Influence of the soft segment nature on the thermomechanical behavior of shape memory polyurethanes

Shape‐memory polyurethanes (SMPUs) represent a highly interesting class of materials due to their applications in different sectors such as biomedical, textile, and aerospace. Moreover, it is possible to synthesize a variety of polyurethanes with different molecular architectures just choosing properly the chemical structure of their components. In this work, it is described the influence of the soft segment on the thermomechanical properties and shape memory behavior of shape memory polyurethanes. The synthesis, based on two‐step polymerization, was prepared by two different soft segments: poly(oxytetramethylene) glycol (PTMG) or poly(ethylene glycol) (PEG). Depending on the molecular architecture achieved, the materials present different properties that were studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Furthermore, the shape memory response of thermally activated SMPUs is determined qualitative and quantitatively by visually monitoring the shape recovery process and by thermomechanical analysis (TMA), respectively. All developed compositions have shown good shape memory behavior, with recovery ratios higher than 99.8%. POLYM. ENG. SCI., 58:238–244, 2018. © 2017 Society of Plastics Engineers     

Thermosetting polyurethanes with water‐swollen and shape memory properties

A series of shape memory polyurethanes (SPU) with different component ratio of PEG, MDI, BDO, and crosslinker DEA were synthesized by stepwise polymerization in DMF. WAXD, SAXS, DMTA, and DTA were used to study the microphase structure of SPU. No obvious phase‐separation and crystalline evidence of the PEG soft segment and hard segment were obtained in this work. The water‐swollen ratio increases with both the increasing molecular weight of PEG soft segment and the decreasing density of the chemical crossbonding. All the samples show good thermally stimulated shape memory properties. When the molar ratio of soft segment to hard segment is close, the shape recovery time reduces along with the increasing density of the chemical crossbonding. When the densities of the chemical crossbonding are similar, the shape recovery time reduces with the increasing molecular weight of the PEG soft segment. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1504–1512, 2002; DOI 10.1002/app.10357     

形状记忆聚氨酯的研究与应用

聚氨酯（Polyurethanes,PUs)是一种多嵌段共聚物，可通过调节原料的组成和配比，得到性能各异的新型功能高分子材料，由硬段和软段组的PUs分子链，具有微相分离的本体结构，符合热致形状记忆高分子（TSMP）的条件，并具有良好的强度，硬度，耐磨性，耐挠曲性和生物相容性等优异性，可望在军事，航空及图书馆经济各项领域得到广泛应用。笔者概括了形状记忆PUs的记忆原理和特征，并对形状记忆PUs的研究现状和应用前景了重点阐述。     

形状记忆高分子网络结构与性能研究进展

综述了近年来形状记忆高分子(SMP)网络结构的研究进展,阐述了各种SMP的网络结构与性能之间的关系,包括互穿网络结构、AB共网络结构、多级网络结构、滑轮环拓扑网络结构、规整网络结构和动态共价网络结构等。最后针对当前SMP存在的关键问题,对其发展方向及趋势进行了展望。     

Studies on thermally stimulated shape memory effect of segmented polyurethanes

The shape memory behavior of a series of polycaprolactone/methane diisocyanate/butanediol (PCL/MDI/BDO) segmented polyurethanes of different composition was studied. The molecular weight of PCL diols was in the range of 1600–7000, and the hard segment content varied from 7.8 to 27% by weight. Film specimens for shape memory measurements were prepared by drawing at temperatures above the melting temperature of the soft segment crystals and subsequent quick cooling to room temperature under constrained conditions. The shape memory process was observed and recorded in a heating process. Parameters describing the recovery temperature, ability, and speed were used to study the influence of structure and processing conditions on the shape memory behavior of the sample. It was found that the high crystallinity of the soft segment regions at room temperature and the formation of stable hard segment domains acting as physical crosslinks in the temperature range above the melting temperature of the soft segment crystals are the two necessary conditions for a segmented copolymer with shape memory behavior. The response temperature of shape memory is dependent on the melting temperature of the soft segment crystals. The final recovery rate and the recovery speed are mainly related to the stability of the hard segment domains under stretching and are dependent on the hard segment content of the copolymers. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1511–1516, 1997     

Influence of dispersant structure on the rheological properties of highly-concentrated zirconia dispersions

Twelve dispersants with different molecular structure features have been compared for their ability to produce low-viscosity suspensions of yttria-stabilised zirconia in organic media. The relationship between the molecular structures and their influence on the rheological properties of YSZ was studied. The effectiveness of a dispersant is mainly determined by its ability to adsorb onto the surface of the powder dispersed in the organic medium, and adsorption of a dispersant was found to be strongly promoted if a chelate ring could be formed with the powder surface. Rheological measurements showed that Solsperse3000, a pentastearic acid oligomer, was the best dispersant for the powder in question. This is explained in terms of the longer chain length of the surfactant molecule. The effectiveness of this dispersant was investigated in five different organic media. Solid loadings up to 52.5 and 55 vol.% with submicron- and micron-powder, respectively, could be reached using Solsperse3000 as the dispersant and terpineol as the organic medium.     

Synthesis and shape memory effects of Si-O-Si cross-linked hybrid polyurethanes

A series of novel Si-O-Si cross-linked organic/inorganic hybrid polyurethanes (HYPUs) with shape memory effect were prepared from isophorone diisocyanate (IPDI), poly(ethylene oxide) (PEO), and a newly synthesized hybrid diol (HD) containing hydrolysable Si-OEt groups. After hydrolyzation and condensation of Si-OEt groups, the resulted films were characterized using wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and shape recovery test to get the insight into the relationship between shape memory behaviors and polymeric structures. The glass transition temperatures (T_g) and storage modulus increased with Si-O-Si cross-linking increasing in the hybrid polyurethanes. The hybrid polyurethanes can recover to their original shapes almost completely in less than 40 s in atmosphere and in less than 10 s in water, respectively, when heated at 25 °C above T_g. The shape memory mechanism is coming from the freezing at low temperature and activation at high temperature of micro-Brownian movement of amorphous molecular chains since the temperature ranges at which the sharpest changes of recovered curvature happened are found to be around their glass transition range. The high ratio of storage modulus below and above accounted for the temporary shape fixing at low temperature. The samples with more Si-O-Si cross-linking have higher storage modulus at high temperature, resulting in faster shape recovery speed but lower temporary shape fixing.     

Influences of phase composition and thermomechanical conditions on shape memory properties of segmented polyurethanes with amorphous reversible phase

We synthesized series of shape memory polyurethanes with amorphous reversible phase (T_g‐SMPUs) and systematically studied their microphase structure and shape memory properties. The T_g‐SMPUs having no or less hard phase showed lower shape recovery. When the volume fraction of hard phase was in the range of 20–30%, the T_g‐SMPUs exhibited the highest shape recovery. As the fraction of hard phase increased further the shape recovery decreased, because more polymer components with higher glass transition temperatures (T_gs) would participate in strain storage. For the T_g‐SMPUs having similar T_gs, those polymers having higher volume fraction of hard phase exhibited higher shape fixity, broader shape recovery region, and larger recovery stress. Increasing deformation strain could raise shape fixity and recovery stress but broaden shape recovery region. The highest recovery stress of a material could be achieved when the deformation occurred at its glass transition temperature below which decreasing deformation temperature could not increase recovery stress further. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Effect of cardanol diol on the synthesis,characterization, and film properties of aqueous polyurethane dispersions

This article reports on the effect of a diol prepared from a renewable resource, cardanol, on the synthesis, film formation and film properties of aqueous polyurethane dispersions. The PU dispersions were prepared by the acetone process from poly(tetramethylene ether)glycol (PTMEG) and isophorone diisocyanate (IPDI) prepolymer at constant NCO/OH ratio of 1:1.1. Dispersions with two different concentrations of cardanol diol (OH value 140 mg KOH/g) were prepared through chain extension and characterized for solid content, particle size, and particle-size distribution (PSD). Free films were prepared by casting and were studied for their thermal, mechanical, viscoelastic, and hydrophobic properties. Due to the broad PSD, the dispersions containing cardanol diol exhibit better film formation property in comparison to the butane diol chain-extended PU. Soft and flexible films were obtained using cardanol diol as chain extender, whereas brittle film was obtained with butane diol chain extender. Morphological characterization using atomic force microscopy (AFM) and scanning electron microscopy (SEM) suggests a heterogeneous and amorphous nature of the polyurethanes-containing cardanol diol. The thermomechanical and viscoelastic properties show that incorporation of cardanol diol decreases the glass transition temperature and modulus of the films but enhances the properties like thermal stability, hydrophobicity, elongation, etc., of the polyurethane films.     

The effect of the incorporation of polystyrene‐based chain extenders on the properties of the shape memory polyurethanes

In this work, the idea of modulating the shape memory properties of polyurethanes by changing their macromolecular architecture through the incorporation of polystyrene‐based moieties was investigated. To study these effects, poly(styrene‐co‐maleic anhydride) (SMA) was incorporated during the synthesis of PU as a potential chain extender. Two sample groups were produced: (i) PU, produced with hydrazine as a chain extender and (ii) PU_SMA, produced with the addition of SMA instead of hydrazine. The results suggest that the SMA incorporation in the PU_SMA chains occurred by the reaction between NCO groups of the PU and maleic anhydride (MA) of the SMA. The presence of SMA was useful in modulating the structure of PU by reducing the soft segment crystallinity and molar mass. These changes in the structure and macromolecular architecture due to the presence of SMA moieties in PU chains led to pronounced improvements in strength, toughness, and the shape recovery ratio. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44471.     

Synthesis and properties of shape memory polyurethanes generated from schiff-base chain extender containing benzoyl and pyridyl rings

In this study, 4,4′-diphenylmethane diisocyanate and polytetramethylene glycol were used to prepare a prepolymer; N,N′-bis(4-hydroxybenzylidene)-2,6-diaminopyridine (BHBP) was used as a chain extender; and these elements were combined to prepare a novel polyurethane, BHBP/PU. Gel permeation chromatography revealed that the molecular weight of the BHBP/PU samples increased as the BHBP content was increased. Fourier transform infrared spectroscopy demonstrated that high BHBP content facilitated strong hydrogen bonding in the samples. Differential thermogravimetry indicated that the initial decomposition temperature of BHBP/PU-3 was approximately 10 °C higher than that of BHBP/PU-1. Differential scanning calorimetry and dynamic mechanical analysis revealed that increasing the BHBP content substantially increased both the glass transition and dynamic glass transition temperatures of the BHBP/PU samples. The tensile strengths of BHBP/PU-1, BHBP/PU-2, and BHBP/PU-3 were 7.7, 10.9, and 21.6 MPa, respectively, with corresponding Young’s moduli of 0.7, 1.9, and 3.3 MPa. These results demonstrated that both the tensile strength and Young’s modulus of the BHBP/PU samples increased as the BHBP content was increased. Moreover, the BHBP/PU samples exhibited excellent shape recovery of >90%.     

PPGDGE改性酸酐对环氧树脂形状记忆性能的影响

以聚丙二醇二缩水甘油醚(PPGDGE)为增韧剂改性环氧树脂E-51/甲基四氢邻苯二甲酸酐固化体系,通过力学性能、耐热性和形状记忆性能测试等研究了PPGDGE用量对该环氧体系性能的影响。结果表明:PPG-DGE添加质量分数为10%时,体系最大形变量增加约43%,形状回复速率增长75%;添加15%PPGDGE时,体系固定率提高了2.2%,回复率提高了4.5%,同时冲击强度提高了65%。PPGDGE的加入使得环氧树脂形状记忆性能有了大幅度提高。     

Synthesis and properties of anionic aqueous polyurethane dispersions

A series of aqueous polyurethane dispersions containing pendant carboxylate anion as the hydrophilic were synthesized, and the particle size and the mechanical properties of the dispersions were measured. The effects of the molar ratio of NCO/OH groups or the other functional groups on the chemical structure and the properties were discussed. The particle size mainly depended on the molar ration of the functional groups. The ? NH groups in urethane and urea linkage formed hydrogen bonding with the carbonyl group (C?O) of other urethane group in the hard segments or ether group (C? O? C) in the soft segments. Fourier transform infrared (FTIR) analysis showed that the higher molar ratio of NCO/OH concentrated the ? NH group, leading to the hydrogen bonding, which resulted in the increasing mechanical strength of the polyurethane. The tensile testing and dynamic mechanical analysis measurement revealed that the pendant carboxylate anion made the modulus and the stiffness of the polyurethane increase. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3461–3465, 2002     

Study on the liquefied‐MDI‐based shape memory polyurethanes

A series of liquefied‐MDI‐based polyurethanes having shape memory behavior, with various soft segments, chain extenders, and micro‐phase separation promoters were synthesized. Their morphology and properties were investigated in terms of thermal properties, dynamic mechanical properties, and shape recovery behavior. The results indicate that the soft segment formed with longer chain segment incline to crystallize during the cooling scans and the resulting SMPU have the higher crystallinity. Meanwhile, the chain extenders, which can enhance the polarity of hard segment, incline to have excellent shape memory properties with bigger storage modulus in rubbery state too. It was also found that the micro‐phase separation promoters have great influence on the shape memory behavior due to the enhancement of micro‐phase separation of SMPU. Furthermore, it was proved again that SMPU with longer soft segment and lower hard segment contents usually showed good shape memory behavior. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Interdependence of structure and properties in segmented polyurethanes

On the basis of Clough and Schneider's studies, who investigated segmented polyurethanes with the use of DSC, we assumed that warming may lead to morphological changes in these compounds. We warmed polymers for 10 h in argon atmosphere at 130°. Morphological changes occurring in polyurethanes at a modified temperature were confirmed with an electron microscope and were found to affect to a high degree the mechanical properties of the polymer investigated.     

Influence of heat treatment on the properties of shape memory fibers. I. Crystallinity,hydrogen bonding,and shape memory effect

Shape memory fibers (SMFs) were prepared via melt spinning. The fibers underwent different heat treatments to eliminate internal stress and structure deficiency caused during melt spinning. The influences of heat treatments on the SMF crystallinity, molecular orientation, hydrogen bonding, and shape memory behavior were studied. It was found with increasing heat‐treatment temperature, the soft segment crystallinity, crystallite dimension, and microphase separation increased, and the hydrogen bonding in the hard segment phase increased. Low temperature heat treatments decreased the shape recovery ratios while increasing the shape fixity ratios as a result of internal stress releasing and molecules disorientation. High temperature heat treatments increased the hard segment stability. Increasing heat‐treatment temperature resulted in the improvement of both the shape recovery and fixity, because it promoted the phase separation. The results from DSC, DMA, XRD, and FTIR were used to illustrate the mechanism governing these properties difference. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Influence of different organic solvents and oxidants on insulating and film-forming properties of PEDOT polymer

Processing of conjugate polymers has always been a challenge because of their poor solubility and infusibility in organic and inorganic solvents. The processibility and applications of intrinsically conductive polymers can be enhanced by producing their solutions or dispersions in different suitable solvents. It can also be achieved by preparing undoped or electrically neutral polymers, which can further be transformed in a semiconductor after an oxidation/reduction reaction. The present study focuses on the preparation of active dispersions of poly(3,4-ethylenedioxythiophene) (PEDOT) conductive polymer in various organic solvents. For this purpose, the polymerization of 3,4-ethylenedioxythiophene (EDOT) monomer was carried out in three different organic solvents, ethanol, 1-butanol, and acetonitrile, with two commonly used oxidants, ferric(III) chloride and ferric(III) p-toluenesulfonate. In this regard, the oxidant and monomer solutions with variable molar concentrations (0.25, 0.5, and 1.0 M) were prepared in particular solvents and then the solutions were mixed with different monomer/oxidant volume ratios. The obtained dispersions of PEDOT can readily be polymerized on the surface of different materials after solvent evaporation and a uniform film can be achieved. The effect of molar as well as volume concentrations of EDOT monomer and oxidant on insulating (undoped/neutral) and film-forming properties of PEDOT was investigated. These dispersions were applied on a transparent PET film and cellulosic fibers (viscose), dried at room temperature and analyzed using scanning electron microscope, optical microscope, and ATR-FTIR spectroscopic analysis. The electrical characterization of undoped PEDOT-coated fibers was performed on Keithley Picoammeter. This study contributes to obtaining a simpler and instantaneous polymerization method of PEDOT preparation and enhancing its application area.     

Predicting the shape of organic crystals grown from polar solvents

A method for predicting the shape of organic crystals grown from polar solvents is presented. The model is an improvement of the recent method developed by Winn and Doherty (A.I.Ch.E. Journal 44 (1998) 2501) for predicting the shape of organic crystals grown from solvents in which the energy of adhesion at the interfaces is dominated by dispersive forces (e.g., non-polar solvents). The principal characteristic of the new method is that it can account for the role of hydrogen donor and hydrogen acceptor atoms in forming strong bonds at the interface. This technique is a first step towards predicting the shapes of organic crystals grown from polar solvents, and has been applied successfully to predict the shape of adipic acid grown from water, and succinic acid grown from water and from propanol.