Urethane Formation Research Articles

Study on gluing reaction between WPI adhesive and bamboo by means of DSC

PurposeThe purpose of this paper is to study interactions between water‐based polymer isocyanate (WPI) adhesive and bamboo by means of differential scanning calorimetry (DSC).Design/methodology/approachThe method of adapting new reference substance replacing aluminium was used due to the special characteristic of WPI adhesive when studying reactions between WPI adhesive and bamboo.FindingsThe methods of changing reference substance could counteract effect of water in the sample on DSC measurement. The results of DSC analysis showed that hardener of WPI adhesive can react with water and also with ‐OH in bamboo and matrix of WPI adhesives. That is to say that a competition exists between urethane formation (covalent bonding of isocyanate with hydroxyl groups in bamboo and matrix in WPI adhesive) and urea formation (isocyanate consumption due to the reaction with water) during the operation of glued bamboo products.Research limitations/implicationsThe method of changing reference substance can be used for other DSC samples in which water cannot be conveniently removed, but this method requires that weight of reference substance to be exactly the same as the sample used in DSC measurement. So accuracy of weighing was very important in this DSC measurement.Practical implicationsThe method developed in this paper provides a simple and practical solution to studying interactions between WPI adhesive and bamboo by means of DSC.Originality/valueChanging reference substance was brought forward as a new method of counteracting effect of water in the sample on DSC measurement. The understanding gained through this study could help improve bonding properties of glued bamboo products.

Fluoro-silsesquioxane-urethane Hybrid for Thin Film Applications

New fluoropolyurethane hybrids containing fluorinated polyhedral oligomeric silsesquioxane were synthesized for thin film applications using fluoro(13) disilanol isobutyl-POSS (FluoroPOSS) and a short chain fluorodiol and diisocyanate. The kinetics of the urethane reaction was monitored using Fourier transform infrared spectroscopy (FTIR) and the formation of urethane was confirmed using (29)Si Nuclear magnetic resonance spectroscopy (NMR). The effect of addition of FluoroPOSS either in the I step or II step of the two step polymerization reaction is evaluated using various spectroscopic, thermal, microscopic, and diffraction techniques. In general, the major shortcoming of the lack of flexibility of fluoropolyurethane from short chain diol and diisocyanate has been overcome by the use of tethered FluoroPOSS. X-ray photoelectron spectroscopy (XPS), atomic force microscpopy (AFM), and contact angle measurements on the hybrid thin films on silicon wafer demonstrate the migration of FluoroPOSS segment to the air-thin film interface when FluoroPOSS is used in I stage reaction, and it resides at the interface when used as a chain extender. However, in both cases, the formed thin film exhibits ultrahydrophobicity with water contact angle of approximately 107 degrees and low contact angle hysteresis and solvent resistance, which are preferable for protective thin film applications.

Catalysis of N‐Methylaniline‐Blocked Polyisocyanate‐Hydroxyl‐Terminated Polybutadiene Cure Reaction

Catalysis of cure reaction between N‐methylaniline‐blocked polyisocyanate and hydroxyl‐terminated polybutadiene was investigated using a variety of tertiary amine and organotin catalysts. The catalytic activity of amine and organotin compounds was determined from the cure‐time results. It was found that the activity of the catalyst depends upon the steric constrain around the catalytic center. The organotin compounds showed higher catalytic activity than the amine catalysts. FTIR results obtained under isothermal condition revealed that DABCO selectively catalyze the urethane formation reaction, whereas DBTDL catalyze both the allophanate formation and urethane formation reactions during curing process. The synergistic effect of amine and organotin mixed catalysts on the cure reaction was also investigated.

Soy‐based polyurethanes by nonisocyanate route

AbstractPolyurethanes by a nonisocyanate route were prepared by reacting carbonated soybean oil with different diamines. The effect of amine structure and carbonate to amine ratio on polyurethane structure and mechanical, physical, and swelling properties was studied. The reactants 1,2‐ethylenediamine, 1,4‐butylenediamine, and 1,6‐hexamethylenediamine were used with the carbonate to amine ratio of 1 : 0.5, 1 : 1, and 1 : 2. It was found that along with urethane formation, the amine group reacted with ester groups to form amides. All amines produced elastomeric polyurethanes with glass transitions between 0 and 40°C and hardness between 40 and 90 Shore A. The reaction of epoxidized soybean oil with carbon dioxide was optimized resulting in complete conversion of epoxy to cyclic carbonate groups ending in polyurethanes with higher crosslinking density and much higher tensile strength than previously reported for similar polyurethanes. Swelling in toluene and water depended on crosslinking density and the polarity of polyurethane networks controlled by the cyclic carbonate‐to‐amine‐ratio. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Study of isocyanate group opening initiated by potassium polyoxyethylene glycolate

The opening of phenyl isocyanate NCO groups initiated by potassium polyoxyethylene glycolate was studied. The rate constants of the initiation, polymerization, cyclic trimerization, and urethane formation reactions proceeding in the system were calculated, and it was concluded that the polymerization makes a predominant contribution to the overall rate of the process. Using IR, UV spectroscopy, and luminescence methods, it was shown that isocyanate groups react via the opening of the carbonyl double bond under the studied conditions. A method for the stabilization of acetal terminal polyisocyanate units by their chemical binding to rare-earth ions was proposed.

Progress toward a Rationally Designed, Chemically Powered Rotary Molecular Motor

Building on prototype 1, which achieves 120 degrees of phosgene-powered unidirectional rotation to rotamer 6 (see Figure 5 in the full article), 7 was designed to accomplish repeated unidirectional rotation (see Scheme 7). Compound 7 contains an amino group on each blade of the triptycene and a 4-(dimethylamino)pyridine (DMAP) unit to selectively deliver phosgene (or its equivalent) to the amine in the "firing position". The synthesis of 7 is described: the key constructive steps are a benzyne addition to an anthracene to generate the triptycene, a stilbene photocyclization to construct the helicene, and a Stille coupling to incorporate the DMAP unit. The DMAP unit was shown to regioselectively relay 1,1'-carbonyldiimidazole (but not phosgene) to the proximal amino group, as designed, but rotation of the triptycene does not occur. Extensive attempts to troubleshoot the problem led to the conclusion that the requisite intramolecular urethane formation, as demonstrated in the prototype (1 --> 4), does not occur with 7 (to give 85) or 97 (to give 100). We speculate that either (i) hydrogen bonding between the hydroxypropyl group and functionality present in 7 but absent from 1 or (ii) a Bürgi-Dunitz (or similar) interaction involving the DMAP (see 106) prevents achievement of a conformation conducive to intramolecular urethane formation.

Hydroxylated hyperbranched polyesters as crosslinking agents for polyurethane networks: Partial modification of the OH chain ends

A 4th generation commercial hyperbranched polyester (HBP) based on bis(hydroxymethyl) propionic acid, bis(MPA), was used as an original crosslinker for polyurethane networks. However a partial modification of the numerous hydroxyl groups was necessary to obtain complete miscibility between the three polyurethane precursors, i.e. macrodiol, diisocyanate and hyperbranched, HB, crosslinking agent. A monofunctional aromatic isocyanate, para-tolylisocyanate, pTI, was used for that purpose. The pristine hyperbranched polyester was at first quite fully characterized, especially concerning the initial distribution of hydroxyl groups between linear, L, and terminal, T, bis(MPA) units. 1H and 13C NMR (both for urethane formation and hydroxyl consumption) and chemical titration were then used and compared for the determination of OH conversion. It appeared that a small part of the modifier was systematically lost in a side reaction with moisture, even though the reactive species had been thoroughly dried. All the remaining pTI molecules produced exclusively urethane end groups. NMR also demonstrated that the hydroxyls born by linear units had a lower reactivity as compared to T-type OH groups. Therefore their relative proportion increases with the modification degree, and more and more modified crosslinkers become less and less reactive. Calorimetric studies performed on pristine and partially modified HB polyesters revealed that hydrogen bonds played an important role as far as thermal behavior was concerned. With increasing modification, T g increases but also ordered domains resulting from strong interactions between hydroxyl groups are progressively replaced by new structures created by self-assembling aromatic urethanes. The latter are responsible for a high-temperature pseudo-melting for highly modified samples. However most of these interactions seem to remain intramolecular since the newtonian behavior of pristine HBP is maintained up to about 110–120 °C for pTI-modified oligomers; but annealing at higher temperature can result in even more ordering and in a final loss of the newtonian behavior.

Cover Picture: Macromol. Mater. Eng. 5/2006

Cover: The reaction of 2,4-toluylene diisocyanate and diethanolamine, as an A2 + B*B2 polymerization system towards hyperbranched poly(urea-urethane)s, was followed using in situ ATR-FTIR spectroscopy. In addition to the decrease of the NCO band the formation of urethane and urea bands of the polymer was analyzed to describe the actual state of synthesis. Further details can be found in the article by K. Sahre,* M. H. Abd Elrehim, K.-J. Eichhorn, and B. Voit on page 470.

Kinetic study of polyurethanes formation by using differential scanning calorimetry

Kinetics of polyurethane formation between several polyols and isocyanates with dibutyltin dilaurate (DBTDL) as the curing catalyst, were studied in the bulk state by differential scanning calorimetry (DSC) using an improved method of interpretation. The molar enthalpy of urethane formation from secondary hydroxyl groups and aliphatic isocyanates is 72±3 kJ mol-1 and for aromatic isocyanates it is 55±2 kJ mol-1 . In the case of a single second order reaction for aliphatic isocyanates reaction, activation energy is 70±5 kJ mol-1 with oxypropylated polyols and 50±3 kJ mol-1 with Castor oil. For aromatic isocyanates and oxypropylated polyols the activation energy is higher around 77 kJ mol-1 .

Polymerizable oil synthesis by hydroxyhalogenation of soybean oil in dense CO 2

The aim of this research is to hydroxybrominate and hydroxychlorinate the double bonds of methyl oleate and soybean oil in dense CO 2. The hydroxychlorination reactions of vegetable oils in dense CO 2 are the first such report in literature. Experiments were performed at the reaction conditions of 8, 25 and 40 °C and 60, 100, 120 and 150 bar. Effects of temperature, pressure, reaction time and the reactant amounts on the extent of reaction are studied. Hydroxybromination and hydroxychlorination reactions are conducted using sodium hypobromite (NaOBr) and sodium hypochlorite (NaOCl) solutions, respectively. The polymerization of the product is performed by urethane formation with toluenediisocyanate at 40 °C. The products were analyzed by NMR and IR spectrometry. Fifty percent consumption of the double bonds was observed in the hydroxybromination reaction of methyl oleate, but no OH addition was determined. In hydroxychlorination reactions of methyl oleate the consumption of double bonds ranges from 40 to 95%, and the introduction of OH groups ranges from 14 to 30%. Best yields were observed when the mole ratio of NaOCl to methyl oleate double bonds is 5 to 1. The consumption of soybean triglyceride double bonds, in the hydroxychlorination reactions, are observed to range from 18 to 75% and the formation of OH groups ranges from 8 to 33%. The highest conversion for one-step hydroxychlorination of soybean is obtained at 25 °C and 120 bar for a reaction time of 6 h, with 10/1 ratio of NaOCl to double bonds. Better results were obtained when the product of the reaction was reintroduced to the reactor and retreated with NaOCl and 75% consumption of double bonds and 33% formation of OH groups were observed.

Synthesis of Sphingosine‐1‐phosphonate and Homosphingosine‐1‐phosphonate

AbstractIn the first approach to homosphingosine‐1‐phosphonate, D‐glucofuranose was selectively deoxygenated at C‐5. Bond cleavage between C‐1 and C‐2 afforded a 5‐deoxy‐D‐threo‐pentose intermediate. (E)‐Selective Wittig reaction with a C14‐chain gave a C19‐intermediate, which was readily transformed into homosphingosine. Formation of a cyclic urethane containing the 3‐amino and the 4‐hydroxy group of the C19‐intermediate permitted regioselective introduction of the phosphonate group at C‐1, thus affording the target molecule after deprotection. In a second and shorter route, C18‐sphingosine was converted to a cyclic urethane containing the 2‐amino and the 3‐hydroxy group of the C18‐chain. C1‐Chain extension by a hydroxymethyl group by introduction of cyanide led to the same C19 cyclic urethane as obtained in the first route. Similarly, the C18 cyclic urethane led to the other target molecule, namely sphingosine‐1‐phosphonate. The third and shortest route to homosphingosine‐1‐phosphonate could be based on regioselective 1‐O‐tosylation of 1,2,3‐(trihydroxy)octadec‐4‐ene. Transformation into a 1,2‐epoxide, then combination of C1‐chain extension and introduction of a phosphonate group with methylphosphonate as reagent, and finally azide introduction, led after functional group liberation to the target molecule. As shown, also truncated derivatives are readily accessible by this route. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Fluoropolyethers end‐capped by polar functional groups. IV. A novel approach to the evaluation of reactivities of hydroxy‐terminated ethoxylated fluoropolyethers in the tin(IV)‐catalyzed reactions with isophorone diisocyanate

AbstractThe effect of catalyst dibutyltin dilaurate (DBTDL) on the kinetics of urethane formation reactions of α,ω‐bis(hydroxy)‐terminated fluoropolyethers Fomblin® Z‐DOL TXs (FPEs) of various molecular weights and poly(oxyethylene) glycol PEG‐400 with isophorone diisocyanate (IPDI) in hexafluoroxylene (HFX) and tetrahydrofuran (THF) at 40 °C and NCO:OH = 2:1 have been studied in a broad range of catalyst (0.10–9.00) ×10−4 M and total reagents (10.0–60.1 wt %) concentrations. The rate of tin‐catalyzed second‐order reactions (with respect to diol and diisocyanate) was found to be proportional to the square root of catalyst concentration [DBTDL]0.5 both in low polar (HFX) and polar (THF) solvents. Effect of catalyst saturation was revealed for all the reaction systems at higher DBTDL concentrations as well as the appearance of the limiting catalyst concentrations Clim below which the rates of reaction were close to zero. Based on these findings new effective rate coefficients have been derived k = kcat/(C − C) that are independent of the total reagent concentration in the range of 10.0–60.1 wt % ([OH] = 0.10–0.91 equiv/L). This new approach highlights that the rate of the tin‐catalyzed urethane formation reactions of α,ω‐bis(hydroxy)‐terminated fluoropolyethers Z‐DOL TXs with IPDI in HFX at 40 °C and NCO:OH = 2:1 increases significantly with increasing MW of FPE from 776 up to 3405. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5354–5371, 2004

Specific Features of Molecular Structure and Viscosity Characteristics of Oligodiene Urethanes

Polycondensation of bifunctional hydroxyl-containing oligodienes with diisocyanates was studied by gel permeation chromatography, IR spectroscopy, and rheokinetic method. The kinetics of oligodiene urethane formation and the properties of the resulting oligomers, including the molecular-weight distribution and viscosity, were studied in relation to the ratio of the isocyanate and hydroxy groups.

Synthesis of [2]- and [3]Rotaxanes by an End-Capping Approach Utilizing Urethane Formation

Abstract Several axle-shaped sec-ammonium salts having hydroxy groups at the terminal ends were allowed to react with 3,5-dimethylphenyl isocyanate in the presence of dibenzo-24-crown-8 ether (DB24C8) in CHCl3 by the catalysis of dibutyltin dilaurate to afford the corresponding [2]rotaxanes in good yields. Several Lewis acids other than dibutyltin dilaurate were effective for the end-capping. Although N,N-dimethylacetamide was not a suitable solvent, the use of chlorobenzene and nitromethane as solvents gave the [2]rotaxane in high yields. When a C2-chiral 26-membered crown ether, prepared from biphenyl-2,2′,6,6′-tetrol and l-tartaric acid, was employed instead of DB24C8, the corresponding optically active [2]rotaxane was isolated in 47% yield. The present method was successfully applied to the synthesis of [3]rotaxane by employing hexamethylene diisocyanate. Thus, end-capping by acid-catalyzed urethane formation from alcohol and isocyanate was demonstrated to be an effective protocol for the synthesis a variety of rotaxanes, based on the sec-ammonium salt/crown ether recognition motif.

CO2 Offgas as a Mechanistic Probe and Scale-up Tool in N-Acylations Using Mixed Anhydrides from Amino Acids and Isobutyl Chloroformate

The reaction pathways of an N-acylation reaction, involving a mixed anhydride intermediate produced from reaction of an amino acid with isobutyl chloroformate, were analyzed using a novel technique involving the quantitation of CO2 evolved during various parts of the process. Under the normal mode of addition, in which chloroformate is added to a carboxylate anion solution, the dominant mode of yield loss to undesired product was shown to be the formation of a symmetric anhydride, implying that byproduct urethane formation was almost exclusively due to reaction of unreacted chloroformate with amine. This result suggests that inferred high concentrations of carboxylate anion present with the normal addition mode should be minimized to decrease yield loss. This hypothesis was confirmed by demonstrating that symmetric anhydride formation is almost eliminated when the reverse addition (viz., addition of carboxylate anion solution to chloroformate) was carried out. These results, in conjunction with the relati...

Scale-up of the synthesis of ureidopyrimidinone functionalized telechelic poly(ethylenebutylene)

The scale-up of the synthesis of high purity hydrogen-bonded supramolecular polymers is described. The synthesis involves functionalization of telechelic hydroxy-terminated poly(ethylenebutylene) with 2-ureido-4[1H]-pyrimidinone quadruple hydrogen-bonding groups via dibutyltindilaurate catalyzed urethane formation. A procedure with optimized reaction conditions was developed and applied on a 10dm3 mini plant scale. The hydrogen-bonded supramolecular polymer was isolated in a yield of 86% (803 g) and the 2-ureido-4[1H]-pyrimidinone functionalization of the end product was accurately determined with 19F NMR to be 99.8% of the available hydroxy end groups in the telechelic hydroxy terminated poly(ethylenebutylene). Tensile tests showed that the product of the optimized large scale synthesis has better mechanical properties than the product of the unoptimized synthesis reported earlier.

Using mixed anhydrides from amino acids and isobutyl chloroformate in N-acylations: a case study on the elucidation of mechanism of urethane formation and starting amino acid liberation using carbon dioxide as the probe

A case study on the elucidation of mechanism of urethane by-product formation and starting amino acid liberation during the conventional two-step isobutyl chloroformate mediated N-acylation is described using carbon dioxide offgas as the probe. The main reason for the urethane formation and starting amino acid liberation was found to be the formation of the symmetrical anhydride of the amino acid during the preparation of the mixed carboxylic–carbonic anhydride intermediate, as determined by quantifying the evolved carbon dioxide. New conditions were developed to minimize this side reaction.

Fluoropolyethers end‐capped by polar functional groups. III. Kinetics of the reactions of hydroxy‐terminated fluoropolyethers and model fluorinated alcohols with cyclohexyl isocyanate catalyzed by organotin compounds

AbstractThe kinetics of the dibutyltin dilaurate (DBTDL)‐catalyzed urethane formation reactions of cyclohexyl isocyanate (CHI) with model monofunctional fluorinated alcohols and fluoropolyether diol Z‐DOL H‐1000 of various molecular weights (100–1084 g mol−1) in different solvents were studied. IR spectroscopy and chemical titration methods were used for measuring the rate of the total NCO disappearance at 30–60 °C. The effects of the reagents and DBTDL catalyst concentrations, the solvent and hydroxyl‐containing compound nature, and the temperature on the reaction rate and mechanism were investigated. Depending on the initial reagent concentration and solvent, the reactions could be well described by zero‐order, first‐order, second‐order, or more complex equations. The reaction mechanism, including the formation of intermediate ternary or binary complexes of reagents with the tin catalyst, could vary with the concentration and solvent and even during the reaction. The results were treated with a rate expression analogous to those used for enzymatic reactions. Under the explored conditions, the rate of the uncatalyzed reaction of fluorinated alcohols with CHI was negligible. Moreover, there was no allophanate formation, nor were there other side reactions, catalysis by urethane in the absence of DBTDL, or a synergetic effect in the presence of the tin catalyst. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3771–3795, 2002

Kinetics and mechanisms of catalyzed and noncatalyzed reactions of OH and NCO in acrylic polyol–1,6‐hexamethylene diisocyanate (HDI) polyurethanes. VI

AbstractFourier transform infrared spectroscopy was used to study the kinetics of noncatalyzed and catalyzed polyurethanes. These studies show that for noncatalyzed acrylic polyol–hexamethylene diisocyanate (HDI) trimer reactions, the reactions between OH and NCO of HDI exhibit second‐order kinetics, with first‐order kinetics with respect to NCO and OH. On the other hand, when dibutyltin dilaurate (DBTDL) is used as a catalyst in acrylic polyol–HDI trimer reactions, the reaction rate is first order with respect to NCO and 0.5 order in OH and DBTDL concentrations. A mechanism for the catalyzed acrylic polyol–HDI trimer crosslinking reactions is proposed and it appears that an equilibrium involving associations between OH and DBTDL exists, resulting in the formation of an active anion, which interacts with NCO to generate polyurethanes. To further verify this mechanism, the influence of acidity on the reaction rate constant was investigated. When the acidity of the system is increased, retardation of urethane formation occurs. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2322–2329, 2002

Amine-Manganese Complex as an Efficient Catalyst for Polyurethane Syntheses

The polyurethane industry has progressed rapidly, and reactions of polyols and isocyanates are wellknown technological processes. The chemical structure of polyurethane is diverse, and as physical properties are discovered, the wide use of polyurethane is spreading accordingly. But there exists a problem: discoloration by air and light. In general, aliphatic isocyanate is used to resolve this problem. However, the reaction rate of aliphatic isocyanates on preparations of polyurethane is very slow compared with aromatic isocyanates. Therefore, tertiary amines1–5 and tin compounds,6–10 having excellent catalytic activity, are used mainly as catalysts for polyurethane formation. In particular, dibutyltin dilaurate (DBTDL) has been used. However, tin is toxic to human beings. Accordingly, a new catalyst or catalytic system is necessary to replace this catalyst. Recently, late transition metal complexes such as metal-β-diketone complexes (Mt(acac)n) are being researched with great interest.11–13 For example, Fe(acac)3 and Cu(acac)2 complexes are used for the reaction between hexamethylene diisocyante (HDI) and alcohols.14, 15 Although there is sufficiently the catalytic activity for only Mt(acac)n complexes, the increase of the catalytic activity is expected by the cocatalyst. The co-catalyst plays important roles in many reactions. On urethane formation reaction, triphenyl bismuth (TPB)-hexafluoroacetylacetonato (f6acac) catalytic system shows high catalytic activity and the existence of the co-catalyst such as f6acac is important to the reaction.16 In the present paper, the activities of Mt(acac)n and tertiary amine-Mt(acac)n catalyst as new group catalytic system are described. The data clearly show that instead of DBTDL, the tertiary amine-Mt(acac)n can be used for catalyst of the reaction between HDI and alcohol. EXPERIMENTAL