight and dosages of suspension chain extenders on the damping property of MPUE was studied. It was demonstrated that strong intermolecular hydrogen bonds can be formed between MPUE molecules due to the carbamate groups and urea groups of the suspension chain extenders. The transformations of various motion modes of the suspended chain were driven by the existence of a large number of ether bonds, which can reduce the micro-phase separation degree in the material matrix, resulting in higher kinetic friction between molecular chains. The damping properties of the material were significantly improved, presenting a maximum increase of 62.3% in the effective damping temperature domain, and a maximum increase of 34.0% in the peak loss factor (tan δ), which was attributed to the synergistic compound effect of multiple motion modes. This high damping MPUE has great application prospects in the fields of acoustic noise reduction and household appliances damping.

New polyurethanes containing cycloaliphatic units in the hard segments. The influence of the microstructure on the thermo‐mechanical and surface properties

AbstractNew linear and cross‐linked polyurethanes with cycloaliphatic units and renewable cross‐linkers (Span 20 and Tween 20) were obtained by two steps polyaddition reaction. The degree of microphase separation was calculated by FTIR‐ATR spectroscopy with higher values for the linear polyurethane with the highest hard segment content (0.88) and lower values for the cross‐linked polyurethane with Tween 20 as cross‐linker (0.35). The results were in accordance with the DSC analysis. The linear or cross‐linked character of the polyurethane structure influenced the thermal, mechanical, and surface properties. The obtained polyurethanes had good thermal stability, with a 5% mass loss at 321°C (HMC 1) and 329°C (HMC 2) for linear polyurethanes and 330°C (HMC 3) and 342°C (HMC 4) for the cross‐linked ones. The morphology and wettability of the cycloaliphatic polyurethanes presented different behavior depending on the amount of the hard segment content and also the chemical structure of the cross‐linker. Linear polyurethanes were characterized by a globular morphology and hydrophobic character, while the use of Tween 20 as cross‐linker led to a fibrillar morphology with a low water contact angle (62°). Mechanical measurements showed that all polyurethanes present elastomeric behavior with high tensile strength values for the linear polyurethanes (33 MPa for HMC 1 and 39 MPa for HMC 2) and lower values of tensile strength for the cross‐linked ones (12 MPa for HMC 3 and 11 MPa for HMC 4), but high elongation at break for all samples (780%–1100%).

Effect of branched structure on microphase separation and electric field induced bending actuation behaviors of poly(urethane–urea) elastomers

Polyurethane elastomers as a type of electroactive polymers have wide applications in soft actuators, soft sensors and energy harvesting due to their high dielectric constant, high electrostriction coefficients, easy processing and structure adjustability, and superior biocompatibility etc. However, the relationship between microstructure and electromechanical properties of EAEs has not been fully understood. In this work, we fabricated the branch structured poly(urethane–urea) elastomers (PUUs) using hydroxy-terminated polybutadiene as soft segment, isophorone diisocyanate and 4,4-diaminodicyclohexylmethane as hard segment, and hydroxyl-terminated four-armed polycaprolactone (PCL410) as branch structured chain extender for improving bending actuation performances, and understanding the relationship between structure and electromechanical properties. The degree of branched structure of PUUs were adjusted by the content of PCL410. The microphase separation kinetics of PUUs was enhanced as increase of PCL410 content, whereas the degree of microphase separation and hard domain size of PUUs were reduced. The mechanical loss and bending actuation stress of PUUs were significantly improved by incorporation of small amount of branched structure into PUU chains. The PUU with 2.60 mol.% of PCL410 showed 5.16 mm of bending displacement and 5.16 Pa of bending actuation stress at 7.2 kV (corresponding to 180 V mm−1 of the nominal electric field), which were 76.3, and 79 times higher than that of PUU without PCL410, respectively. The electric field induced bending actuation mechanism of branch structured PUUs was suggested that the bending actuation mechanism of branch structured PUUs is caused by electrostrictive effect from dipole orientation induced bending deformation of constrained segments and asymmetric charge density distribution on both anode and cathode sides of PUU films. Our results can provide new insight on design novel electroactive polyurethane elastomers.