Free Isocyanate Research Articles

SYNTHESIS OF CELLULOSE DERIVATIVES CONTAINING AMINO ACID RESIDUES AND THEIR ADSORPTION OF METAL IONS

The reactive cellulose intermediate having free isocyanate groups (isocyanate cellulose) was synthesized by treatment of cellulose with 2, 4-tolylene diisocyanate (2, 4-TDI). The reaction of the isocyanate cellulose with amino acids and their esters were studied to obtain the cellulose derivatives containing amino acid residues. The reaction was carried out by heating mixtures of the isocyanate cellulose and amino acid derivatives under various reaction conditions. The free isocyanate groups were reacted with amino acid esters in dimethylsulfoxide (DMSO) at low temperature under nitrogen atmosphere, in high conversion to give cellulose derivatives containing amino acid residues. The amounts of amino acid esters bound to the isocyanate cellulose through the urea linkage were 0.35-1.07mmol/g.The selective adsorption and chelate formation of metal ions onto cellulose derivatives containing amino acid residues were investigated. The results indicated that lysine-cellulose and cysteinecellulose, obtained by the saponification of the cellulose derivatives containing amino acid esters, had 0.051 and 0.056mmol/g of adsorption sites for copper (II) ion, respectively.

The thermal decomposition of polyurethanes and polyisocyanurates

AbstractThe thermal decomposition of a number of TDI‐ and MDI‐based biscarbamates (model compounds for polyurethane foams) between 200°C and 1000°C showed that the urethane linkage undergoes an O‐acyl fission at about 300°C to generate the free isocyanate and alcohol. In the case of the flexible foam analogues, the newly generated TDI reacts further to generate volatile polyureas, termed ‘yellow smoke’. The MDI residues generated in the decomposition of a rigid foams react to yield non‐volatile polycarbodiimides. Both the yellow smokes and the polycarbodiimides decompose above 600°C to give a mixture of nitriles (including HCN) as well as a number of olefinic and aromatic compounds. The use of 13C labeling indicated that HCN and all the other nitriles generated during the high temperature decompositions originate in the thermal fission of the aromatic ring, the nitrile carbon being the 2‐, 4‐ or 6‐ carbon of MDI.

The Thermal Decomposition of Isocyanurates

AbstractThe thermal decomposition of two isocyanurates and an MDI‐based polycarbodiimide was studied by high temperature infrared spectroscopy, thermogravimetric analysis and differential thermal analysis. The results (confirmed by large scale pyrolysis) show that the s‐triazine moiety decomposes above 400°C to generate free isocyanate groups. The latter may react further to give carbodiimides or ureas.

Photochemical curing of oligomers containing isocyanate groups

The photochemical polymerization of compositions comprising mixtures of oligomers containing free isocyanate groups, and vinyl monomers, has been investigated by EPR and infrared spectroscopy, and by GLC analysis. It is shown that in the course of irradiation isocyanates initiate homopolymerization of vinyl monomers, entering into the polymer chain as telomers. Using as an example, an oligomeric di-isocyanate and a number of acrylic and methacrylic esters, films were obtained and their physicomechanical properties were investigated.

DRY‐RO membranes from cellulose acetate carbamates

AbstractCellulose acetate carbamates (CACs) are the polymers which result when organic isocyanates are reacted with the free hydroxyl groups of cellulose acetate (CA). CACs are more hydrolytically stable and exhibit physical properties which are superior to those of their CA mixed ester analogs. Two synthetic approaches to CACs have been utilized in this study: (1) preformation, i.e., separate synthesis of such polymers prior to their inclusion in solutions for membrane casting; and (2) in situ formation, i.e., the inclusion of blocked isocyanates in standard dry process casting solutions of CA followed by thermal activation of the resultant dry membranes leading to regeneration of free isocyanate and subsequent CAC formation. Preformed CAC polymers have been prepared utilizing phenyl‐, 3‐chloropropyl‐, 3‐bromopropyl‐, and 3‐bromopropyl‐(isothio)‐, isocyanates. Polymers containing omega‐halocarbamate moieties were quaternized with dimethylbenzylamine to produce ionogenic (QCAC) polymers containing quaternary ammonium groups. DRY‐RO membranes from the QCACs exhibit flux/rejection values varying between 6–8 gfd at 98% rejection and 20 gfd at 90% rejection (0.5% NaCl feed at 400 psi and 25°C). In situ formation of CAC membranes has been effected with tolylene‐ and hexamethylene‐diisocyantes, with quaternized isocyanate monomers employed for the preformed CAC polymers, and with specially tailored diisocyanates containing ionogenic groups. Crosslinking rendered all of the membranes acetone insoluble. Inasmuch as in situ formation substitutes the easy synthesis of blocked isocyanate monomers for the more difficult separate synthesis of preformed CAC polymers, it is anticipated that the former will replace the latter.

Optimizing the properties of isocyanate-terminated polyurethane prepolymers by statistically designed experiments

The properties of isocyanate-terminated polyurethane prepolymers were optimized through the use of statistically designed experiments. A simple 2 × 2 factorial with centerpoint statistical design was used to determine the effect the diol-to-triol ratio and per cent free isocyanate had on the viscosity of the prepolymer. Combinations of a 1000 or 2000 molecular weight diol with either a 1500 or 4100 molecular weight triol showed that a reasonable range of viscosity could be maintained only with the 4100 molecular weight triol. A nine-point design was then utilized to predict the best levels of free isocyanate and polyol ratio that would yield cured urethane polymers with the highest tensile strengths, moduli, and elongations. With this design, second-order equations were computed that predict the mechanical responses of urethane polymers based on the free isocyanate and polyol ratio used in its formulation.

Dyeing of Polyurethane Elastomeric Materials in Nonaqueous Media

Polyurethane elastomeric materials have the affinity to react chemically in organic media with disperse dyes containing free amino groups. This is probably due to the presence of free isocyanate groups in the polyurethane macromolecule. The presence of a chemical linkage was proved by thin-layer chromatography, diazotization, and coupling. Similarly, other compounds containing an active hydrogen atom, e.g. primary amines and alkyl mercaptanes, react with the same material.

Über Reaktionen mit Betain, IX / Reactions with Betaine, IX

Dimethylsulfoniumphenacylbromide reacts with arylisocyanates in the presence of N-ethyldiisopropylamine to stable dioxo-S-ylides (1-5). Compounds 6-16 are obtained by variation of the starting sulfonium salts and isocyanates. Tolyl-2,4-diisoyanate yields with dimethylsulfoniumphenacylbromide the 1:2 adduct 17, while with the corresponding triphenylphosphoniumbromide the 1:1 adduct 18, with a free isocyanate group, is obtained.

Effect of molecular structure on the thermal aging properties of flexible urethane foams

AbstractA series of flexible urethane foams was formulated from diisocyanate‐terminated polyether prepolymers, using both a polyether diol and an ethylenediamine tetraglycol as extenders. The long‐term compression set characteristics and the compression deflection properties of these foams were studied. The swelling effect in a solvent, the free isocyanate content, and the role of a carbon black filler on the flexible urethane foam formulation were also evaluated. It was concluded that the total amount of diisocyanate used in the formulation, rather than a variation in the type of isocyanate, has the greatest influence on molecular structure.

The role of water in the synthesis of urethane polymers from polyesters

AS IS well known, water can react with various compounds containing isocyanate groups and is therefore Of great importance in the Synthesis of urethane polymers [1]. From a stud ~ of the reaction of water with mono-isocyanates, a scheme was proposed according to which the reactions take place in two stages: 1) amine formation and 2) interaction of the amine obta ined with isocyanate, as a result of which symmetric di-N-substi tuted urea is formed. In fact, the interaction of water with isocyanates, apparently, takes place according to a much more complex system, by the formation of numerous unstable intermediate products [2, 3]. In the case of asymmetrical di-isocyanates, water firstly reacts with the most reactive isocyanate groups: thus, for example, during the interaction of telinyl-2,4-di-isocyanate (2,4-TDC) with water, the isocyanate group which is in the p-position in relation t o the methyl group, takes part in the reaction, whereas the less active o-NCO-group does not react , under certain conditions. In addition, the formation of an electropositiv.e urea group reduces the reactivit y of free isocyanate groups even more [4, 5]. The reaction of water with isocyanates depends to a considerable extent on the medium in which the reaction occurs and firstly on the solubility of the components [6]. As far as the reactions of water are concerned during the synthesis of urethane polymers, they have been very little investigated and the literature available refers to polyurethane foams.

STUDIES ON THE STABILITY OF THE DIMER OF 2,4-TOLYLENE DIISOCYANATE

A series of carbamates of the dimer of 2,4-tolylene diisocyanate was prepared from different alcohols, leaving the uretidine-dione ring unaffected. Di-sec-butylamine and dibenzylamine did not affect the dimer ring and reacted only with the two free isocyanate groups. However, di-n-propylamine, di-n-butylamine, and di-n-amylamine ruptured the ring, and diureas of the monomer were obtained. Alkaline reduction changed the dimer ring into a ureylene link and a N-substituted amide was formed by the Leuckart reaction. Hydrazine hydrate gave an unsymmetrical monosubstituted urea whereas hydroxylamine broke the ring and gave the corresponding oxime of the formamide.