Studies on preparation and properties of porous biodegradable poly(NIPAAm) hydrogels

A series of biodegradable porous hydrogels, based on thermosensitive N‐isopropylacrylamide (NIPAAm) and biodegradable crosslinker‐polycaprolactone diacrylate (PCLdA) that was synthesized from polycaprolactone diol with acryloyl chloride were prepared by photopolymerization at low temperature. The effect of the crosslinker content and gelation method on the swelling behaviors and physical properties for the poly(NIPAAm) hydrogels was investigated. Results showed that the swelling ratio of the gel in deionized water decreased with an increase of the content of polycaprolactone (PCL) segment in the poly(NIPAAm) hydrogels. The properties of the gels crosslinked with PCLdA were compared with those crosslinked with N, N′‐methylenebisacrylamide (NMBA). The results showed that the critical gel transition temperatures (CGTT) of the gels crosslinked with PCLdA were lower than those of the gels crosslinked with NMBA due to the hydrophobicity of the PCL segment. The results also showed that the gels crosslinked with PCLdA had higher mechanical strength and crosslinking density than those gels crosslinked with NMBA. Comparing the porous gels with nonporous gels, the results showed that the swelling ratio and CGTT of the porous gels were higher than those of the nonporous gels, and the transition temperature curve was smoother for the porous gels. The porous gels also exhibited more rapid thermal response and faster degradation rates. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effects of reaction and cure temperatures on morphology and properties of poly(ester‐urethane)

Poly(ester‐urethane) was synthesized from poly(ethylene glycol adipate) (PEG) and 2,4‐toluene diisocyanate (TDI) to study the effects of reaction temperature and cure temperature on the crystallization behavior, morphology, and mechanical properties of the semicrystalline polyurethane (PU). PEG as soft segment was first reacted with TDI as hard segment at 90, 100, and 110°C, respectively, to obtain three kinds of PU prepolymers, coded as PEPU‐90, PEPU‐100, and PEPU‐110. Then the PU prepolymers were crosslinked by 1,1,1‐tris (hydroxylmethyl) propane (TMP) and were cured at 18, 25, 40, 60, and 80°C. Their structure and properties were characterized by attenuated total reflection Fourier transform infrared, wide‐angle X‐ray diffraction, scanning electron microscopy, dynamic mechanical analysis, and tensile testing. With an increase of the reaction temperature from 90 to 100°C, the crystallinity degree of soft segment decreased, but interaction between soft and hard segments enhanced, leading to the increase of the glass transition temperature (T_g) of soft domain and tensile strength. When the cure temperature was above 60°C, miscibility between soft and hard segments of the PEPU films was improved, resulting in relatively low crystallinity and elongation at break, but high soft segment T_g and tensile strength. On the whole, all of the PEPU‐90, PEPU‐100, and PEPU‐110 films cured above 60°C possessed higher tensile strength and elongation at break than that of the films cured at other temperatures. The results revealed that the reaction temperature and cure temperature play an important role in the improvement of the crosslinking structure and mechanical properties of the semicrystalline PU. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 708–714, 2006     

Study on the influence of thermal characteristics of hyperbranched polyurethane phase change materials for energy storage

A series of hyperbranched polyurethane (HB‐PU) phase change induced energy storage materials were prepared by polyethylene glycol (PEG), methylene diphenyl 4,4′‐diisocyanate (MDI), and hyperbranched polyester polyalcohol via a two‐step process. The influence of thermal characteristics of HB‐PU was investigated using differential scanning calorimetry (DSC) and wide‐angle X‐ray diffraction (WAXD). It has been found that the thermal characteristics of HB‐PU are affected by some factors. Such as the molecular weight and content of soft segment, once the M_n of PEG soft segments is larger than the critical M_n (2000 g/mol), both the phase change enthalpy and temperature increase as M_n of PEG soft segment and soft segment content (SSC) increase. The influence of the microstructure of hard segment originates from diisocyanate and hyperbranched polyester polyalcohol, HB‐PUs with regular microstructure and lower generation of hyperbranched polyester polyalcohol have high energy storage capability. Furthermore, the conditions of measurement affect the thermal characteristics of materials. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Thermoreversible hydrogels. XVIII. Synthesis,swelling characteristics,and diffusion behaviors of porous,ionic, thermosensitive hydrogels

Porous, ionic, thermosensitive hydrogels were prepared from N‐isopropylacrylamide, a cationic monomer [trimethyl (acrylamido propyl) ammonium iodide (TMAAI)], an anionic monomer [acrylic acid (AA)], a zwitterionic monomer [N′,N′‐dimethyl (acrylamido propyl) ammonium propane sulfonate], or a nonionic monomer [poly(ethylene glycol) methyl ether acrylate], and a pore‐forming agent [poly(ethylene glycol) (PEG)] of different molecular weights. Some fundamental properties and dynamic swelling kinetic parameters and solute permeation for these porous gels were investigated. The results showed that the gel containing the cationic monomer TMAAI had a higher equilibrium swelling ratio. The diffusion coefficients showed that the swelling rates for the gels with the anionic monomer AA and PEG with a higher molecular weight (20,000) were faster. The results showed that the fast swelling–deswelling behavior for the porous structure gels was due to them being more available than the gels with long hydrophilic side chains. In addition, the interactive force between the solutes and gels and the solute permeation through the porous gels were investigated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2214–2223, 2003     

Crystalline order and mechanical properties of as‐electrospun and post‐treated bundles of uniaxially aligned polyacrylonitrile nanofiber

This study investigates the crystalline order and mechanical properties of as‐electrospun and posttreated polyacrylonitrile nanofibers. To keep the nanofibers under tension during the posttreatment, a modified method of preparing bundles such as multifilament yarn was used in which the alignment of the nanofibers and linear density of the bundles were controlled successfully. An increase in the nanofibers' diameter from 240 to 500 nm led to the E modulus, ultimate strength, and elongation at break of the bundles rising from 836 MPa, 45 MPa, and 38% to 1915 MPa, 98 MPa, and 120%, respectively. The crystallinity index (%) and coherence length of the nanofiber bundles were evaluated through wide‐angle X‐ray diffraction. The mechanical properties and crystalline order of the nanofiber bundles were both increased as a result of the posttreatment. Wide‐angle X‐ray diffraction patterns of annealed bundles showed equatorial diffraction from the (101 0) reflection at ～ 5.1 Å and from the (112 0) reflection at ～ 3 Å. The values of the coherence length, crystallinity index (%), ultimate strength, and E modulus of the bundles prepared from 240‐nm nanofibers increased from negligible, 2%, 1109 MPa, and 48 MPa to 54 Å, 35%, 2235 MPa, and 95 MPa after annealing at 85°C in a mixture of water (95 wt %) and N,N‐dimethylformamide (5 wt %), respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effects of Temperature on Morphology and Properties of Films Prepared from Poly(ester‐urethane) and Nitrochitosan

Summary: Novel elastic materials were prepared by mixing semicrystalline polyester‐based polyurethane (PU) synthesized at 100 °C with nitrochitosan (NCH) and 1,1,1‐tris(hydroxylmethyl)propane as crosslinker, and then by curing the mixture at 18, 25, 40, 60, and 80 °C. The effects of cure temperature on the crystallization behavior, miscibility, and mechanical properties of the PUNCH materials were studied by attenuated total reflection Fourier transform IR, wide‐angle X‐ray diffraction, scanning electron microscopy, dynamic mechanical analysis, X‐ray photoelectron spectroscopy, and tensile test. The results indicated that the crystalline structure of the blend films was more easily interrupted as the cure temperature increased, leading to a decrease of the degree of crystallinity. With an increase of cure temperature, the blend films exhibited high crosslinking density and tensile strength, and the phase separation between hard and soft segments of PU enhanced, resulting in a decrease in the glass transition temperature (T_g) of soft segment. Interestingly, the composite films keeping high elongation at break possessed tensile strength higher than that of the native poly(ester‐urethane). The enhanced mechanical properties of the blend films can be attributed to the relatively dense crosslinking network and strong intermolecular hydrogen bonding between NCH and PU. Therefore, this study not only provided a novel way by adding NCH into PU matrix to prepare elastic materials, which would remain functional characteristic of chitosan, but also expanded the application field of chitosan.

The cure temperature dependence of the tensile strength and elongation at break for the PEPU‐100 and PUNCH‐100 films.     

Structure and mechanical properties of thermoplastic polyurethane,based on hyperbranched polyesters

A series of hyperbranched polyurethane (HB‐PU) were synthesized using hyperbranched polyester as a precursor. Morphology of these HB‐PU films was investigated using atomic force microscopy and wide‐angle X‐ray diffraction; it's molecular dynamics was studied by dynamic mechanical analysis. FTIR studies showed that hard segments get more aggregated to form domains in the HB‐PU block copolymer as hard segment content increases. Such domain formation has a significant influence on the mechanical and thermomechanical properties of HB‐PU, such as maximum stress and elongation at break. Especially, maximum stress and elongation at break increased significantly at 25 wt % of hard segment content, and the highest loss tangent was observed at the same composition. Heat of crystallization as measured by differential scanning calorimetry is also dependent on the hard segment content, and the control of hard segment content in PU block copolymers is very important in determining their physical properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5266–5273, 2006     

Effect of porosigen on the swelling behavior and drug release of porous N‐isopropylacrylamide/poly(ethylene glycol) monomethylether acrylate copolymeric hydrogels

A series of porous thermoreversible hydrogels were prepared from N‐isopropylacrylamide (90 mol %) and poly(ethylene glycol) methylether acrylate (10 mol %), which was derived from poly(ethylene glycol) monomethylether, N,N′‐methylenebisacrylamide, and porosigen, or poly (ethylene glycol) (PEG) with different molecular weights (MWs). The influence of pore volume in the gel on the physical properties, swelling kinetics, and solute permeation from these porous gels was investigated. The results show that the surface areas, pore volumes, and equilibrium swelling ratios for the porous gels increased with increasing MW of PEG, but the shear moduli and effective crosslinking densities decreased with increasing MW of PEG. The results from the dynamic swelling kinetics show that the transport mechanism was non‐Fickian. The diffusion coefficients of water penetrating into the gels increased with increasing pore volume of the gels. In addition, we also studied solute permeation through the porous gel controlled by temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5490–5499, 2006     

Effects on the structure and properties of membranes formed by blending polydimethylsiloxane polyurethane into different soft‐segment waterborne polyurethanes

Polydimethylsiloxane polyurethane (PDMS‐PU), which was synthesized from PDMS as the soft segment, was blended into a variety of ester‐ or ether‐based soft‐segment waterborne polyurethanes with different concentrations to investigate the crystallization, thermal, and physical properties of the membrane formations. According to X‐ray analysis, the ether‐based PUs, synthesized from soft segments of poly(propylene glycol) (PPG1000) or poly(ethylene glycol) (PEG2000), were found to have maximum crystallinity at a 5% blending ratio of PDMS‐PU, but the ester‐based PU, synthesized from soft segments of polycaprolactone (PCL1250), had decreased crystallinity at a 5% blending ratio. Differential scanning calorimetric analysis revealed that the T_g,s values of PUs were highest when the blending ratio of PDMS‐PU was 5%–10%, except for PU from PCL1250. Moreover, ether‐based PUs showed maximum T_m,h values, but the T_m,h of the ester‐based PU was greatly reduced when PU with PCL1250 was blended with PDMS‐PU. In addition, the PU from PEG2000 had the highest melting entropy. Mechanical property analysis showed that the stress of ether‐based PUs would be increased when PUs were blended with a small amount of PDMS‐PU and that the stress of PU from poly(tetramethylene glycol) (PTMG1000) increased to its greatest value (20–30 MPa). On the other hand, the ester‐based PU, from PCL1250 blended with PDMS‐PU, would have reduced stress. On the whole, the stress and strain of PU from PEG1000 had excellent balance. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 210–221, 2006     

Characterization of Native Cellulose/Poly(ethylene glycol) Films

Water molecules retained in native cellulose gels obtained from Acetobacter xylinum (AX) were displaced by poly(ethylene glycol)s (PEG) of different molecular weight. The so obtained native cellulose/PEG material, characterized in film form by differential scanning calorimetry, dynamic mechanical thermal analysis and wide angle X‐ray scattering, revealed that strong interactions occur between PEG and cellulose and that the polymer mixture is in the rubbery state at ambient temperature. Moreover, it could be dyed in supercritical carbon dioxide by disperse dyes, thus exhibiting typically lipophilic properties and suitability to be employed as a biocompatible support for lipophilic active species.     

Thermal and surface characterization of polyurethane–urea clay nanocomposite coatings

This paper reports synthesis and characterization of polyurethane–urea (PU‐urea) and the nanocomposites derived from the PU‐urea with silicate clays. Organophilic montmorillonite cotreated by cetyl trimethyl ammonium bromide (CTAB) was synthesized and used to prepare PU‐urea/montmorillonite nanocomposites coatings. PU‐ureas were prepared from polyethylene glycol (PEG), polypropylene glycol (PPG), trimethylol propane (TMP), and 4,4′‐diphenylmethane diisocyanate (MDI) by reacting excess diisocyanate with polyether glycols. The excess isocyanate of the prepolymers was cured with atmospheric moisture. The synthesized moisture cured PU‐urea and nanocomposites were characterized by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetric (DSC), and angle resolved X‐ray photoelectron spectroscopy (AR‐XPS). The thermal stability of the PU‐urea nanocomposites was higher relative to the mother PU‐urea films. DSC results showed a slight enhancement in the soft segment glass transition temperature after 3 wt % clay loading. The surface properties showed an enrichment of the soft segment toward the surface. An enhancement in the hard segment composition in the nanocomposite coatings has resulted in enhancing the phase mixing process. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2393–2401, 2006     

Preparation and characterization of aliphatic polyurethane and hydroxyapatite composite scaffold

Novel porous composite scaffolds for tissue engineering were prepared from aliphatic biodegradable polyurethane (PU) elastomer and hydroxyapatite (HA). It was found that the aliphatic PU was possible to load up to 50 wt % HA. The morphology and properties of the scaffolds were characterized by scanning electron microscope, X‐ray diffraction, infrared absorption spectra, mechanical testing, dynamic mechanical analysis, and in vitro degradation measurement. The results indicated that the HA/PU scaffolds had an interconnected porous structure with a pore size mainly ranging from 300 to 900 μm, and 50–200 μm micropores existed on the pores' walls. The average pore size of macropores and micropores are 510 and 100 μm, respectively. The compressive strength of the composite scaffolds showed higher enhancement with increasing HA content. In addition, the polymer matrix was completely composed of aliphatic component and exhibited progressive mass loss in vitro degradation, and the degradation rate depended on the HA content in PU matrix. The porous HA/PU composite may have a good prospect to be used as scaffold for tissue engineering. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation and properties of in‐situ polymerized polyurethane/stearate intercalated layer double hydroxide nanocomposites

The present work deals with the effect of stearate intercalated layered double hydroxide (St‐LDH) loadings on the morphological, mechanical, thermal, adhesive and flame retardant properties of polyurethane (PU)/St‐LDH nanocomposites prepared by the in situ polymerization method. X‐ray diffraction and transmission electron microscopy studies confirmed that exfoliation takes place at 3 wt% loading followed by intercalation at higher filler loadings in the PU matrix. The exfoliated structure has been further verified by atomic force microscopy. The measurements of stress‐strain, thermogravimetric analysis, dynamic mechanical analysis, lap shear strength and peel strength analysis showed that the nanocomposites containing 3 wt% St‐LDH exhibit excellent improvement in tensile strength (ca 175%) and log storage modulus (ca 14%), while PU/St‐LDH (5 wt%) possesses optimum improvement in glass transition temperature (ca 6 °C), lap shear strength (200%) and peel strength (130%) over neat PU. In addition, the gradual improvements in limiting oxygen index value with St‐LDH loading indicated the higher effectiveness in providing better barrier properties as well as better flame retardant behavior. Copyright © 2012 Society of Chemical Industry     

Effect of porosigen and hydrophobic monomer on the fast swelling–deswelling behaviors for the porous thermoreversible copolymeric hydrogels

A series of porous thermoreversible copolymeric hydrogels were prepared from N‐isopropylacrylamide (NIPAAm) and hydrophobic monomers such as 2,2,3,3,4,4,5,5‐octafluoropentyl methacrylate (OFPMA) and n‐butyl methacrylate (BMA) and CaCO₃ or poly(ethylene glycol) 8000 (PEG8000) as porosigen by emulsion polymerization. The effect of hydrophobic monomers and porosigens on the fundamental properties, such as equilibrium swelling ratio, swelling kinetics, gel strength, crosslinked densities, etc., and fast swelling–deswelling behavior for the present copolymeric hydrogels were investigated. Results showed that the deswelling rates for the gels porosigened by CaCO₃ were more rapid than those gels foamed by PEG8000. Results also showed that the swelling rates for the gel foamed by CaCO₃ were higher than those for the gel foamed by PEG8000. At the same time, results also showed that the gels with OFPMA foamed by CaCO₃ exhibit a faster swelling–deswelling behavior than those gels with BMA. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3152–3160, 2006     

Synthesis and characterization of nanocomposites of silicon dioxide and polyurethane and epoxy resin interpenetrating network

Nanocomposites with varying concentrations of nanosized silicon dioxide particles were prepared by adding nanosilica to interpenetrating polymer networks (IPN)s of polyurethane and epoxy resin (PU/EP). The PU/EP IPNs and nanocomposites were studied by dynamic mechanical analysis, scanning electronic microscopy, wide‐angle X‐ray diffraction and small‐angle X‐ray scattering. The result showed that adding nanosize silicon dioxide can improve the properties of compatibility, damping and phase structure of IPN matrices. Copyright © 2003 Society of Chemical Industry     

Miscibility,morphology, structure,and properties of porous cellulose–soy protein isolate hybrid hydrogels

Porous hybrid hydrogels were fabricated by mixing cellulose (CEL) and soy protein isolate (SPI) solutions, followed by crosslinking with epichlorohydrin. Their miscibility, morphology, structure, and properties were investigated by wide‐angle X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy, dynamic mechanical analysis, rheological measurement, and swelling tests. The results show that CEL performed as a “scaffold” of pore walls and contributed to the good mechanical properties, while SPI performed the role of an “extender” of pore size and was responsible for the high water absorbency. The incorporation of CEL (stiff chains) and SPI (hydrophilic groups) in the hybrid hydrogel constructed the porous structure. This work provides a method for the fabrication of hydrogels with porous structure through the combination of a stiff material as a “scaffold” and a hydrophilic material as an “extender.” © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43853.     

Polymeric carbon nanocomposites from multiwalled carbon nanotubes functionalized with segmented polyurethane

Multiwalled carbon nanotubes (MWNT) were functionalized with segmented polyurethanes (PU) by the “grafting to” approach. Raman and X‐ray photoelectron spectroscopy (XPS) spectra show that the sidewalls of MWNTs have been functionalized with acid treatment, and the amount of COOH increases with increasing acid treatment time. FTIR and X‐ray diffraction (XRD) spectra confirm that PU is covalently attached to the sidewalls of MWNTs by esterification reaction. Similar to the parent PU, the functionalized carbon nanotube samples are soluble in highly polar solvents, such as dimethyl sulfoxide (DMSO) and N,N‐dimethylformamide (DMF). The functionalized acid amount and the grafted PU amount were determined by thermogravimetric analyses (TGA). Comparative studies, based on SEM images between the PU‐functionalized and chemically defunctionalized MWNT samples, also reveal the covalent coating character. Dynamic mechanical analysis (DMA) of nanocomposite films prepared from PU and PU‐functionalized MWNTs show enhanced mechanical properties and increased soft segment T_g. Tensile properties indicate that PU‐functionalized MWNTs are effective reinforcing fillers for the polyurethane matrix. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Morphology and water vapor permeability of temperature‐sensitive polyurethanes

A series of segmented polyurethanes (PUs) were prepared, in which five different polyols and hexamethylene diisocyanate were used as soft segments, and 4,4′‐diphenylmethane diisocyanate, hydrophilic segment poly (ethylene glycol) 200 (PEG 200), and chain extender 1,4‐butanediol were used as hard segment. Morphology of the PUs was investigated using differential scanning calorimetry, wide angle X‐ray diffraction, polarizing microscopy, and transmission electron microscopy. Water vapor permeability of the membranes as a function of temperature was tested accordingly. Results show that the presence of PEG200 interferes the crystallization of hard segment in these PUs, and at the same time, increases phase compatibility between soft and hard segment in the PET‐PU. It leads to a lower crystal melting temperature and degree of crystallinity of soft segment in the segmented PU than those of pure polyols, and no crystallization existing in hard segment. A morphological model is proposed, that is, aggregated soft‐segment‐rich domains can be observed clearly in the PUs with high crystallinity in soft segment, while identifiable hard domains are well‐distributed in the soft segment domains in the PU with low crystallinity. Within the temperature range of crystal melting, water vapor permeability of the PU membranes increases significantly with increase of temperature. Such temperature‐sensitive property is triggered by crystal melting of soft segment. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Polyurethane electrospun mats strengthened and toughened by physically blended polyhedral oligomeric silsesquioxane

In this work, polyfunctional polyhedral oligomeric silsesquioxane (POSS) with glycidyl ether groups was physically blended with end‐capped polyurethane (PU) to improve the mechanical strength of PU electrospun mats. It was found that not only the tensile strength was elevated, but also the elongation‐at‐break was greatly improved. Fourier transform infrared spectroscopy results suggested that no chemical reaction happened, and there was no hydrogen bonding between POSS and PU, but the mobility of the PU chains was restricted. Wide‐angle X‐ray diffraction patterns showed that POSS aggregated inside the PU electrospun fibers. Scanning electron microscopy observation showed apparent die‐swelling, indicating that the elasticity of PU chains was enhanced. This was always the result of strengthened chain–chain interactions. From the experimental observations, it was speculated that a physical polymer–particle network was established through attachment of PU chains onto the POSS nanoparticles and embedment of PU chains inside the POSS aggregates, which results in the simultaneous improvements in strength and extensibility. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40902.     

Calcium ion‐induced self‐healing pattern of chemically crosslinked poly(acrylic acid) hydrogels

Poly(acrylic acid) hydrogels crosslinked with N,N′‐methylenebisacrylamide were synthesized by free radical polymerization. Polymerization conditions had a significant influence over the gel content and swelling behaviour of the hydrogels. The incorporation of calcium ions led to the origin of a self‐healing feature. The self‐healing behaviour and mechanical performance of the hydrogels were systematically investigated. The hydrogels showed good tensile strength of 1 MPa and excellent stretchable behaviour where hydrogels regained instantaneously. Hydrogel pieces joined together to become an integrated matrix as soon as two cut pieces were brought in contact. The hydrogels possessed a marked healing efficiency of 97% within 6 h at room temperature without any external intervention. The results are explained in terms of the dynamic mobility of calcium ions within the dual‐crosslinked networks of the poly(acrylic acid) hydrogels. © 2017 Society of Chemical Industry