The exceptional low temperature flexibility of polyurethane copolymer grafted with dimethylphenyl group

The grafted 3,5-dimethylphenyl group remarkably improved the low temperature flexibility of a polyurethane (PU) copolymer. The rigid and blunt shape of 3,5-dimethylphenyl was designed to interrupt molecular interactions and to disturb the close contact between PU chains and, thus, to improve the flexibility at extremely low temperature, while maintaining high and reproducible tensile and shape memory properties at ambient temperature. The effect of the 3,5-dimethylphenyl group on the flexibility of PU was tested at −30 °C together with a linear PU, and the reason for the exceptional flexibility at low temperature is discussed.     

Grafting of Triphenylmethyl Group onto Polyurethane and the Impact on the Shape Recovery and Flexibility at Extremely Low Temperature

The bulky and rigid triphenylmethyl group was grafted onto polyurethane (PU) to reduce the molecular attractions between hard segments and to improve the mobility of the PU chain under freezing conditions. The triphenylmethyl-grafted PU exhibited improvement in the cross-link density, solution viscosity, maximum tensile stress, shape recovery at 10 °C, and low temperature flexibility compared with the plain PU. The soft segment melting was not affected by the grafted triphenylmethyl group, whereas the soft segment crystallization disappeared with the increase of the triphenylmethyl group content. The glass transition temperature (T_g) increased with the increase of the triphenylmethyl group content. The rapid increase of the tensile strength and shape recovery at 10 °C resulted from the cross-linking effect, whereas the strain at break and shape retention at -25 °C slightly decreased with the increase of the triphenylmethyl group content. The triphenylmethylgrafted PU displayed an excellent low temperature flexibility even at -50 °C due to the improved mobility of the PU chain compared to ordinary PU.     

The grafting of recycled polyol from waste polyurethane foam onto new polyurethane and its impact on shape recovery and water vapor permeation

Recycled polyols from waste polyurethane (PU) foams were grafted onto PU to improve the properties such as tensile strength, shape recovery, low-temperature flexibility, and water compatibility. The recycled polyol was either purified by column chromatography before grafting or was used directly for grafting. The soft segment melting temperature of PU did not notably increase with the addition of polyol, whereas the glass transition temperature increased with increased polyol content. The tensile strength sharply increased at low polyol content and decreased at high polyol content, while the strain at break did not significantly change with an increase in polyol content. The shape recovery at 10 oC notably improved compared with unmodified PU and remained high after four cyclic tests. Polyol-grafted PU demonstrated better lowtemperature flexibility and reduced the water vapor permeability of PU membranes. Overall, grafting recycled polyol onto PU significantly improved the tensile stress, shape recovery, and low-temperature flexibility of PU.     

Structure-property relationship and shape memory effect of polyurethane copolymer cross-linked with pentaerythritol

Polyurethane block copolymers chemically cross-linked by pentaerythritol, a four-way cross-linker, are tested for the shape memory effect. One of the copolymers shows higher shape recovery than any other shape memory copolymer synthesized by us so far. The copolymer maintains a surprising 94 % shape recovery after the third cyclic test. The four-way cross-linking by pentaerythritol and interaction between hard segments are mainly responsible for the very high shape recovery. Tensile mechanical properties also significantly improve by cross-linking. Glass transition temperature (T _g ) slightly increases with cross-linking content. Other characterization such molecular weight, IR, and X-ray diffraction is also carried out to understand the arrangement of copolymer chains.     

Effect of cross-linking agent structure on the shape memory property of polyurethane block copolymer

Effect of cross-linking agent on the shape memory and mechanical property of polyurethane (PU) block copolymer is comprehensively investigated. The selected chemical cross-linking agents are glycerol, 1,2,6-trihydroxyhexane, and 2,4,6-trihydroxybenzaldehyde that are differentiated from each other in having remote hydroxyl group and aromatic ring. Significant increase in maximum stress was observed for all of the cross-linked PUs, although the cross-linker structure was different. Structural change of PU after cross-linking as evidenced by differential scanning calorimetry and infrared spectra was not detected, suggesting that interaction between PU chains remained intact. Shape recovery went to as high as 95 % after cross-linking for all of the cross-linking agents, and shape retention did not improve even if cross-linker was used. The remarkable increase in shape recovery and maximum stress definitely originated from the employment of a cross-linking agent, and the effect of different cross-linker structure on shape memory and mechanical property is discussed.     

Glucose cross-linking of polyurethane copolymer and its impact on the elevation of mechanical properties and shape memory effect

Effect of glucose cross-linking on the shape memory and mechanical properties of polyurethane (PU) block copolymer was investigated. Glucose was selected due to its large number of free hydroxyl groups, easy availability, miscibility with other reactants, and cyclic structure. The glycerol cross-linking did not affect the molecular interaction and phase separation of hard and soft segments in polyurethane structure as judged from IR and DSC analysis. Viscosity of glucose cross-linked PU increased after cross-linking due to the cross-linked structure. Maximum stress drastically improved with the adoption of glucose as a cross-linker together with a slight increase in strain at break. Shape recovery also increased with the adoption of glucose as a cross-linker, and shape recovery was not diminished after four cyclic shape recovery tests. In contrast, shape retention significantly decreased if glucose was included for two different hard segment contents. Finally, glucose cross-linking was compared with other cross-linkers used in shape memory polymer and the advantage of glucose cross-linking was discussed.     

Effect of glycerol cross-linking and PDI on the shape memory effect and mechanical properties of polyurethane

A series of shape memory polyurethane (PU) copolymers synthesized from 1,4-phenyldiisocyanate (PDI), poly(tetramethyleneglycol) (PTMG), 1,4-butanediol (BD) as a chain extender, and glycerol as a cross-linking agent were tested for the mechanical properties and the shape memory effect at the temperature 20 °C above melting temperature (T _m), and were compared with other PUs synthesized from 4,4′-methylene-bis-phenyldiisocyanate (MDI), PTMG, and BD. Mechanical properties and shape memory effect were improved substantially by adopting both PDI and glycerol. Interestingly, enthalpy of melting and T _m were not affected by the glycerol content. Vibration and shock absorption ability was investigated by measuring both loss tan δ and storage modulus with dynamic mechanical analyzer (DMA).     

Laterally crosslinked polyurethane copolymers with polycarbonate as a soft segment

The polyurethane (PU) copolymer was laterally crosslinked with an extra MDI, in which a more rigid polycarbonatediol replaced the conventional poly(tetramethyleneglycol) as a soft segment. What is the impact of the possible molecular interaction between polycarbonate soft segments and lateral crosslinking. The structural change after crosslinking and the impact of new soft segment were followed by infrared spectra, crosslink density, UV-VIS spectra, and relative viscosity. The tensile stress could improve as much as 554 % by selecting the polycarbonate soft segment and the lateral crosslinking. Shape recovery was over 90 % for the entire series and reproducible for four test cycles. The adoption of polycarbonate soft segment and lateral crosslinking significantly could improve the tensile strength and shape recovery compared to PU with polyetherdiol or polyesterdiol soft segment.     

Preparation of Epoxy Shape Memory Polymers for Deployable Space Structures Using Flexible Diamines

In order to develop epoxy shape memory polymers (ESMPs) with high switching temperature and excellent toughness for deployable space structures, the crosslink density and chain flexibility of candidate ESMP samples were tunned by adding two flexible poly(oxypropylene) diamines, Jeffamine D-230 (D230) and Jeffamine D-400 (D400), as a secondary curing agent. The desired switching temperature of ESMPs for deployable space structures was set within the range of 120-135°C. By adding D230 and D400, the switching temperature of the ESMPs could be adjusted to within this range by increasing their crosslink density, and their impact strength could be significantly increased due to the stress relaxation properties of the diamines’ flexible molecular chains. The modulus and tensile strength of the ESMPs increased, but elongation at break decreased, in proportion to the diamine content. The ESMPs with a suitable switching temperature for deployable space structures had a high elongation at break greater than 22 % and good shape recovery and shape fixity ratios. The larger the value of shape recovery ratio, the faster the shape recovery speed.     

Characterization and mechanical properties of prepolymer and polyurethane block copolymer with a shape memory effect

The prepolymer and the final polyurethane (PU) block copolymer were synthesized by reacting 4,4-methylene bis(phenylisocyanate) with poly(tetramethylene glycol) and the prepolymer with 1,4-butanediol as a chain extender, respectively, to investigate the relation between phase separation and it’s resulting properties. According to FT-IR data, the phase separation of hard and soft segments in the prepolymer and the PU block copolymer grew bigger by increasing the hard segment content, and the PU showed more dominant phase separation than the prepolymer. The heat of fusion due to soft segments decreased in both the prepolymer and the PU by increasing the hard segment content, whereas the heat of fusion due to hard segments increased in the PU did not appear in the prepolymers. The breaking stress and modulus of the prepolymer increased by increasing the hard segment content, and the elongation at break decreased gradually, and the PU showed the highest breaking stress and modulus at 58 % hard segment content. However, the best shape recovery of the PU was obtained at 47 % hard segment content due to the existence of proper interaction among the hard segments for shape memory effect. Consequently, the mechanical properties and shape memory effect of the PU were influenced by the degree of phase separation, depending on the incorporation of chain extender as well as the hard segment content.     

The characterization and effects of the alizarin series dyes grafted to polyurethane copolymers on the photoluminescence and low temperature flexibility

Alizarin-series dyes (alizarin, alizarin red S, alizarin yellow GG, or mordant orange) are grafted onto shape memory polyurethane (PU) through an allophanate bonding, and the photoluminescence and the low-temperature flexibility of the resulting PUs are tested. The PU is mainly composed of 4,4′-methylenebis(phenylisocyanate) (MDI), poly (tetramethyleneglycol) (PTMG), and 1,4-butanediol (BD), and the dye is connected, through another MDI, to the carbamate moiety of the PU chain. The PUs with different dye contents are characterized, and their shape recovery and photoluminescence properties are compared. With respect to the tensile mechanical properties, the maximum stress increases up to 50 MPa, and the strain remains above 1000 % even after the dye is grafted onto the PU. The shape recovery is as high as 99 %, and the shape retention improves as the dye content increases. Finally, the photoluminescence of the PUs is demonstrated by the luminescent light emission test, and the dye-grafted PU shows excellent low-temperature flexibility compared with that of linear PU.     

A novel biodegradable polyurethane based on hydroxylated polylactic acid and tung oil mixtures. I. Synthesis,physicochemical and biodegradability characterization

A novel biodegradable polylactic acid-based polyurethane (PU) was synthesized via a chain extension reaction between hydroxylated polylactic acid (PLA-OH) and hydroxylated tung oil (HTO) using 1,6-hexamethylene diisocyanate (HDI) to link the two polyols and dibutyltin dilaurate (DBTDL) as a catalyst. Both PLA-OH and HTO, as polyols, were separately synthesized in our laboratory. Three different molecular weights of PLA-OH prepolymers were used, and the molar ratio of PLA-OH to HTO was also changed to investigate the effect of these two parameters on the structure and properties of the final PUs. Chemical structures of PLA-OH, HTO, and final PUs were investigated by Fourier transform infrared (FTIR) and Hydrogen-1 nuclear magnetic resonance (¹HNMR) spectroscopies. Thermal transitions and thermal stability of the final PUs were, respectively, studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The FTIR and ¹HNMR results showed that the chain-extension reaction of the two polyols with HDI was sufficiently achieved. The TGA results showed that the polyurethanes based on the lower molecular weight PLA segments were more thermally stable; it was not degraded up to 270 °C. DSC results showed that incorporating HTO in the PU chains led to formation of more flexible PU chains, while the glass transition temperatures of the PUs of higher PLA-OH molecular weights were higher than those of lower ones.     

Characterization of the ion-paired polyurethane copolymers

The polyurethane (PU) copolymer was grafted with either 3-dimethylaminopropanol as a basic pendant group or 4-hydroxylphenylacetic acid as an acidic pendant group. The two types of PU were mixed in solution to form ion-pairing between acidic and basic pendant groups. The structural change after grafting and ion-pairing was followed by acid-base titration, infrared spectra, differential scanning calorimetry, and absolute viscosity. The tensile stress can be raised as much as 70 % by the control of the ion-pairing ratio of acidic and basic PUs. Shape recovery was over 80 % and reproducible for four test cycles. The minor control of tensile properties of PU was possible through the ion-pairing method.     

Morphology and mechanical properties of thermo-molded bioplastics based on glycerol-plasticized wheat gliadins

Glycerol-plasticized wheat gliadin bioplastics were prepared through thermo-molding method. The effect of glycerol content on the morphology and the mechanical properties of wheat gliadin bioplastics was studied. Morphology, tensile properties (tensile strength and elongation at break), dynamic mechanical properties and rheological properties were evaluated in relation to glycerol content. Experimental results reveal that the morphology, the glass transition temperatures (T_g) of both the gliadin-rich and the glycerol-rich domains and the tensile properties are closely linked to the glycerol content. The time–temperature superposition (TTS) fails to be applied to the dynamic loss modulus G″ (all temperatures) and the dynamic storage modulus G′ (above 80 °C) of wheat gliadin bioplastics.     

Dependence of montmorillonite dispersion in nanocomposites on polymer matrix and compatibilizer content, and the impact on mechanical properties

A series of polyurethane (PU)/monmorillonite (MMT) or nylon 66/MMT nanocomposite were prepared by melt-compounding method to take a close look at the MMT dispersion in the nanocomposite depending on the polymer matrix and the compatibilizer content. Cloisite 30B, the brand name, was selected as MMT, because surface was covered with methyl tallow bis-2-hydroxyethyl ammonium group and the reduced surface hydrophilicityity rendered MMT dispersed better in polymer matrix compared to bare MMT. MMT dispersion, due to the difference in hydrophilicity and the fondness of similar hydrophilicity, was better in nylon than PU. Maximum stress and tensile modulus could be increased by the control of MMT content for both nylon and PU, and the compatibilizer, when added at the same MMT content, also could increase the tensile properties of both nylon and PU. It was found from this investigation that the good dispersion of MMT in polymer matrix can improve the mechanical properties of nanocomposite.     

Selective cationic surfactant detection in aqueous solution by polyurethane copolymer linked with metal ion indicator

Polyurethane (PU) copolymer is laterally linked with three kinds of metal ion indicator (calcein, calmagite, or eriochrome black T), with which free metal ion in aqueous solution is intended to be detected by PU color change. Metal ion detection by the indicator-PU fails due to the poor permeation of hydrophilic metal ion into hydrophobic PU layer. Instead, three surfactants with different ionic head groups, aerosol OT (AOT), cetyltrimethylammonium bromide (CTAB), and sodium dodecylsulfate (SDS), are tested for metal ion. Cationic CTAB exhibits an instant PU color change, but anionic AOT and SDS do not respond at all. Reason for the selective detection of cationic surfactant is the complex formation between cationic surfactant and indicator. Molecular interactions between PUs are affected by the laterally linked indicators based on the results by infrared spectra and differential thermal analysis. UV-vis spectra reveal that extra peak arising from the linked indicator appears compared to plain PU. The lateral linking of indicator to PU demonstrates, as well as the selective surfactant detection, a 454 % increase in tensile strength and reproducible shape recovery as high as 99 % compared to plain PU.     

Kinetics of two-step emulsion polymerization of poly(n-butyl methacrylate)/poly(methyl methacrylate) polymer networks

Poly(n-butyl methacrylate)/poly(methyl methacrylate) polymer networks were synthesized by two-step emulsion polymerization with sodium dodecylsulfonate and polyoxyethylene nonylphenolether as the emulsifier, distilled water as the continuous medium, and potassium persulfate as the initiator. The kinetics of two-step emulsion polymerization was studied. Effects of emulsifier concentration, initiator concentration, and polymerization temperature on monomer conversion and polymerization rate were investigated in detail. Experimental data indicate that both the steady state polymerization rate and monomer conversion increase with the augment of emulsifier concentration, initiator concentration, or reaction temperature.     

Dyeing properties of novel azo disperse dyes derived from phthalimide and color fastness on poly(lactic acid) fiber

The coloration of poly(lactic acid) (PLA) fiber with 18 carbocyclic monoazo disperse dyes bearing a hydrolyzable phthalimide ring fused to the aromatic ring of their diazo components has been investigated. The phthalimidyl nitrogen atom was substituted with either a n-butyl, sec-butyl, or isopropyl group, while the adjoining phenyl ring bore a substitution pattern typical of commercial colorants. There was a broad correlation between percentage dye exhaustion onto PLA and that onto polyester (PET) fiber, although significant differences in certain instances were apparent with no clear trends regarding dye structure. Attempts to explain the observed percentage exhaustion values by mapping them to calculated partition coefficient or solubility parameter values were unsuccessful. Wash fastness was relatively good compared to that of some conventional disperse dyes applied to PLA. As was found to be the case with PET, the wash fastness of dyes on PLA tended to be highest when their diazo ring was substituted with electron acceptors.     

Structure and properties of syndiotactic polystyrene fibers prepared in high-speed melt spinning process

High-speed melt spinning of syndiotactic polystyrene was carried out using high and low molecular weight polymers, HMs-PS and LMs-PS, at the throughput rates of 3 and 6 g/min. The effect of take-up velocity on the structure and properties of as-spun fibers was investigated. Wide angle X-ray diffraction (WAXD) patterns of the as-spun fibers revealed that the orientation-induced crystallization started to occur at the take-up velocities of 2–3 km/min. The crystal modification wasα-form. Birefringence of as-spun fibers showed negative value, and the absolute value of birefringence increased with an increase in the take-up velocity. The cold crystallization temperature analyzed through the differential scanning calorimetry (DSC) decreased with an increase in the take-up velocity in the low speed region, whereas as the melting temperature increased after the on-set of orientation-induced crystallization. It was found that the fiber structure development proceeded from lower take-up velocities when the spinning conditions of higher molecular weight and lower throughput rate were adopted. The highest tensile modulus of 6.5 GPa was obtained for the fibers prepared at the spinning conditions of LMs-PS, 6 g/min and 5 km/min, whereas the highest tensile strength of 160 MPa was obtained for the HMs-PS fibers at the take-up velocity of 2 km/min. Elongation at break of as-spun fibers showed an abrupt increase, which was regarded as the brittle-ductile transition, in the low speed region, and subsequently decreased with an increase in the take-up velocity. There was a universal relation between the thermal and mechanical properties of as-spun fibers and the birefringence of as-spun fibers when the fibers were still amorphous. The orientation-induced crystallization was found to start when the birefringence reached — 0.02. After the starting of the orientation-induced crystallization, thermal and mechanical properties of as-spun fibers with similar level of birefringence varied significantly depending on the processing conditions.     

Comparision of the properties of UV-cured polyurethane acrylates containing different diisocyanates and low molecular weight diols

UV-curable polyurethane acrylate prepolymers were prepared from diisocyanates [isophorone diisocyanate (IPDI), 2,4-toluene diisocyanate (TDI), or 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI)], diols [ethylene glycol (EG), 1,4-butane diol (BD), or 1,6-hexane diol (HD)], polypropylene glycol as a polyol. UV-curable mixtures were formulated from the prepolymer (90 wt%), reactive diluent monomer trimethylol propane triacrylate (10 wt%), and photoinitiator 1-hydroxycyclohexyl ketone (3 wt% based on prepolymer/diluent). The effects of different diisocyanates/low molecular weigh diol on the dynamic mechanical thermal properties and elastic recovery of UV-cured polyurethane acrylate films were examined. The tensile storage modulus increased a little in the order of EG>BD>HD at the same diisocyanate. Two loss modulus peaks for all samples are observed owing to the glass transition of soft segments (T _gs ) and the glass transition temperature of hard segments (T _gh ). For the same diisocyanate,T _gs decreased, however,T _gh increased, in the order of HD>BD>EG. The elastic recovery also increased in the order of HD>BD>EG at the same diisocyanate. In case of same diols,T _gh increased in the order of H₁₂MDI>TDI>IPDI significantly. The ultimate elongation and elastic recovery increased in the order of TDI>IPDI>H₁₂MDI at the same diol.