Enhanced dynamic mechanical and shape‐memory properties of a poly(ethylene terephthalate)–poly(ethylene glycol) copolymer crosslinked by maleic anhydride

Dimethyl terephthalate (DMT) and ethylene glycol (EG) were used for the preparation of poly(ethylene terephthalate) (PET), and poly(ethylene glycol) (PEG) was added as a soft segment to prepare a PET–PEG copolymer with a shape‐memory function. MWs of the PEG used were 200, 400, 600, and 1000 g/mol, and various molar ratios of EG and PEG were tried. Their tensile and shape‐memory properties were compared at various points. The glass‐transition and melting temperatures of PET–PEG copolymers decreased with increasing PEG molecular weight and content. A tensile test showed that the most ideal mechanical properties were obtained when the molar ratio of EG and PEG was set to 80:20 with 200 g/mol of PEG. The shape memory of the copolymer with maleic anhydride (MAH) as a crosslinking agent was also tested in terms of shape retention and shape recovery rate. The amount of MAH added was between 0.5 and 2.5 mol % with respect to DMT, and tensile properties and shape retention and recovery rate generally improved with increasing MAH. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 27–37, 2002     

Effect of glucose crosslinking on thermomechanical properties and shape memory effect of PET‐PEG copolymers

Poly(ethylene terephthalate) (PET) and poly (ethylene glycol) (PEG) copolymers crosslinked with glucose as a crosslinker are prepared to improve their mechanical and shape memory properties compared to the one without crosslinking. Composition of PEG and glucose is varied to search for the one with the best mechanical and shape memory properties. The highest shape recovery rate is found in the copolymer composed of 25 mol % PEG‐200 and 2.0 mol % glucose. The result that crosslinking by glucose improves the shape recovery rate and supports the high shape recovery rate under the repetitive cyclic test conditions, compared to the one without crosslinking, will be discussed in the points of the structure and shape memory mechanism. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermomechanical and water‐responsive shape memory properties of carbon nanotubes‐reinforced hyperbranched polyurethane composites

Shape memory composites of hyperbranched polyurethane (HBPU) and acid‐treated multi‐walled carbon nanotubes (MWNTs) were prepared using an in situ polymerization method. HBPUs with different hard segments contents were synthesized via the A₂ + B₃ approach using poly(ethylene glycol) (PEG) as a soft segment, 4,4′‐methylene bis(phenylisocynate), castor oil, and 1,4‐butanediol as hard segment. Compared to HBPU, the HBPU/MWNT composites showed faster shape recovery and double the shape recovery stress in the thermomechanical shape memory test, which was dependent on the MWNTs content and HBPU hard segment content. The water‐responsive shape memory effect of HBPU/MWNT composites was considered to result from the combined contribution of hydrophilic PEG and well dispersed MWNTs in highly branched HBPU molecules. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermal and mechanical properties of poly(ε‐caprolactone)/polyhedral oligomeric silsesquioxane nanocomposites

Poly(ε‐caprolactone) (PCL)/trisilanolphenyl polyhedral oligomeric silsesquioxane (TspPOSS) nanocomposites were prepared by solution mixing followed by film casting. Wide‐angle X‐ray diffraction and field‐emission scanning electron microscopy observations showed that the POSS molecules formed crystal domains and dispersed uniformly on the nanoscale in the PCL matrix. Fourier transform infrared analysis of the nanocomposites revealed that there are hydrogen‐bonded interactions between the silanol group of the TspPOSS and carbonyl oxygen of the PCL. Differential scanning calorimetry, tensile testing, and dynamic mechanical analysis (DMA) showed that, with increasing POSS content in the nanocomposites, the melting temperature and degree of crystallinity decreased while glass transition temperature, tensile modulus and strength increased without sacrificing the ductility of the PCL. DMA results also demonstrated the presence of a rubbery plateau above the melting temperature of the PCL/TspPOSS nanocomposites, and the moduli at the plateau region increased with increasing POSS content in the nanocomposites, implying that the PCL/TspPOSS nanocomposites formed a physically crosslinked structure. The physically crosslinked PCL/TspPOSS nanocomposites exhibited a thermally triggered shape memory effect. Copyright © 2012 Society of Chemical Industry     

Hydrogen-bonded poly(vinyl alcohol)-boehmite composites exhibiting excellent shape memory properties

Poly(vinyl alcohol) (PVA) networks cross-linked by inorganic nanofillers-boehmite (AlOOH) nanowires via strong hydrogen bonding was prepared by a facile strategy. These PVA-AlOOH composites displayed significantly enhanced mechanical and thermal properties due to the excellent mechanical property and high heat resistant of AlOOH nanowires, as well as the strong hydrogen bonding formed between PVA and AlOOH. Interestingly, it was worth mentioning that the PVA-AlOOH composites exhibited excellent shape memory behavior. The strong hydrogen bonding between PVA matrix and AlOOH nanowires acted as the hard segments to maintain the permanent shape, while the weak one between PVA chains served as switching segments to fix the temporary shape and recover to the permanent shape. This physical cross-linked system provided a simple and efficient strategy to obtain smart shape memory materials.     

Morphology and properties of shape memory thermoplastic polyurethane composites incorporating graphene‐montmorillonite hybrids

A novel hybrid containing graphene oxide (GO) and montmorillonite (MMT) was first synthesized by solution reaction. Then shape memory thermoplastic polyurethane (TPU) composites incorporating MMT–GO hybrid was fabricated via melt blending. Infrared spectra indicated that GO and MMT have been combined together through chemical hydrogen bonding. Tensile tests showed that MMT‐GO hybrids provided substantially greater mechanical property enhancement than using MMT or GO as filler alone. With only 0.25 wt % loading of MMT–GO hybrid (the mass ratio of MMT:GO is 1:1), there was a relatively high improvement in tensile properties of TPU composites, compared with those of TPU/GO and TPU/MMT composites at the same filler content. Thermal analysis indicated that MMT‐GO hybrids enhanced the thermal decomposition temperatures of TPU composites. Shape memory property tests showed that the shape fixing rate of TPU composites was effectively enhanced by incorporating MMT–GO hybrid. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46149.     

Fabrication of poly(ε‐caprolactone) (PCL)/poly(propylene carbonate) (PPC)/ethylene‐α‐octene block copolymer (OBC) triple shape memory blends with cycling performance by constructing a co‐continuous phase morphology

In this paper, a triple shape memory material was prepared by ultra‐simple melt blending from poly(ε‐caprolactone) (PCL), poly(propylene carbonate) (PPC) and ethylene‐α‐octene block copolymer (OBC). The obtained material possessed a co‐continuous phase morphology and presented an excellent triple shape memory effect (triple‐SME). Theoretical prediction demonstrated that a special continuous phase morphology could be constructed by adjusting the proportions of the blend. Moreover, the results indicated that a close relationship existed between the phase morphology and the triple‐SME of PCL/PPC/OBC. The sample with 35 vol% PPC content contributed to the formation of a continuous phase morphology and exhibited the optimal triple‐SME. Additionally, the sample PCL/PPC/OBC (32.5/35/32.5) showed outstanding structure and performance stability during cycle loading–unloading tests, which evidenced the prominent cycling shape memory property (nearly 100% shape fixing and recovery of temporary shape). Overall, this work could provide an efficient, convenient and recyclable method to obtain high‐performance shape memory materials. © 2020 Society of Chemical Industry     

Shape‐memory effects of radiation crosslinked poly(ϵ‐caprolactone)

Poly(?‐caprolactone) (PCL) with different molecular weight were crosslinked by γ‐radiation. The radiation crosslinking features were analyzed by Soxhlet extraction with toluene and the Charlesby–Pinner equation. The crosslinking degree is relative to molecular weight and radiation dose; the relation between sol fraction and dose follows the Charlesby–Pinner equation. All the samples were crystalline at room temperature, and the radiation crosslinking had a little effect on the crystallinity and the melting behavior of PCL. The shape‐memory results indicated that only those specimens that had a sufficiently high crosslinking degree (gel content is higher than about 10%) were able to show the typical shape‐memory effect, a large recoverable strain, and a high final recovery rate. The response temperature of the recovery effect (about 55°C) was related to the melting point of the samples. The PCL shape‐memory polymer was characterized by its low recovery temperature and large recovery deformation that resulted from the aliphatic polyester chain of PCL. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1589–1595, 2003     

微波驱动咪唑类聚离子液体/聚乙烯醇形状记忆材料

结合微波驱动原理、聚离子液体（PIL）及形状记忆聚合物的结构特性,目的是设计合成完全基于聚合物、能在微波驱动下快速回复的聚离子液体/聚乙烯醇（PVA）形状记忆复合材料。首先合成了乙烯基咪唑功能性离子液体单体（[ViEtIm][BF₄],ILM）,之后在含有戊二醛的PVA溶液中对ILM进行原位聚合生成PIL,将PIL引入到交联PVA中,形成聚乙烯基咪唑PIL/PVA形状聚合物复合材料（SMPC）。用核磁对ILM和PIL的结构进行了表征,证明了所合成目标化合物的结构准确性。介电性能测试结果显示PIL/PVA有较高的介电常数和介电损耗,当P[ViEtIm][BF₄]含量从0增加到30%时PIL/PVA复合材料的介电损耗因子呈增大趋势,可见PIL是一种有效的微波吸收介质。弯曲法测试结果表明该复合材料在微波驱动下具有很好的形状记忆效应,所有复合材料的形变固定率都接近100%且形变回复率都高达80%以上,且PIL的含量和微波输出功率的大小对材料回复率和回复时间有显著影响。140 W的微波足以驱动PIL/PVA SMPC发生回复,280 W下40 s内可以完成,微波功率增大到420 W时SMPC在20 s内可回复到起始形状。     

Shape memory effect of poly(methylene‐1,3‐cyclopentane) and its copolymer with polyethylene

Poly(methylene‐1,3‐cyclopentane) (PMCP) cyclopolymerized from 1,5‐hexadiene by metallocene catalyst, rac‐(ethylenebis(1‐indenyl))Zr(N(CH₃)₂)₂ is partially crystalline and has a value of elongation at break of more than 400% in the temperature range 25–85 °C. The shape memory effect of PMCP with moderate molecular weight is enhanced by sequentially polymerized polyethylene segments, the crystalline phase of which seems to strengthen the fixed structure which memorizes the original shape. The glass transition temperature or melting temperature of PMCP can be selectively used as shape recovery temperature when an appropriate deformation temperature is chosen. © 2002 Society of Chemical Industry     

Studies of the moisture‐sensitive shape memory effect of pyridine‐containing polyurethanes

Shape memory polymers have been much researched in recent years. In the work reported, moisture‐sensitive shape memory effects (SMEs) of novel pyridine‐containing shape memory polyurethanes (Py‐SMPUs) were investigated systematically. The results show that the strain recovery start immersion time (t_s), strain recovery immersion time (t_r) and final strain recovery immersion time (t_e) are prolonged with a decrease of relative humidity as well as a decrease of temperature. The final strain recovery decreases with a decrease of relative humidity as well as an increase of temperature. The key component affecting the moisture‐sensitive SME is the N,N‐bis(2‐hydroxyethyl)isonicotinamide (BINA) unit. The lower limit of BINA content for Py‐SMPUs to exhibit a good moisture‐sensitive SME is 30 wt%. The addition of diphenylmethane diisocyanate (MDI) and 1,4‐butanediol (BDO) enhances the moisture‐sensitive shape recovery. The final shape recovery decreases with a decrease of BINA content or an increase of MDI–BDO content. In addition, t_s, t_r and t_e become shorter in the Py‐SMPUs with higher BINA content or with lower MDI‐BDO content. Copyright © 2011 Society of Chemical Industry     

Dynamic mechanical and mechanical properties of polypropylene/poly(vinyl butyral)/mica composites

Three-component composites consisting of polypropylene (PP) matrix, poly(vinyl butyral) (PVB) modifier, and mica filler at various ratios of matrix to modifies and a constant mica content (30 wt %) were prepared by using two different kinds of PVB, viz., PVB and PVB-P. By correlating with the morphology, the dynamic mechanical and mechanical properties of the composites are studied in detail. PVB component in PP/PVB/mica composites cannot display a reinforcing effect to PP/mica binary composites, while impact strength of the composites are reduced further. It associates with incompatibility between PP and PVB, and as well as higher glass transition temperature of PVB. For PP/PVB-P/mica composites, stiffness decreases and, meanwhile, impact strength increases when PVB-P content is 7 wt %. The improvement of impact strength on PP/mica binary composites at the composition is due to a little affinity between the PP matrix and the plasticizer of PVB-P. Moreover, a minor amount of PP-g-MA in the 63/7/30 PP/PVB/mica composites only acts as an adhesion promoter. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2003–2011, 1997     

Preparation and properties of MWCNTs/poly(acrylonitrile‐ styrene‐butadiene)/epoxy hybrid composites

Poly(acrylonitrile‐styrene‐butadiene) (ABS) was used to modify diglycidyl ether of bisphenol‐A (DGEBA) type epoxy resin, and the modified epoxy resin was used as the matrix for making multiwaled carbon tubes (MWCNTs) reinforced composites and were cured with diamino diphenyl sulfone (DDS) for better mechanical and thermal properties. The samples were characterized by using infrared spectroscopy, pressure volume temperature analyzer (PVT), thermogravimetric analyzer (TGA), dynamic mechanical analyzer (DMA), thermo mechanical analyzer (TMA), universal testing machine (UTM), and scanning electron microscopy (SEM). Infrared spectroscopy was employed to follow the curing progress in epoxy blend and hybrid composites by determining the decrease of the band intensity due to the epoxide groups. Thermal and dimensional stability was not much affected by the addition of MWCNTs. The hybrid composite induces a significant increase in both impact strength (45%) and fracture toughness (56%) of the epoxy matrix. Field emission scanning electron micrographs (FESEM) of fractured surfaces were examined to understand the toughening mechanism. FESEM micrographs reveal a synergetic effect of both ABS and MWCNTs on the toughness of brittle epoxy matrix. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Morphology,mechanical properties,and thermal stability of poly(L‐lactic acid)/poly(butylene succinate‐co‐adipate)/silicon dioxide composites

Poly(butylene succinate‐co‐adipate) (PBSA) and two types of SiO₂ (hydrophilic or hydrophobic) were used to modify poly(L ‐lactic acid) (PLLA). The mechanical properties, rheological and thermal behavior, phase morphology, and thermal stability of PLLA/PBSA/SiO₂ composites were investigated. The impact strength, flexural strength, and modulus of PLLA/PBSA blends increased after the addition of hydrophobic SiO₂ without decreasing the elongation at break, and the elongation at break monotonically decreased with increasing hydrophilic SiO₂ content. The melt elasticity and viscosity of the PLLA/PBSA blend increased with the addition of SiO₂. The hydrophilic SiO₂ was encapsulated by the dispersed PBSA phase in the composites, which led to the formation of a core–shell structure, whereas the hydrophobic SiO₂ was more uniformly dispersed and mainly located in the PLLA matrix, which was desirable for the optimum reinforcement of the PLLA/PBSA blend. The thermogravimetric analysis results show that the addition of the two types of SiO₂ increased the initial decomposition temperature and activation energy and consequently retarded the thermal degradation of PLLA/PBSA. The retardation of degradation was prominent with the addition of hydrophobic SiO₂. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation of chitosan‐g‐poly(acrylamide)/montmorillonite superabsorbent polymer composites: Studies on swelling,thermal, and antibacterial properties

Superabsorbent composites based on chitosan‐g‐poly(acrylamide) and montorillonite (CTS‐g‐PAAm/MMT) were synthesized through in situ radical polymerization by grafting of crosslinked acrylamide onto chitosan backbone in presence of MMT at different contents. The formation of the grafted network was confirmed by attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR), thermogravimetric analysis (TGA), and differential scanning calorimetery (DSC). The obtained porous structure was observed by scanning electron microscope (SEM). The presence of clay and its interaction with chitosan‐g‐poly(acrylamide) (CTS‐g‐PAAm) matrix was evidenced by ATR‐FTIR analysis. The morphology was investigated by both X‐ray diffraction (XRD) and SEM analyses. It was suggested the formation of mostly exfoliated structures with more porous structures. Besides, the thermal stability of these composites, observed by TGA analysis, was slightly affected by the clay loading as compared to the matrix. These hydrogel composites were also hydrolyzed to achieve anionic hydrogels with ampholytic properties. Swelling behaviors were examined in doubly distilled water, 0.9 wt % NaCl solution and buffer solutions. The water absorbency of all superabsorbent composites was enhanced by adding clay, where the maximum was reached at 5 wt % of MMT. Their hydrolysis has not only greatly optimized their absorption capacity but also improved their swelling rate and salt‐resistant ability. The hydrolyzed superabsorbent showed better pH‐sensitivity than the unhydrolyzed counterparts. The results of the antibacterial activity of these superabsorbents composites against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), assayed by the inhibitory zone tests, have showed moderate inhibition of the bacteria growth. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39747.     

Triple one-way and two-way shape memory poly(ethylene-co-vinyl acetate)/poly(ε-caprolactone) immiscible blends

Triple one-way and two-way shape memory polymers (1W-SMPs and 2W-SMPs) are highly desirable for many practical applications due to the multiple shape transformation. In this work, the blend with co-continuous structure is fabricated based on poly(ethylene-co-vinyl acetate) (EVA) and poly(ε-caprolactone) (PCL), which shows excellent triple one-way and two-way shape memory properties. It is found that the blends have two independent crystallization peaks and two independent melting peaks. With the increase of dicumyl peroxide (DCP) content, the crystallization temperature, melting temperature, and crystallinity of both EVA and PCL in the blends gradually decreases. The blends show great dual and triple one-way shape memory property, and the phenomena of elongation induced by oriented crystallization and contraction induced by melting are clearly seen. Moreover, the blends exhibit remarkable and recyclable triple two-way shape memory performance, with an average shape recovery magnitude of 97.3% and an average actuation magnitude of 50.6%. In terms of the excellent triple one-way and two-way shape memory performance, the EVA/PCL blends may have potential applications in the fields of soft robotics, actuators, and cranes. The new preparation method of triple 2W-SMPs can be used to fabricate other triple 2W-SMPs with commercial polymers.     

Synthesis of poly(cyclooctene) by ring‐opening metathesis polymerization: Characterization and shape memory properties

Cis‐cyclooctene was polymerized via ring‐opening metathesis polymerization using a well‐defined ruthenium catalyst (Grubbs' type) under varying reaction conditions. Control over molecular weight was achieved by the inclusion of a chain transfer agent and its influence on the behavior of the obtained polymers was evaluated. The resulting polymers were characterized by means of differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical thermal analysis. Taking into account their thermal behavior, samples of appropriate molecular weight were subjected to a suitable treatment by chemical crosslinking to obtain a material showing thermally induced shape memory effect. The material recovers its original shape after several cycles of deformation into different shapes. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and properties of TiO2‐filled poly(acrylonitrile‐butadiene‐styrene)/epoxy hybrid composites

Poly (acrylonitrile‐butadiene‐styrene) (ABS) was used to modify diglycidyl ether of bisphenol‐A type of epoxy resin, and the modified epoxy resin was used as the matrix for making TiO₂ reinforced nanocomposites and were cured with diaminodiphenyl sulfone for superior mechanical and thermal properties. The hybrid nanocomposites were characterized by using thermogravimetric analyzer (TGA), dynamic mechanical analyzer (DMA), universal testing machine (UTM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The bulk morphology was carefully analyzed by SEM and TEM and was supported by other techniques. DMA studies revealed that the DDS‐cured epoxy/ABS/TiO₂ hybrid composites systems have two T_gs corresponding to epoxy and ABS rich phases and have better load bearing capacity with the addition of TiO₂ particles. The addition of TiO₂ induces a significant increase in tensile properties, impact strength, and fracture toughness with respect to neat blend matrix. Tensile toughness reveals a twofold increase with the addition of 0.7 wt % TiO₂ filler in the blend matrix with respect to neat blend. SEM micrographs of fractured surfaces establish a synergetic effect of both ABS and TiO₂ components in the epoxy matrix. The phenomenon such us cavitation, crack path deflection, crack pinning, ductile tearing of the thermoplastic, and local plastic deformation of the matrix with some minor agglomerates of TiO₂ are observed. However, between these agglomerates, the particles are separated well and are distributed homogeneously within the polymer matrix. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

热固性环氧树脂形状记忆效应研究

将新型的高分子固化剂与环氧树脂(EP)进行共混,经适度交联固化后制备出一种具有较低玻璃化转变温度(Tg)的无定型EP体系,并对该EP固化体系的力学性能、形状记忆特性和动态力学性能等进行了研究。结果表明:适度交联固化的EP体系具有良好的形状记忆特性,固化剂用量是影响该形状记忆体系综合性能的主要因素;其最大形变恢复率均为100%,形变恢复速率基本上随固化剂用量增加而增大,最大形变恢复速率为0.023 s-1;形变固定率随固化剂用量增加而减小,当w(固化剂)=37.5%或54.5%时,形变固定率为100%或96%。     

Hybrid multi‐scale epoxy composites containing conventional glass microfibers and electrospun glass nanofibers with improved mechanical properties

A mechanically flexible mat consisting of structurally amorphous SiO₂ (glass) nanofibers was first prepared by electrospinning followed by pyrolysis under optimized conditions and procedures. Thereafter, two types of hybrid multi‐scale epoxy composites were fabricated via the technique of vacuum assisted resin transfer molding. For the first type of composites, six layers of conventional glass microfiber (GF) fabrics were infused with the epoxy resin containing shortened electrospun glass nanofibers (S‐EGNFs). For the second type of composites, five layers of electrospun glass nanofiber mats (EGNF‐mats) were sandwiched between six layers of conventional GF fabrics followed by the infusion of neat epoxy resin. For comparison, the (conventional) epoxy composites with six layers of GF fabrics alone were also fabricated as the control sample. Incorporation of EGNFs (i.e., S‐EGNFs and EGNF‐mats) into GF/epoxy composites led to significant improvements in mechanical properties, while the EGNF‐mats outperformed S‐EGNFs in the reinforcement of resin‐rich interlaminar regions. The composites reinforced with EGNF‐mats exhibited the highest mechanical properties overall; specifically, the impact absorption energy, interlaminar shear strength, flexural strength, flexural modulus, and work of fracture were (1097.3 ± 48.5) J/m, (42.2 ± 1.4) MPa, (387.1 ± 9.9) MPa, (12.9 ± 1.3) GPa, and (30.6 ± 1.8) kJ/m², corresponding to increases of 34.6%, 104.8%, 65.4%, 33.0%, and 56.1% compared to the control sample. This study suggests that EGNFs (particularly flexible EGNF‐mats) would be an innovative type of nanoscale reinforcement for the development of high‐performance structural composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42731.