Diisocyanate Compounds Research Articles

The MDI-Mediated Lateral Crosslinking of Polyurethane Copolymer and the Impact on Tensile Properties and Shape Memory Effect

Polyurethane (PU) has long been investigated due to its excellent mechanical properties, shape memory effect, and biocompatibility, and was grafted with pendant functional groups to tailor the polymer characteristics without affecting their basic structure. Actually, polyethyleneglycol has been grafted to polyurethane to improve biocompatibility in biomedical applications, and low temperature flexibility could be improved by the pendant naphthol group grafted to PU. In the field of shape memory polyurethane, mechanical and shape memory properties could be improved by terminal crosslinking with glycerol, pentaerythritol, and dextrin. Alternatively, a flexible crosslinking method was devised to demonstrate both high mechanical strength and shape recovery. The carbamate group has been frequently employed as the grafting point due to advantages such as ample linking sites, high reactivity, and mild coupling conditions, and activated with diisocyanate compound. The question is whether the diisocyante compound used for grafting pendant group to PU chain can crosslink another chain under the mild reaction condition, although such allophanate linking is known to require high temperature. In this investigation, the possibility of lateral crosslinking of PU under mild reaction condition and the impact on tensile properties and shape recovery are examined. The PU was synthesized based on previous methods, wherein 4,4'-methylenebis(phenyl isocyanate) (MDI) and poly(tetramethyleneglycol) (PTMG, Mn=2000) function as hard and soft segments, respectively, and 1,4-butanediol (BD) was used as a chain extender. The specific mole ratios of the reaction mixture are summarized in Table 1. In this investigation, the second MDI was intended to link PU chains through carbamate group and its impact on tensile properties and shape memory effect was tested. The urethane surface grafting with diisocyanate was already well established and could be carried out under mild reaction conditions. In this experiment, the usage of catalyst such as dibutyltin dilaurate or triethylamine was avoided due to the aggregation problem and the grafting reaction could go on homogeneously even without catalyst. The scheme of the MDI-mediated crosslinking is shown in Figure 1. The crosslink density was calculated from a polymer swelling experiment to determine whether the second MDI could really crosslink PU chains, which could explain the unusual tensile properties of the PU. The crosslink density was found to abruptly increase with the inclusion of second MDI

Novel poly(azomethine-urethane)s and their polyphenol derivatives derived from aliphatic diisocyanate compound: Synthesis and thermal characterization

Until now, only a few kinds of poly(azomethine-urethane)s (PAMUs) including aromatic hydroxy benzaldehyde and aminophenol compounds were obtained and studied with thermal degradation steps. However, oligo/polyphenol-based PAMUs have not been synthesized yet. In this study, some kinds of this class of PAMUs were synthesized in three steps. At the first step polyurethane (PU) was synthesized by the copolymerization reaction of 2,4-dihydroxybenzaldehyde with hexamethylene diisocyanate (HDI) under argon atmosphere. At the second step, the poly(azomethine-urethane)s (PAMUs) were obtained by graft copolymerization of the preformed PU with aminophenols (2-aminophenol, 3-aminophenol, and 4-aminophenol). At the last step the obtained PAMUs were converted to the polyphenol derivatives via oxidative polycondensation reaction (OP). The structures of the obtained compounds were confirmed by FTIR, UV-vis, 1H-NMR, and 13C-NMR techniques. The number-average molecular weight (Mn), weight average molecular weight (Mw) and polydispersity index (PDI) values of the synthesized compounds were determined by the size exclusion chromatography (SEC). The synthesized compounds were also characterized by solubility tests, TG-DTA, and DSC. Fluorescence measurements were carried out in various concentrated DMF solutions to determine the optimum concentrations to obtain the maximal PL intensities. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Poly(lactic acid) blends with desired end-use properties by addition of thermoplastic polyester elastomer and MDI

The disadvantages of the poor mechanical properties of polylactic acid (PLA) limit its ability to be used in a wide number of applications. Melt blending of PLA and thermoplastic polyester elastomer (TPEE) has been performed in an effort to toughen the PLA without significant losses in modulus and ultimate tensile strength. In order to enhance the compatibility of PLA and TPEE, a diisocyanate compound was used as a reactive modifier. The thermal and mechanical properties, miscibility and phase morphologies of the blends were investigated. A blend of PLA and TPEE with a modifier does not lead to an important drop in tensile strength and modulus whereas the elongation at break is characterized by a significant increase (above 300%), compared with that of neat PLA and PLA/TPEE. The blends of PLA/TPEE/Modifier were found by thermal and fractured surface analysis to be an immiscible system with the addition of a modifier. However, the relative ductility of PLA/TPEE/Modifier is 34 times higher than that of neat PLA. The brittle fracture of neat PLA was transformed into a ductile fracture by the addition of a modifier.

Enhancement of physical properties of thermoplastic polyether-ester elastomer by reactive extrusion with chain extender

The branched thermoplastic polyether-ester elastomer (TPEE) and diisocyanate compound was melt extruded in an effort to enhance melt viscosity for the blow moulding process. The chain-extended TPEE was prepared with melt condensation of a branched TPEE and 4,4′-diphenylmethane diisocyanate (MDI) for enhancement of the molecular weight of TPEE. The effects of MDI contents as a chain extender on melt, thermal, mechanical and rheological properties of the chain-extended TPEE were investigated. By using a solution and melt viscosity analysis, the chain-extended TPEE was found to be an enhancement of molecular weight and a lightly cross-linked structure. The intrinsic viscosity (IV) increased and melt flow index (MI) decreased with an increasing amount of MDI due to the reaction between the hydroxyl end groups of TPEE and isocyanate groups of MDI. The chain-extended TPEE does not lead to an important drop in elongation at break. The tensile strength and the tear strength are characterized by a significant increase, compared with a branched TPEE. The storage modulus, loss modulus and the complex viscosity of the chain-extended TPEE were also higher. The modified Cole–Cole plots revealed that the chain-extended TPEE shows a higher elasticity than the branched TPEE. The chain-extended TPEE has more suitable melt and rheological properties for the blow moulding processes.

New polymer syntheses, part 45: Corrosion inhibition behavior of novel polyurea derivatives based on diarylidenecycloalkanone moieties in the polymers backbone

A novel class of interesting polyurea derivatives 6a-c and 7a-c was synthesized using solution polycondensation technique by the interaction of 1 mole of bis (2-aminothiazol-4-ylbenzylidene)cycloalkanones monomers 3a,b with one moles of diisocyanate compounds in pyridine. The model compounds 4 and 5 were synthesized by the interaction of one mole of monomers 3a or 3b with two moles of phenylisocyanate in pyridine and their structures were confirmed by correct elemental and spectral analyses. The resulting polymers were characterized by elemental and spectral analyses, beside solubility and viscometry measurements. X-ray analysis showed these polymers having high degree of crystallinity in the region 2θ = 5–60°. In addition, the morphological properties of selected examples were tested by SEM, and the electrical properties of these polymers were measured. Moreover the corrosion inhibition behavior of diarylidenecycloalkanone monomers and selected examples of polyurea derivatives were carried out on steel in 0.5 M H2SO4 at 40°C giving cathodic, anodic and mixed inhibition.

New polymer syntheses, Part 44: Synthesis, characterization, and corrosion inhibition behavior of new polyurea derivatives based on diaryl ether in the polymers backbone

AbstractA new interesting class of polyurea derivatives 5a‐c was synthesized using solution polycondensation technique by the interaction of 1 mol of 4,4′‐bis(2″‐aminothiazol‐4″‐yl)diphenyl ether monomer 3 with 1 mol of diisocyanate compounds in pyridine. The model compound 4 was synthesized by the interaction of 1 mol of monomers 3 with 2 mol of phenylisocyanate in pyridine, and the structure was confirmed by correct elemental and spectral analyses. The resulting polymers were characterized by elemental and spectral analyses besides solubility and viscometry measurements. The thermal properties of those polymers were evaluated by TGA, DTG, and DTA measurements and correlated to their structural units. In addition, the morphological properties of a selected example were tested by SEM, and the electrical properties of these polymers were measured. On the other hand, the corrosion inhibition properties of selected example of polyurea derivatives were carried out on steel in 0.5M H2SO4 at 40°C giving cathodic inhibition. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

“Click” Chemistry as a Promising Tool for Side-Chain Functionalization of Polyurethanes

Linear polyurethanes (PUs) having alkyne groups located along the backbone have been synthesized by reacting two different alkyne-functionalized diols with a diisocyanate compound. 1H NMR and FTIR proved the presence of these functional groups and the ability for the introduction of an elevated and controllable amount of functional groups that do not interfere with the PU chemistry. TGA measurements demonstrated that the incorporated alkyne diol in the PU materials strongly improves the final char yield. In the second part of the work, the copper catalyzed Huisgen 1,3-dipolar cycloaddition was undertaken between the alkyne-functionalized PUs and a variety of azide compounds such as benzyl azide and different fluorinated azide compounds, resulting in side-chain functionalized PUs with varying degree of functionalization. 1H NMR spectra clearly indicated the quantitative yields of the “click” reaction.

Synthesis and Modifications of Polyurethanes for Biomedical Purposes

Polyurethanes are known as a class of polymers with very high ‘hemocompatible‘ properties. In this study polyurethanes were prepared in various compositions and in medical purity without using any solvent, catalyst or additives. For the synthesis of polyurethanes, toluene diisocynate, diphenylmethane diisocynate or hexamethylene diisocynate were used as diisocyanate compounds and polypropylene-ethylene glycol or polypropylene glycol were used as polyol compounds. The surfaces were modified with plasma glow-discharge by using various gas atmospheres and by applying different powers. Some samples were also modified by heparin immobilization to increase the blood compatibility. Chemical structure, mechanical strength, thermal behavior, oxygen permeability, water contact angle values, as well as protein and cell attachment capabilities of the prepared and modified polyurethanes were examined as possible candidates for biomedical applications. Plasma altered the chemistry of the surface, increased hydrophilic character, and caused a decrease in protein adsorption as the applied power was increased. On the other hand, an optimum power value which caused maximum attachment for Vero cells was observed. In-vitro experiments carried out with blood cells, plasma modification caused an increase on cell adhesion while further heparin immobilization resulted with a significant decrease.

Polymeric coatings that mimic the endothelium: Combining nitric oxide release with surface-bound active thrombomodulin and heparin

Multi-functional bilayer polymeric coatings are prepared with both controlled nitric oxide (NO) release and surface-bound active thrombomodulin (TM) alone or in combination with immobilized heparin. The outer-layer is made of CarboSil, a commercially available copolymer of silicone rubber (SR) and polyurethane (PU). The CarboSil is either carboxylated or aminated via an allophanate reaction with a diisocyanate compound followed by a urea-forming reaction between the generated isocyanate group of the polymer and the amine group of an amino acid (glycine), an oligopeptide (triglycine) or a diamine. The carboxylated CarboSil can then be used to immobilize TM through the formation of an amide bond between the surface carboxylic acid groups and the lysine residues of TM. Aminated CarboSil can also be employed to initially couple heparin to the surface, and then the carboxylic acid groups on heparin can be further used to anchor TM. Both surface-bound TM and heparin's activity are evaluated by chromogenic assays and found to be at clinically significant levels. The underlying NO release layer is made with another commercial SR–PU copolymer (PurSil) mixed with a lipophilic NO donor (N-diazeniumdiolated dibutylhexanediamine (DBHD/N2O2)). The NO release rate can be tuned by changing the thickness of top coatings, and the duration of NO release at physiologically relevant levels can be as long as 2 weeks. The combination of controlled NO release as well as immobilized active TM and heparin from/on the same polymeric surface mimics the highly thromboresistant endothelium layer. Hence, such multifunctional polymer coatings should provide more blood-compatible surfaces for biomedical devices.

Polymerization compounding of polyurethane-fumed silica composites

Polymerization Compounding (PC) offers the possibility to design composite materials by controlling the architecture of a grafted polymer on the surface of solid substrates to be incorporated in a polymer matrix. The approach consists in involving the surface of a reinforcement in a polymerization process of a polymer to be used either as a matrix in the final composite or else as a special surface treatment to enhance solid/polymer interface properties in the composite. The PC process is illustrated here with fumed silica as a solid substrate and polyurethane as a matrix. The hydroxyl sites on silica particles were reacted consecutively with a toluene diisocyanate (TDI) compound and then with either bis-phenol-A (BA) or hydroxy-terminated polybutadiene (HTPB) in order to obtain the desired coating. Soxhlet extractions were conducted to confirm grafting of the polymer on the solid surface. The amount of grafted polymer was evaluated by thermogravimetric analysis. Modified particles were incorporated into HTPB/TDI compounds at concentrations as high as 25% w/w. Water absorption, thermorheological as well as mechanical properties all show clear contribution of the improved bonding between the solid phase and the binder. POLYM. ENG. SCI. 46:360–371, 2006. © 2006 Society of Plastics Engineers

Kinetics of the in situ polymerization and in situ compatibilization of poly(propylene) and polyamide 6 blends

AbstractIn previous articles, we reported on a novel reactive extrusion process to obtain a compatibilized blend of polymer A and polymer B. It consisted in polymerizing the monomer of polymer A in the presence of polymer B. A fraction of the latter contained initiating sites from which the polymerization of monomer A took place. As such, both polymer A and a graft copolymer of polymer A and polymer B were formed in the process. That process was called in situ polymerization and in situ compatibilization of polymer blends. Its feasibility was illustrated for in situ polymerized and in situ compatibilized poly(propylene) and polyamide 6 (PP/PA6) blends. The latter were prepared by activated anionic polymerization of ϵ‐caprolactam (CL) in the presence of PP in a batch mixer and a twin‐screw extruder, respectively. A fraction of the PP contained isocyanate groups from which PA6 grafts were formed. Sodium caprolactam (NaCL) was used as the catalyst and a diisocyanate compound was used as the activator. In this study, we report on the effects of various parameters on the kinetics of the anionic polymerization of CL in the presence of PP. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1498–1504, 2004

Hydrogels for an accommodating intraocular lens. An explorative study.

In this study it was investigated whether hydrogels could be used for an accommodating lens. The requirements of such a hydrogels are a low modulus, high refractive index, transparency, and strength. Since conventional hydrogels do not possess this combination of properties, a novel preparation method and new polymers are introduced. As starting materials poly(1-hydroxy-1,3-propanediyl), poly(ethylene-co-vinyl alcohol), poly(vinyl alcohol), and poly(allyl alcohol) were used. The first three were cross-linked with a number of diisocyanate compounds. Network formation was performed at low concentrations in a good solvent. Mixing of the polymer solution and cross-linker appeared to be crucial for transparency. Poly(1-hydroxy-1,3-propanediyl), cross-linked with a slow reacting diisocyanate block, shows the most promising properties with respect to refractive index, transparency, tensile strength, and modulus. Poly(allyl alcohol) hydrogel was made by compression molding. The hydrogel was transparent and had a high refractive index and low modulus. It was concluded that hydrogels could be used as accommodating lens material.

Isocyanate-free moisture cure coatings

Novel isocyanate-free moisture curepolyurethane coatings with excellent properties have been formulated and evaluated. These coatings utilize polyols derived from the renewable resource soybean oil and its simple derivatives. The coating is autocatalytic and does not require continuous exposure to moisture for the development of full properties. A series of soybean oil-based polyols were synthesized by treating either the raw oil or epoxidized soybean oil (ESO) by a variety of reagents including long chain fatty acids. In a series of model reactions the above polyols were reacted with various diisocyanate compounds, at molar ratio of NCO/OH=1.5:1–3:1 to obtain prepolymers with residual NCO% of around 1.8. The isocyanate-free moisture curable resin was obtained by coapping the prepolymer with of aminosilane followed by the addition of a small amount of methanol. Typical clearcoat formulations become tack-free in less than an hour, recoatable in about one hour, and reach a functional cure stage in 24 hr at 40% RH and 25°C.

Preparation and characterization of cyclodextrin polymer and its high-performance liquid-chromatography stationary phase.

Cyclodextrin (CD) polymers were synthesized from the reaction of native CDs with a hexamethylene diisocyanate (HDI) compound in a dried DMF solution. The obtained CD polymer contained a range of 8-14% N due to HDI by elemental analysis. The physical and chemical properties of the CD polymers were characterized by IR, solid state 13C NMR, TGA, and DSC, respectively. An HPLC column was prepared using the CD polymer with a carbamate linker by a slurry method. Separation of the phenol isomers was conducted using the CD polymer stationary phase and CD by HPLC. Furthermore, an inclusion complex of the phenol isomer was studied by FT-Raman spectroscopy. From the HPLC and FT-Raman results, inclusion phenomena of o-, m-, and p-nitrophenol onto CD and CD polymers were analyzed.

Rheokinetic studies on the formation of urethane networks based on hydroxyl terminated polybutadiene

Rheokinetic studies on the formation of copolyurethane networks based on hydroxyl terminated polybutadiene, poly(12-hydroxy stearic acid-co-TMP) ester polyol and different isocyanates, such as toluene-di-isocyanate, hexamethylene-di-isocyanate, isophorone-di-isocyanate and methylene-di-cyclohexyl di-isocyanate were undertaken by following the build up of viscosity of the reaction mixture during the bulk polymerization reaction between the hydroxyl telechelic pre-polymers and the di-isocyanate compounds. Linear rheokinetic plots were obtained by plotting ln(viscosity) versus time and the slopes of which, are the rate constants for the viscosity build up. The rate constants range from 0.038×10 −2 to 27.1×10 −2 min −1 and were found to have strong dependence on the isocyanate type, NCO/OH equivalent ratio ( r-value) and copolyurethane composition as well as the structural characteristics, such as functionality distribution of the pre-polymers and the nature of the hydroxyl group.

Determination of 1‐octanol/water partition coefficients of isocyanate compounds by an HPLC method

The octanol/water partition coefficients (P ow) of six monoisocyanate and five diisocyanate compounds were determined by high performance liquid chromatograph (HPLC) methods. Two HPLC peaks, a broad tailed peak followed by a sharp one, were observed with all compounds. The later peak was identified as the isocyanate compound. The P ow value for each isocyanate compound was determined by fitting the capacity factor of the peak to the regression equation drawn from those of reference compounds. The hydrophobic substituent constants for the isocyanate group were calculated with each of the compounds. The value of this constant was strongly dependent on the type of carbon bound to the isocyanate group and the average values for the aromatic and aliphatic isocyanate groups were 0.35 and — 0.52, respectively. Because of the reactivity of those compounds in the aquatic environment, the P ow has little relevance to calculation of their environmental fate and ecotoxicity.

Separation of aqueous phenol through polyurethane membranes by pervaporation. II. Influence of diisocyanate and diol compounds and crosslinker

The influence of diisocyanate and diol compounds of polyurethane and crosslinking agent on the separation of phenol aqueous solution by pervaporation was investigated. Polyurethanes were prepared by polyaddition of diisocyanate and diol compounds and trimethylolpropane (TMP) using dibutyltindilaulate as a catalyst. The polyurethane membrane was prepared by a casting method and was sandwiched with a porous polypropylene membrane (Celgard® 2500). Pervaporation measurement was carried out under vacuum on the permeate side, and the permeant was collected with a liquid nitrogen trap. Little influence of diisocyanate compounds on the phenol permselectivity through diisocyanate–polytetramethyleneglycol [PTMG(1000)] membranes was observed since the influence on the solubility and the diffusivity was small. The phenol permselectivity was increased with an increase in the molecular weight of PTMG and polycaprolactone diol (PCL) for the 1,6-diisocyanato hexane (HMDI)–PTMG and HMDI–PCL membranes. It was considered that the increase in phenol diffusivity can be attributed to an increase in phenol selectivity. The permeability and selectivity of HMDI–[PTMG(2900)–TMP] membrane was relatively constant below the 2% TMP content. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 439–448, 1999

Chemical stabilization of collagen based biomaterials

Collagen-based biomaterials are usually stabilized either by physical or chemical crosslinking to control the rate of biodegradation of the material, to suppress its antigenicity and to improve the mechanical properties. Several chemical crosslinking methods for collagen-based biomaterials are known. In principal these methods can be divided into two groups. The use of bifunctional reagents to bridge free amine groups of lysine or hydroxylysine residues on different polypeptide chains has long been used. Glutaraldehyde crosslinking is the most extensively studied and is a frequently applied method for the stabilization of collagen-based biomaterials. The major disadvantage of this approach is that toxic reagents are introduced in the material which upon release car result in cytotoxic reactions in both in vitro and in vivo application. Hexamethylene diisocyanate and (poly)epoxy compounds arc bi(poly)functional compounds that have been studied as an alternative to glutaraldehyde crosslinking. Crosslinking can also be achieved by activation of the carboxylic acid groups of glutamic and aspartic acid residue followed by reaction with an amine group of another polypeptide chain to give an amide bond. This concept was already introduced in the early 80’s by the use of cyanamide as an activating agent for the crosslinking of reconstituted collagen. The major advantage of such an approach is that no (toxic) reagents are introduced in or may be released from the material. Based on this idea a crosslinking method has been developed using a water soluble carbodiimide to activate carboxylic acid groups of the polypeptide chains. Addition of N-hydroxysuccinimide to the carbodiimide containing crosslinking solution to substitute the formed 0-acylisourea groups by succinimate esters not only increased the rate of crosslinking but also resulted in crosslinked materials with increased stability towards enzymatic degradation. Collagen samples crosslinked via this method were not cytotoxic as determined with an in vitro cell culture system using human skin fibroblasts.

The reaction of glass fiber with diisocyanate and its application

AbstractThe synthesis of reactive glass fiber having isocyanate groups were tried by reacting silanol groups on the surface of glass fiber with diisocyanate compounds. The effect of solvent, influence of the structure of diisocyanate, and effect of amine catalyst were examined, and results that the reactivity increased with increasing the polarity of solvent, when aromatic diisocyanate was used, and with increasing the basicity of amine catalyst were obtained. Further, glass fiber having isocyanate groups was addition‐reacted with diol, and diol added glass fiber was synthesized.

The guinea pig model of diisocyanate sensitization: I. Immunologic studies

Two strains of guinea pigs were parenterally immunized with well-characterized diisocyanate-protein conjugates. Hapten-specific IgE antibodies were detected in the sera of English short-hair strain guinea pigs immunized with either toluene diisocyanate-human serum albumin (TDI-HSA) or hexamethylene diisocyanate-HSA (HDI-HSA) when these sera were analyzed by the 168 hr passive cutaneous anaphylaxis (PCA) technique followed by intravenous challenges with conjugates of respective ligands coupled to an unrelated carrier protein, transferrin. IgG 1 antibodies and precipitating antibodies were demonstrated in Hartley strain guinea pigs immunized with TDI/HDI-HSA conjugates. The hapten specificity of these antibodies was proved by PCA inhibition experiments and antibody absorption experiments. In the precipitating antibody system, this was further confirmed by immunoelectrophoretic analysis. Cross-reactivity between HDI and TDI was not observed in the PCA experiments. However, apparent cross-reactivity in the double gel diffusion experiments was due to new antigenic determinants formed by isocyanates after conjugation with proteins. It was therefore apparent that immune responses of guinea pigs immunized with protein conjugates of bifunctional isocyanates were heterogeneous and involved multiple specificities for hapten, carrier protein, and new antigenic determinants. It was postulated that the complex nature of the immune response generated by diisocyanate compounds in the guinea pig may also serve as a more appropriate model of isocyanate-induced human sensitivity reactions, which are known to involve diverse immunologic and nonimmunologic mechanisms.