Alkyl-1-alkoxyethylphosphinous acid aluminum salts

Details Alkyl-1-alkoxyethylphosphinous acid aluminum salts Alkyl-1-alkoxyethylphosphinous acid aluminum salts

1999-11-17

2001-05-08

Vollano, Jean F. (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Phosphorus acids or salts thereof

C562S008000

Reexamination Certificate

active

06229044

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to novel aluminum salts of alkyl-(1-alkoxyethyl)-phosphinic acids, their preparation and their use as flame retardants.
2. Description of the Prior Art
Polymers are frequently made flame retardant by adding to them phosphorus-containing or halogen-containing compounds or mixtures thereof. Some polymers are processed at high temperatures, e.g. at 250° C. or above. For this reason, many known flame retardants are not suitable for such applications, because they are too volatile or are not sufficiently heat-stable.
Alkali metal salts of dialkylphosphinic acids are thermally stable and are already proposed as flame retardant additives for polyester (DE-A1-2 252 258). They must be introduced in amounts of up to 30% by weight and some have an adverse corrosion-promoting effect on the processing machinery.
Furthermore, the salts of dialkylphosphinic acids with an alkali metal or a metal from the second or third main group or subgroup of the Periodic Table of the Elements have been used for the preparation of flame-resistant polyamide molding compositions, in particular the zinc salts (DE-A1-2 447 727). Low-flammability thermoplastics may also be prepared by using said salts of phosphinic acids in combination with nitrogen bases such as melamine, dicyandiamide or guanidine (DE-A1-28 27 867).
A further large class of salts of phosphinic acid are the polymeric metal phosphinates. These are nonionic coordination complexes and are soluble in organic solvents. They are suitable as flame retardant components for halogenated aromatic polymers and for polyesters (U.S. Pat. Nos. 4,078,016; 4,180,495), polyamides (U.S. Pat. No. 4,208,321) and polyester/polyamides (U.S. Pat. No. 4,208,322).
Dialkylphosphinic acids are prepared by free-radically catalyzed addition of olefins onto phosphonous acid monoesters and the subsequent hydrolysis of the dialkylphosphinic esters thus produced. Monoesters of phosphonous acid are produced from phosphonous acids. These are obtained by hydrolysis of dichlorophosphines. The processes are technically complex and proceed over a plurality of stages. Industrially simple preparation processes for salts of phosphinic acids which start from dichlorophosphines are therefore sought.
SUMMARY OF THE INVENTION
The object is achieved by novel aluminum salts of alkyl-(1-alkoxyethyl)-phosphinic acids of the formula (I)
where R
1
is an unbranched or branched alkyl radical having 1 to 6 carbon atoms, preferably methyl, ethyl, n-propyl, isopropyl, n-butyl or tert-butyl, and R
2
is an unbranched or branched alkyl radical having 1 to 4 carbon atoms, preferably methyl or ethyl, and a process for preparing the aluminum salts of the formula (I), which comprises reacting alkyl-(1-alkoxyethyl)phosphinic acids of the formula (II)
with aluminum hydroxide in a molar ratio of approximately 3:1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The phosphinic acids of the formula (II) are prepared by known methods from alkyldichlorophosphines and acetaldehyde diacetals (V.S. Tsivunin et al., Zh. Obshch. Khim. 40 (102) 1970, 12, 2560 (1970).
For example, alkyldichlorophosphine is reacted with acetaldehyde diacetal to give alkyl-(1-alkoxyethyl)phosphinic chloride, which is then hydrolyzed to give the corresponding phosphinic acid. The phosphinic acids formed are then reacted in a known manner (EP-A-699 708) with aluminum hydroxide in a molar ratio of 3:1. In this reaction the phosphinic acid and the aluminum hydroxide are stirred in water at 80-100° C. until the aluminum phosphinate according to the invention has been formed virtually quantitatively. Preferably, the reaction is carried out in suitable solvents or solvent mixtures, e.g. in glacial acetic acid. To reduce the duration of the reaction, it is also possible to carry out the preparation of the salts of phosphinic acid according to the invention under pressure at temperatures of 110-250° C.
The salts of phosphinic acid, after drying well, preferably under reduced pressure at temperatures of 150-200° C., are used as flame retardants for polymer molding compositions, e.g. for polyesters such as poly(butylene terephthalate).
Polyesters are polymers which contain repeating units bound via an ester group in the polymer chain. Polyesters which can be used according to the invention are described, for example, in “Ullmann's encyclopedia of industrial chemistry”, ed. Barbara Eivers, Vol. A21, Chapter ‘Polyesters’ (pp. 227-251), VCH, Weinheim-Basle-Cambridge-New York 1992, which is incorporated herein by reference.
The amount of the salt of phosphinic acid of the formula (I) to be added to the polymer can vary within broad limits. Generally, 5 to 30% by weight are used, based on the polymer. The optimum amount depends on the nature of the polymer and on the type of the salt of phosphinic acid used and can readily be determined by experiments.
The salts of phosphinic acid according to the invention can be used in various physical forms, depending on the type of the polymer used and on the desired properties. Thus, for example to achieve an enhanced dispersion in the polymer, the salts of phosphinic acid can be ground to give a finely particulate form. If desired, mixtures of different salts of phosphinic acid can also be used.
The salts of phosphinic acid according to the invention are thermally stable, and neither decompose the polymers during processing nor affect the production process of the polyester molding composition. The salts of phosphinic acid are not volatile under preparation and processing conditions for polymers.
The salt of phosphinic acid can be incorporated into the polymer by mixing the two and then melting the polymer in a compounding unit (e.g. in a twin-screw extruder) and homogenizing the salt of phosphinic acid in the polymer melt. The melt can be taken off as extrudate, cooled and granulated. The salt of phosphinic acid can also be metered directly into the compounding unit.
It is also possible to admix the flame-retardant additives to finished polyester granules and process the mixture directly on an injection molding machine or to melt the flame-resistant additives in advance in an extruder, to granulate them and process them after a drying process.
The flame-retardant additive can also be added during the polycondensation. In addition to salts of phosphinic acid according to the invention, fillers and reinforcing agents such as glass fibers, glass beads or minerals such as chalk can be added to the formulations. In addition, the products can comprise other additives, such as stabilizers, lubricants, colorants, nucleating agents or antistatics.


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