Melamine polyols

Hydrolysis. In principle, both urethane and melamine polyol crosslinks are susceptible to hydrolysis,... 

Polymers. AH nitro alcohols are sources of formaldehyde for cross-linking in polymers of urea, melamine, phenols, resorcinol, etc (see Amino RESINS AND PLASTICS). Nitrodiols and 2-hydroxymethyl-2-nitro-l,3-propanediol can be used as polyols to form polyester or polyurethane products (see Polyesters Urethane polymers). 2-Methyl-2-nitro-l-propanol is used in tires to promote the adhesion of mbber to tire cord (qv). Nitro alcohols are used as hardening agents in photographic processes, and 2-hydroxymethyl-2-nitro-l,3-propanediol is a cross-linking agent for starch adhesives, polyamides, urea resins, or wool, and in tanning operations (17—25). Wrinkle-resistant fabric with reduced free formaldehyde content is obtained by treatment with... 

Hardness in the H to 2H range is adequate for many industrial coatings thus the data in Table III show that it is possible to make coatings with adequate hardness from the BA/CHDM polyester. Further, these coatings have fair impact resistance and flexibility. Both the 133 and the 150 C bakes are probably sufficient to drive the co-dondensation reaction of polyol with melamine resin close to completion, and some degree of self-condensation of the excess melamine resin can be expected, especially at 150 C.[15] Self-... 

Enamel Properties. Clear coatings were formed by crosslinking the PHBA-modified oligomers with a standard melamine resin. Baking at 175° was necessary to obtain optimal properties. The cured films were glossy and nearly transparent except for films made from 60/40 PHBA ratio polyol. Adhesion was excellent. 

The use of polyols such as pentaerythritol, mannitol, or sorbitol as classical char formers in intumescent formulations for thermoplastics is associated with migration and water solubility problems. Moreover, these additives are often not compatible with the polymeric matrix and the mechanical properties of the formulations are then very poor. Those problems can be solved (at least partially) by the synthesis of additives that concentrate the three intumescent FR elements in one material, as suggested by the pioneering work of Halpern.29 b-MAP (4) (melamine salt of 3,9-dihydroxy-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5,5]-undecane-3,9-dioxide) and Melabis (5) (melamine salt of bis(l-oxo-2,6,7-trioxa-l-phosphabicyclo[2.2.2]octan-4-ylmethanol)phosphate) were synthesized from pentaerythritol (2), melamine (3), and phosphoryl trichloride (1) (Figure 6.4). They were found to be more effective to fire retard PP than standard halogen-antimony FR. 

The main components of intumescent compositions are most often a polyacid, a carbon source, and an expansion agent. In some cases, the carbon source is the host polymer itself and the expansion process is generated by the decomposition products of the polymer or the acid source, e.g., melamine pyrophosphate (MPP). The most frequent polyacid used is APP. Polymers such as those mentioned above are generally preferred rather than polyols due to exudation, water solubility, and difficulties with processing for the filled polymer. Several studies mention the use of OMMT as a nanofiller introduced in the polymer playing the role of carbon source. In other studies, the silicate is blended with all the components of the flame-retarded polymer. 

The same method is applicable to control critical temperature where the reaction between polyphosphates and polyols takes place. For example, melamine polyphosphate-polyol system, which is stable at the degradation temperature of PP, has been activated for application in polyolefins [47], An activating effect is ascribed also to the char-forming polymers in intumescent nanocomposites, according to the blending approach [48],... 

Since melamine is not soluble in the polyol or MDI, it should be very fine dispersed so that it does not interfere with the foaming process. The effect of melamine particle size on properties of flexible PU foams was studied by Kageoka et al.69 They reported that the foam with the finer particles showed higher hardness, better tensile properties, and less flammability than that with the larger ones. A flame-retarded foam with better physical properties can be manufactured by a polyol including melamine particles smaller than the strut thickness of the resultant foam. 

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. 

The polyols for rigid foams (referred to as rigid polyols) discussed before (Chapters 13 and 14), are based on the alkoxylation of different polyols or polyamines, commercialised in a relatively high purity form. Some important starters for rigid polyols are obtained by the synthesis of the starter in situ, before the alkoxylation reaction, by the condensation reaction of some aromatic compounds (phenols, melamine and so on) with aldehydes (mainly formaldehyde), followed by the reaction of the resulting condensate with alkylene oxides. Some important rigid polyols based on the condensates mentioned are ... 

Melamine is a very thermoresistant aromatic heterocyclic compound, with three -NH2 groups, which makes it very attractive for use as a starter for polyol synthesis. Unfortunately, melamine is very difficult to directly alkoxylate with PO or EO. This difficulty is because of the amidic structure (melamine is the amide of cyanuric acid) and because of the tautomeric forms (characteristic to all amides) [31] ... 

Melamine is soluble only in water and has low solubility in dimethylsulfoxide (DMSO) and in other aprotic dipolar solvents (9% at 120 °C), in glycerol or ethylene glycol (10% at 140 °C). In the majority of other usual solvents it is insoluble. Kucharski and Lubczak discovered a new class of reactive solvents for melamine [36] poly (hydroxymethyl) derivatives of cyclohexanone, acetone, nitromethane which are able to dissolve 50-60% melamine. Melamine can be totally propoxylated or ethoxylated at lower temperatures (70-90 °C), in aprotic dipolar solvents (for example DMSO, dimethylformamide, N-methyl pyrrolidone and so on), in the presence of quaternary ammonium hydroxides as catalysts [for example tetrabutyl ammonium hydroxide (TBAH)], at a low reaction rate (reaction 15.35), for a very long reaction time (40-50 hours) [31, 37]. The resulting hexafunctional polyols give very thermostable rigid PU (up 200 °C). 

A useful synthetic variant to melamine-based polyols is to alkoxylate the condensates of melamine with carbonyl compounds. 

By the propoxylation of the synthesised melamine derived Mannich base, without catalyst, a hexafunctional polyether polyol is obtained (reaction 15.40). 

Other transformations of melamine in polyols are based on the reaction of melamine with ethylene carbonate and with alkanolamines. 

Reacting melamine with ethylene carbonate or propylene carbonate, at 150-200 °C, in liquid medium (for example a Mannich polyol derived from phenol), 2-hydroxyalkyl carbamates of melamine are obtained [4] (reaction 15.42). The reaction developed in the absence of this liquid polyol takes place with difficulty and with decomposition. Ethylene carbonate is reactive, but propylene carbonate has a much lower reactivity. 

By using the synthesised hydroxyalkyl carbamates of melamine as polyols, rigid PU foams were obtained with good physico-mechanical properties, low friability and inherent self extinguishing properties. A highly aromatic polyol, based on the reaction of benzoguanamine with ethylene carbonate was successfully synthesised [4]. 

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