Celite‐mediated linking of polyurethane block copolymers and the impact on the shape memory effect

Celite, a porous inorganic material with enormous surface area and hydroxyl groups on the surface, was used as a cross‐linker of polyurethane (PU) copolymer chains to improve its shape memory and mechanical properties. PU copolymers with different Celite contents were prepared and characterized by IR, DSC, and universal testing machine. The glass transition temperature of PU copolymers was maintained around 20°C independent of Celite content. The shape memory and mechanical properties were dependent on when Celite was added during the polymerization reaction. The reaction in which Celite was added at the middle stage of polymerization showed the best shape memory and mechanical properties. The best shape recovery of PU was found at 0.3 wt % Celite and increased to 97% even after the third cycle. Likewise, the shape retention also maintained a remarkable 86% after three cycles. The reasons underlining the high shape recovery and shape retention by adopting Celite as a cross‐linker are discussed in this article. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Microstructural and mechanical property evolutions of shape memory polyurethane during a thermodynamic cycle

To better understand the shape memory behaviors of synthesized shape memory polyurethane (SMPU) sealant with a tailored transition temperature (T_t) for concrete pavement joints, the thermal and dynamic mechanical properties of SMPU were first characterized to determine the shape memory switching temperature of SMPU. Then the microstructural and mechanical property evolutions of SMPU in the original, programmed, and recovered states during a five‐step thermodynamic cycle were discussed, respectively. The results indicate that the tailored T_t of prepared SMPU can be used as the shape memory switching temperature to match its working temperature. Further, the programming causes the phase separation in SMPU, leading to an obvious anisotropy. The SMPU has satisfactory shape memory performance. The orientation of molecular chains in soft segments is confirmed along the stretching direction. The oriented molecular chains can restore to the naturally curled state during the free recovery. Finally, the programming improves the mechanical properties of SMPU. The recovered SMPU shows a slight decrease in mechanical properties because of the partially impaired crystal structures and broken molecular segments during the programming and recovery. It is concluded that the synthesized SMPU with the specially tailored T_t is suitable to use as a sealant of concrete pavement joints. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45703.     

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     

Triple‐shape memory properties of polyurethane/polylactide–polytetramethylene ether blends

A facile method to prepare triple‐shape memory polymers was developed by blending polyurethane and polylactide–polytetramethylene with well‐separated glass transition temperatures. The thermal properties of the blends were characterized using modulated differential scanning calorimetry and differential scanning calorimetry. Field emission scanning electron microscopy, Fourier transform infrared spectroscopy and wide‐angle X‐ray diffraction were used to characterize the microstructures and crystal structures of the blends. The mechanical properties were also evaluated. The versatile triple‐shape memory effect and quantitative shape memory response were evaluated by consecutive thermal mechanical experiments based on a two‐step programming process and subsequent progressive thermal recovery. The results show that the blends have phase‐separated microstructures resulting in an ability to fix two temporary shapes independently and can recover to their original shapes sequentially. The blends have excellent triple‐shape memory properties and may have some applications in multi‐shape coatings, adhesives, films and temperature sensing or actuating elements. © 2015 Society of Chemical Industry     

Blocking of soft segments with different chain lengths and its impact on the shape memory property of polyurethane copolymer

The arrangements, whether block or random type, of the soft segments of polyurethane block copolymers prepared with MDI and two kinds of poly(tetramethylene glycol) (PTMG; MW of 1000 or 2000) in various ratios were compared for possible effects on the physical properties of the copolymers. A long soft segment, PTMG‐2000, was superior in all mechanical properties (strain, stress, and modulus) because a long chain length could provide more motional freedom than a short one (PTMG‐1000) could and therefore was helpful in forming strong interchain attractions among hard segments. Inclusion of more PTMG‐2000 led to a lower T_g and a peak shift in infrared spectra. The arrangement of two soft segments in a block‐type copolymer, a key finding in this study, was controlled by separately synthesizing two prepolymers, each with a different chain length, and connecting two prepolymers in a second step. Random‐type copolymers prepared for purposes of comparison were allowed to react with two PTMGs in one step. Two types of copolymers were compared, and the reason for the differences in the shape memory property are discussed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1435–1441, 2007     

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.     

Water vapor permeability and mechanical properties of fabrics coated with shape‐memory polyurethane

Water vapor permeable fabrics were prepared by coating shape‐memory polyurethane (PU), which was synthesized from poly(tetramethylene glycol), 4,4′‐methylene bis(phenylisocyanate), and 1,4‐butanediol, onto polyester woven fabrics. Water vapor permeability and mechanical properties were investigated as a function of PU hard‐segment content or polymer concentration of the coating solution. Water vapor permeability of PU‐coated fabrics decreased dramatically with increased concentration of coating solution, whereas only a slight change was observed with the control of PU hard‐segment content. The coated fabric showed the clear appearance of a nonporous PU surface according to SEM measurements. Attainment of high water permeability in PU‐coated fabrics is considered to arise from the smart permeability characteristics of PU. Mechanical properties of coated fabrics, although there was some variation depending on the concentration of coating solution, were primarily affected by PU hard‐segment content. Fabrics coated with PU hard‐segment content of 40% showed the lowest breaking stress and modulus as well as the highest breaking elongation, which could be interpreted in terms of the dependency of mechanical properties of coated fabrics on PU hard‐segment content and the yarn mobility arising from a difference in penetrating degree of coating solution into the fabric. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2812–2816, 2004     

交联型与线形水性聚氨酯的形状记忆性能比较

由聚酯多元醇、2,4–甲苯二异氰酸酯、二羟甲基丙酸等合成了水性聚氨酯乳液,对乳液性能进行了研究;对制得的聚氨酯胶膜进行了红外分析、DSC测试和形状记忆性能测试;用丙三醇和三羟甲基丙烷作为扩链制得的交联水性聚氨酯与用1,4–丁二醇制得的线形水性聚氨酯进行了性能比较,结果表明:不同扩链剂对水性聚氨酯的性能有一定的影响,与线形水性聚氨酯相比,交联型水性聚氨酯具有较好的形状记忆性能,形状恢复率可达92%～97%。     

Dependency of the shape memory properties of a polyurethane upon thermomechanical cyclic conditions

The relationship between the shape memory properties and thermomechanical cyclic conditions was investigated with a type of shape memory polyurethane (SMPU). The thermal and dynamic mechanical properties of the polyurethane were examined by using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). It was found that the SMPU exhibited good shape memory effects (SMEs) at deformation temperatures ranging from T_g to T_g + 25 °C. The strain recovery ratios increased with the increase of deformation speed and with the decrease in maximum strain. The recovery ratios also increased with increasing fixing speed. Therefore, in practical applications, in order to obtain better SMEs, the SMPU should be cooled to its frozen state as soon as possible after being deformed at a high temperature. The ‘fixity’ dramatically increased with the decrease in fixing temperature. To obtain optimal SMEs, the polymer has to be reheated up to the temperature at which the polymer deformed. In addition, the recovery ratios of the SMPU could increase slightly with the increase of recovery time. Copyright © 2004 Society of Chemical Industry     

高力学性能医用聚氨酯手套的制备研究

利用水性聚氨酯乳液,采用浸渍成型工艺制备聚氨酯手套。考察了交联剂、TiO_2、温度等条件对聚氨酯薄膜力学性能的影响。结果表明:在不降低手套力学性能的前提下,可添加一定量的二氧化钛作为颜料,添加交联剂可以改善聚氨酯手套的力学性能,并达到行业要求。     

Dynamic mechanical properties of sandwich‐structured epoxy beam composites containing poly(ethyleneterephthalate)/poly(ethyleneglycol) copolymer with shape memory effect

To make smart vibration‐controlling composite laminate, a few poly(ethylene terephthalate) (PET) and poly(ethylene glycol) (PEG) copolymers with shape memory ability were prepared. After selecting the best composition of PET–PEG copolymer in mechanical properties, a crosslinking agent such as glycerine, sorbitol, or maleic anhydride (MA) was included for crosslinked copolymer, followed by analysis of its effect on mechanical, shape memory, and damping properties. The highest shape recovery was observed for copolymer with 2.5 mol % of glycerine, and the best damping effect indicating vibration control ability was from copolymer with 2.5 mol % of sorbitol. With the optimum copolymers in hand, sandwich‐structured epoxy beam composites fabricated from an epoxy beam laminate and crosslinked PET–PEG copolymer showed that impact strength increased from 1.9 to 3.7 times depending on the type of copolymer, and damping effect also increased as much as 23 times for the best case compared to epoxy laminate beam alone. The resultant sandwich‐structured epoxy beam composite can be utilized as structural composite material with vibration control ability, and its glass transition temperature can be controlled by adjustment of PET, PEG, or crosslinking agent composition. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3141–3149, 2003     

The modification of graphene with alcohols and its use in shape memory polyurethane composites

Graphene prepared by the thermal reduction of graphite oxide was modified by reactions with methanol or 1‐butanol using aqueous HBF₄ solution as a catalyst. Results showed that the reaction created hydroxyl groups on the graphene and at the same time reduced the number of defects. Gravimetry, thermogravimetry, X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy showed that the alcohols had reacted with epoxide groups on graphene. Raman spectroscopy showed that the defects in the graphene were repaired through other accompanying reactions. The reinforcing effect of graphene, observed in the tensile properties and the shape memory behavior of graphene/polyurethane composites, was increased when the graphene was modified with methanol. However, decreases in density and glass transition temperature were evident for the composites made with alcohol‐modified graphene. These results show that the newly created hydroxyl groups on graphene produce effective covalent bonds with the polyurethane chains of the matrix; however, the increased number of bonds restricts the rearrangement of the matrix molecules for dense packing. The covalent bonds between graphene and polyurethane chains enhanced shape recoverability and reduced the hysteresis brought about by repeated thermomechanical cycles. Copyright © 2012 Society of Chemical Industry     

Bio‐based thermoplastic polyurethane and polyamide 11 bioalloys with excellent shape memory behavior

Bio‐based blends of commercially available polyester based bio thermoplastic polyurethane (TPU) and castor oil based polyamide 11 (PA11) of different ratios are prepared by melt processing. The blends properties such as shape memory behavior through unconstrained and constrained recovery, interfacial interaction, morphology, dynamic mechanical, rheological, and mechanical behavior are studied. A strong interface between the two polymeric phases due to hydrogen bonding observed through morphology indicates that TPU and PA11 are well compatible. The complex viscosity of blends ranges between that of neat PA11 and TPU. Thermal analysis shows that higher the TPU content lower the melting point (T_m ) corresponding to PA11 and the crystallization temperature (T_c ) remains unaltered. Adding TPU to PA11 ductility and impact strength of the blends increases significantly with the small reduction in their tensile strength. Shape memory behavior investigation reveals that, blends recover almost 95% of the applied deformation when heated at zero load and they recovered a stress of 1.8–3.2 MPa in constrained recovery during three consecutive thermomechanical cycles. The reported results on bioalloys promotes the usage in multidisciplinary field of intelligent devices, such as ergonomic grips and sports shields. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44794.     

液化MDI基形状记忆聚氨酯扩链剂的选择研究

在选定液化MDI和聚己二酸丁二醇酯(PBAG)软段原料的前提下，采用双酚A(FA)、乙二醇(ED)、1，4-丁二醇(BD)、1，6-己二醇(HD)、一缩乙二醇(DE)扩链剂合成了一系列形状记忆聚氨酯(SMPU)；用FT-IR、DSC对样品的结构进行了分析，并考察了它们的形状记忆性能和力学性能。结果发现，扩链剂对SMPU有一定影响，用FA、ED扩链的SMPU具有较好的微相分离，而DE扩链的具有较好的软段结晶性能；FA、HD的SMPU具有较低的形状回复温度和较快的形状回复速率，HD、DE扩链的则具有较好形状固定性能，FA、DE扩链的SMPU循环使用性能较好；同时FA、HD的SMPU具有较高的弹性模量与力学强度。     

Biodegradable polyurethane based on random copolymer of L‐lactide and ϵ‐caprolactone and its shape‐memory property

A series of biodegradable polyurethanes (PUs) are synthesized from the copolymer diols prepared from L ‐lactide and ε‐caprolactone (CL), 2,4‐toluene diisocyanate, and 1,4‐butanediol. Their thermal and mechanical properties are characterized via FTIR, DSC, and tensile tests. Their T_gs are in the range of 28–53°C. They have high modulus, tensile strength, and elongation ratio at break. With increasing CL content, the PU changes from semicrystalline to completely amorphous. Thermal mechanical analysis is used to determine their shape‐memory property. When they are deformed and fixed at proper temperatures, their shape‐recovery is almost complete for a tensile elongation of 150% or a compression of 2‐folds. By changing the content of CL and the hard‐to‐soft ratio, their T_gs and their shape‐recovery temperature can be adjusted. Therefore, they may find wide applications. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4182–4187, 2007     

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     

Reconfiguration and shape memory triggered by heat and light of carbon nanotube–polyurethane vitrimer composites

Thermoset shape‐memory polymers (SMPs) are widely applied because of their superiority in maintaining permanent shapes. However, the inferiority of this material is also conspicuous, namely the loss of reprocessing ability owing to the chemically crosslinked structure. Fortunately, a new class of SMPs, known as “vitrimers,” was discovered, which can be reshaped or reprocessed via topological rearrangement due to the existence of dynamic covalent bonds. Thus, this new thermoset SMP could become a novel solution. In this paper, carbon nanotube–polyurethane vitrimer (CNT‐PUV) composites have been prepared, which possess the capability of thermally induced shape memory based on entropy changes and thermal reconfiguration based on transcarbamoylation reactions of carbamate bonds. In addition, the introduction of CNTs endows them with properties of near‐infrared (NIR) triggered shape memory and reconfiguration due to the photothermal conversion effect of CNTs. Besides, due to the character of the NIR laser, step‐by‐step shape recovery of CNT‐PUVs is realized from predefined temporary shapes to a permanent shape. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45784.     

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     

Effect of cross‐linking time on the thermal and mechanical properties and pervaporation performance of poly(vinyl alcohol) membrane cross‐linked with fumaric acid used for dehydration of isopropanol

Cross‐linked poly (vinyl alcohol) membranes were prepared using fumaric acid as the cross‐linking agent and were used for the pervaporation separation of water/isopropanol mixtures. Cross‐linking process was carried out at 150°C at three different times of 10, 30, and 60 min. The membranes were characterized by different known methods of FT‐IR, TGA, XRD as well as tensile test. The effects of cross‐linking time on the thermal and mechanical properties of the membranes and also their pervaporation performance were investigated. Formation of more ester groups by increasing the cross‐linking time was confirmed by the FT‐IR results. TGA analyses showed that thermal stability of the membranes is improved by prolonging the duration of cross‐linking process. This was due to the formation of more compact structure in the membranes. The XRD results revealed that the crystalline regions of the membranes were relatively diminished with an increase in the cross‐linking time. No specific trend was observed for the variation of tensile strength at break with the cross‐linking time. The PVA membrane cross‐linked for 60 min showed high selectivity of 1492 for water permeation for the feed mixture containing 10 wt % water. The temperature dependency of the permeation flux was investigated using Arrhenius relationship, and the activation energy values were calculated for total permeation (E_p), water (E_pw), and IPA (E_pIPA) fluxes. Lower value of E_pw in comparison with E_pIPA supported excellent dehydration performance of the cross‐linked membranes. Despite large increase in activation energy of water with prolonged cross‐linking time, the selectivity was improved. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2013     

Study on mechanical,thermal and shape memory properties of polycarbonate/thermoplastic polyurethane blends

The objective of the study is preparation of shape memory blend of polycarbonate (PC) and thermoplastic polyurethane (TPU). Polycarbonate is blended with three types of TPUs and subsequently mechanical, thermal, morphological, and shape memory properties of the PC/TPU blends are studied. When TPU content in the blend is higher than 40% (by weight), the glass transition temperature related to PC is not shown in the differential scanning calorimetry thermogram, indicating loss of PC properties. The 60/40 optimized blend of PC/TPUs exhibits maximum increment of about 1100% in elongation and 43% decrement in tensile strength. The shape recovery of the optimized blend obtained by addition of 40% (by weight) of TPUs in PC polymer is found to be 65% and shape fixity is 97%. These results suggest that the blend of PC/TPU may be utilized for various applications where shape memory property is required including strategic applications.