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.     

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

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

Shape memory effect of poly(L‐lactide)‐ based polyurethanes with different hard segments

A series of biodegradable polylactide‐based polyurethanes (PLAUs) were synthesized using PLA diol (M_n = 3200) as soft segment, 4,4′‐diphenylmethane diisocyanate (MDI), 2,4‐toluene diisocyanate (TDI), and isophorone diisocyanate (IPDI) as hard segment, and 1,4‐butanediol as chain extender. The structures and properties of these PLAUs were studied using infrared spectroscopy, differential scanning calorimetry, tensile testing, and thermomechanical analysis. Among them, the MDI‐based PLAU has the highest T_g, maximum tensile strength, and restoration force, the TDI‐based PLAU has the lowest T_g, and the IPDI‐based PLAU has the highest tensile modulus and elongation at break. They are all amorphous. The shape recovery of the three PLAUs is almost complete in a tensile elongation of 150% or a twofold compression. They can keep their temporary shape easily at room temperature (20 °C). More importantly, they can deform and recover at a temperature below their T_g values. Therefore, by selecting the appropriate hard segment and adjusting the ratio of hard to soft segments, they can meet different practical demands for shape memory medical devices. Copyright © 2007 Society of Chemical Industry     

Novel moisture-sensitive shape memory polyurethanes containing pyridine moieties

In this communication, novel moisture-sensitive shape memory polyurethane (SMPU) was synthesized from 1,6-hexamethylene diisocyanate (HDI) and N,N-bis(2-hydroxylethyl) isonicotinamide (BINA) and 1,4-butanediol (BDO). Results show that the BINA based SMPUs have excellent moisture absorption properties which are not only influenced by the temperature, but also by the relative humidity (RH). As a result, high strain recovery with fast recovery speed is obtained after immersion in the moisture condition for a short time. FT-IR spectra provide a proof to the mechanism of moisture-sensitive SME which is based on the dissociation or disrupt of hydrogen bonding in the pyridine ring induced by moisture absorption. Thus, the strain recovery is achieved in the moisture-sensitive SMPUs by decreasing the glass transition temperature (T_g) below ambient temperature without external heating.     

Effect of molecular weight on shape memory behavior in polyurethane films

Understanding the relationship between the number‐average molecular weight (M_n) and the shape memory behavior of polymers is crucial for a complete picture of their thermomechanical properties, and hence for the development of smart materials, and, in particular, in textile technology. We report here on the study of shape memory properties as a function of M_n of polymers. Shape memory polyurethanes (SMPUs) of different M_n were synthesized, with various catalyst contents or molar ratio(r = NCO/OH) in the composition. In particular, two types of SMPU, namely T_m and T_g types according to their switch temperature type, were synthesized to compare the influence of M_n on their shape memory behavior. X‐ray diffraction, differential scanning calorimetry, dynamic mechanical analysis, and shape memory behavior results for the SMPUs are presented. The results indicate that the melting temperature (T_m), the glass transition temperature (T_g), the crystallinity, and the crystallizability of the soft segment in SMPUs are influenced significantly by M_n, before reaching a critical limit around 200 000 g mol^?1. Characterization of the shape memory effect in PU films suggests that the T_m‐type films generally show higher shape fixities than the T_g‐type films. In addition, this shape fixity decreases with increasing M_n in the T_g‐type SMPU, but the shape recovery increases with M_n in both types of SMPU. The shape recovery temperature, in contrast, decreases with M_n as suggested by the result of their thermal strain recovery. It is concluded that a higher molecular weight (M_n > 200 000 g mol^?1) is a prerequisite for SMPUs to exhibit higher shape recovery at a particular temperature. Copyright © 2007 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     

Biobased chain extended polyurethane and its composites with silk fiber

The biobased chain extended polyurethane (PU) was synthesized by reacting castor oil based polyol with different diisocyanates [toluene‐2,4‐diisocyanate (TDI) and hexamethylene diisocyanate (HMDI)] and chain extender such as glutaric acid. Biocomposites have been fabricated by incorporating the silk fiber into both TDI‐ and HMDI‐based PUs. The effect of incorporation of silk fiber into TDI‐ and HMDI‐based neat PU on the physicomechanical properties such as density, surface hardness, tensile strength, and percentage elongation have been investigated. The dynamic mechanical properties and the thermal stability of neat PUs and the silk fiber incorporated PU composites have been evaluated. The TDI‐based neat PU has showed higher mechanical properties compared to HMDI‐based PU. The incorporation of 10% silk fiber into TDI‐ and HMDI‐based PU resulted in an enhancement of tensile strength by 1.8 and 2.2 folds, respectively. The incorporation of silk fiber into biobased chain extended PU increased the glass transition temperature (T_g) of the resultant biocomposites. The morphology of tensile fractured neat PUs and their biocomposites with silk fiber was studied using scanning electron microscope (SEM). POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

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     

Polyurethanes with monodisperse rigid segments based on a diamine–diamide chain extender

Polyether(bisurethane‐bisurea‐bisamide)s (PEUUA) based on poly(tetramethylene oxide) (PTMO) were synthesized by chain extension of PTMO endcapped with a diisocyanate (DI), and a diamine–diamide extender. The prepolymers were PTMOs with molecular weights between 1270 and 2200 g mol^?1, either endcapped with 4,4′‐diphenylmethane diisocyanate (MDI), 2,4‐toluene diisocyanate (2,4‐TDI), or 1,6‐hexane diisocyante (HDI) and with a low content of free diisocyanate (<0.1 wt %). The diamine–diamide (6A6) extender was based on hexamethylene diamine (6) and adipic acid (A). In this way, segmented polyurethanes with monodisperse rigid segments (DI‐6A6‐DI) were obtained. The PEUUAs were characterized by DSC as well as temperature‐dependent FTIR and DMTA. The mechanical properties of the polymers were evaluated by compression set and tensile test measurements. The polyurethanes with monodisperse rigid segments displayed low glass transition temperatures, almost temperature‐independent rubbery plateaus and sharp melting temperatures. The crystallinities of the hard segments were 70–80% upon heating and 40–60% upon cooling. The rate of crystallization was moderately fast as the supercooling (T_m ? T_c) was in the order 36–54°C. The polyurethanes based on HDI had a much higher rubber modulus as compared to the MDI and 2,4‐TDI‐based polymers, because of a higher degree of crystallinity and/or a higher aspect ratio of the crystallites. The HDI residues are flexible and not sterically hindered and could therefore be more easily packed than MDI or 2,4‐TDI residues. Polyurethanes with monodisperse DI‐6A6‐DI hard segments have interesting properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Shape memory crosslinked polyurethanes containing thermoreversible Diels‐Alder couplings

Crosslinked polyurethanes (PUs) containing irreversible (allophanate) and reversible Diels‐Alder chemical bonds were synthesized using various diisocyanates (methylene diphenyl diisocyanate MDI, 1,6‐hexamethylenediisocyanate HDI) and poly(?‐caprolactone) ((PCL) with different molecular weights (M_n = 10 kg/mol, 25 kg/mol, 50 kg/mol) as diol component. The melting/crystallization of PCL and the reversible DA bonds acted as temperature‐activated switches for shape memory performances, while allophanate network provided the permanent crosslinks for these PUs. The reversible DA bonds were obtained by the reaction of diisocyanate‐ended prepolymers with furfurylamine (FA) followed by the addition of bismaleimide (BMI). The permanent crosslinks between the linear chains containing DA bonds were achieved using additional amounts of diisocyanates (MDI or HDI). The above reaction path was supported by infrared spectroscopic results and swelling experiments. Tensile mechanical and shape memory properties in tension of the PUs were determined and discussed as a function of composition and crosslink densities deduced from swelling and dynamic mechanical analysis. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44145.     

Crosslinked polyurethanes with shape memory properties

A series of shape memory polyurethanes (SMPUs) was prepared from polycaprolactone diol (PCL) 4000, 1,4‐butanediol (BDO), dimethylol propionic acid (DMPA), triethylamine, and 4, 4′‐diphenylmethane diisocyanate (MDI), to which excess MDI or glycerin were added to obtain crosslinked shape memory polyurethanes. Their mechanical, thermomechanical, thermal and shape memory properties were investigated by using differential scanning calorimetry (DSC), Fourier‐transform (FT‐IR) spectroscopy, dynamic mechanical analysis (DMA) and tensile testing. The results showed that crosslinked SMPUs have better thermal and thermomechanical properties than those prepared from linear polyurethanes and display good shape memory effects. Copyright © 2005 Society of Chemical Industry     

Synthesis,characterisation, and chemical degradation of segmented polyurethanes with butylamine for chemical recycling

Polyurethane elastomers (PU) have been synthesized from polytetramethylene glycol 2000 (PTMG 2000); 4, 4′‐diphenylmethane diisocyanate (MDI) and 1, 4‐butanediol (BD) as chain extender. This synthesis has been done in two steps known as prepolymer methods. The concentration of soft segments and hydrogen attachment in the matrices, have been studied. The results show that the glass transition of the soft segment T_g(s) do not take any changes with the concentration of the soft segment in the matrices. Although, the glass transition temperature of the hard segment T_g(H) increases when the concentration of the hard segment increases in the matrices. In general, the properties of the polyurethane elastomers depend on the extenders nature, the synthesis methods, phase segregation etc. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Development of shape memory polyurethane based on polyethylene glycol and liquefied 4,4′‐diphenylmethane diisocyanate using a bulk method for biomedical applications

In this study, a series of shape memory polyurethanes (SMPUs) were synthesized successfully by the bulk polymerization method from liquefied 4,4′‐diphenylmethane diisocyanate (L‐MDI), 1,4‐butanediol (BDO) and polyethylene glycol (PEG). The influence of the hard segment content (HSC) on the structure, morphology, properties and biocompatibility of PEG based SMPUs (PEGSMPUs) was carefully investigated. The results show that a microphase separation structure composed of a semicrystalline soft phase and an amorphous hard phase is formed in the PEG6000/L‐MDI/BDO system. Crystallization of the PEG soft segment is influenced by the hard segments. The PEG semicrystalline soft phase serves as a reversible phase while the L‐MDI?BDO hard segment acts as physical netpoints. Finally, a cyclic tensile test shows that all PEGSMPUs have good shape recovery (e.g. above 80%), whereas good shape fixity can only be achieved when the HSC is less than 35 wt%. The Cell Counting Kit 8 assay also demonstrates that only PEGSMPUs containing less than 40 wt% HSC have low cytotoxicity. It is thus concluded that PEGSMPUs bearing both good shape memory effects and good biocompatibility can be used as shape memory materials for biomedical applications when the HSC is less than 35 wt%. © 2014 Society of Chemical Industry     

Novel synthetic strategy toward shape memory polyurethanes with a well-defined switching temperature

Shape memory polyurethanes (SMPUs) have been synthesised via a novel synthetic methodology, resulting in an improvement of the phase separation in the multi-block structure of the polyurethane and in its shape memory properties. ABA block copolymers based on semi-crystalline poly(-caprolactone) and amorphous poly(propylene oxide) (PPO) were used as precursor for the SMPUs. For their synthesis, poly(-caprolactone) diols have been converted into isocyanate end-capped prepolymers by using a mixture of 3(4) isocyanato-1-methyl-cyclohexylisocyanate isomers, after which a coupling with low-T_g poly(propylene oxide) oligomers is done. The shape memory polymers are obtained by reaction of the ABA block copolymers with hexamethylenediisocyanate and 1,4-butanediol as chain extender. Using this new strategy, a flexible segment (PPO) was introduced between the hard and the switching segments of the SMPU. For comparison, SMPUs without flexible segment have also been prepared with the conventional synthetic route. DSC, isostrain experiments and cyclic shape memory tests revealed narrower switching temperatures for the SMPUs including a flexible segment.     

Effects of TDI and FA‐703 on physico‐mechanical properties of polyurethane dispersion

A series of water dispersion polyurethanes dispersions (PUDs) were prepared by polyaddition reaction using isophorone diisocyanate (IPDI), toluene diisocyanate (TDI), poly(oxytetramethylene) glycol (PTMG), dimethylol propionic acid (DMPA), and triol (trade name FA‐703). Various formulations were designed to investigate the effects of process variables such as TDI and FA‐703 on the physico‐mechanical properties of PUD. IR spectroscopy was used to check the end of polymerization reaction and characterization of polymer. Evolution of the particle size distribution, contact angle, T_g, molecular weight, viscosity, and mechanical properties of the emulsion‐cast films were significantly affected by variable content of TDI and FA‐703. Average particle size of the prepared polyurethane emulsions and contact angle decrease with increase of content of FA‐703 and TDI. Molecular weight, T_g, tensile strength, tear strength, hardness, viscosity and elongation at break increase with increase of content of FA‐703 and TDI. The increase of molecular weight, tensile strength, tear strength and elongation at break properties are interpreted in terms of increasing hard segments, chain flexibility, and phase separation in high content of FA‐703 and TDI‐based polyurethane. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermomechanical properties and shape memory effect of epoxidized natural rubber crosslinked by 3‐amino‐1,2,4‐triazole

A thermally induced shape memory polymer based on epoxidized natural rubber (ENR) was produced by curing the ENR with 3‐amino‐1,2,4‐triazole as a crosslinker in the presence of bisphenol‐A as a catalyst. Dynamic mechanical and tensile analysis was conducted to examine the variation of glass transition temperature, stiffness, and extensibility of the vulcanizates with the amount of curatives. Shape memory properties of the ENR vulcanizates were characterized by shape retention and shape recovery. It was revealed that the glass transition temperature of the ENR vulcanizates could be tuned well above room temperature by increasing the amount of curing agents. Also, ENR vulcanizates with T_g higher than ambient temperature showed good shape memory effects under 100% elongation, and the response temperatures of the recovery were well matched with T_g of the samples. Copyright © 2006 Society of Chemical Industry     

Toughening epoxy resin with blocked isocyanate containing soft chain

A series of imidazole (MI) blocked 2,4‐toluene diisocyanate (TDI) with polyethylene glycol (PEG‐400) as soft segment (PEG‐MI‐b‐TDI) were synthesized for toughening and curing the bisphenol A type epoxy resin (E‐44). Fourier transform infrared (FTIR) spectrum indicates that the NCO groups of the isocyanate molecule are blocked with MI. For curing epoxy systems, elimination of epoxy group and the formation of urethane bonds were studied by FTIR spectroscopy. The results of mechanical property were shown that the tensile shear and impact strengths of neat MI and MI‐b‐TDI cured E‐44 are lower than those of PEG‐MI‐b‐TDI cured E‐44. Based on the scanning electron microscope studies, microstructure evolutions of the E‐44 cured by different curing agents were imaged. The mechanical, thermal, and dynamic mechanical properties were measured by universal testing machine, differential scanning calorimeter and dynamic mechanical analyzer (DMA). The toughness of E‐44 cured by PEG‐MI‐b‐TDI was effectively improved without sacrificing the tensile shear strength. Based on the DMA studies, the long soft chain of PEG brought in a noticeable lowering in the glass transition temperature (T_g). The glass transition temperature is near 165°C for the neat MI cured E‐44, which is higher than the T_gs of the other curing agents cured epoxy. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41345.     

Comparison of the effects of linking diglycidyl ether‐terminated PDMS and BPA onto polyurethane with respect to the tensile and thermal properties

Flexible poly(dimethylsiloxane) (PDMS) or rigid bisphenol A (BPA) with diglycidyl ether end groups was linked to polyurethane (PU), which was composed of 4,4′‐methylenebis(phenyl isocyanate) as a hard segment and poly(tetramethylene ether)glycol as a soft segment. A control PDMS (CPDMS) series was prepared with an additional deprotonation step by NaH. The spectroscopic, thermal, tensile, shape memory, and low‐temperature flexibility properties were compared with those of plain PU to investigate the effects of linking the flexible PDMS or the rigid BPA on PU. The soft segment melting peaks were not affected by the PDMS content for the PDMS series but disappeared as the BPA content increased in the BPA series. The soft segment crystallization of PU was completely disrupted as the linked BPA content increased in the differential scanning calorimetry results and disappeared in the dynamic mechanical analysis results. The glass transition temperature (T_g) of the BPA series increased with increasing BPA content, whereas that of the PDMS series remained the same. The tensile strength of the PDMS series sharply increased with increasing PDMS content. The shape retention of the BPA series at ?25 °C sharply decreased as the BPA content increased. Finally, the BPA series linked with rigid aromatic BPA demonstrated excellent low‐temperature flexibilities compared with the PDMS series and plain PU. Compared with PUs linked with PDMS, PUs linked with rigid BPA demonstrated a significant change in the cross‐link density, thermal properties, shape retention, and low‐temperature flexibility. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43284.     

Engineering plastics from lignin. XV. Polyurethane films from chain-extended hydroxypropyl lignin

A series of polyurethane (PU) films was prepared from chain-extended hydroxypropyl lignins (CEHPL). In appearance, these films ranged from brittle and dark brown to rubbery and bronze. The thermal, mechanical, and network properties of these PUs were investigated by DMTA and DSC analysis. All films exhibited single T_g's which varied between ?53° and 101°C, depending on lignin content. From swelling experiments, molecular weight between crosslinks (M _c) was determined and found to vary over 2.5 orders of magnitude. The M _c's were related to the change in T_g that accompanied network formation. Stress–strain experiments showed a variation in Young's modulus between 7 and 1300 MPa. Most of the variation in material properties was related to lignin content and to a lesser extent to diisocyanate type, hexamethylene diisocyanate, or toluene diisocyanate. The source of the CEHPL had no effect on the observed properties. From these results it was concluded that the properties of PUs can be controlled and engineered for a wide variety of practical uses.