Physical and surface properties of polyurethane hydrogels in relation with their chemical structure

Polyethylene glycol (PEG)/castor oil (CO)‐based polyurethanes were prepared by one‐shot bulk polymerization method with the potential for biomedical applications. Hexamethylene diisocyanate and 1,4‐buthane diol were used as diisocyanate component and chain extender, respectively. Polyurethanes were prepared (1) with crosslinker and catalyst, (2) with crosslinker and without catalyst, and (3) without crosslinker and catalyst. The effects of the ratio of CO to PEG, and presence/absence of the crosslinker and catalyst on some physical and surface properties of the polyurethanes were investigated. The glass transition temperatures of prepared polyurethanes are below room temperature. The swelling ratio increased and the water contact angle decreased with increasing amount of PEG in polymer structure. The samples prepared with crosslinker and without catalyst showed the highest swelling ratio. Gas permeability of the samples was measured in a gas permeability system and surface roughness was determined by scanning electron microscope and atomic force microscope. Protein adsorption studies were performed for the samples synthesized without crosslinker and catalyst by using bovine serum albumin and bovine serum fibrinogen. Unexpected results were obtained for the samples which have low contact angles. They exhibited relatively high protein adsorption. POLYM. ENG. SCI., 54:1182–1191, 2014. © 2013 Society of Plastics Engineers     

Synthesis of polyhedral oligomeric silsesquioxane nano‐crosslinked poly(ethylene glycol)‐based hybrid hydrogels for drug delivery and antibacterial activity

The synthesis is reported of novel hybrid hydrogels based on ethylenediaminetetraacetic acid dianhydride and poly(ethylene glycol) (PEG) with octa‐aminopropyl polyhedral oligomeric silsesquioxane hydrochloride salt (OA‐POSS) as a nano‐crosslinker under solvent‐free conditions. The molecular weight of PEG was varied between 600 and 1000 Da. The synthesized hydrogels were characterized using various techniques. Further, the swelling behavior and antibacterial activity of the hydrogels and release kinetics of metronidazole (MTZ) as a model drug from them were evaluated. Experimental results demonstrate that hydrogels with tunable properties can be synthesized by varying the PEG molecular weight and type of crosslinker (hybrid or organic). Among the synthesized hybrid hydrogels, that crosslinked by OA‐POSS with long PEG chains (1000 Da) showed the highest swelling degree (2000%), drug encapsulation efficiency (88%) and extent of MTZ release (96%). © 2018 Society of Chemical Industry     

Structure‐property relationship in polyurethane elastomers containing starch as a crosslinker

Polyurethane elastomers were synthesized using polypropylene glycol (PPG 2000) as the polyol and starch as the multifunctional crosslinker in varying concentrations. Thermal and mechanical properties were measured by DSC, DMA and tensile tests. The morphology was examined by SEM. The swelling behavior of the polyurethanes in various solvents was investigated and the solubility parameter was determined. All these properties were compared with those of polyurethanes containing 1,1,1 ‐trimethylol propane (TMP) as the crosslinker. Starch‐based polyurethanes exhibited better mechanical properties. The effect of varying the starch:TMP ratio on the mechanical strength was also studied. With increasing starch content, the tensile strength and elongation increased. The starch‐based PUs exhibited two glass transitions, whereas TMP‐based PUs exhibited one T_g. No significant difference in the T_gs of the two PUs was observed. The activation energy of St‐PU calculated from DMA was 69 kcal/mol. Soil degradation tests indicated greater biodegradability in polyurethanes containing starch than in those containing TMP.     

Physical properties of crosslinked polyurethane

Polyester based polyurethanes were synthesized from low molecular weight polyester (M_n 2000) and 4,4′-methylene bis(phenyl isocyanate) (MDI) with butanediol as a chain extender and glycerol as a crosslinker. The polyester was synthesized from adipic acid and glycol which was a mixture of 1,6-hexanediol and 1,2-propanediol. The effect of the crosslinker content on the degree of H-bond formation in the hard segments and the physical properties of polyurethanes were studied by differential scanning calorimetry (DSC), thermal mechanical analysis (TMA), Fourier transform infrared spectroscopy (FTIR) and mechanical testing. The experimental results revealed that incorporation of a triol crosslinker into the hard segments of polyurethane results in a decrease of hard segment H-bond formation. The mechanical data indicate that the mechanical properties of polyurethanes depend on the concentrations of physical and chemical crosslinks and that there is an optimum concentration of triol crosslinker for the tensile stress and elongation properties. © 1998 Society of Chemical Industry     

Synthesis and properties of siloxane-crosslinked polyurethane-urea/silica hybrid films from castor oil

A novel hybrid diol (HD) crosslinker has been synthesized with hydrolyzable –Si–OR groups from 3-amino propyl trimethoxy silane and 3-glycidoxy propyl trimethoxy silane. Its chemical structure was confirmed by Fourier transform infrared spectroscopy, ¹H and ¹³C nuclear magnetic resonance spectroscopy to introduce it as a crosslinker in the castor oil, a renewable resource, to develop functional organic inorganic hybrid coatings. A series of castor oil-based organic–inorganic hybrid materials were prepared from castor oil, isophorone diisocyanate, and the different weight percentages of synthesized HD. Dynamic mechanical thermal analysis, thermogravimetric analysis, differential scanning calorimetry, and the universal testing machine were employed to characterize the hybrid films. The measured properties were found to be strongly influenced by the weight ratio of HD to the castor oil-based polyurethanes. The glass transition temperatures (T _g) for the cured hybrid films were found to be 26–72°C. Antibacterial activity, in vitro hydrolytic degradation, and swelling properties of the hybrid films have been studied. The cured hybrid films exhibited excellent antibacterial activity, which was enhanced with addition of the HD. The alkoxy silane-crosslinked castor oil-based coatings have shown better mechanical and viscoelastic properties in comparison to the control (uncrosslinked castor oil-based polyurethane-urea) coatings. The results showed that the weight percent of the HD is the main factor that controls the thermal, antimicrobial, mechanical, swelling, and degradation properties of these hybrid films.     

Carbohydrate crosslinked biocompatible polyurethanes: Synthesis,characterization, and drug delivery studies

A series of novel polyurethanes (PUs) with carbohydrate crosslinkers was synthesized. The drug loading and release kinetics were studied by using lamotrigine as a model drug. The polymers were designed in such a way that the drug release was tailored by differences in the stoichiometry of polymers. All the PUs were characterized for thermal and morphological properties by using differential scanning calorimetry and thermogravimetric analysis and scanning electron microscope , respectively. The encapsulation of drug inside PU matrix was confirmed via Fourier transform ‐ infrared (FT‐IR) spectra and scanning electron microscope . The kinetics and release mechanisms were observed to be a function of stoichiometric parameters such as type of crosslinker, polyol/crosslinker ratio and polyol/chain extender ratio. All the PUs were observed to be non‐cytotoxic in normal lung cell line L132. The synthesized PUs exhibited good mechanical strength, tunable release rates and biocompatibility that can be utilized in biomedical applications like wound dressing, biomedical implants , and drug delivery carriers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42223.     

Synthesis and characterization of POSS hybrid organogels using Menschutkin quaternization chemistry

The present research describes a series of organic–inorganic hybrid gels based on polystyrene and polyhedral oligomeric silsesquioxanes (POSSs) prepared using free radical copolymerization and Menschutkin chemistry techniques. In the first step, poly(styrene‐co‐chloromethylstyrene) is readily achieved by thermally initiated radical copolymerization and the subsequently obtained copolymer reacts with diethanolamine functional POSS nanoparticles which are employed as the crosslinker. The resulting hybrid network possesses ionic moieties and inorganic POSS nanoparticles. The POSS‐containing hybrid gels exhibit excellent organic solvent absorption and show good mechanical behaviour. Gel containing 0.8 × 10^?3 mmol of POSS(DEA)₈ (DEA, diethanolamine) reached the highest swelling ratio; hence, the corresponding gel can absorb organic solvent up to 20× its weight. The rate constant, coefficients and diffusional behaviour of hybrid organogels in organic solvent were examined as well. The organic solvent intake of the hybrid gel follows a non‐Fickian type diffusion. © 2018 Society of Chemical Industry     

Polymers from renewable resources. XIII. Interpenetrating polymer networks derived from castor oil–hexamethylene diisocyanate and polymethacrylamide

Several castor oil‐based polyurethanes (PUs) samples were synthesized using various diisocyanates such as hexamethylene diisocyanate (HMDI) with varying NCO/OH ratios. All the PUs were reacted with methacrylamide (MAM) using an ethylene glycol dimethacrylate (EGDM) crosslinker and benzoyl peroxide as an initiator. Thermogravimetric analysis of the polymers was followed using a computer analysis method for assigning the kinetic mechanism. The degradation steps are discussed in the light of kinetic parameters. The scanning electronic microscopy of some of the interpenetrating polymer networks (IPNs) were studied and the morphology was examined. The samples were subjected to wide‐angle X‐ray diffraction analysis. Ruland and Vonk's method was used to calculate the degree of crystallinity. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1349–1353, 2001     

Shape‐memory polyurethanes minimally crosslinked with hydroxyl‐terminated AB2‐type hyperbranched polyurethanes

A series of shape‐memory polyurethanes based on poly(ϵ‐caprolactone) diol were prepared with novel hydroxyl‐terminated hyperbranched polyurethanes as crosslinkers and were characterized by Fourier transform infrared spectroscopy, ¹H‐NMR, gel permeation chromatography, differential scanning calorimetry, scanning electron microscopy, wide‐angle X‐ray diffraction, dynamic mechanical analysis, tensile testing, and shape‐memory testing. The molecular weight of the soluble polymers ranged from 5.1 × 10⁴ to 29.0 × 10⁴ g/mol. The differential scanning calorimetry and wide‐angle X‐ray diffraction data indicated that when the crystallinities of the crosslinked polymers were compared to that of linear polyurethane, this parameter was improved when the crosslinker was in low quantity. The storage modulus ratios obtained from the dynamic mechanical analyses data of the crosslinked polymers were also high compared to that of the linear polyurethane. As a result, crosslinked polymers showed better shape‐memory properties compared to the linear polyurethanes. Also, the that incorporation of the hyperbranched polymer as a crosslinker into the polyurethane chain improved the thermal and mechanical properties of the polymer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of solvent exposure on the properties of hydroxy‐terminated polybutadiene‐based polyurethanes

Hydroxy‐terminated polybutadiene‐based prepolyurethanes and diamine chain extended polyurethane‐ureas were prepared and treated with various organic solvents in the moisture‐cured state in order to modify their ultimate strength. FTIR studies with solvent‐treated polyurethanes and polyurethane‐ureas confirmed that organic solvents penetrated inside the polyurethane hard segments and affected hydrogen bonding. The polar and non‐polar solvents showed different abilities to penetrate into polyurethane hard segments. Solvent treatment after moisture curing increased the tensile strength of these polyurethanes and polyurethane‐ureas with respect to control samples. The stress–strain behaviour of solvent‐treated polyurethane follows the constrained junction model. The change in hard segment crystallinity on solvent treatment has been explained by wide‐angle X‐ray diffraction study. The better orientation in polybutadiene soft segments evidenced from SEM (scanning electron microscopy) pictures is believed to be the main reason behind the improved tensile properties of solvent‐treated polyurethane samples. The effect of solvent treatment, as well as stretching, on the diffusion coefficient of hexane in polyurethanes was investigated. Copyright © 2003 Society of Chemical Industry     

Thermoresponsive crosslinked isocyanate‐free polyurethanes by Diels‐Alder polymerization

This new study is a continuation of our previous work on thermocleavable nonisocyanate polyurethanes (NIPUs), but it is focused on crosslinked networks. Two systems are studied: the first system involves a dicyclocarbonate adduct with a PPO‐bicyclocarbonate and a triamine as crosslinker. The second system involves a tetracyclocarbonate DA adduct as crosslinker with the same PPO‐bicyclocarbonate and a difunctional amine. Firstly, Diels‐Alder adducts are synthesized and characterized. Then they are copolymerized to yield two types of cleavable polymer networks. The thermal behavior of synthesized polymers is fully characterized. Finally, by SEC, it was demonstrated that the obtained NIPU polymer chains are sliced up by rDA reaction. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44408.     

Gum arabic–acrylic superabsorbing hydrogel hybrids: Studies on swelling rate and environmental responsiveness

The swelling rate and the environmental sensitivity of novel superabsorbent gum arabic–acrylic hydrogel hybrids were investigated. The swelling kinetics of the hydrogel hybrids was studied by means of a Voigt‐based viscoelastic model. The effects of concentration of the initiator, crosslinker, and the monomer ratio on the swelling rate were studied. The superswelling properties of the hydrogel hybrids were evaluated in various environmental pH, salinity and solvent–water mixtures. The optimally prepared hydrogel, MR5, showed a reproducible on–off switching behavior when the swelling medium was alternatively changed between distilled water and alkaline solutions. The hydrogel hybrid MR5 was also tested to be swollen and deswollen alternatively in distilled water and sodium chloride solution. The sorption–desorption behavior was found to be quite repeatable. A similar capability was interestingly observed when a calcium chloride solution with the same molar concentration was used. The swelling changes of the hydrogel hybrid were examined in various water–solvent systems including the aqueous solutions of methanol, ethanol, acetone, ethylene glycol, glycerol, and dimethylsulfoxide. One and/or two volume‐phase transitions were induced by the nonsolvents. The transitions were explained according to the solubility parameters of the solvents and water–solvent mixtures. The swelling–deswelling capability of the hydrogel in alternatively changed solvent–water mixtures was also studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5667–5674, 2006     

Physical Properties of Tri-isocyanate Crosslinked Polyurethane

Polyester based polyurethanes were synthesized from low molecular weight polyester (M_n2000) and 4,4-methylene bis(phenyl isocyanate) (MDI) with butanediol as a chain extender and tris(6-isocyanatohexyl) isocyanurate (HDT-LV), a tri-NCO terminated compound, as a crosslinker. The polyester was synthesized from adipic acid and glycol, which was a mixture of 1,6-hexanediol and 1,2-propanediol. Two series of crosslinked polyurethanes were prepared. One series were prepared using HDT-LV crosslinked on hard segments and the other series were crosslinked on soft segments. The effect of crosslinker content on the degree of hard segment H-bond formation and phase segregation of polyurethanes was investigated using DSC (differential scanning calorimetry) and FTIR (Fourier transform infrared spectroscopy). The experimental results revealed that the incorporation of tri-NCO crosslinker into the hard-segments of polyurethane resulted in a decrease of hard segment H-bond formation with increasing crosslinker content. However, only a slight decrease of hard segment H-bonding was observed with increasing tri-NCO crosslinker content while it was incorporated into soft segments.     

Development of new poly(ϵ‐caprolactone)/chitosan films

This study reports for the first time the production of poly(?‐caprolactone)/chitosan (PCL/CHT) films by solvent casting using a mixture of formic acid/acetone (70:30 vol%). Both uncrosslinked and crosslinked films with the natural crosslinker genipin were developed. The mechanical properties of the samples were analyzed by dynamical mechanical analysis (DMA) in the hydrated state. DMA was also successfully used for the first time to monitor in situ the crosslinking process as a function of time and crosslinker concentration. The compatibility between the polymers in the blended films was analyzed by Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). It was found that phase distribution is highly dependent on the blend composition. The developed films could potentially be used in different applications, such as tissue engineering scaffolds. © 2013 Society of Chemical Industry     

Synthesis and oil absorption of poly(butylmethacrylate)/organo‐attapulgite nanocomposite by suspended emulsion polymerization

A series of polybutylmethacrylate/organo‐attapulgite (PBMA/organo‐APT) nanocomposites were prepared by suspended emulsion polymerization using ethylene glycol dimethacrylate (EGDMA) as a crosslinker, and organo‐APT treated by different quaternary ammonium salt (C12, C16, and C18) as an inorganic component. The nanocomposites were characterized by means of Fourier transform infrared spectroscopy and scanning electron microscopy (SEM), showing that organo‐APT participated in polymerization by which a nanocomposite structure was formed. The effects of crosslinker and organo‐APT with different alkyl chain length on oil absorbency were investigated. The swelling kinetics in toluene, chloroform and gasoline were also systematically studied. The results reveal that introducing organo‐APT with moderate hydrophobic‐chain length into the PBMA polymeric network can improve oil absorption capability and swelling rate. POLYM. COMPOS., 2013 © 2013 Society of Plastics Engineers     

Total replacement of solvent in polyurethane synthesis using carbon dioxide soluble 1,3‐dichlorodistannoxane catalysts

This work demonstrates catalytic synthesis of polyurethanes using 1,3‐dichlorodistannoxane catalysts ( 1 ) in carbon dioxide (CO₂) and carbon dioxide expanded liquids (CXL). Catalytic polyurethane synthesis was also performed in pure organic solvent (dimethylformamide) for comparison. In this study, mainly, 4, 4′‐methylene‐bis‐(phenyl isocyanate) (MDI) as the diisocyanate precursor and ethylene glycol (EG) as the diol precursor were used for polyurethane synthesis. In addition to MDI, hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), and p‐isocyanatobenzylisocyanate (PIBI) were also used for polyurethane synthesis with different diols or triol in CO₂. Polyurethanes with a molecular weight ranging from 3000 to 70,000 were synthesized depending upon the combination of diisocyanate and diol used. Comparable yields of polyurethanes were obtained using an all butyl group substituted ( 1a ) catalyst in CO₂ (55 bars, 50°C) and in DMF (50°C). Additionally, the yield and polydispersity index (PDI) of polymer formed in neat CO₂ was comparable with those synthesized in the largely used organic solvent DMF. Interestingly, catalyst 1a in CXL (55 bars, 50°C) gave higher yields, and polymers with lower PDI (1.19). Reactions carried out in scCO₂ at 145 bars using PIBI and EG were found to be about three times faster than the reaction carried out in DMF. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of pyridazine content and crosslinker structure on the properties of polyurethane elastomers

This article studies the development of a series of heterocyclic polyurethanes (PUs) with various pyridazine content and different crosslinker structure in their main chains. All of the isocyanate‐terminated PU prepolymers were prepared from poly(tetramethylene oxide) glycol of molecular weight 1400 (Terathane 1400) and 1,6‐hexamethylene diisocyanate. The properties of the obtained linear and crosslinked pyridazine‐based PU were compared with the properties of common PUs obtained by chain extension with 1,4‐butanediol. All the obtained PUs were characterized through spectral and thermal behavior. The pyridazine‐based PU showed improved thermal stability with 10% weight loss at temperatures above 370–400°C. With the increase of pyridazine content the values of Young's modulus are higher and the strain at break decreases. Increasing pyridazine content leads to increased films surface hydrophilicity. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Porous crosslinked copolymers of octadecyl acrylate with acrylic acid as sorbers for crude petroleum spills

Bulk and suspension polymerization were used to prepare octadecyl acrylate/acrylic acid (ODA/AA) copolymers. AA content ranged from 0 to 90 mol%. Divinyl benzene was used as a crosslinker at several concentrations (1, 4 and 10 wt%). Isopropyl alcohol or dioctyl phthalate and methyl benzoate were used as the reaction solvents in the presence of poly(vinyl alcohol) as a dispersing agent and 2,2‐azobis isobutyronitrile as the initiator. The polymers so prepared were coated onto poly(ethylene terephthalate) nonwoven (NWPET) fibers. The effects of copolymerization, feed composition, crosslinker concentration and reaction medium or solvent on morphology including porosity and the dynamic mechanical and swelling properties of the crosslinked polymers were determined. Swelling tests were performed in toluene and in 10% crude petroleum diluted with toluene. Bulk polymerization does not result in the formation of a continuous liquid absorbing material while suspension polymerization enables sorbers to be obtained with desired properties. Coating ODA/AA copolymers onto NWPET increases liquid absorption. © 2013 Society of Chemical Industry     

Sorption behavior of biodegradable polyurethanes with carbohydrate crosslinkers

Polyether–polyurethanes (PUs) with a series of carbohydrate crosslinkers: monosaccharide (glucose), disaccharide (fructose) and polysaccharide (starch), were synthesized. The kinetics of swelling was studied in industrially important solvents like toluene, xylene and chlorobenzene. The R value and diol / triol ratio were varied to study the effect on crosslink density and sorption. It was observed that the swelling extent increased with increasing concentration of crosslinker in the polymer. Interestingly the effect of diisocyanate concentration on extent of sorption varied with the type of carbohydrate used for crosslinking. Considering the effect of diisocyanate concentration, the PUs containing disaccharide sucrose showed greater solvent uptake. Though the sorption behaviours were different, the solubility parameters of all PUs were the same irrespective of the type and concentration of the crosslinkers. All the PUs were observed to be biodegradable with glucose containing PUs exhibiting highest weight loss. Scanning electron microscope revealed absence of phase segregation in all the PU systems. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Aqueous polyurethane dispersions: A comparative study of polymerization processes

Restrictions on volatile organic compounds have forced the producers of solvent‐based polymers to develop safer products. Water dispersions of polyurethanes are successfully replacing solvent‐borne products in the coating industry, but relatively little systematic work has been reported that compares polyurethanes obtained by different processes. In this study, polyurethanes were produced with three polymerization processes: in a solution, in a dispersion with the acetone process, and in a dispersion with the prepolymer mixing process. The same prepolymer was synthesized in all cases, and the reaction was concluded under the conditions required by the three different methods. In the first phase, nonextended polyurethanes were prepared with different functional group ratios (NCO/OH), and an evaluation of the quality of the dispersions and solutions and of the morphology of the dry polymers was made by a comparison of the products from the three preparation routes. Second, the growth of the molecular weight in water was studied for the prepolymer mixing process. NCO‐terminated prepolymers were dispersed in water and then extended by aliphatic diamines. The extender was added in different percentages that referred to the NCO equivalents of the prepolymer. This led to an evaluation of the effect of the dispersing medium on chain extension. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 716–723, 2003