Ha Youn Kim

Impact of cholesterol grafting on molecular interactions and low temperature flexibility of polyurethanes

A series of polyurethanes (PUs) containing grafted cholesterol (UA series) and a control series blended with free cholesterol (UB series) were prepared: the spectroscopic, thermal, tensile, shape memory, and low temperature flexibility properties of these series were compared with those of unmodified PU. For both the UA and UB series, the soft segment melting temperature (Tm) was not affected by the cholesterol content. Differential scanning calorimetry (DSC) results showed that the crystallization of the hard segment of the UA series was completely inhibited as the grafted cholesterol content increased, which were supported by dynamic mechanical analysis (DMA) results for the storage modulus. As the cholesterol content increased, the glass transition temperature (Tg) of the UA series increased and remained the same for the UB series. The tensile strength in the UA series sharply increased with the cholesterol content, unlike that of the UB series. The strain at break in the UA series remained the same as the cholesterol content increased, whereas that of the UB series decreased significantly. As the cholesterol content increased, the shape recovery of the UA series remained above 90% at 45 °C and sharply increased at 0 °C. Finally, the UA series containing grafted cholesterol demonstrated excellent low temperature flexibilities compared to the UB series and unmodified PU.

Modification of polyurethane by graft polymerization of poly(acrylic acid) for the control of molecular interaction and water compatibility

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 Tm did not change, but ΔHm decreased for the UA, IUA, and C series. The Tg 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.

Preparation of urethane-acrylates by the photo-polymerization of acrylate monomers using a benzophenone initiator grafted onto a polyurethane copolymer

Photo-polymerization of the acrylate monomers, butylacrylate or 2-hydroxyethyl methacrylate, was initiated by polyurethane (PU) grafted benzophenone to prepare a series of urethane acrylate (UA) polymers. The UA polymers were characterized based on their thermal, spectroscopic, mechanical, and low temperature flexibility properties. In this system, poly(acrylate) chains grew from the grafted benzophenone by photo-polymerization and affected the molecular interactions between PU polymers. The soft segment glass transition temperature (Tg) and melting temperature (Tm) were unaffected by the grafted poly(acrylate) chains. The tensile mechanical strength and the tensile strain of the UA series increased significantly with the attachment of the poly(acrylate) chains. Furthermore, shape recovery and shape retention remained high as the test cycle was repeated. Low temperature flexibility testing demonstrated that the synthesized UA was more flexible at a lower temperature than the unmodified PU.

Effect of the ionized carboxyl group on the water compatibility and the antifungal activity of the benzimidazole-grafted polyurethane

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.

Characterization and Effect of Covalently Grafted Benzoic Acid on the Low Temperature Flexibility and Water Vapor Permeability of a Polyurethane Copolymer

ABSTRACT 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. GRAPHICAL ABSTRACT

The effect of pendant tertiary butyl group on the shape recovery of polyurethane copolymer under freezing

The effect of the pendant tertiary butyl group on the shape recovery and tensile properties of a polyurethane (PU) block copolymer was investigated. The pendant tertiary butyl group was designed to interrupt molecular interactions and to disturb the close contact between PU chains through its bulky structure and, thus, to improve the shape recovery at subzero temperatures, while maintaining high and reproducible tensile properties and the shape recovery at ambient temperature. The attachment of the tertiary butyl group did make a difference in the phase separation of the hard and soft segments in the PU structure, as determined from the results of infrared and differential scanning calorimetry. The crosslink density and the intrinsic viscosity experienced an unusual increase with the tertiary butyl content due to partial crosslinking by the grafting reagent. Shape recovery and retention were reproducible after performing repeated shape memory tests. Finally, the effect of the tertiary butyl group on the shape recovery at −10°C was compared with that of linear PU, and the reason for the remarkable flexibility is discussed.

Shape memory polymer with mechanical strength and low-temperature flexibility using a grafted functional group

ABSTRACT 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.

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.

Low Temperature Shape Recovery Effect of Polyurethane Copolymer Grafted with Pendant n-Butyl Group

Effect of the pendant n-butyl group on shape recovery and tensile properties of polyurethane (PU) block copolymer was investigated. The grafted n-butyl group was intended to keep PU chains away and to deter molecular interaction between PU chains by its flexible chains, and thus improve shape recovery at subzero temperature while maintaining high and reproducible tensile properties and shape recovery at ambient temperature. The attachment of n-butyl group did not make any change in the molecular interaction and phase separation of hard and soft segments in PU structure as judged from IR and DSC analysis. Cross-link density and intrinsic viscosity increased with the increase of n-butyl content due to the partial cross-linking by the linking reagent. Shape recovery and shape retention were not diminished after cyclic shape memory tests. Finally, the effect of n-butyl group on low temperature shape recovery was compared with linear ones and the potential application of this finding was discussed.

Contrasting thermal behavior and low-temperature flexibility of PDMS-grafted and poly(2-ethylhexyl acrylate)-grafted polyurethane

ABSTRACT 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 Tg of the P series gradually increased, whereas the Tg of 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.