Diisocyanate Structure Research Articles

Effect of diisocyanate structures on the properties of liquid crystalline polyurethanes

AbstractThermotropic liquid crystalline polyurethanes (LCPUs) were synthesized through the polyaddition reaction of 2,4‐toluene diisocyanate (2,4‐TDI), 4,4′‐diphenylmethane diisocyanate (MDI), or o‐toluidine diisocyanate (ODI) with 4,4′‐bis(6‐hydroxyhexoxy)biphenyl, and the effect of the structures of the diisocyanates on the properties of LCPUs were investigated. Intrinsic viscosities of the polymers were in the range of 0.23–0.30 dL/g. Mesomorphic behavior of the polyurethanes were investigated by differential scanning calorimetry, polarized optical microscopy, and wide‐angle X‐ray scattering. Different mesomorphic behaviors were observed according to the different structural characteristics of diisocyanates. Polyurethanes employing 2,4‐TDI and MDI exhibited monotropic behaviors, while that with ODI showed enantiotropic behavior. POLYM. ENG. SCI., 47:439–446, 2007. © 2007 Society of Plastics Engineers.

Polyurethane networks from formiated soy polyols: Synthesis and mechanical characterization

AbstractPolyurethanes can be prepared using polyols obtained from vegetable oils in natura, such as castor oil, or from functionalized vegetable oils, such as hydroxylated soybean oil. These polyurethanes have different valuable properties, determined by their chemical composition and cross‐linking density. In this study, soy epoxy polyols with different OH contents were prepared through a one‐step reaction using the method of in situ performic acid generation. Polyols with OH functionalities from 1.9 to 3.2 were reacted in bulk with different diisocyanates at a NCO/OH molar ratio of 0.8 and 60°C for 24 h. Mechanical properties of the polyurethanes were determined by dynamic mechanical thermal analysis, hardness (Shore A), and swelling measurements. Polymer networks with glass‐transition temperatures (Tg) from −13 to 48°C were obtained. We observed that the higher the OH functionality of the polyols, the higher the Tg and cross‐linking density of the polyurethane network. The influence of diisocyanate structure (rigid or flexible chain), curing temperature, and curing reaction time on mechanical properties was also investigated.

Synthesis and properties of polyurethane resins based on liquefied wood

AbstractThree polyurethane resins were synthesized from liquefied wood and three diisocyanates, i.e., TDI, IPDI, and HDI. The liquefied wood was obtained by the liquefaction of benzylated wood wastes using Dibasic esters (DBE) as solvent with hydrochloric acid as catalyst for 3 h, at 80°C. The thermal stability and microphase morphology of polyurethane films were investigated by TG, DSC, WAXD, and SEM methods. The experimental results indicated that polyurethane resins from liquefied wood had higher thermal stability than traditional ones, and the special structure and the difference of chemical structure of diisocyanates resulted in the crytallinity and microphase separation of obtained polyurethanes. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 351–356, 2004

Formation, structure and properties of polymer networks: theory and modelling

The application of a Monte-Carlo (MC) algorithm to account fully for loop formation in RA2 + R'B3 and RA2 + R'B4 polymerisations is described. The resulting interpretation of experimental elastic moduli of hexa- methylene diisocyanate(HDI)-based polyurethane networks prepared at different dilutions shows it is essential to account for elastic losses in loop structures of all sizes. An important parameter, x, is introduced, namely the average fractional loss of elasticity per larger loop structure relative to the loss per smallest loop structure. Values of x vary between 0.50–0.60, depending on junction point functionality, reactant or network chain stiffness and number of skeletal bonds per smallest loop structure. Application of the MC calculations to the formation and resulting structure of diphenylmethane diisocyanate(MDI)-based polyurethane networks and poly(dimethyl siloxane) (PDMS) networks again predicts significant reductions in modulus due to loop structures. However, comparison with experimental modulus data shows that the reductions in modulus due to loops are outweighed by increases due to chain interactions and to topological entanglements.

Formation, structure and properties of polymer networks: theory and modelling

The application of a Monte-Carlo (MC) algorithm to account fully for loop formation in RA2 + R′B3 and RA2 + R′B4 polymerisations is described. The resulting interpretation of experimental elastic moduli of hexamethylene diisocyanate(HDI)-based polyurethane networks prepared at different dilutions shows it is essential to account for elastic losses in loop structures of all sizes. An important parameter, x, is introduced, namely the average fractional loss of elasticity per larger loop structure relative to the loss per smallest loop structure. Values of x vary between 0.50–0.60, depending on junction point functionality, reactant or network chain stiffness and number of skeletal bonds per smallest loop structure. Application of the MC calculations to the formation and resulting structure of diphenylmethane diisocyanate(MDI)-based polyurethane networks and poly(dimethyl siloxane) (PDMS) networks again predicts significant reductions in modulus due to loop structures. However, comparison with experimental modulus data shows that the reductions in modulus due to loops are outweighed by increases due to chain interactions and to topological entanglements.

Thermal and dynamic mechanical behavior of polyurethanes based on diisocyanates and diethanolamine derivatives with mesogenic groups in side chain

Thermotropic polyurethanes were prepared from three commercial diisocyanates of various flexibility and eight diols (based on diethanolamine derivatives) with mesogenic groups in side chain with stoichiometric ratio of reactive isocyanate and hydroxy groups. Polymers were studied by dynamic mechanical spectroscopy, X-ray scattering, differential scanning calorimetry and polarizing microscopy. The effect of structure changes in the diisocyanates and diols, in particular changes in the end substituents bound to the mesogen, were investigated. Introduction of mesogenic diols into the polymers suppresses the occurrence of mesophases in comparison with neat diols; in the case of simple end substituents (such as hydrogen, nitro and nitrile), the mesophases disappear completely regardless of the structure of diisocyanate. Stiff end substituents (phenyl and alkoxy groups) stabilize the mesophases to such an extent that the negative influence of long polymer chains is compensated and the liquid–crystalline (LC) properties are recovered. Generally, the polymers prepared from the stiffest 2(4)-methyl-1,3-phenylene diisocyanate exhibit a most pronounced LC behavior.

Effects of chemical structure of diisocyanate in polyurethanes on the diffraction efficiency

Abstract In this study, we report the syntheses and diffraction efficiency of four different disperse red-polyurethanes (DR-PU n ’s) containing azobenzene group in the side chain. The effects of chemical structures of diisocyanates in four different DR-PU n ’s were studied on the diffraction efficiency induced by the laser beam. The DR-PU n ’s with toluene-2,4-diisocyanate or toluene-2,6-diisocyanate exhibited diffraction efficiencies, but the DR-PU n ’s with diphenyl structure of diisocyanate in the main chain did not show diffraction efficiencies. It was found that for the DR-PU2 having the molecular weight larger than 16,000 shows good optical storage behavior and that the maximum diffraction efficiency reached to 0.35%.

Synthesis and characterisation of castor oil-urethane acrylate oligomers

Castor oil-urethane acrylate (CVA) oligomers have been synthesised and characterised by infra-red spectroscopy (FT-IR), gel permeation chromatography(GPC) to study the relationship between the reaction kinetics and the structure of the products. It is shown that the chain terminating reaction between 2,4-toluene diisocyanate (2,4TDI) and hydroxyethylacrylate (HEA) to form isocyanatoethyl acrylate (IEA) obeys a second order mechanism, as does the chain extension reaction of IEA and castor oil (CAS). From the data of the polymerisation rate constant and the apparent activation energy, it can be seen that the different structure of CVA oligomer is dependent mainly on the different reactivities of both para and ortho NCO groups in 2,4TDI. Whereas the apparent viscosity of the CVA oligomer is related to the structure of diisocyanates. Results from the dynamic mechanical spectrum (DMS, the abstract of dynamic mechanical spectrum, a kind of detection method) indicate that the hard segment content of oligomers is then increased up to 59% (wt.). A phase-separated structure is formed and leads to the highest tensile strength (18.2MPa). When the hard segment content is increased to 67% (wt.), the dynamic modulus is reduced and the single depletion peak from DMS is exhibited at the temperature of 100.7°C.

Properties of segmented polyurethanes derived from different diisocyanates

Various segmented polyurethane materials with a polyurethane hard segment (HS) content of 40 wt % were prepared by bulk polymerization of a poly(tetramethylene ether) glycol with Mn of 2000, 1,4-butanediol, and various diisocyanates. The diisocyanates used were pure 4,4′-diphenylmethane diisocyanate (MDI), 2,4-toluene diisocyanate (T100), toluene diisocyanate containing 80% 2,4-isomer and 20% 2,6-isomer (T80), isophorone diisocyanate (IPDI), hydrogenated 4,4′-diphenylmethane diisocyanate (HMDI), and 1,6-hexane diisocyanate (HDI). The segmented polyurethane materials were characterized by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile properties, tear strength, and Shore A hardness. The DSC and DMA data show that the thermal transitions are influenced significantly by the diisocyanate structure. In the segmented polyurethane materials with aliphatic HS, the polyether soft segment (SS) is immiscible with the HS. However, in the segmented polyurethane materials with aromatic HS, the SS is partially miscible with the HS. The diisocyanate structure also influences the mechanical properties significantly and is described as the effect of symmetry and chemical structure of the HS. Various solution polymerized polyurethane resins with solid content of 30 wt % were also prepared and their thickness retention, water resistance, and yellowing resistance were determined for the evaluation of their usage as wet process polyurethane leather. The polyurethane resin with aliphatic HS show poorer thickness retention but better yellowing resistance. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 167–174, 2000

Synthesis and properties of polyurethanes based on bisphenol-S derivatives

The relationship between the structure and property of polyurethane elastomer derived from bisphenol-S derivatives/diisocyanate system was studied. The effects of the amount of soft segment of diol, including ester and ether, as well as the effects of structure of diisocyanate on the mechanical properties of elastomer were discussed on the basis of the results obtained from the hardness, tensile strength, elongation, swelling, dynamic mechanical analysis, and X-ray diffraction. Also, the thermal properties of polyurethane elastomer were also investigated by d.s.c. and t.g.a. analyses. The d.s.c. and dynamic properties results demonstrated that the new polyurethanes exhibit a range of glass transition temperatures from − 25 to 48°C, and temperature at loss tan δ peak from 81.0 to 13.7°C. Moreover, t.g.a. results showed that the addition of an ester group increased the thermal stability of polyurethanes.

Influence of the parameters of encapsulation process and of the structure of diisocyanates on the release of codeine from resinate encapsulated in polyurea by interfacial water promoted polyreaction

Wet resinate beads consisting of carboxylic ion exchange resin and codeine have been coated with polyureas by use of interfacial water promoted polyreaction of various diisocyanates. Retardation of drug release from coated resinates was estimated based on the measurement of codeine concentration during elution in simulated gastric juice. It has been found that the rate of codeine release depends on the parameters of encapsulation process: type of diisocyanate used, content of water in resinate, duration of swelling of resinate with water, diisocyanate/resinate weight ratio, reaction time and temperature.

Preparation and Physical Properties of Polyurethane Elastomers Containing Mesogenic Moieties*

The mesogenic diols containing azobenzene, benzophenone and biphenyl moieties with an alkoxy flexible spacer were synthesized, and the linear polyurethanes were prepared by the polyaddition of these diols with diisocyanates such as 2,4-toluene diisocyanate and 4,4'-diphenylmethane diisocyanate. From the measurement of DSC and polarizing optical microscopy with the hot stage, it was found that most resulting polyurethanes revealed a thermotropic liquid crystalline behaviour and the temperature of mesomorphic phase was effected significantly by the molecular structure of diisocyanates and the chain length of flexible spacers. On the other hand, the segmented polyurethanes were prepared by the chain extension of isocyanate-terminated prepolymers with these mesogenic diols. As the results, it was found that the incorporation of mesogenic moieties to the hard segment of the polyurethanes contributed to the enhancement of thermal stability and mechanical properties.

Effect of initiator structure on physical and thermal properties of nylon‐6

AbstractNylon‐6 is synthesised from ε‐caprolactam by an anionic polymerisation method, through a two‐step process using sodium metal as a catalyst and diisocyanate‐caprolactam block initiator. Two different aliphatic diisocyanates are used. The effects of diisocyanate structure and concentration on percentage cryslallinity, molecular weight, density and thermal properties of nylon are discussed.

Kinetic study of the reactions between hydroxylated polybutadiene and isocyanates in chlorobenzene—IV. Reactions with tolylene diisocyanate, 3-isocyanatomethyl-3, 5, 5-trimethylcyclohexyl isocyanate and hexamethylene diisocyanate

A comparative kinetic study of the reactions of three diisocyanates [tolylene diisocyanate (TDI), 3-isocyanatomethyl-3, 5, 5,-trimethylcyclohexyl isocyanate (IPDI) and hexamethylene diisocyanate (HDI)] with a hydroxyl-terminated polybutadiene (R-45M) was carried out in chlorobenzene solution. The kinetic data were compared with those obtained previously using toluene as solvent and with the data for the reaction between the prepolymer and the dimer diacid diisocyanate (DDI) reported in preceding papers. It was observed that TDI reacted more quickly than the three other diisocyanates. DDI and HDI showed similar reactivities at lower temperatures; with increasing temperature, DDI reacted more quickly than HDI. IPDI showed slightly lower reactivity than HDI. The kinetic data indicated that the effect of the solvent depends on the diisocyanate structure.

Understanding the Dynamic Properties of Polyurethane Cast Elastomers

Knowledge of the dynamic and high temperature properties of polyurethane elastomers is critical to their use in high dynamic stress applica tions that include automotive belting, roller covers, tires and wheels. The devel opment of elastomeric systems for such demanding applications requires a means of characterizing these systems in terms of mechanical properties and high-temperature performance using limited quantities of material. Dynamic Mechanical Spectroscopy (DMS) is a powerful and versatile technique which is capable of providing this information with quick turn-around times and small sample size requirements. While highly theoretical and often complex explana tions of dynamic mechanical measurements exist in abundance, little pub lished information can be found that is directed towards polyurethane cast systems and expressed in easy to understand terms. This paper attempts to fill this void by offering a qualitative explanation of basic DMS theoretical princi ples and providing practical guidelines for interpreting DMS data for a series of cast polyurethane elastomers. To assist the system formulator in the selection of diisocyanate structure, polyol backbone and molecular weight, curative and stoichiometry, the effects of each of these parameters on dynamic properties are demonstrated. DMS test results are correlated to those results generated by other dynamic test meth ods, and examples of how DMS has been used to accurately predict performance in real-life applications are discussed.

Pulmonary effects of a polyisocyanate aerosol: Hexamethylene diisocyanate trimer (HDlt) or desmodur-N (DES-N)

Desmodur-N (DES-N) or hexamethylene diisocyanate trimer (HDIt), a biuret structure of hexamethylene diisocyanate, is a viscous liquid used for durable coatings and is applied by brushing or spraying. DES-N aerosol has been shown to be primarily a pulmonary irritant following a single exposure in mice. To explore the pulmonary effects of this agent further, groups of guinea pigs were exposed to concentrations ranging from 8 to 121 mg/m 3 of DES-N for 3 hr. Prior to and following exposure, each animal was challenged with 10% CO 2 in 20% O 2 and 70% N 2 to evaluate their pulmonary performance. Following a single exposure, these animals displayed a concentration-dependent increase in respiratory rate and decrease in tidal volume, as well as coughing and apnea. Their ventilatory response to 10% CO 2 was abnormal and characteristic of a lung restriction response. Some airflow limitation was seen during expiration but this occurred more often during air breathing than during CO 2 challenge. With daily exposures repeated for 11 consecutive days, guinea pigs began to adapt to the exposures as indicated by a return to a normal ventilatory response to CO 2. This adaptation occurred within the first 5 days of exposures. From Days 6 to 11, there was a demonstrable effect, but the level of response was much less than that following the first exposure. No cumulative effect could be demonstrated with this polyisocyanate and the effect was found to be different than that for mono- or diisocyanates. Acceptable levels of exposure to this polyisocyanate for industrial workers are suggested.

The Relative Thermal Stability of Polyurethane Elastomers: Effect of Diisocyanate Structure

Castable Polyurethane Elastomers (PUs) based on the polycaprolactone diol Capa 225 and the five different diisocyanates trans 1,4-cyclohexane diisocyanate (CHDI), p-phenylene diisocyanate (PPDI), 4,4’-diphenylmethane diisocyanate (MDI), 80:20 molar mixture of 2,4- and 2,6-toluene diisocyanate (TDI) and 4,4’-dicyclohexylmethane diisocyanate (H12MDI) were synthesised by the use of 1,4-butane diol (1,4-BD) as a chain extension agent. The thermal deformation properties of the resulting polyurethane elastomers were measured by Dynamic Mechanical Thermal Analyser (DMTA) and Differential Scanning Calorimetry (DSC). The temperature at which the value of storage modulus (log E’) changes significantly is considered to indicate the limit of thermal stability of the polyurethanes. It is found that the storage modulus of the CHDI based PU only started to decrease at 181°C while the storage modulus of the H12MDI based polyurethane started to decrease at the much lower temperature of 100°C. The PPDI, MDI and TDI based PUs have thermal stabilities which fall in between these two temperatures. According to this data it can be concluded that the structure of diisocyanates has a distinct influence on the thermal stability of the polyurethane and the CHDI based polyurethane can be demonstrated to have a relatively higher temperature stability than other diisocyanate based polymers.

Effect of diisocyanate structure on viscoelastic, thermal, mechanical and electrical properties of cast polyurethanes

AbstractStructure property relationship of four different diisocyanates is studied in detail. The isocyanates selected are TDI, MDI Crude, HDI, and IPDI. Physical properties such as mechanical, dynamic mechanical, electrical, and thermal are studied. Dynamic mechanical analyses are based on the compound resonance principle. Among all, IPDI‐based polymer showed mediocre trend and TDI‐based polymer showed best properties.

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 influence of the structure of aromatic diisocyanates on the preparation and the properties of polyurethanes

The comparative reactivities of the following aromatic diisocyanates were studied: 4,4′-stilbene diisocyanate- trans, 4,4′-diisocyanatodiphenyl ether, methylene-bis-(4-phenylisocyanate), 4,4′-bibenzyl diisocyanate and 1,5-naphthalene diisocyanate. Polyurethanes were prepared from ethylene glycol and these diisocyanates. The more reactive was the diisocyanate, the less stable was the polyurethane to thermal degradation and ultraviolet radiation.