Melamine/formaldehyde crosslinkers: characterization, network formation and crosslink degradation

Conductometric and potentiometric titration behavior of emulsions of ethyl acrylate copolymers with acrylic acid and methacrylic acid was investigated. On the conductometric titration curves of the emulsions of the copolymers with more than 5 mole-% of the acids, two equivalence points, based on the copolymerized acids, were observed, but only one equivalence point was observed on potentiometric titration. Almost all of the copolymerized acids could be detected by both titration methods. The change in optical density of the dilute emulsions with their pH was measured. The particles of these emulsions were studied under an electron microscope. These results showed that, when the pH of the emulsions was raised, the surface layers of the particles began to dissolve and their cores started to swell near the pH of their first equivalence points. When the pH was again lowered the dissolved polymers coagulated, tiny particles were formed, and the swollen cores were dehydrated. The surface layers thickened with increasing amount of the copolymerized acid. These behaviors were very similar in the emulsions of the copolymers with acrylic acid and methacrylic acid. The quantity of water-soluble polymers formed in the course of the emulsion copolymerization was approximately 3–4% or slightly more. This quantity depended only slightly upon the amount and type of the copolymerized acid. The acid contents of the water-soluble polymers were higher in cases of the copolymers with acrylic acid than in those with methacrylic acid. No relationship with the amount of copolymerized acid was established.

Some physicochemical properties of poly (ethyl acrylate) emulsions containing carboxyl groups

This review covers various strategies that enable self-crosslinking of acrylic emulsion, and gives a detailed idea of different one component (1K) crosslinking systems along with their reac...

Advances in self-crosslinking of acrylic emulsion: what we know and what we would like to know

We have developed a kinetic model of the crosslinking reaction of hydroxy-functional acrylic copolymers with fully alkylated melamines. This model accurately describes the extent of the crosslinking reaction as a function of cure time and melamine concentration in coating films. Using this model, we have determined the effects of acid catalyst concentration and strength and the effects of cure temperature on the rate constant of the crosslinking reaction. The rate constant is proportional to the catalyst concentration and to the square root of the acid constant of the catalyst. The temperature dependence of the rate constant follows an Arrhenius rate law with an activation energy of 12.5 kcal/mol independent of catalyst type. Amine salts of p-toluenesulfonic acid have been compared with p-toluenesulfonic acid as catalysts in these coatings at different bake temperatures. These kinetic results have been used in a network structure model to calculate the cure response of these coatings as a function of formulation variables.

Crosslinking kinetics and network formation in organic coatings containing hexamethoxymethylmelamine

Thermal analysis methods (differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical thermal analysis) were used to characterize the nature of polyester-melamine coating matrices prepared under nonisothermal, high-temperature, rapid-cure conditions. The results were interpreted in terms of the formation of two interpenetrating networks with different glass-transition temperatures (a cocondensed polyester-melamine network and a self-condensed melamine-melamine network), a phenomenon not generally seen in chemically similar, isothermally cured matrices. The self-condensed network manifested at high melamine levels, but the relative concentrations of the two networks were critically dependent on the cure conditions. The optimal cure (defined in terms of the attainment of a peak metal temperature) was achieved at different oven temperatures and different oven dwell times, and so the actual energy absorbed varied over a wide range. Careful control of the energy absorption, by the selection of appropriate cure conditions, controlled the relative concentrations of the two networks and, therefore, the flexibility and hardness of the resultant coatings. (C) 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Cbem 41: 1603-1621, 2003.

Thermal characterization of polyester–melamine coating matrices prepared under nonisothermal conditions

The mechanism of cure has been studied in coating systems comprising blends of ammonium salts of acrylic acid–acrylic ester copolymers and alkoxymethylmelamines. Experiments were conducted both on the resin components themselves and on model compounds having analogous chemical structures. Curing of the resin begins with loss of ammonia to regenerate free carboxyl groups, rather than loss of water to form amides. The alkoxy group is eliminated, and ester crosslinks are formed between the carboxyl and the methylolmelamine. Base binding studies on cured films show that the extent of crosslinking depends on the exact composition of the resin system and the presence or absence of an acidic catalyst. These variables can be adjusted to provide essentially quantitative crosslinking in the cured coating, as shown by the complete disappearance of unreacted carboxyl groups.

Crosslinking reactions of acrylic polymers containing carboxyl groups with melamine resins

The polymerization of ethylene with the monocyclopentadienyl titanium trichloride‐triethylaluminum complex as the catalyst

Resinous compositions and process of preparing same

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Crosslinking reactions of acrylic polymers containing carboxyl groups with melamine resins

The polymerization of ethylene with the monocyclopentadienyl titanium trichloride‐triethylaluminum complex as the catalyst

Resinous compositions and process of preparing same