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1.
Thermoset polymers are known for their superior thermomechanical properties, but the chemical crosslinking typically leads to intractability. This is reflected in the great differences between thermoset and thermoplastic shape‐memory polymers; the former exhibit a robust shape memory but are not capable of redefining the permanent shape. Contrary to current knowledge, we reveal here that a classical thermoset shape‐memory polyurethane is readily capable of permanent reshaping (plasticity) after a topological network rearrangement that is induced by transcarbamoylation. By employing the Jianzhi technique (also known as kirigami), unexpected shape‐shifting versatility was observed for this otherwise classical material. As the essential carbamate moiety in polyurethanes is one of the most common polymer building units, we anticipate that our finding will have significant benefits beyond shape shifting.  相似文献   

2.
形状记忆聚合物是一种典型的智能材料,具有质轻、形变量大、可对多种刺激进行响应等优点.根据形状记忆过程的可逆性进行分类,形状记忆效应可以分为2种:单向与双向形状记忆效应.与不可逆的单向形状记忆过程相比,双向形状记忆过程是可逆的,样品不需要使用者进行再次变形,就可以在原始形状与临时形状之间进行可逆转换,因此其具有极高的实用价值与广阔的应用前景,受到各国研究人员的广泛关注,成为当前的研究热点之一.本文总结了近年来所研究的双向形状记忆结晶聚合物及其复合材料,包括恒外力条件下(外力≠0)的准双向形状记忆结晶聚合物,无外力条件下的双向形状记忆结晶聚合物及其复合材料.具体来说,前者包括在恒外力作用下的化学或物理交联的结晶聚合物.后者包括双层或核-壳聚合物复合材料、由分步交联得到的双网络交联结晶聚合物、化学交联的双组分结晶聚合物、具有较宽熔融转变的化学交联结晶聚合物与物理交联的结晶聚合物.重点关注了这些材料的制备方法、影响因素及相应的双向形状记忆机理,并对其研究前景进行了展望.  相似文献   

3.
郑宁  谢涛 《高分子学报》2017,(11):1715-1724
动态共价交联聚合物的研究具有悠久的历史,其早期的工作着眼于如何解决应力松弛带来的聚合物材料力学性能降低的问题.20世纪90年代以来,利用动态共价键来主动设计聚合物网络的特殊可适性逐渐成为研究主流,其中包括自修复和重加工性.然而,受到动态共价键的种类、通用性及所实现功能的特异性等限制,对于动态共价交联聚合物网络的研究尚停留在基础阶段.本文以本课题组近期在动态共价交联形状记忆聚合物的研究为基础,结合其他相关工作,展示了通用共价键(酯键及氨酯键)的动态可逆性,并利用其设计了具有特殊性能和潜在商业化价值的形状记忆聚合物.在此基础上,我们提出分子结构设计及宏观性能均不同于传统热塑性和热固性形状记忆聚合物的第3类形状记忆聚合物,即热适性形状记忆聚合物.  相似文献   

4.
This article reports a chromic polymer, which is responsive to its shape memory properties and has both the behavior of shape memory polymers and chromic materials. We employed a strategy to fabricate such a smart material, which represents a new principle for making chromic materials. This material is made of shape memory polyurethane with tetraphenylethylene units (0.1 wt %) covalently connected to the soft‐segments (PCL, Mw = 4000). The material displays biocompatibility, shape fixity of 88–93%, and almost 100% shape recovery and has reversible mechanochromic, solvatochromic, and thermochromic shape memory effect. The memory chromism represented by the reversible change of emission intensity shows negative correlation with shape fixity, temperature, and existence of solvent. It may be explained that when the soft segments are molten or dissolved in solvent, the shape recovery switch is open, the AIE units are free from crystal binding and can migrate easily to larger areas, thus the AIE units/particles are far apart from each other and the barrier for rotation of phenyl groups is reduced, which lead to the reduction of emission intensity, appeared by no colors or pale colors, and vice versa. Since the switch is a fundamental structural character of SMPs, the shape memory properties have led to the chromism and we call this memory chromic. © 2013 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2014 , 52, 104–110  相似文献   

5.
It is known that particular types of semi‐crystalline/elastomer polymer blends exhibit shape memory effects (SME) due to the dispersion of two immiscible phases. In this study, the crystal structure of polylactic acid (PLA)/ thermoplastic polyurethane (TPU) based shape memory polymer (SMP) is altered by incorporating small amounts of montmorillonite (MMT) nanoclay. The results indicate the incorporation of MMT can improve the compatibility of the two different polymers. Moreover, the presence of MMT affects the total crystallinity of the SMP and improves mechanical properties. Lastly, uniaxial stretching deformation can be applied to the SMP at room temperature conditions while maintaining its shape memory properties. With 1 wt % MMT particles, the recovery ratio (Rr) was nearly 95%, which indicated a strong recovery effect. The shape‐fixing ratio (Rf) remained above 95% for all composites due to plastic deformation applied at room temperature. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1197–1206  相似文献   

6.
In this study a series of hyperbranched modified shape‐memory polymers were subjected to constrained shape recoveries in order to determine their potential use as thermomechanical actuators. Materials were synthesized from a diglycidyl ether of bisphenol A as base epoxy and a polyetheramine and a commercial hyperbranched poly(ethyleneimine) as crosslinker agents. Hyperbranched polymers within the structure of the shape‐memory epoxy polymers led to a more heterogeneous network that can substantially modify mechanical properties. Thermomechanical and mechanical properties were analyzed and discussed in terms of the content of hyperbranched polymer. Shape‐memory effect was analyzed under fully and partially constrained conditions. When shape recovery was carried out with fixed strain a recovery stress was obtained whereas when it was carried out with a constraining stress the material performs mechanical work. Tensile tests at TgE′ showed excellent values of stress and strain at break (up to 15 MPa and almost 60%, respectively). Constrained recovery performances revealed rapid recovery stress generation and unusually high recovery stresses (up to 7 MPa) and extremely high work densities (up to 750 kJ/m3). The network structure of shape‐memory polymers was found to be a key factor for actuator‐like applications. Results confirm that hyperbranched modified‐epoxy shape memory polymers are good candidates for actuator‐like shape‐memory applications. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1002–1013  相似文献   

7.
This review is focused on the use of ionomers in shape memory polymers. Ionomers are polymers that contain less than ∼15% ionic groups. The incompatibility between the ion-pairs and the polymer backbone drives microphase separation producing dispersed ionic aggregates, which can physically crosslink the polymer. Shape memory polymers are responsive materials that can be deformed to program a temporary shape and then recovered on application of an external stimulus. Through the review of the main types of ionomers used in shape memory polymers, polyurethanes and polyester ionomers, polyolefin and polyaromatic ionomers, and perfluorosulfonic acid ionomers (i.e., Nafion®) it will be shown that ionomers can produce robust thermoplastic shape memory polymers and in many cases impart unique properties which allow advanced shape memory materials to be obtained including antibacterial, high temperature, and multishape memory polymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1389–1396  相似文献   

8.
In this work, a bilayer shape memory polymer (SMP) composite plate with two-way shape memory behavior is simulated, in which two types of styrene-based SMPs with well-separated glass transition temperatures are assembled in parallel. The finite element (FE) software ABAQUS is selected to exhibit the two-way shape memory effect during the shape recovery step and the Generalized Maxwell Model with the WLF equation is applied to characterize the temperature-dependent properties of the SMP bilayer plates. The effect factors of axial predeformation, thermal expansion coefficient and plate thickness are all considered for the two-way shape memory behavior of the styrene-based bilayer SMP plate. After that, a smart gripper composed of four SMP composite plates is proposed to realize grabbing and releasing functions for one-step and staged heating recovery. The FE results provide some necessary theoretical guidelines for future soft smart structural designs and optimization.  相似文献   

9.
Research in the field of liquid crystalline polymers has recently witnessed the introduction of liquid crystalline hydrogels. Here, we report the synthesis and characterization of a new liquid crystalline network featuring elastomeric softness, water‐swelling and shape memory characteristics. By comparing with a nonmesogenic network prepared using the same procedure, we reveal structure–property relationships of the liquid crystalline and crystalline polymer networks. Wide angle and small angle X‐ray scattering studies were used to examine the liquid crystalline ordering in both dry and hydrated states. Such ordering was found to be related to the observed shape memory and actuation (two‐way shape memory) properties and these phenomena are highlighted with demonstrations of shape change in response to heat and water stimuli. This study provides insight into the mechanisms affecting the shape evolution of water activated anisotropic liquid crystalline hydrogels and enables the future design of materials or devices for a variety of applications such as biomaterials interacting with body fluids in a hydrated state. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 38–52  相似文献   

10.
Covalently crosslinked polyurethane/urea polymers were synthesized using diamine monomers modified with pendant glucose groups and 2,4‐toluene diisocyanate, poly(ethylene glycol) (PEG), and 1,1,1‐tris(hydroxymethyl)ethane (triol) comonomers. The polymers showed shape memory behavior with a switching temperature dependent on the glass transition temperature. The glass transition temperature is tuned by varying the mole ratio between the glucose‐diamine and PEG used in the polymerization. Increasing PEG content resulted in decreasing glass transition temperature, and a glass transition temperature of 39 °C, close to physiological temperatures, was obtained. The fixed shape showed gradual shape recovery behavior, but a fixity of 70% was achieved when the material was stored at 25 °C. The polymer recovered to the permanent shape when heated to 50 °C. Finally, the surface of a film of the polymer can be sulfated to achieve increased blood‐compatibility without sacrificing the shape memory properties. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2252–2257  相似文献   

11.
Biodegradable polylactide (PLA) and its copolymers with shape memory properties have attracted great interests because of their important application prospects in biomedical field. In this study, random poly(L‐lactide‐co‐trimethylene carbonate‐co‐ε‐caprolactone) (LTCL) terpolymers with different molar ratio were synthesized and characterized. Monomer ε‐caprolactone (ε‐CL) was used in this study instead of glycolide in preliminary study of LTG terpolymers to investigate the transition temperature and the shape memory performance. Characterization on crystallization, mechanical properties, shape fixing, and recovery ratios of the terpolymers was conducted to investigate the correlation between crystallization and shape memory performance of LTCL terpolymers. The results are consistent with the formation of crystallized LLA segments, which could act as crosslinks, strengthened the stationary phase within the polymer matrix, and significantly improved the shape memory performance of LTCL terpolymers. For example, LTCL801010 is a crystalline polymer with high shape fixity and shape recovery ratio; its shape recovery temperature is 39°C. LTCL terpolymers with high CL content do not show shape memory performance for the rubbery at room temperature. Based on this study, PLA materials with shape memory property can be designed through the selection of monomers or the adjustment of comonomer ratio. These polymers with recovery temperature close to 37°C are expected to be used in human body such as scaffolds in tissue engineering.  相似文献   

12.
The invention of inverse vulcanization provides great opportunities for generating functional polymers directly from elemental sulfur, an industrial by‐product. However, unsatisfactory mechanical properties have limited the scope for wider applications of these exciting materials. Here, we report an effective synthesis method that significantly improves mechanical properties of sulfur‐polymers and allows control of performance. A linear pre‐polymer containing hydroxyl functional group was produced, which could be stored at room temperature for long periods of time. This pre‐polymer was then further crosslinked by difunctional isocyanate secondary crosslinker. By adjusting the molar ratio of crosslinking functional groups, the tensile strength was controlled, ranging from 0.14±0.01 MPa to 20.17±2.18 MPa, and strain was varied from 11.85±0.88 % to 51.20±5.75 %. Control of hardness, flexibility, solubility and function of the material were also demonstrated. We were able to produce materials with suitable combination of flexibility and strength, with excellent shape memory function. Combined with the unique dynamic property of S?S bonds, these polymer networks have an attractive, vitrimer‐like ability for being reshaped and recycled, despite their crosslinked structures. This new synthesis method could open the door for wider applications of sustainable sulfur‐polymers.  相似文献   

13.
Shape memory polymers (SMPs) are a class of responsive polymers that have attracted attention in designing biomedical devices because of their potential to improve minimally invasive surgeries. Use of porous SMPs in vascular grafts has been proposed because porosity aids in transfer of fluids through the graft and growth of vascular tissue. However, porosity also allows blood to leak through grafts so preclotting the materials is necessary. Here hydrogels have been synthesized from acrylic acid and N‐hydroxyethyl acrylamide and coated around a porous SMP produced from lactose functionalized polyurea‐urethanes. The biocompatibility of the polymers used to prepare the cross‐linked shape memory material is demonstrated using an in vitro cell assay. As expected, the hydrogel coating enhanced fluid uptake abilities without hindering the shape memory properties. These results indicate that hydrogels can be used in porous SMP materials without inhibiting the shape recovery of the material. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1389–1395  相似文献   

14.
以磺酸甜菜碱(SBMA)和2, 3-二羟基甲基丙烯酸丙酯(GMMA)为共聚单体、硼酸为交联剂通过自由基聚合制备了一种两性离子聚合物,该聚合物表现出良好的温度、湿度多重响应形状记忆性能。氯化钠与磺酸甜菜碱之间静电屏蔽作用,降低形状记忆转变温度,使形变行为满足不同环境要求。动态硼酯键和可逆离子静电作用赋予了材料优异的自修复功能。本研究模拟两性离子聚合物作为伤口敷料通过湿度响应形状记忆行为实现对伤口位置紧密贴合的过程,为设计新型功能性伤口敷料提供新方法。  相似文献   

15.
This study develops a new type of moisture‐sensitive shape memory polymer based on zwitterionic copolymers synthesized with acrylic acid (AA) and 3‐Dimethyl (methacryloyloxyethyl) ammonium propane sulfonate (DMAPS). The moisture absorption properties of zwitterionic copolymers are particularly investigated in this paper. The results demonstrate that the DMAPS/AA copolymers possess a sulfobetaine structure and form a two‐phase separation structure. The zwitterionic copolymers show both good hydrophilic properties and moisture absorption properties. Both AA and DMAPS segments influence the hydrophilic properties and moisture absorption of the composite copolymer. The moisture absorption process is well modeled by Fick's second law in its initial stage. The moisture absorption is mainly determined by immersion conditions and the given materials' structure. Moisture absorption speed and saturated moisture absorption both increase with an increase in DMAPS content as well as the immersion temperature. The increased moisture absorption rate and higher saturated moisture absorption results from the higher activation energy of diffusion. The DMAPS/AA copolymers demonstrate adequate moisture‐sensitive shape memory effects. Stain recovery is faster in the zwitterionic copolymers containing higher DMAPS content, whereas the final shape recovery decreases with an increase of DMAPS content. Finally, it is proposed that not only good moisture absorption units are required but also physical crosslinks should be improved for moisture‐sensitive shape memory polymers. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

16.
In this study, a material is designed which combines the properties of shape‐memory and electroactive polymers. This is achieved by covalent cross‐linking of polyvinylidene fluoride. The resulting polymer network exhibits excellent shape‐memory properties with a storable strain of 200%, and fixity as well as recovery values of 100%. Programming upon rolling induces the transformation from the nonelectroactive α‐phase to the piezoelectric β‐phase. The highest β‐phase content is found to be 83% for a programming strain of 200% affording a d33 value of −30 pm V−1. This is in good accordance with literature known values for piezoelectric properties. Thermal triggering this material does not only result in a shape change but also renders the material nonelectroactive.

  相似文献   


17.
A series of shape‐memory epoxy thermosets were synthesized by crosslinking diglycidyl ether of bisphenol A with mixtures of commercially available hyperbranched poly(ethyleneimine) and polyetheramine. Thermal, mechanical and shape‐memory properties were studied and the effect on them of the content and structure of the hyperbranched polymer was discussed. Measurements showed that the glass transition temperature can be tailored from 60 °C to 117 °C depending on the hyperbranched polymer content, and all formulations showed an appropriate glassy/rubbery storage modulus ratio. Shape‐memory programming was carried out at TgE′ given the excellent mechanical properties of the materials, with maximum stress and failure strain up to 15 MPa and 60%, respectively. The resulting shape‐memory behavior was excellent, with maximum shape recovery and shape fixity of 98% as well as a fast shape‐recovery rate of 22%/min. The results show that hyperbranched poly(ethyleneimine) as a crosslinking agent can be used to enhance mechanical and shape‐memory properties with different effects depending on the crosslinking density. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 924–933  相似文献   

18.
Like shape memory polymers, a novel phenomenon of stress memory was shown in which the stress of a material can respond to an external stimulus. This concept was further enlightened by a switch‐spring‐frame model that would eliminate the limitation of existing models which overlooked the stimulus responsive nature of such polymers. The discovery being reported in this article was stemmed from a real case study into shape memory polymer fibers in compression stocking for varicose veins. The breakthrough of stress memory enabled researchers to develop applications needing stimuli‐responsive forces, which can broaden the horizon of such smart polymers in emerging smart products in many multidisciplinary fields such as sensors, stress garments, and massage devices, electronic skins, and artificial muscles. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 893–898  相似文献   

19.
Shape memory polymers (SMPs) and shape memory polymer composites have drawn considerable attention in recent years for their shape memory effects. A unified modeling approach is proposed to describe thermomechanical behaviors and shape memory effects of thermally activated amorphous SMPs and SMP‐based syntactic foam by using the generalized finite deformation multiple relaxation viscoelastic theory coupled with time–temperature superposition property. In this paper, the thermoviscoelastic parameters are determined from a single dynamic mechanical analysis temperature sweep at a constant frequency. The relaxation time strongly depends on the temperature and the variation follows the time–temperature superposition principle. The horizontal shift factor can be obtained by the Williams–Landel–Ferry equation at temperatures above or close to the reference temperature (Tr), and by the Arrhenius equation at temperatures below Tr. As the Arruda–Boyce eight‐chain model captures the hyperelastic behavior of the material up to large deformation, it is used here to describe partial material behaviors. The thermal expansion coefficient of the material is regarded as temperature dependent. Comparisons between the model results and the thermomechanical experiments presented in the literature show an acceptable agreement. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

20.
Polymer networks showing a thermally induced shape‐memory effect were prepared through the crosslinking of oligo(?‐caprolactone)dimethacrylates under photocuring with or without an initiator. The influence of the molecular weight of the oligo(?‐caprolactone)dimethacrylates and the initiator concentration on the macroscopic properties of the polymer networks was investigated. The isothermal and nonisothermal crystallization behavior of the polymer networks was evaluated as a basic principle of the functionalization process. Shape‐memory properties such as the strain fixity and strain recovery rate were quantified with cyclic thermomechanical tensile experiments for different maximum elongations. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1369–1381, 2005  相似文献   

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