Soybean oil‐based shape‐memory polyurethanes: Synthesis and characterization

Shape‐memory polymers (SMPs) have wide range of applications due to their ability to sense environmental stimuli and reshape from a temporary shape to a permanent shape. Plant oil‐based polymeric materials are highly concerned in recent years in consideration of petroleum depletion and environmental pollution. However, plant oil‐based polymers are rarely investigated regarding their shape‐memory characteristics though bio‐based SMPs are highly desired nowadays. In this study, a series of soybean oil‐based shape‐memory polyurethanes (SSMPUs) are prepared through a mild chemo‐enzymatic synthetic route, and their properties are fully characterized with tensile testing, DSC, dynamic mechanical analysis (DMA), and shape‐memory testing. Results show that SSMPUs are soft rubbers with tensile strength in the range of 1.9–2.2 MPa and glass transition temperature in the range of 2–5°C, and possess good shape recoveries at RT when stretching ratio is 10, 20, and 30%, respectively. This work would promote the development of high‐value‐added plant oil‐based shape‐memory polyurethanes. Practical applications: Using annual renewable plant oil as feedstock, the synthesized SSMPUs show good shape recovery properties, which will make them applicable as potential alternatives to petroleum‐based shape‐memory materials. The simple and mild preparation process also contributes to the further exploration of plant oil to value‐added functional materials.     

Synthesis and characterization of novel aromatic polyamides derived from 2,2′‐bis(p‐phenoxyphenyl)‐4, 4′‐diaminodiphenyl ether

BACKGROUND: Wholly aromatic polyamides (aramids) are high‐performance polymeric materials with outstanding heat resistance and excellent chemical stabilities due to chain stiffness and intermolecular hydrogen bonding of amide groups. Synthesis of structurally well‐designed monomers is an effective strategy to prepare modified forms of these aramids to overcome lack of organo‐solubility and processability limitations. RESULTS: A novel class of wholly aromatic polyamides was prepared from a new diamine, namely 2,2′‐bis(p‐phenoxyphenyl)‐4,4′‐diaminodiphenyl ether (PPAPE), and two simple aromatic dicarboxylic acids. Two reference polyamides were also prepared by reacting 4,4′‐diaminodiphenyl ether with the same comonomers under similar conditions. M?_w and M?_n of the resultant polymers were 8.0 × 10⁴ and 5.5 × 10⁴ g mol^?1, respectively. Polymers resulting from PPAPE exhibited a nearly amorphous nature. These polyamides exhibited excellent organo‐solubility in a variety of polar solvents and possessed glass transition temperatures up to 200 °C. The 10% weight loss temperatures of these polymers were found to be up to 500 °C under a nitrogen atmosphere. The polymers obtained from PPAPE could be cast into transparent and flexible films from N,N‐dimethylacetamide solution. CONCLUSION: The results obtained show that the new PPAPE diamine can be considered as a good monomer to enhance the processability of its resultant aromatic polyamides while maintaining their high thermal stability. The observed characteristics of the polyamides obtained make them promising high‐performance polymeric materials. Copyright © 2009 Society of Chemical Industry     

Sustainable shape memory polymers based on epoxidized natural rubber cured by zinc ferulate via oxa-Michael reaction

Although various shape memory polymers (SMPs) or diverse applications have been widely reported, the SMPs based on rubbers have been rarely realized due to the low triggering temperature of rubbers. In another aspect, the SMPs based on sustainable substances are highly desired for the growing shortage in fossil resources. In the present study, we accordingly developed the sustainable SMPs with tunable triggering temperature, based on natural rubber (NR) and ferulic acid (FA) as the raw materials. Specifically, the SMPs are based on a crosslinked network of epoxidized natural rubber (ENR) crosslinked by in situ formed zinc ferulate (ZDF) via oxa-Michael reaction. The excellent shape memory effect (SME) is found in these SMPs, as evidenced by the high fixity/recovery ratio and the tunable triggering temperature. With the incorporation of natural halloysite nanotubes (HNTs), the stress and recovery rate of the SMPs are found to be tunable, which widens the application of this kind of SMPs. The combination of adoption of sustainable raw materials, and the excellent and tunable SME makes these SMPs potentially useful in many applications, such as various actuators and heat-shrinkable package materials.     

Fourier transform infrared study of supramolecular polyurethane networks containing pyridine moieties for shape memory materials

Non‐covalent interactions are increasingly used in the molecular self‐assembly of well‐defined structures. In this study, a series of pyridine‐containing polyurethanes (PUPys) were synthesized with diisocyanates and pyridine derivatives. Fourier transform infrared spectroscopy was employed to identify the vibration frequencies and investigate the relationship of shape memory effect (SME) and hydrogen‐bonded supramolecular structure of the PUPys. The results show that a large fraction of strong hydrogen bonds are formed in the urethane group as well as in the pyridine ring. Moreover, the hydrogen bonding in the pyridine ring not only shows a response to a temperature stimulus in the PUPys, but is also responsive to moisture in N,N‐bis(2‐hydroxylethyl)isonicotinamine (BINA)/hexamethylene diisocyanate (HDI)‐based PUPys; the hydrogen bonds in the urethane group have a higher dissociation temperature and show little response to moisture absorption. Accordingly, the PUPys are expected to show thermally induced and moisture‐induced SMEs. Finally, the shape recovery process of films in the shape of flowers induced by temperature and moisture supports the idea that the PUPys could be used as thermally induced shape memory polymers (SMPs), and the BINA/HDI‐based PUPys could be used as moisture‐sensitive SMPs. Copyright © 2009 Society of Chemical Industry     

Stress memory of a thermoset shape memory polymer

The performance of stress recovery and shape recovery are equally important for high performance shape memory polymers (SMPs) in emerging applications. However, unlike shape recovery, stress recovery does not always follow a monotonic behavior, i.e., “stress plateau,” “stress overshoot,” and “stress undershoot” can be observed. In order to reveal the complicated stress memorization and recovery behavior, this study employs a phenomenological model which considers the recovery stress as the sum of residual programming stress, memorized stress, thermal stress, and relaxed stress for amorphous crosslinked SMPs. This model is demonstrated by a stress recovery experiment in which a polystyrene based SMP was programmed at two prestrain levels above the glass transition temperature, i.e., 20% (neo‐Hookean hyperelastic region) and 50% (strain‐hardening region), and two fixation temperatures, i.e., 20°C (below T_g) and 45°C (within the T_g region), respectively. In addition, a clear distinction between the memorized stress and recovery stress is presented. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42112.     

Synthesis and characterization of poly(ester‐ether‐imide)s derived from 5‐(4‐trimellitimidophenoxy)‐1‐trimellitimido naphthalene

A series of novel aromatic poly(ester‐ether‐imide)s with inherent viscosity values of 0.44–0.74 dL g^?1 were prepared by the diphenylchlorophosphate‐activated direct polycondensation of an imide ring‐containing diacid namely 5‐(4‐trimellitimidophenoxy)‐1‐trimellitimido naphthalene ( 1 ) with various aromatic dihydroxy compounds in the presence of pyridine and lithium chloride. Owing to comparison of the characterization data, an ester‐containing model compound ( 2 ) was also synthesized by the reaction of 1 with phenol. The model compound 2 and the resulted polymers were fully characterized by FT‐IR and NMR spectroscopy. The ultraviolet λ_max values of the poly(ester‐ether‐imide)s were also determined. The resulting polymers exhibited an excellent organosolubility in a variety of high polar solvents such as N,N‐dimethylacetamide, N,N‐dimethylformamide, dimethyl sulfoxide, and N‐methyl‐2‐pyrrolidone. They were soluble even in common less polar organic solvents such as pyridine, m‐cresol, and tetrahydrofuran on heating. Crystallinity of the polymers was estimated by means of wide‐angle X‐ray diffraction. The resulted polymers exhibited nearly an amorphous nature. From differential scanning calorimetry thermograms, the polymers showed glass‐transition temperatures between 221 and 245°C. Thermal behaviors of the obtained polymers were characterized by thermogravimetric analysis, and the 10% weight loss temperatures of the poly(ester‐ether‐imide)s were found to be over 410°C in nitrogen. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis of high temperature polyaspartimide-urea based shape memory polymers

Thermally activated shape memory polymers (SMPs) have attracted great interest in recent years for application in adaptive shape-changing (morphing) aero structures. However, these components require materials with transition temperatures well above the glass transition temperatures of most widely available SMPs while also maintaining processability and property tailorability. In the present study, a series of novel polyaspartimide-urea based polymers are synthesized and characterized. The glass transition temperature and shape memory properties are varied using a diisocyanate resin creating a urea crosslinking moiety between the polyaspartimide chains. Overall, a family of high temperature SMPs was synthesized and characterized showing high thermal stability (>300 °C), toughness, strong shape memory effects, and tailorable properties.     

Synthesis and characterization of poly(arylene ether s‐triazine)s containing alkyl‐, aryl‐ and chloro‐substituted phthalazinone moieties in the main chain

Soluble and heat‐resistant polymers have great potential for use as processable, high‐temperature polymeric materials. In this study, four types of new poly(arylene ether s‐triazine)s containing alkyl‐, aryl‐ and chloro‐substituted phthalazinone moieties in the main chain were prepared through direct solution polycondensation of 2,4‐bis(4‐fluorophenyl)‐6‐phenyl‐s‐triazine with each of methyl‐, phenyl‐ and chloro‐substituted phthalazinones. A key feature of these polymers is the incorporation of phthalazinone and side groups into the poly(arylene ether s‐triazine) backbone to endow them with good solubility while maintaining other attractive properties. The polymers were obtained in high yields, and had inherent viscosities ranging from 0.38 to 0.55 dL g^?1. Their structure was characterized using Fourier transform infrared and NMR spectra and elemental analysis. The polymers were almost amorphous, and soluble in N‐methyl‐2‐pyrrolidone, pyridine, N,N‐dimethylacetamide, hot N,N‐dimethylformamide and sulfolane. Tough and nearly transparent films obtained by direct solution casting exhibited good mechanical properties. The resulting polymers displayed glass transition temperatures ranging from 255 to 265 °C and thermal decomposition temperatures for 10% mass loss ranging from 476 to 599 °C, according to differential scanning calorimetry and thermogravimetric analysis, respectively. The reactivity of substituted phthalazinones in nucleophilic displacement reactions and the effect of the side groups on the physical properties of the polymers were also investigated. The results obtained revealed that such s‐triazine‐containing polymers possessed good solubility while maintaining acceptable thermal stability and high mechanical strength with the incorporation of alkyl‐, aryl‐ and chloro‐substituted phthalazinone moieties into their backbones, which makes them an attractive series of high‐performance structural materials. Copyright © 2010 Society of Chemical Industry     

Shape‐memory polymer networks with Fe3O4 nanoparticles for remote activation

Shape‐memory polymers (SMPs) have recently shown the capacity to actuate by remote heating via the incorporation of magnetic nanoparticles into the polymer matrix and exposure to an alternating magnetic field. In this study, methacrylate‐based thermoset SMP networks were synthesized through free‐radical polymerization with varying amounts of Fe₃O₄ magnetite (0, 1, and 2.5 wt %). Furthermore, the chemistry of the networks was controlled to maintain a constant glass transition temperature (T_g) while varying the degree of chemical crosslinking. Remote heating of the networks was shown to be a direct function of the nanoparticle concentration and independent of the chemistry. Magnetite reinforcement was shown to influence the thermomechanical properties of the networks; increasing Fe₃O₄ concentrations led to decreases in T_g and rubbery modulus. However, networks with a higher degree of crosslinking were more resistant to thermomechanical changes with respect to magnetite concentration. Strain to failure was shown to decrease with the addition of nanoparticles and the free‐strain shape‐memory cycle was investigated for all of the networks. Networks with lower degrees of crosslinking and high magnetite concentrations showed a significant amount of irrecoverable strain. Last, the use of remotely heated shape‐memory materials is discussed in light of potential biomedical applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

New soybean oil–styrene–divinylbenzene thermosetting copolymers. v. shape memory effect

A series of new shape memory polymers are synthesized by the cationic copolymerization of regular soybean oil, low saturation soybean oil (LoSatSoy oil), and/or conjugated LoSatSoy oil with styrene and divinylbenzene, norbornadiene, or dicyclopentadiene initiated by boron trifluoride diethyl etherate or related modified initiators. The shape memory properties of the soybean oil polymers are characterized by the deformability (D) of the materials at temperatures higher than their glass‐transition temperatures (T_g), the degree to which the deformation is subsequently fixed at ambient temperature (FD), and the final shape recovery (R) upon being reheated. It is found that a T_g well above ambient temperature and a stable crosslinked network are two prerequisites for these soybean oil polymers to exhibit shape memory effects. Good shape memory materials with high D, FD, and R values are prepared by controlling the crosslink densities and the rigidity of the polymer backbones. The advantage of the soybean oil polymers lies in the high degree of chemical control over the shape memory characteristics. This makes these materials particularly promising in applications where shape memory properties are desirable. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1533–1543, 2002; DOI 10.1002/app.10493     

Characterization and strain‐energy‐function‐based modeling of the thermomechanical response of shape‐memory polymers

Shape‐memory polymers (SMPs) are an emerging class of active polymers that can be used on a wide range of reconfigurable structures and actuation devices. In this study, an epoxy‐based SMP was synthesized, and its thermomechanical behaviors were comprehensively characterized. The stress–strain behavior of the SMP was determined to be nonlinear, finite deformation in all regions. Strain‐energy‐based models were used to capture the complicated stress–strain behavior and shape‐recovery response of the SMP. Among various strain energy functions, the stretch‐based Ogden model provided the best fit to the experimental observations. Compared to the sophisticated models developed for SMPs, the strain‐energy‐based model was found to be reliable and much easier to use for practical SMP designs. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41861.     

Effect of the crosslinking density and programming temperature on the shape fixity and shape recovery in epoxy–anhydride shape‐memory polymers

In addition to the fabrication of thermoset epoxy–anhydride shape‐memory polymers (SMPs), a systematic experimental investigation was conducted to characterize the crosslinking density, micromorphology, thermal properties, mechanical properties, and shape‐memory effects in the epoxy SMP system, with a focus on the influence of the crosslinking density and programming temperature on the shape‐fixity and shape‐recovery behaviors of the polymers. On the basis of the crosslinking density information determined by NMR technology, we concluded that the effect of the crosslinking density on the shape‐fixity behaviors was dependent on the programming temperature. The advantage of a nice combination of crosslinking density and programming temperature provided an effective approach to tailor the actual shape recovery within a wide range. The increasing crosslinking density significantly improved the shape‐recovery ratio, which could be further improved through a decrease in the programming, whereas the crosslinking density was more fundamental. This exploration should play an important role in the fabrication and applications of SMP materials. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40559.     

High transition temperature shape memory polymers (SMPs) by telechelic oligomer approach

This work describes the synthesis and comparative shape memory properties of cross-linked networks derived from epoxy and cyanate ester monomers containing polyether oligomers as reactive shape memory segments. The hydroxy telechelic oligomers viz. polyethyleneglycol (PEG), polypropyleneglycol (PPG), and polytetramethyleneglycol (PTG) are reacted with epoxy–cyanate ester matrix resulting in shape memory polymers with high transition temperatures. The soft oligomer segments act as flexible linker unit which interconnect oxazolidone, isocyanurate and triazine ring structures in the cross-linked polymer. The resultant cyclomatrix SMPs exhibit high transition temperatures 132, 178 and 161 °C respectively for PEG, PPG and PTG integrated SMPs. The E_g/E_r ratios are increased in the order PEG < PTG < PPG. The PTG and PPG based SMPs show shape retention of 99% and shape recovery of >98% with recovery time <100 s. All the SMPs display good thermal stabilities (both inert and oxidative) above 275 °C.     

Thermomechanical and shape memory properties of thermosetting shape memory polymer under compressive loadings

Shape memory polymers (SMPs) are an emerging class of active polymers that may be used for a range of reconfigurable structures. In this study, the thermomechanical and shape memory behavior of a thermosetting SMP was investigated using large‐scale compressive tests and small‐scale indentation tests. Results show that the SMP exhibits different deformation modes and mechanical properties in compression than in tension. In glassy state, the SMP displays significant plastic deformation and has a much higher modulus and yield strength in comparison to those obtained in tension. In rubbery state, the SMP behaves like a hyperelastic material and again has a much higher modulus than that obtained in tension. The SMPs were further conditioned separately in simulated service environments relevant to Air Force missions, namely, (1) exposure to UV radiation, (2) immersion in jet‐oil, and (3) immersion in water. The thermomechanical and shape recovery properties of the original and conditioned SMPs were examined under compression. Results show that all the conditioned SMPs exhibit a decrease in T_g as compared to the original SMP. Environmental conditionings generally result in higher moduli and yield strength of the SMPs in the glassy state but lower modulus in the rubbery state. In particular, the UV exposure and water immersion, also weaken the shape recovery abilities of the SMPs. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Facile control of high temperature shape memory polymers

Glass transition temperature (T_g) is crucial in determining application areas of high temperature shape memory polymers (SMPs), but some T_gs are difficult or uneconomic to be obtained. Here we introduce a facile way to prepare high temperature SMPs with controllable T_gs from 183 to 230 °C by copolymerization of polyimides, and relationships between T_gs and diamine components of the shape memory copolyimides agree with Fox Equation. These copolyimides can fix temporary shape and return to original shape nicely, and the possible mechanisms of their high shape fixity and shape recovery are analyzed on the basis of thermomechanical properties and molecular structures. The copolymerization of shape memory polyimides has offered an effective way to obtain high temperature SMPs with desired properties. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44902.     

Effect of diisocyanate on pyridine containing shape memory polyurethanes based on N,N‐bis(2‐hydroxylethyl)isonicotinamide

This article demonstrates a comparative investigation about the effect of diisocyanate on pyridine containing shape memory polyurethanes (Py‐SMPUs), which are synthesized with N,N‐bis(2‐hydroxylethyl)isonicotinamide (BINA) and four different diisocyanates: 1,6‐hexanediisocyante (HDI), isophorone diisocyanate (IPDI), methylene diphenyl diisocyanate (MDI), and tolylene diisocyanate (TDI). Results show that all BINA–SMPU systems have amorphous reversible phase. Comparatively, the MDI–BINA and TDI–BINA systems show higher T_g; and the HDI–BINA and IPDI–BINA systems show better thermal stability. In addition, the HDI–BINA and the IPDI–BINA systems exhibit good thermal‐induced shape memory effect and good moisture‐sensitive shape memory effect due to their better moisture absorption properties. Particularly, the HDI–BINA system has better response speed and better shape recovery. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40721.     

Synthesis and characterization of new thermally stable poly(ester‐imide)s derived from 2,2′‐bis(4‐trimellitimidophenoxy)biphenyl and 2,2′‐bis(4‐trimellitimidophenoxy)‐1,1′‐binaphthyl and various aromatic dihydroxy compounds

A series of new alternating aromatic poly(ester‐imide)s were prepared by the polycondensation of the preformed imide ring‐containing diacids, 2,2′‐bis(4‐trimellitimidophenoxy)biphenyl (2a) and 2,2′‐bis(4‐trimellitimidophenoxy)‐1,1′‐binaphthyl (2b) with various aromatic dihydroxy compounds in the presence of pyridine and lithium chloride. A model compound (3) was also prepared by the reaction of 2b with phenol, its synthesis permitting an optimization of polymerization conditions. Poly(ester‐imides) were fully characterized by FTIR, UV‐vis and NMR spectroscopy. Both biphenylene‐ and binaphthylene‐based poly(ester‐imide)s exhibited excellent solubility in common organic solvents such as tetrahydrofuran, m‐cresol, pyridine and dichloromethane. However, binaphthylene‐based poly(ester‐imide)s were more soluble than those of biphenylene‐based polymers in highly polar organic solvents, including N‐methyl‐2‐pyrrolidone, N,N‐dimethylacetamide, N,N‐dimethylformamide and dimethyl sulfoxide. From differential scanning calorimetry thermograms, the polymers showed glass‐transition temperatures between 261 and 315 °C. Thermal behaviour of the polymers obtained was characterized by thermogravimetric analysis, and the 10 % weight loss temperatures of the poly(ester‐imide)s was in the range 449–491 °C in nitrogen. Furthermore, crystallinity of the polymers was estimated by means of wide‐angle X‐ray diffraction. The resultant poly(ester‐imide)s exhibited nearly an amorphous nature, except poly(ester‐imide)s derived from hydroquinone and 4,4′‐dihydroxybiphenyl. In general, polymers containing binaphthyl units showed higher thermal stability but lower crystallinity than polymers containing biphenyl units. Copyright © 2005 Society of Chemical Industry     

Synthesis and characterization of aromatic/cycloaliphatic poly(amide‐ imide‐imide)s from bis(4‐amino‐ 3,5‐dimethylphenyl) cycloalkane derivatives

A series of novel aromatic diamines containing cycloaliphatic moieties was synthesized by the reaction of cycloalkanones like cyclohexanone and cycloheptanone with 2,6‐dimethylaniline. The tetrimide diacid was synthesized using the prepared diamine with 3,3′,4,4′‐benzophenonetetracarboxylic acid dianhydride/pyromellitic dianhydride and p‐aminobenzoic acid. The polymers were prepared by treating the tetrimide diacid with different aromatic diamines. The structures of the monomers and polymers were identified using elemental analysis and Fourier transform infrared, ¹H NMR and ¹³C NMR spectroscopy. The polymers show excellent solubility. The polymers are amorphous and have high optical transparency. They also show good thermal stability and their T_g value is found to be in the range 268–305 °C. Copyright © 2007 Society of Chemical Industry     

Synthesis and properties of biodegradable supramolecular polymers based on polylactide‐block‐poly(δ‐valerolactone)‐block‐polylactide triblock copolymers

Biodegradable supramolecular polymers (SMPs) were synthesized by the end‐functionalization of polylactide‐block‐poly(δ‐valerolactone)‐block‐polylactide (PLA–PVL–PLA) triblock copolymers with 2‐ureido‐4[1H]‐pyrimidinone (UPy) self‐complementary quadruple hydrogen‐bonding units. The end‐functionalized PLA–PVL–PLA copolymers exhibit the typical characteristics of thermoplastic elastomers. Thermal properties, crystallization behavior, crystalline structure and other properties of SMPs can be adjusted by changing the length and stereostructure of PLA blocks. The UPy groups retard the crystallization of PLA and PVL blocks, and the crystallization of PVL blocks is also depressed with increasing PLA blocks. Tensile testing reveals that the prepared SMPs present excellent mechanical properties, and dynamic mechanical analysis indicates that the heat resistance of l ‐SMPs is better than that of d ,l ‐SMPs. Shape memory property of SMPs was also studied, and the recovery ratio of SMPs with PDLLA blocks can reach 100%. The recovery ratio of l ‐SMPs is depressed as the crystallizable PLLA blocks increase. This study has systemically investigated the effect of the composition, stereostructure and crystallizability of PLA blocks on the properties of SMPs, which would provide potential approaches for the synthesis of biodegradable SMPs with tunable properties. © 2017 Society of Chemical Industry     

Recent advance on constitutive models of thermal‐sensitive shape memory polymers

Shape memory polymers (SMPs) are a novel class of shape memory materials which can store a deformed (temporary) shape and recover an original (permanent) shape under a shape memory thermomechanical loading–unloading cycle. The deformation mechanisms of SMPs are very complicated, but the SMPs also have a lot of advantages and the widespread application value and prospect. So developing proper constitutive models that describe thermomechanical properties of SMPs and the shape memory effect is very challenging and of great theoretical and application value. Based on the deformation mechanisms and considerable experimental investigations of SMPs, researchers have developed many constitutive models. This article investigates the deformation mechanism and introduces the recent research advance of the constitutive models of thermal‐sensitive SMPs. Special emphases are given on the micromechanical constitutive relations in which the deformation is considered being based on the microstructure of the SMPs. Finally, the lack of research and prospects for further research are discussed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012