DD224602A1 - PROCESS FOR PREPARING MONODISPERSER MELAMINE / FORMALDEHYDE-LATICES - Google Patents

Abstract

The invention relates to a process for preparing monodisperse melamine / formaldehyde latices having particle sizes in the range from 0.1 to 15 m by polycondensation of melamine and formaldehyde in aqueous medium. In accordance with the invention, methylolmelamines having 1.5 methylol groups per molecule and a concentration of 5 to 70 g / l are reacted at temperatures of 343 to 373 K and a pH of between 3.5 and 6.5. During or after the polycondensation reaction, the surface of the latex particles can be modified by addition of condensable compounds and / or labeled by the addition of dyes, especially fluorescent dyes. The polymer dispersions of uniform particle size obtained in this way can be used in medical diagnostics, as calibration particles for optical and / or electronic particle size determination apparatus and their distribution, for various investigations in colloid chemistry and for fluorescence microscopy.

Description

Title of the invention

Process for the preparation of monodisperse melamine / formaldehyde latexes

Field of application of the invention

The invention relates to a process for the preparation of monodisperse melamine / formaldehyde latices having particle sizes in the range of .0.1 to 15, by polycondensation of melamine and formaldehyde in an aqueous medium. Such latices are for use in medical diagnostics, as calibration particles for Apparatus for optical and / or electronic particle size determination and their distribution, suitable for various investigations in colloid chemistry and for fluorescence microscopy.

Characteristic of the known technical solutions

The preparation of monodisperse latices is possible in principle by polymerization and polycondensation and is extensively described in these two variants both in the scientific and in the patent literature.

In the main polymerization processes used, water-insoluble monomers are dispersed in water and, at elevated temperature and with the exclusion of oxygen, the reaction is initiated by a free-radical generator »

As monomers for the preparation of such monodisperse latices are described:

- Styrenes (3, Polym · Sei ·, Polym. Chem. Ed. 3J5 (1977)

2193-2218; Colloid Polymer Sei. 252 (1974) 464-471);

styrene-containing copolymers, for example, carboxylated polystyrene, carboxylated polystyrene-butadiene copolymers (A * C * S. Preprints, 1974, 155-160, 3 Colloid, Interface Sei, 49 (1974) 425-432);

Styrenic acrylate copolymers (US Pat. No. 3,501,432);

various methacrylate-based monomers

(3 · Cell Biology 64 (1975) 75-88, Macromolecules 9 (1976) 328-336);

Glutaraldehyde (US Pat. Nos. 4,267,234 and 4,267,235) j

- Vinylpyridine (U.S. Patent 4,170,685);

Acrolein (J. Cell Sei, 56 (1932) 157-175)

The latices produced on the basis of polymerization generally have a number of disadvantages which are expressed as follows:

limited particle size (particle sizes above 1, in order to be difficult to realize by means of polymerization processes),

time-consuming and relatively complicated reaction conditions,

Some of the described monomers are complex and / or commercially rarely available in their preparation,

- Formation of surface active Qligomererj

- low density «

- elaborate Rainigungsoperationen for the manufactured Latices. (The removal of impurities present in the system, such as residual monomers, oligomers, salts, and the like, takes place, for example, by steam distillation, centrifugation or ultrafiltration »).

A major advance over this state of the art are the polymer latexes based on melamine and formaldehyde, which are accessible by the folic condensation reaction, the preparation of which is described in the two Soviet patents 441 272 and 933 666. As the starting materials used for the polycondensation are water-soluble On the other hand, the small polymer particle stability and the relatively strong dependence of the particle size distribution on the quality of the starting materials used melamine and especially Formaldehyde are considered. Due to changing quality of the two starting materials virtually no reproducible particle sizes can be produced

Object of the invention

It is the object of the invention to provide monodisperse latices with particle sizes also over 1 μm and relatively large uniformity, which optionally have functional groups for binding biologically active substances, such as antigens, antibodies, enzymes, or fluorochromes on the surface of the Latex particles contain »

Explanation of the essence of the invention

The object is achieved by means of a process for preparing monodisperse melamine / formaldehyde latexes having particle sizes in the range of 0.1 to 15 to obtain by polycondensation of melamine and formaldehyde in an aqueous medium, according to the invention methylolmelamines having a content of ^ 1.5 methylol groups per Molecule and a concentration of 5 to 70 g / l at temperatures of 343 to 373 K and a pH between 3.5 and 6.5 for implementation

During or after the polycondensation reaction, the surface of the latex particles can be modified by addition of condensable compounds containing amino, carboxyl, sulfonic acid or phosphonic acid groups. The latex particles can likewise be oxidized during or after their preparation with dyes, especially with fluorescent dyes to be marked ·

The Methylolmelamine necessary for the successful implementation of the method according to the invention are easily accessible by reaction of melamine and formaldehyde in a molar ratio of 1.5 to 5 moles of formaldehyde per mole of melamine under alkaline conditions, preferably in the pH range between 10 and 11. The defined methylolmelamines prepared in this way are readily soluble in water at elevated temperature, preferably above 343 K, and become more gradual upon addition of an acidic catalyst, eg. 3 × dilute formic acid, and adjustment of a pH in the range from 3.5 to 6.5 Temperature increase to about 373 K to monodisperse polymer particles polycondensed · The condensation reaction takes place both with stirring and by simply leaving the dissolved reaction components to stand.

The production of the latices with a particular polymer particle size lying in the described range between 0.1 and 15 μm is achieved by varying the type and concentration of the methylolmelamine used, by adjusting the pH and the temperature at which the catalyst acid is added, as well as by varying the heating rate, finely dispersed latices result in the use of methylol melamines with a high methylol group content when working at low pH, higher heating rate and acid addition at higher temperature. "In contrast, when using methylol melamines with low methylol groups content, when working in very weakly acidic medium, a moderate heating rate and an acid addition at a temperature in the lower region increasingly coarsely dispersed latices.

The polymer dispersions of uniform particle size obtained according to the invention are advantageously purified by oligomers and excess formaldehyde by ultrafiltration, sedimentation and centrifuging. The removal of residual formaldehyde from the prepared polymer dispersions can also be carried out in such a way that the aqueous dispersion at a pH below 4 urea is added ·

The monodisperse latices prepared according to the invention have been stable over a period of more than 12 months. Optionally deposited latex particles can be redispersed in a simple manner, for example by shaking or stirring.

AusführungsbeispieIe

Example 1

Preparation of a Methylolraelamine

545 g of a 16.5% aqueous formaldehyde solution (3 mol) are adjusted to a pH of 9.5 with iNaOH and heated to 343 K. 125 g of melamine (1 mol) are added to this solution while stirring, and the clear reaction solution is cooled. The precipitated crystalline trimethylolmelamine is filtered off with suction, washed with ammonia water and methanol and dried in air Refrigerator at approx. 277 K

Example 2

Preparation of monodisperse melamine / formaldehyde latexes

In a temperature-controlled reaction vessel equipped with stirrer, thermometer and pH electrode, 1.5 l of distilled water are introduced and heated to 343 K. After dissolving 30 g of pentamethylolmelamine is heated to about 363 K and 0.37 % Formic acid adjusted to a pH of 5.0. The forming polymer particles are left for 15 minutes at 363 K and after

the cooling by ultrafiltration of oligomers and formaldehyde freed · The polymer particles obtained have a diameter of 0.5 to

Example 3

In a reaction vessel according to Example 2, 1.5 l of distilled water and 90 g of trimethylolmelamine are introduced and heated with stirring to 343 K. Thereafter, 0.85 % pure formic acid are added to the clear solution to adjust the pH to 5, 5 added · A slow increase in temperature to 368 K results in a latice whose polymer particles have a diameter of about 12 μm *

Example 4

Preparation of a Surface-Modified Melamine / FornraXdehyde Latex

For the incorporation of functional groups into the surface of the polymer particles, the polycondensation according to Example 2 or Example 3 is carried out in the presence of, for example, amino acids, sulfobetaines, aminophosphonic acids in amounts of from 2 to 20 mol percent, based on the amount of methylolmelamine used. The monodisperse latices thus prepared contain the polymer surface -C © ₂ H, -SO ₃ H, - ^p O ₂ ^{H as} charged groups

Example 5

Preparation of Dyed or Fluorescence-Labeled Non-Disperse Melamine / Formaldehyde Latexes

The addition of dyes with free amino groups (safranin, fuchsin) or dyes with acidic groups such as -COOH ₁ -OSO ₃ H, -SO ₃ H in the dye molecule (Titangelb, Alizarin S, Disulfinblau VN) to the reaction mixture according to Example 2 or. Example 3 provides L3tices with correspondingly intensely colored polymer particles

Example 6

The addition of aminofluorochromes (ethidium bromide, aminofluorescein, fluorescein isothiocyanate in excess of ethylenediamine) to the reaction mixture of Example 2 or 3eispiei 3 provides latices with intense fluorescence · Such fluorescence-labeled latex but are also obtained when the fluorochromes are added after completion of the polycondensation reaction of the latex dispersion.

Fluorochromes with acidic groups in the molecule (eosin, rhodamine B, Na-fluorescine) can also be used for fluorescence labeling.

Excess fluorochrome is removed by repeated washing with distilled water (sedimentation and resuspension).

Claims (3)

invention claim 1 »Process for producing tnonodisperse melamine / formaldehyde latices having particle sizes in the range from 0.1 to 15 / μm by polycondensation of melamine and formaldehyde in an aqueous medium, characterized in that methylolmelamines containing <1.5 methylol groups be reacted per molecule and at a concentration of 5 to 70 g / l at temperatures in the range between 343 and 373 K and a pH between 3.5 and 6.5 » Method according to item 1, characterized in that the surface of the latices is modified during or after the polycondensation by the addition of condensable compounds which carry amino, carboxyl, suyl-phosphonic or phosphonic acid groups. 3 · Method according to points i and 2, characterized in that the latexes are marked during or after the polycondensation with dyes, preferably with fluorescent dyes.