Search

Poly(dimethylsiloxane) (PDMS) was grafted onto polyurethane (PU), and Epichlorohydrin and Bisphenol A were attached to the free ends of PDMS groups and used to link the grafted PDMS to thereby introduce flexible crosslinks between the PU chains. The flexible crosslinks enhanced the crosslink density and solution viscosity of PU but did not change the melting and crystallization behaviors of the soft segments of PU. In particular, the flexible PDMS crosslinks increased the maximum tensile stress by up to 300% and the maximum tensile strain up to 180%. The shape recovery capability at 10°C and the shape retention capability at −25°C were maintained above 90% with the flexible crosslinking. Grafted PDMS moderately improved the low-temperature flexibility of PU due to its flexibility at low temperature. The flexible crosslinks of grafted PDMS successfully improved the tensile strength, shape recovery, and low-temperature flexibility of the PU. [ABSTRACT FROM AUTHOR]

The antifungal agent carbendazim and the water-compatible functional group 2,4,6-tris(dimethylaminomethyl)phenol (TDMP) were jointly grafted to polyurethane (PU) to develop a water-compatible antifungal PU. The water compatibility of the PU surface improved strikingly after the protonation of TDMP, as confirmed by water contact angle tests. The combined grafting of carbendazim and TDMP affected the melting and glass transition of soft segments and sharply increased the tensile stress and shape recovery capability. Carbendazim was selected as a grafted antifungal functional group due to its wide effective range of antifungal activity and its large production volume. PUs with grafted carbendazim and TDMP completely suppressed the growth of a mixture of fungi, unlike ordinary PU. Therefore, the joint grafting of both carbendazim and TDMP led to improved water compatibility, breaking tensile stress, shape recovery capability, and antifungal activity. [ABSTRACT FROM AUTHOR]

Graft polymerization of poly(ethylene glycol) methyl ether acrylate (PEGA) onto polyurethane (PU) was conducted to improve its water compatibility, tensile mechanical strength, shape memory, and low-temperature flexibility properties, as well as to control its water vapor permeability (WVP). Control PUs containing free poly(PEGA) were also prepared to compare with the poly(PEGA)-grafted PUs. The water compatibility of PU notably improved due to the grafting of poly(PEGA) based on water contact angle results. The soft segment melting temperature and glass transition temperature were not changed with the increase in the PEGA content. The tensile strength of PU sharply increased due to the grafting of poly(PEGA), whereas the free poly(PEGA) in the control PUs did not cause a similar increase. The maximum strain of PU was not affected by the grafting of poly(PEGA). The shape recovery at 0°C significantly increased compared with the unmodified PU. The low-temperature flexibility of PU improved, and the WVP through the PU membrane was reduced by the grafting of poly(PEGA) onto PU. [ABSTRACT FROM AUTHOR]

The surface of polyurethane (PU) was modified by the graft polymerization of N,N-dimethylaminoethyl methacrylate (DAMA) and acrylic acid (AA) to enhance its water compatibility. Portions of poly(DAMA) and poly(AA) could be ionized by mutual acid–base neutralization and could notably improve the surface hydrophilicity of PU. The water contact angle, water absorption, and water vapor permeation test results jointly demonstrate the increase in water compatibility resulting from the inclusion of poly(DAMA) and poly(AA) in PU. The melting and glass transition temperatures of PU were not significantly influenced by the grafting of poly(DAMA) and poly(AA) onto PU. Small portions of the grafted poly(DAMA) and poly(AA) were involved in the cross-linking of PU, which sharply increased the shape recovery and the breaking tensile stress while maintaining high shape retention and breaking tensile strain. [ABSTRACT FROM AUTHOR]

Phthalic acid (PA) was grafted onto polyurethane (PU) in the PA series due to its rigid aromatic structure and carboxyl groups, but PA was simply blended with PU in the control CPA series. The cross-link density and solution viscosity of the PA series notably increased with increasing PA content, and the same parameters of the CPA series did not increase. The maximum tensile stress of the PA series sharply increased due to the chemical cross-linking of the grafted PA, and the tensile strain at break slowly decreased with increasing PA content. The shape recovery of the PA series at 10 °C rapidly increased upon the grafting of PA; however, that of the CPA series decreased with increasing PA content. The hydrophilicity of PU was enhanced by the grafting of PA based on the water contact angle and water vapor permeation results. The low temperature flexibility of the PA series improved more than that of the CPA series under freezing conditions with increasing PA content due to the chemical cross-linking and steric and electrostatic repulsion between PU moieties. Overall, the grafted PA definitely increased the maximum tensile stress, shape recovery, and low temperature flexibility of PU. [ABSTRACT FROM AUTHOR]

Grafting of niclosamide or salicylanilide onto polyurethane (PU) was executed to develop antifungal effectiveness and barnacle repelling capability in seawater compared with underivatized PU. The PU surface was simultaneously modified to improve the surface hydrophilicity by inserting dimethylolpropionic acid into PU frame or by grafting recycled polyols onto PU. Surface modifications of PU significantly affected its properties, such as cross-link density, tensile and shape memory properties, and flexibility under freezing conditions relative to the unmodified PU. The modification of PU surface also notably influenced the glass transition and the melting and crystallization related to soft segments. The breaking tensile stress and the shape recovery were enhanced significantly after the grafting of polyol due to chemical cross-linking, whereas the breaking tensile strain was not reduced. Some PU samples demonstrated complete antifungal effectiveness against a mixture of fungi, and barnacle growth on PU films was limited in the specifically modified PUs. [ABSTRACT FROM AUTHOR]

Noticeable enhancements in the (a) breaking tensile stress and (b) shape recovery rate after the grafting of polystyrene onto PU in PS series. [ABSTRACT FROM AUTHOR]

Benzimidazole as an antifungal agent and poly(acrylic acid) as a hydrophilic group were grafted together onto polyurethane (PU) to synthesis the antifungal PU. Benzimidazole was chosen as a key antifungal agent because of its proven fungal growth control against a wide spectrum of fungi. The hydrophilicity of antifungal PU was notably escalated after the grafting of poly(acrylic acid) based on the water contact angle results, but the melting and glass transition of soft segment in PU did not notably change by the grafting of benzimidazole and poly(acrylic acid). The synthesized antifungal PUs exhibited a sharp increase in the breaking tensile stress and shape recovery due to the slight chemical cross‐linking between PUs. The benzimidazole‐grafted PUs containing the poly(acrylic acid) demonstrated a clear suppression in the growth of a group of fungi. Therefore, the antifungal PUs with enhanced tensile strength and shape recovery capability were successfully synthesized using the combined grafting of benzimidazole and poly(acrylic acid) onto PU. [ABSTRACT FROM AUTHOR]

Bis(2-hydroxyethyl) terephthalate (BHETPA) was grafted onto polyurethane (PU) to investigate the effects of BHETPA, which contains a rigid aromatic group and flexible hydroxyethyl groups, on the physical properties of PU. The cross-link density, viscosity, tensile strength, and shape recovery notably increased with an increase of BHETPA due to chemical cross-linking by BHETPA. A PU sample demonstrated excellent low-temperature flexibility compared with plain PU, showing complete recovery at approximately 0°C. Therefore, grafting BHETPA onto PU modified the thermal behavior and greatly improved the tensile stress, shape recovery, and low-temperature flexibility of PU compared to plain PU. [ABSTRACT FROM AUTHOR]

Abstract: Polycaprolactam or polycaprolactone was graft‐polymerized onto polyurethane (PU) to control the water vapor permeation and improve the tensile strength of PU. The tensile strength of the PU sharply increased with the grafting of polycaprolactam or polycaprolactone, without a decrease in the tensile strain. The soft segment melting properties did not significantly change with the increase in the lactam or lactone content. The shape recovery and shape retention of the PU series remained high after the grafting. The water vapor permeability (WVP) was reduced by the grafting of the polycaprolactam, whereas the WVP was increased by the grafting of polycaprolactone. [ABSTRACT FROM AUTHOR]

Graft polymerization of norbornene monomers onto polyurethane (PU) was tested to reduce the intermolecular attractions between PUs using the rigid bicyclic ring structure of norbornene, to control the soft segment thermal properties, and to enhance the tensile, shape memory, and low-temperature flexibility properties compared with those of unmodified PU. The soft segment crystallization temperature (Tc) sharply decreased with the increase in norbornene, whereas the soft segment melting temperature (Tm) was not significantly changed by the norbornene content. However, the glass transition temperature (Tg) increased with the incorporation of norbornene. The tensile strength sharply increased with the increase in norbornene due to the chemical cross-linking between the grafted poly(norbornene), whereas a significant decrease in the maximum strain was not observed. The shape recovery at 10 °C sharply increased from 47% to approximately 90% after the graft polymerization of norbornene, and the shape retention at −25 °C decreased with the increase in norbornene. Finally, the graft polymerization of norbornene onto PU demonstrated enhanced low-temperature flexibility due to the reduced restrictions of rotational and translational mobility. [ABSTRACT FROM AUTHOR]

ABSTRACT: Epichlorohydrin (ECH) was used as a cross‐linking agent for a series of polyurethanes (PU series). The spectroscopic, thermal, tensile, shape memory, low‐temperature flexibility, and water vapor permeability properties of these PUs were compared with those of a control polyurethane series (CPU series) without ECH cross‐linking. In the thermal test, the soft segment crystallization of the PU series disappeared as the ECH cross‐linking increased. The glass transition temperature (Tg) of the PU and CPU series slightly increased with the increase in ECH content. The tensile strength of the PU series sharply increased at a critical ECH content, whereas that of the CPU series did not. The breaking strain of the PU and CPU series remained the same with the increase in ECH content. The shape recovery of the PU series remained above 90% at 45°C but increased moderately with the increase in ECH content at 0°C. Finally, the PU series with ECH cross‐linking demonstrated better low‐temperature flexibility and lower water vapor permeability than the unmodified PU. [ABSTRACT FROM AUTHOR]

Hybrid polyurethane-silica composites were prepared using a sol-gel reaction between tetraethyl orthosilicate and triethoxysilyl groups grafted onto polyurethane. The TS series contained the same polyurethane composition but the tetraethyl orthosilicate content varied. Soft segment Tm and Tg values were not affected by the tetraethyl orthosilicate content, while AH for soft segment melting and crystallization increased with the tetraethyl orthosilicate content. The tensile strength sharply increased from the cross-linking of the grafted silica at low tetraethyl orthosilicate concentrations but decreased with the increase of tetraethyl orthosilicate content because excess silica inhibited cross-linking. The shape recovery of the TS series improved during cyclic tests, and shape retention slightly decreased as the test cycles repeated. Low temperature flexibility moderately improved with the formation of grafted silica. Therefore, the grafted sol-gel silica formation demonstrated a tensile strength improvement and reproducible shape recovery. [ABSTRACT FROM AUTHOR]

The graft polymerization of tert-butyl acrylate ( TBA) onto polyurethane ( PU) was conducted to prepare a series of samples that was compared to a control series comprising a physical mixture of poly( TBA) and PU. Maximum tensile stress sharply increased because of chemical cross-linking via poly( TBA), whereas tensile breaking strain slightly diminished by the grafted poly( TBA). Percent shape recovery at 10°C rapidly increased by the additional grafting of poly( TBA), whereas control series decreased with increases in TBA monomer content. Chemical cross-linking from the grafted poly( TBA) was responsible for the enhancement of shape recovery. Low-temperature flexibility tests from −35°C demonstrated that a proper composition of grafted poly( TBA) could enhance the flexibility of PU below 0°C. Overall, the grafted poly( TBA) greatly stepped up the maximum tensile stress, recovery capability to original form, and flexibility of PU at very low temperature. [ABSTRACT FROM AUTHOR]

Two series of polyurethane (PU) containing 2,2-bis(hydroxymethyl)propanoic acid (DMPA) and the grafted benzimidazole (BI) were prepared to compare their antifungal activities. The DMPA carboxyl group of BN series was completely ionized using a strong base (NaOH) and the DMPA carboxyl group of BT series was partly ionized by a weak base (trimethylamine). The BN series exhibited a faster decrease in maximum tensile strength and strain at break compared to the BT series. The fully ionized DMPA carboxyl group of BN series severely affected the thermal and mechanical properties. Finally, the BN series demonstrated a complete suppression of fungal growth ( Chaetomium globosum) whereas unmodified PU and the BT series could not fully suppress the growth of fungi at the same BI content. Therefore, the complete ionization of DMPA carboxyl group played an important role in the antifungal activity. [ABSTRACT FROM AUTHOR]

We have researched the functionalized polyurethane (PU) that can exhibit a wide range of interesting performances unattainable from the ordinary PU. We found that the grafted Phenol Red sharply increased the tensile mechanical strength due to the chemical crosslinking by Phenol Red. In addition, shape recovery at 0°C improved from 24% up to 84%, and the shape retention at −30°C decreased as the Phenol Red content increased. The Phenol Red-grafted PU demonstrated flexibility, even at −50°C, and a full recovery at −5°C. Therefore, Phenol Red-grafted PU exhibited a sharp improvement in tensile stress, shape recovery, and low-temperature flexibility, which was not attainable in ordinary PU. The Phenol Red-grafted PU performed better than other functionalized PU we have developed. [ABSTRACT FROM AUTHOR]

Citric acid (CA) was used as a grafted group onto polyurethane (PU) to form a CA-grafted PU series, with a control PU series containing free CA prepared for comparison. With an increase in the CA content, the enthalpy change during the melting increased for the PU and CPU series, and the glass transition temperature increased with the increase in CA content for the PU series but not for the CPU series. The tensile strengths of the PU series sharply increased with the CA content, whereas those of the CPU series did not. The PU series demonstrated better low-temperature flexibility and water permeability than the unmodified PU. [ABSTRACT FROM AUTHOR]

Polyurethanes containing polycaprolactone diol or poly(tetramethylene ether)glycol as a soft segment and 4,4′-methylenebis(phenyl isocyanate) as a hard segment were used as a polymer frame. Polydimethylsiloxane was grafted onto polyurethanes to reduce the molecular interactions and to improve the mobility of polyurethanes, and the plasticizing groups,n-butyl and 2-ethylhexyl, were attached to polyurethanes by graft polymerization. With an increase in the polydimethylsiloxane content, theTgof the polydimethylsiloxane–polyurethanes gradually increased, whereas theTgof then-butyl and 2-ethylhexyl-attached polyurethanes was not affected by a change in their composition. The polydimethylsiloxane-grafted polyurethanes demonstrated excellent tensile strength, shape recovery, and low-temperature flexibility. [ABSTRACT FROM AUTHOR]

Polydimethylsiloxane (PDMS) was grafted onto polyurethane (PU) to form a P series, and 2-ethylhexyl acrylate (EHA) was graft-polymerized onto PU to form an E series. The spectroscopic, thermal, tensile, shape memory, and low-temperature flexibility properties of the P and E series were compared. With an increase in the PDMS content, the Tgof the P series gradually increased, whereas the Tgof the E series was not affected by an increase in the EHA content. The tensile strength of the P and E series sharply increased with the PDMS or EHA content without a significant decrease in tensile strain. The shape recovery of the P and E series remained high after four repeated tests. However, shape retention of the P series significantly decreased with an increase in the PDMS content. Finally, the P series demonstrated excellent low-temperature flexibility from −35°C compared with the E series and control PUs. [ABSTRACT FROM AUTHOR]

Polyurethane was grafted with benzoic acid (BA series) or a phenyl group (C series) to compare the impact of the grafted groups on water contact angle, tensile strength, shape memory, and low temperature flexibility. Benzoic acid is different from a phenyl group because it has both a rigid phenyl ring and a carboxyl group. The tensile strengths of the BA and C series substantially increased compared to that of the unmodified polyurethane. The BA series with the grafted benzoic acid exhibited excellent low temperature flexibility compared to the C series with the grafted phenyl group. [ABSTRACT FROM PUBLISHER]

Polyurethane (PU) was graft polymerized with poly(acrylic acid) (PA) to form a PA-grafted PU (UA) series, and a control PU (C) series containing free PA was also prepared for comparison. The grafted PA could be ionized, and an ionized PA-grafted PU (IUA) series was separately prepared. The spectroscopic, thermal, tensile, shape memory, low-temperature flexibility, and water permeability properties of the polymer series were compared. With an increase in the PA content, the T did not change, but Δ H decreased for the UA, IUA, and C series. The T did not significantly change with the increase in PA content for the UA, IUA, and C series. The tensile strengths of the UA and IUA series sharply increased with the PA content, whereas that of the C series did not. The breaking strain of the UA, IUA, and C series remained the same with the increase in PA content. The shape recovery and shape retention of the PU-PA series remained high after four repeated tests. Finally, the IUA series PU demonstrated better low-temperature flexibility and water compatibility than the unmodified PU. [ABSTRACT FROM AUTHOR]

A polyurethane series containing grafted polystyrene and a Control series with free polystyrene were prepared, and their spectroscopic, thermal, tensile, shape-memory, and low-temperature flexibility properties were compared. The grafted polystyrene significantly reduced the ΔHcand also reduced the crystallization peaks of the polyurethane series. The tensile strength of the polyurethane series sharply increased with polystyrene content, whereas the Control series did not. The shape recovery of the polyurethane series remained high but the shape retention gradually decreased after four repeated tests. Lastly, the polyurethane series grafted with polystyrene demonstrated excellent low-temperature flexibility. [ABSTRACT FROM AUTHOR]

Polyurethane was linked to graphite modified with a phenol or 4-phenylethanol group on its surface, and the composite polymer was characterized regarding its thermal, spectroscopic, mechanical, and shape-memory properties as well as its electric conductivity. Graphite as a filler was covalently linked to a polyurethane backbone composed of 4,4′-methylenebis(phenylisocyanate) and 1,4-butanediol as hard segments and poly(tetramethyleneglycol) as a soft segment. The two different polyurethane series, differing in their modifying spacer, show similar structural characteristics and exhibit a small degree of cross-linking due to the agent used for the covalent linking of graphite to the polyurethane frame. The tensile mechanical strength and shape-recovery characteristics remain high as the graphite content is increased when compared to the linear polyurethane polymer without the linked graphite. Regarding the tensile mechanical properties, the maximum stress increases up to 436% compared to the linear polyurethane, and the maximum strain goes up to 1744%. Shape recovery reaches values as high as 93%, and shape retention gradually decreases as the graphite content increases. The electric conductivity of graphite-linked polyurethane exhibits a sharp increase as the graphite content increases, but the blended graphite polyurethane has very poor electric conductivity at higher graphite contents. The implication of this finding is discussed, and the synthesized polymers are compared with other conductive polymer composite. [ABSTRACT FROM AUTHOR]

A series of polyurethanes (PUs) grafted with poly(isobornyl acrylate) (PIBA) was prepared to form a series (denoted the I series), which was compared with the PUs containing free PIBA (denoted the C series). The bulky and rigid bicyclic isobornyl groups attached to the PIBA chains were intended to hinder the molecular interactions between PU chains and improve the low temperature flexibility of the PUs. The soft segment melting temperature (Tm) was not changed by the increase of the isobornyl acrylate (IBA) content; however, the enthalpy change of melting (ΔHm) sharply decreased. The C series PUs did not exhibit similar differences in response to the IBA content change. The tensile strength of the I series sharply increased at low IBA content due to the physical crosslinking and decreased at high IBA content due to the repulsion between PU chains. The I series demonstrated an improved low temperature flexibility compared with the unmodified and the C series PUs. [ABSTRACT FROM AUTHOR]

Polyurethane (PU) grafted with several well-known pH indicators (alizarin yellow, bromocresol green, bromocresol purple, or thymol blue) via spacer is characterized for thermal, spectroscopic, mechanical, and shape memory properties, as well as for PU color change to aqueous solution with various pH values. The PU polymer frame is composed of 4,4′-methylenebis(phenylisocyanate) (MDI), which acts as a hard segment, poly(tetramethyleneglycol) (PTMG) as a soft segment, and a covalently linked pH indicator. The four different PU series studied in this work display characteristic color dependent upon the grafted indicator type. The PU series also exhibit a small degree of cross-linking due to the grafting agent used to covalently link the indicator to the PU frame. The tensile mechanical strength and the shape recovery of the indicator-grafted PU remain high after repeated tests compared to that of the plain linear PU. Regarding the tensile mechanical properties, the maximum stress and the strain increase to 424 and 1,880 %, respectively, for indicator-grafted PU compared to the linear PU. Furthermore, the shape recovery is observed to reach 98 % and improves after each test cycle. A reversible color change is observed after repeated exposure to aqueous solutions with varying pH values and is confirmed with UV-VIS spectra results. [ABSTRACT FROM AUTHOR]

Cellulose derivatives, such as cellulose acetate, cellulose acetate butyrate, or cellulose acetate phthalate, were used both as crosslinkers and water vapor permeation pathways in polyurethane (PU) to improve mechanical properties and to control water vapor permeation through the hydrophobic PU membrane. Cellulose derivatives do not only act as crosslinkers; they may replace the butanediol partially or completely to become a chain extender in PU synthesis. The soft segment melting temperature was observed at approximately 20°C and was not affected by the cellulose derivative content. However, the enthalpy change for melting significantly increased with the cellulose derivative content. Forming crosslinkages with the cellulose derivatives significantly increased the tensile strength of the PU, but the tensile strain remained similar, even when the cellulose derivative content was raised. Water vapor permeability (WVP) at 50°C was definitely improved by including the cellulose derivatives but was not proportional to the cellulose derivative content. The hydrophobic PU layer was converted into a partially water vapor-permeable membrane by including cellulose derivatives. [ABSTRACT FROM PUBLISHER]

The impact of the pendant anthryl group on the low temperature flexibility and tensile properties of a polyurethane block copolymer was investigated. The pendant anthryl group was designed to interrupt molecular interactions and to disturb the close contact between polyurethane (PU) chains through its rigid aromatic rings; thus, to improve the flexibility at extremely low temperatures, while maintaining high and reproducible tensile properties and the shape recovery at ambient temperatures. The attachment of the anthryl group was confirmed using the infrared (IR), nuclear magnetic resonance (NMR), and ultraviolet-visible (UV-VIS) spectroscopy. Increasing the anthryl content led to an unusual increase in the crosslink density due to partial crosslinking by the grafting reagent. The shape recovery and retention results were reproducible after performing repeated shape memory tests. Finally, the effect of the anthryl group on the shape recovery at −30 °C was compared with that of linear PU, and the reason for the remarkable flexibility at low temperature is discussed. [ABSTRACT FROM AUTHOR]

A flexibly cross-linked shape memory polyurethane (SMPU) was converted to a magnetic polymer by making a composite with a ferromagnetic particle (Fe3O4). The flexibly cross-linked SMPU has already displayed excellent mechanical and shape memory properties; the design of a magnetically responsive material allowed for a unique and novel SMPU. Among the three different composite preparation methods (melt-mixing, solvent blending, and in situ reaction mixing), the melt-mixing method was the best and attained even distribution of magnetic particles and high mechanical and shape memory properties. Differential scanning calorimetric and infrared results showed that the polymer structure was not affected by melt-mixing. In tensile testing, the maximum stress of the composite reached 39 MPa, and the strain at break also increased to 2495%. Shape recovery exhibited maximums as high as 99% and displayed similar values after repetitive shape recovery test cycles. Finally, the magnetic property of SMPU was characterized by a superconducting quantum interference device magnetometer and demonstrated in the magnetic attraction test. The potential applications of the magnetic and flexible SMPU are discussed. [ABSTRACT FROM PUBLISHER]

Shape memory polyurethane (SMPU) flexibly crosslinked by a hydrophobic poly(dimethylsiloxane) (PDMS) spacer at its side through allophanate bonding was tested for shape recovery at −30 °C and compared to a linear SMPU. The SMPU was composed of 4,4′-methylenebis(phenylisocyanate) (MDI), poly(tetramethyleneglycol) (PTMG), 1,4-butanediol (BD), and PDMS that was connected to SMPU chains by a second MDI. The mechanical and shape memory properties of two types of SMPU, differing in PTMG and PDMS content, were compared. In the best case, a 283% increase in maximum stress compared to the linear polymer was attained without any sacrifice of strain. Shape recovery at 45 °C increased to 91% and remained at more than 80% after four cyclic tests. Shape recovery at 0 °C could be improved by increasing PDMS content, and the critical shape recovery temperature decreased with increasing PDMS content. The PDMS-crosslinked SMPU demonstrated instant shape recovery at −30 °C in comparison with the linear SMPU that must be warmed to room temperature for complete shape recovery. The extraordinary shape memory results were analyzed and are discussed together with differential scanning calorimetry and infrared data. [ABSTRACT FROM PUBLISHER]

The effects of the dextrin cross-linking and hard-segment content on the shape-memory property of a polyurethane (PU) block copolymer were investigated. Although dextrin was selected due to its large number of free hydroxyl groups and ubiquitous availability, it is unfortunately insoluble in most organic solvents. The insolubility of dextrin was resolved by attaching a phenyl group onto the dextrin to reduce its hydrophilicity. The phase separations of hard and soft segments were not dependent on the dextrin cross-linking and hard-segment content, as per the results obtained from FTIR, DSC, and XRD analysis. An increased content of chemically cross-linked dextrin increased the maximum stress, but did not decrease the strain for most cases. The cross-linking density increased with increasing dextrin content, as expected. After dextrin cross-linking, the shape recovery rate was generally over 90%, and remained the same after four cyclical tests, while a low shape retention rate was observed for most cases. The best shape-memory effect, considering both the shape recovery and retention rate, was found for a PU consisting of 35 wt.% hard segment and 2 wt.% dextrin. Finally, dextrin was compared to other cross-linking compounds, such as glycerol and pentaerythritol, in this investigation. [ABSTRACT FROM AUTHOR]

Effect of glycerol cross-linking and hard segment content on the shape memory property of polyurethane block copolymer is comprehensively investigated. Phase separation of hard and soft segment is dependent on glycerol cross-linking and hard segment content as judged from FT-IR and DSC data. Hydrogen bonding and dipole–dipole interaction between hard segments provides strong interaction between copolymer chains in addition to chemical cross-linking by glycerol. As the hard segment content increases, the copolymer shows better tensile mechanical properties and higher melting temperature of soft segment ( T m). Effect of glycerol cross-linking on mechanical properties and T m of soft segment is low compared to hard segment effect. Although XRD peak at 2θ = 19.5° is observed, clear difference between the copolymers with various hard segment and cross-linking content is not observed. Significant increase in shape recovery rate in the case of 30 wt% hard segment copolymer is observed after glycerol cross-linking. The drastic change of the properties of polyurethane block copolymer is discussed in the point of copolymer chain interaction. [ABSTRACT FROM AUTHOR]

Abstract: Effect on shape memory and mechanical properties of polyurethane (PU) copolymers by changing the chain extender from 1,4-butanediol (BD) to ethylenediamine (ED) was investigated. PU copolymers composed of the different ratio of hard and soft segment were prepared and characterized by IR, DSC, XRD, and UTM. Glass transition temperature of PU increased to room temperature range by adopting ED as a chain extender. The XRD peak pattern changed with hard segment content. ED type PU achieved the high mechanical properties at lower hard segment content than BD type PU. Especially, strain at break of ED type significantly improved compared to BD type. Shape recovery rates were similar for both types of PU, but ED type showed better shape retention rate than BD type. The reason for the differences between two types of PU is discussed in this paper. [Copyright &y& Elsevier]

A series of shape memory polyurethane copolymers synthesized from 1,4-phenyldiisocyanate (PDI) and poly(tetramethyleneglycol) (PTMG) plus 1,4-butanediol as chain extender were compared with similar ones from 4,4′-methylene-bis-phenyldiisocyanate (MDI) and PTMG in various shape memory tests at temperature ranges of ±20 °C around glass transition temperature (Tg). Similarity and some differences between two series were found in other characterization methods such as IR spectra, phase transition, and mechanical properties. Especially, Tg increased with the content of hard segment (PDI or MDI) and both copolymers generally showed similar Tg at the same content of hard segment. In addition, vibration and shock absorption ability was investigated by measuring both loss tan δ and storage modulus with dynamic mechanical analyzer. [Copyright &y& Elsevier]