Ureas polycondensation with

Diamine 108 led to 95% ee for the alkylation of l,3-diphenyl-2-propenyl acetate with 90% yield. By polycondensation with a diacid chloride or polyaddition with a diisocyanate, this ligand led, respectively, to an insoluble poly(amide) 109 or poly(urea) 110 with excellent yields. Poly(amide) 109 gave a better ee (80%) than poly(urea) 110 (38%), albeit with a lower conversion (respectively, 38 and 72%), when they were used as palladium hgands... 

Conditions to be met in oven drying enamels depend also on the composition of the binder. Paint systems containing melamine-formaldehyde or urea-formaldehyde resins, for instance, harden by polycondensation with other resins, such as epoxy resins, short-oil alkyd or acrylic resins at elevated temperatures. Baking is carried out at temperatures between 100 and almost 200°C and may last from a few minutes to more than an horn. A general trend towards energy conservation has shifted public attention towards binders which require low baking temperatures. 

A poly(inude-urea) can be synthesized in a two-stage procedure including the condensation reaction between 2-anunophenol, 2-amino thiophenol, or m-phenylenedianune and 3,5-diaminobenzoic acid in the presence of poly(phosphoric acid). Then this product is refluxed in glacial acetic acid with trimellitic anhydride to get an aromatic poly(amide-imide) with ben-zazole hetero rings. From these products, poly(imide-urea)s can be obtained by the direct polycondensation with aromatic diamines [15]. 

Thermosets are formed by crosslinking (curing) of reactive linear and branched macromolecules and can be manufactured by polycondensation, polymerization and polyaddition. Thermosets can therefore be processed once only with the application of heat and pressure to form semi-finished products or finished articles and cannot be recovered their processing is irreversible. Amongst the most familiar thermosets are the combinations of formaldehyde with phenol, resorcinol etc. (phenolics), urea, aniline, melamine and similar combinations (aminoplastics). 

The reactive oligomer which is an important ingredient in the present research can be obtained by the polycondensation of an alkylol derivative of urea or alkalation alkylol derivative with N-alkylolacrylamide in the presence of acid or its salt. 

Special type of template polycondensation product was obtained by Papisov at al Polycondensation of urea with formaldehyde in the presence of polyCacrylic acid) gives polycomplexes or polycomplex composites with various structures and properties. The... 

First step (a) represents the initial system - solution of the poly(acrylic acid) (urea and formaldehyde are not shown). Then, growing macromolecules of urea-formaldehyde polymer recognize matrix molecules and associate with them forming polycomplex. This process leads to physical network formation and gelation of the system (step b). Further process is accompanied by polycomplex formation to the total saturation of the template molecules by the urea-formaldehyde polymer (step c). Chemical crosslinking makes the polycomplex insoluble and non-separable into the components. In the final step (c), fibrilar structure can be formed by further polycondensation of excess of urea and formaldehyde. 

The influence exerted by the matrix on the direction of the elementary growth steps of the daughter chains was observed for the matrix polymerization of 4PV on polyacids when the daughter P4VP had ionene structure 81), and for the matrix polycondensation of urea and formaldehyde in water, with PAA being present 88,89). In the latter case, the daughter chains of PFU contained the structures... 

Several poly(urea urethane) oligomers 28 (Figure 12) were prepared by one-component polycondensation of iV-(hydroxyalkyl)-2 -oxo-1,3-diazepane-l-carboxamides, which act as intramolecular blocked isocyanates <2005PLM 1459>. These oligomers are semicrystalline materials and their melting points show the odd/even effect observed earlier for [ ]-polyamides, [ ]-polyurethanes, poly(ester amide)s, and poly (amide urethane)s. Further analysis showed that the polymers are stable up to ca. 205-230 °C, the polymers with the lower number of methylene groups in the amino alcohol decomposing at the lowest temperature. 

The optimum temperature of polycondensation of urea with formaldehyde is 30-40°C. 

Polycondensation at room temperature between two or more fast-reacting intermediates is becoming widely used because of its convenience and speed. The interfacial polycondensation system, in particular, which employs two immiscible liquids, is applicable to a wide voriety of chemical structures amides, urethanes, esters, sulfonates, sulfonamides, and ureas. Many products can be made at low temperature which could not be formed by melt methods because of their infusibility or thermal instability. The low temperature procedures are subject to the effect of many variables, but these are readily controlled and acceptable conditions for use with new polymers or intermediates can usually be found. The processes are readily scaled up in simple batch equipment or continuous reactors. Special areas of application are the direct formation of fibers from the reactants and polycondensation on fiber substrates. 

The unextractable acid in wood plays a major role in the catalysis of the urea-formaldehyde polycondensation reaction. The significance of this indication must be viewed in contrast to previous investigations which have attempted to correlate properties of wood with the properties or amounts of extractives. It would not be prudent to generalize regarding the effect of unextracted acids because only seven species were studied. However, in future studies these observations may be found to be generally true for most, if not all, species. 

Binders are at the heart of mineral and glass wool [1]. The best binders are based on resole resins prepared by the polycondensation reaction of phenol with formaldehyde in the presence of a basic catalyst [2]. To such resoles, urea is added to improve fire resistance and scavenge free formaldehyde. 

These low-molecular-weight, thermosettable polycondensation products of formaldehyde with urea, melamine, or mixtures of both belong to the family of aminoplasts [8]. All of them give duroplastic films after final processing [9], Products of this industry are omnipresent in almost every private and public building [10]. 

A number of organotin polyesters, polyamides, polythiols, polyethers, and polyaminoesters have been synthesized from dialkyltin halides with dicarboxylic acids, diols, diamines, dithiols, urea, thiourea, amino acids, and hydroxyl acids involving polycondensation reactions. These polymers have potential applications as thermostabilizers for PVC. 

It was shown earlier that (diphenylamine-p-tolylive-cyanate) urea (DTCU) may be used as antioxidant of thermo- and photooxidative destruction of AC. It was interesting to use DTCU for increasing antioxidative stability of PCA. With this purpose small amount of DTCU were introduced into e - caprolactam directly before its polycondensation, which was carried out according to well known methods [132]. Content of DTCU additives in polycondensation mixture was 0,5 - 3% from caprolactam mass. 

Since the reactions with phosphorus compounds give relatively high yields of carboxylic amides and esters and ureas, they have been extended to the direct polycondensations of dicarboxylic acids with diamines and bisphenols, of free a-amino acids or dipeptides, and of carbon dioxide and carbon disulfide with diamines under mild conditions to give polyamides, polyesters, polyureas, and polythioureas. 

Several copolymers and condensates of oxidized starches with polymers have been developed. For example, products of starch dialdehyde condensation with acrylamide were prepared for further copolymerization with various monomers to form resins for coatings, molding powders,585 and materials for immobilization of enzymes, for instance, alpha amylase.586 Hypochlorite-oxidized starches were also reacted with acrylonitrile.507,521 Hypochlorite-oxidized starches were allowed to react with allylated starch dialdehyde,587 polycondensates of ammonia-dimethylamine-epichlorohydrin,588 polycondensates of starch dialdehyde with melamine,589 urea433,541,590 capable of precipitation of tannin591, carboxyamides,411 urea and formaldehyde,592 proteins,524,593,594 polyfyinyl alcohol),595 alkylammonium salts,519,596 alkoxyalkylamines,597... 

Other polycondensation reactions which lead to finely dispersed polymers in liquid polyethers are the polycondensation reactions of urea and melamine with aqueous formaldehyde [92-95]. The reaction medium is usually polyether polyols, PO homopolymers or PO-EO copolymers (random or block copolymers), with MW of 3000-5000 daltons. During the polycondensation reaction, the aminoplast polymer precipitates, being insoluble in polyether and water (water from formaldehyde solution and reaction water), is eliminated by vacuum distillation. A variant of this reaction is to develop the polycondensation in water, and water containing the aminoplast polymer (as a viscous solution) is added to a polyether polyol, under vacuum, and at high temperature (100-130 °C), water being continuously eliminated from the reaction medium. The aminoplast insoluble polymer precipitates in the form of fine particles. 

A synthetic variant is to react firstly the polyether with a small quantity of TDI. The resultant extended polyether, containing urethane groups, participates together with urea groups in polycondensation reactions with aqueous formaldehyde. Thus a true nonaqueous dispersant is formed in situ, with an aminoplast block and a polyether block, which probably assures the efficient stabilisation of the resulting aminoplast dispersion. 

More recently Dieterich and Reiff (166) have described the formation of aqueous urethane dispersions by the dispersion of ionomer melts with subsequent polycondensation in two-phase systems. The principle of this procedure consists of reacting molten ionic modified polyester or polyether prepolymers containing NCO groups with urea to yield bis(biuret), followed by methylolation by means of aqueous formaldehyde in a homogeneous phase, and the resulting plasticized melt of methylolated ionic urethane bis(biurets) dispersed in water at 50-130 °C. These steps can be represented schematically as follows ... 

Melamine (2,4,6,-triamino-1,3,5-triazine) is obtained by trimerization of cyanamide or commercially by thermal cyclocondensation of urea at 400°C with elimination of NH3 and CO2. Polycondensation of melamine with formaldehyde produces melamine resins that are used as plastics, glues and adhesives. Cyanuric acid 15 (2,4,6-trihydroxy-1,3,5-triazine) was obtained by Scheele (1776) from pyrolysis of uric acid and was the first 1,3,5-triazine derivative known. Cyanuric acid is synthesized by trimerization of isocyanic acid and is tautomeric with isocyanuric acid 16 ... 

Another belt-shaped molecule is cucurbituril (53) which was presumably synthesized as early as 1905 by Behrend et al. [42]. The structural formula of 53 was resolved in 1981 by Freeman. Mock, and Shih [43] only when modern spectroscopic methods were available. Cucurbituril (53) is easily obtained from urea, glyoxal, and formaldehyde in an acid-catalyzed condensation reaction with glycoluril (52) as an intermediate. The initially formed polycondensation product, insoluble in all common solvents, is treated with hot concentrated sulfuric acid. After dilution with water and subsequent boiling a solid is obtained in a yield of 40-70%. The H-NMR spectrum shows only three signals of equal intensity and the infrared spectrum suggests retention of the glycoluril moieties. The compound is not suitable for usual mass spectrometry due to its low volatility. However, an X-ray crystal structure of the calcium complex obtained from sulfuric acid solution was undertaken. 

Microencapsulation by interfacial polycondensation is a usefiil method to microencapsulate a liquid core material. Especially, polyurea and polyurethane microcapsules have been extensively investigated in various industries [209]. For example, aliphatic hexamethylene diisocyanate (HMDI) and aliphatic ethylene diamine (EDA) have been used to prepare polyurea microcapsules containing insecticide called diazinon [210]. A urea linkage is formed immediately by the reaction between an amine and an isocyanate group (see Figure 4.31), and a polyurea is synthesized by the reaction between an amine with two or more amine groups and an isocyanate with two or more isocyanate groups. 

The results and eflectiveness of Eqs. (7) were checked also for other, quite dilferent polymers, namely the polycondensates of resordnol-formaldehyde, of melamine urea formaldehyde (MUF), of PF, and of quebracho and pine polyflavonoid tannins hardened with formaldehyde. The comparison of the energies of interaction obtained by measures of TMA deflection and the use of this formula compared well with the results already obtained for their energy of adhesion with crystalline cellulose in previous work [16 10]. It appears, then, that the formula works also for entanglement rather than just cross-linked networks. 

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