PT79155B

PT79155B - Microencapsulated naturally occuring pyrethrins

Info

Publication number: PT79155B
Application number: PT7915584A
Authority: PT
Original assignee: Pennwalt Corp
Priority date: 1984-08-29
Filing date: 1984-08-29
Publication date: 1986-08-19
Also published as: PT79155A

Abstract

Process comprises (a) forming a suspension in an aq. emulsion of (I), an isocyanate and an acyl halide, with at least one of the isocyanate and acyl halide being polyfunctional; and (b) adding an amine to the emulsion, in an amt. such that less than 1000 ppm (based on total wt.) of the amine is unreacted, to produce microcapsules of (I) with a shell of polyamide-polyurea.

Description

DESCRIPTION OF THE INVENTION

This order is a continuation of the US Series, NS. No. 177,213, filed August 11, 1980, and relates to the patent application of Ooseph Simkin and Houiard Bohm, entitled "Entomological Active Coating Materials for Comestible Packaging", Series NS, 177,212, filed August 11, 1980, both of which are hereby cited by reference.

This invention describes a process for the formulation of microencapsulated insecticides of the pyrethrin family. More in particular is disclosed a process for microencapsulating natural pyrethrins employing polyamide-polyurea capsule wall which is also applicable to the microencapsulation of natural "synergized" pyrethrins. This invention also relates to the preparation of the resulting microencapsulated insecticides and methods of their use.

Pyrethrins are a class of entomologically active materials that are based on certain naturally occurring species of pyrethrin plants. Both natural and synthetic pyrethrins have been recognized as insecticidal agents. A further advantage of pyrethrins as insecticides is their relatively low toxicity to mammals and certain other non-insect species. Thus, eirp, trinas are known as an "environmentally acceptable" class of insecticides.

A serious drawback to the wider use of pyrethrins as insecticides is that they are labile to oxidation, hydrolysis and other degradations. As a consequence, the entomological activity of pyrethrins decreases with time; they are thus known to be relatively non-persistent. While lack of persistence may be beneficial in certain cases such as use in the vicinity of households, for many applications lack of persistence is a major drawback. Thus, for example, the use of native pyrethrins in agriculture is not economically feasible due to the lack of persistence. As will be seen,

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of pyrethrin insecticides is a goal to be achieved; there has been progress towards this objective on several fronts. Thus, certain insecticides derived synthetically from pyrethrin have been formulated with greater resistance to degradation and concomitantly of greater persistence. Further attempts to increase the persistence of pyrethrin pesticides have focused on partial isolation of the insecticide from the environmental degrading effects. Thus, for example, U.S. Patent 4 056 610 to Barber, Or. Et al. Describes the formulation of microencapsulated insecticides, including pyrethrins, with polyurea microcapsules with ultraviolet light photo-stabilizing materials which minimize photooxidation of the encapsulated species. As will be explained in more detail below, traditional methods of microencapsulation, such as those practiced in U.S. Patent 3,577,515 of 1 / ane gaer, 3,270,100 of Oolkovski, 3,429,827 to Ruus or 3,959,464 to DeSavigny, when applied to pyrethrins natural pyrethrins do not provide acceptable microencapsulated polyamide-polyurea natural pyrethrins for use in many processes. This invention overcomes. This and other drawbacks.

The process of this invention constitutes a modification of known processes for the formulation of microencapsulated materials. In this regard, again reference is made to the American patents of Andegaer and DeSavigny, both assigned to the signatory of this invention, both patents referenced herein. The Sarber patent, 4 056 610 which describes a microencapsulation approach of inter alia pyrethrins, is limited to polyurea type encapsulation systems and is not directed to the polyamide-polyurea systems of the present invention Thus the patents of 1 / andagaer and DeSavigny are recommended for a fundamental understanding of interfacial polymerization techniques and methods that lead to microencapsulation employing the polyamide-polyurea systems.

In general, the microencapsulation technique of l / andegaer and DeSavigny is carried out by interfacial polymerization. According

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In this technique, a dispersed phase of a pyrethrin-containing liquid is established in a continuous phase, the first phase of the at least two further reactants further comprising reacting with each other to form the wall of the capsule by condensation polymerization. The second of the complementary reagents is then introduced into the continuous phase; the polymerization occurs at the interface between the dispersed droplets and the continuous suspension medium. Those skilled in the art will appreciate that more than two complementary reagents may be incorporated into the polymer in various combinations in any of the immiscible liquid phases provided that the contact between the two complementary reagents occurs by mixing.

In general it is desirable to prepare microcapsules with crosslinked binding walls. As Vandegaer acknowledges, this crosslinking is possible by including one or more "polyfunctional" species in the polymer system. "Polyfunctional" is here to mean "having at least three reactive functions per molecule". Those of skill in the art will know that these functions ("functionalities") may be the same or different. They will also know that it is not necessary for all molecules of a constituent species to have 3 or more functions to be polyfunctional; so a species can be considered polyfunctional when it has at least two reactive functions. For example, the polymethylene polyphenylisocyanate may be considered polyfunctional, in which, on average, each molecule may have only about 2.6 reactive functions.

It is therefore necessary that at least one of the steps, ie organic or organic, comprises at least one polyfunctional species in order to ensure the cross-linking of the capsule walls. Those skilled in the art will appreciate that the degree of interconnection ("crcss-linking") can be controlled by regulating the amount of polyfunctional species relative to all polymerizable materials.

The first and second reactive species are chosen so as to be reactive with each other under the reaction conditions. Those skilled in the art who have reviewed the Vandegaer

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DeSavigny, referred to herein for reference, will recognize that there are many options for the first and second reactive species and that many polymer products may result from the reaction. Thus, the capsule walls may comprise amide (sulfonamide, etc.) urethane, urea, ester and many other functions. In practicing this invention it has been found convenient to use polyamide-polyurea systems.

It has been found that the general method of microcapsulation taught by Vandegaer and DeSavigny is relatively inefficient in providing satisfactorily microencapsulated insecticidal material when using polyamide-polyurea systems. Thus the Vandegaer micro-encapsulation technique with polyamide-polyurea for natural pyrethrins produces in practice an appreciable amount of sticky material. This manifests itself in the tendency of the microcapsules to clump or glue together in reports. The agglomeration of microcapsules results in their inability to move freely; the agglomeration measure is the inability of substantial portions of capsules to pass a 40 mesh screen. Thus, the non-agglomerated capsules will pass through a sieve of 40 meshes in an extension of at least 60, - preferably 90%. Most preferably the non-agglomerated capsules will further pass a 50 mesh sieve to an extent of at least about 80%. Such agglomerated microcapsules are unsuitable for the use of spray formulations, especially in the control of structural pests and in agriculture, for coating and for other uses. Although the mechanism that occurs and causes sticky or agglomerated material in such systems is not well understood, it is believed that the chemical nature of the natural pyrethrins may interfere with the polymerization process of the capsule wall. Alternatively, it is possible that impurities normally associated with natural pyrethrins and pyrethrin preparations are responsible for that interference which causes agglomeration according to the old microencapsulation techniques. In particular, it is believed that the natural pyrethrins or impurities associated therewith can react with the anions in the microcapsulation systems, resulting in agglomeration. The Vandegaer and DeSavigny patents

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both describe encapsulation techniques which cause the addition of the amino components in near instant time. This rapid addition is believed to facilitate agglomeration when the microencapsulation methods with polyamide urea are applied to the natural pyrethrins. This invention overcomes these drawbacks and provides microencapsulated natural pyrethrins which free form without agglomerating.

In accordance with the practice of the present invention the microencapsulated natural pyrethrins are formulated by a microencapsulation process in which the nature of the reactants, the order of addition of the reactants and the rate of addition of the reactants are carefully controlled. More in particular, polyamide-polyurea mierocapsules containing natural pyrethrins are formed from isocyanato-acylhalide-amine reaction systems employing a modification of the Vandegaer interfacial polymerization process. This modification comprises careful monitoring of the rate of addition of the amine component to the aqueous suspension of the natural pyrethrin and isocyanate acylhalide.

More in particular, the amine is metered and introduced into the suspension at a rate that avoids localized excess of amine. This process reduces the reaction between natural pyrethrins, or associated impurities, with the amino component by keeping the amine concentration low. It has been found necessary to maintain the free amine concentration at 1000 ppm or below, based on the weight of the blend. Consequently, microencapsulated natural, non-agglomerated and freely moving pyrethrins can be obtained for many entomolagic purposes.

In accordance with the practice of this invention, the natural pyrethrins and the component or components of the first reactj species. which comprises polyfunctional isocyanates and acylhalides, are mixed into an organic mixture with or without additional organic agents. This mixture is then emulsified in an aqueous continuous phase, at a suitable pH, to form a droplet dispersion of organic material containing pyrethrins. The second reactive species comprising the polyfunctional amine is then introduced, in a controlled fashion, into the slurry under agitation. THE

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efficiency of this step is critical to the practice of the present invention. It has been found that when the amine component is added to the suspension at a relatively high speed, as described in the Vandegaer and DeSavigny patents, so that the concentration of free amine exceeds 1000 ppm, the product becomes tacky and agglomerates to a greater or lesser degree. It has been found, however, that when the amine component is slowly added so that the free amine concentration remains below 1000 ppm, the product does not stick or agglomerate to obtain free-moving microencapsulated natural pyrethrins. Thus it has been found that the rate of addition of the amine complementary reagent to the unreacted complementary reagent in the immiscible phase or dispersion dispersed in water is a critical variable for obtaining useful microencapsulated natural pyrethrins.

Although the rate of addition of the second amine-containing reactive component to the suspension or dispersion is best described by the results achieved, that is, by obtaining non-sticky, non-agglomerated microencapsulated natural pyrethrins than by any quantitative measurement operation of an absolute velocity addition, certain quantitative measures of the rate of addition may be provided. Thus, in general, the amine containing component will be poured very slowly, preferably dropwise, into the suspension or dispersion. More in particular, the rate of addition of the amine should be such that a low concentration of amine is maintained in the reaction vessel, below 1000 ppm, until practically all isocyanates and / or acylhalides have reacted. Those skilled in the art will recognize that the duration of the amine addition will vary with the chosen reagents, reaction scale and other variables. For a 20-mole scale, about 30 minutes will usually suffice for amine additions. Although for this purpose the qualitative standards help to define the proper rate of addition of the amine component, such velocity is even better. terminated individually, for each set of reaction parameters. This determination is within the routine of the art experts when informed of the desired result. So when

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warned that a non-sticky, non-agglomerated microencapsulated material will result, when a sufficiently low addition rate is adopted and that tacky and agglomerated material will result at higher addition rates, experts of the art will readily determine the appropriate rate of reaction for any given system. In any case, only a suitable product will be prepared if the concentration of free amine is below about 1000 ppm.

Pyrethrins suitable for the various arrangements of this invention may be any of the active constituents of the natural pyrethrins and related plants. Thus, pyrethrin I, which is the pyrethrolone ester of chrysanthemocarboxylic acid which is believed to be the most potent insecticidal ingredient of the pyrethrin fl uols; pyrethrin II, the ester p1 may be used. chromate-dicarboxylic acid backlit. In addition, a number of other insecticidal agents derived from pyrethrin fluorine, such as cinerin I and cinerin II, which are 3- (2-butenyl) -4-methyl-2-oxo-3-cyclopenten-1-yl ester of the chrysanthemum mono-carboxylic and dicarboxylic acid respectively can be used as well as pyrethrin preparations of the trade and correlated insecticides such as pyrethrin powder or extract. Although this invention has been developed for the purpose of overcoming the difficulties of microencapsulation of natural pyrethrins, it is also suitable for the microencapsulation of synthetic pyrethrins. Thus permethrin, resmethrin, allethrin, cypermethrin and other synthetic pyrethrins may be used. It is also possible to use mixtures of natural pyrethrins and sire pyrethrins in one or more arrangements of this invention.

According to a preferred arrangement of this invention, the pyrethrin or insecticide insecticide may be "synergized" by techniques well known to those skilled in the art. Thus, pyrethrins or mixtures of pyrethrins may become more biologically active by the inclusion of Synergistic agents such as piperonyl butoxide, 4-dodecyl-4'-dodecyloxy-2-hydroxybenzophenone, or other well known synergists. Pesticides, Cremlyn (Wiley, 1978), pp. 47-48.

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synergized pyrethrins including natural pyrethrins are commercially available and are all suitable for use in one or more arrangements of the invention. Synergistic agents will be a ques. so of choice for practitioners of this invention; the term "pyrethrin" encompasses formulations of pyrethrins which also include synergists.

According to this invention, microencapsulated natural pyrethrins can be formulated employing polyamides-polyureas. (cross-linked) as constituents of the walls

of the capsules. In practice of this method the first reactive species, which includes pyrethrin in the suspended droplets, includes polyfunctional isocyanates and / or polyfunctional acylhalides. The second reactive species, introduced into the continuous liquid phase, comprises at least one amine.

Suitable compositions for the first reactive species are the higher polyfunctionality ditri- and isocyanates, together with polymers formed therefrom. Thus the isocyanates such as para-phenylene diisocyanate; meta-phenylene diisocyanato] naphthalene-1,5-diisocyanate; tetrachloro-m-phenylene diisocyanate; 2,4-toluene diisocyanate; 2,6-toluene diisocyanate;

4,4-diphenyl diisocyanate; dichlorodiphenylmethane diisocyanates; bibenzyl diisocyanate; bitolylene diisocyanate; diphenoester diisocyanates; dimethyldiphenyl diisocyanates; polymethylene polyphenyl isocyanates; triphenylmethane-4,4,4'-triisocyanate;isopropylbenzene-alpha-diisocyanate; and the like can be used as components of the first reactive species. These polyfunctional isocyanates can be used either as monomers or as polymers. For example, polymethylene polyphenyl iso, cyanate (known by its trademark Upjohn PAPI R) and similar polymers are preferred constituents of the first reactive species.

Examples of acylhalides suitable for use as components of the first reactive species are sebacoyl chloride; ethylene-bis-chloroformate; phosgene; azelaoyl chloride; adipoyl chloride; terephthaloyl chloride; dodecadioic acid chloride; dimer acid chloride; 1,3-benzene-flufonyl-dichloride; tri

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mesoyl chloride; 1,2,4,5-benzene-tetraacetic acid chloride; 1,3,5-beri

zeno-trisulfonyl chloride; trimeric acid chloride; citric acid chloride; and 1,3,5-benzene-tris-chloroformate. According to this preferred method, the first reactive species is formulated such that the polymer resulting from the reaction of the first and second reactive species is crosslinked from about 10% to about 95%. That is to say, from about 10% to about 95% of the polymers of the polyurethane cell wall form part of a three-dimensional polymeric crosslinking.

Preferably a cross-linking of about 20% to about 50% is used, and the components of the first reactive species are preferably chosen so as to achieve this. The degree of cross-linking present in the final polymer product can be controlled by observing the tri-, tetra- and even higher functionality in the isocyanate and acylhalide components of the first reactive species. Thus an increase of tri-, tetra- and higher functionality isocyanates and polyacyl halides increases cross-linking in the final product.

The amine which may be used as a component of the second reactive species may be chosen from a wide variety of compounds having two or more amine functions. Examples of suitable amines are ethylenediamine; phenylenediamine; toluenediamine; hexamethylenediamine; hexamethylenetriamine; diethylenetriamine; diethylene tetramine; piperaimine, 1,3,5-benzenetriamine-trihydrochloride; 2,4,6-triaminotoluene-trichlorhydrate

tetraethylenepentamine; pentaethylenehexamine; polyethylene amide 1,3,6-triaminonaphthalene; 3,4,5-triamino-1,2,4-triazole; melamine; 1,4,5,8-tetraaminoanthraquinone; etc.; it is clear that mixtures may be used.

The process for the formulation of microencapsulated natural pyrethrins may advantageously utilize numerous species other than pyrethrins and capsule wall components. Thus, formulations according to this invention may include clays, pigments, viscosity modifiers, polymers, polymers, suspending agents, colorants, antifoaming agents, preservatives, anti-oxidants, UV stabilizers and the number 968

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other families of materials will occur to those skilled in the art. It is particularly useful to incorporate anti-oxidants and UV stabilizers simultaneously with the pyrethrins for microencapsulation. The addition of these agents further serves to protect the pyrethrins from degradation and thus improve the overall persistence of the insecticide compositions formulated herein.

Those skilled in the art will appreciate that the average wall thickness of the capsule that may be used in the microencapsulation process of this invention may be varied if we vary the relative amounts of the materials relative to the encapsulation compositions. relative thickness of the capsule wall as well as the degree of pre-crosslinking. the polymer in the capsule will affect the rate of diffusion of pyrethrin through the wall and will influence both the persistence of the insecticide and its potency at any time. As previously mentioned, control of the polyfunctionality of the isocyanates and / or acylhalides will vary the amount of cross-linking in the walls of the resulting capsules. In this way the degree of dispersion of the material can be controlled, the intensity of the agitation can be controlled and emulsifying agents can be brought together in the aqueous phase, as is well known to those skilled in the art. The wall thickness of the microcapsule can be controlled by the amount of reactive intermediates available for the formation of polymers. While the amount of insecticide, expressed in weight ratio relative to the amount of the encapsulating composition, may vary widely from about 2: 1 to about 10: 1, a weight ratio of about 5: 1 is preferred for many applications. Those of skill in the art, if they follow the above general guidelines, having regard to the references of Vandegaer and DeSavigny incorporated herein by reference, can readily formulate microencapsulated natural insecticides according to the present invention, obtaining the desired weight ratio of insecticide relative to the polymer.

Natural microencapsulated insecticides may be useful. different ways. Thus, aqueous suspensions of in

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Secticides can be used for crop spraying or for insect control. A preferred use of microencapsulated natural insecticides of this invention is discussed in the NS Series application. 177 212, August 11, 1980, entitled Entomologically Active Coating Materials for Comestible Packaging. Thus the microencapsulated products produced in accordance with this invention may be included in the coating formulations and used to coat various packaging materials suitable for containing edible products. Such coated packaging materials have been shown to have a high persistence against insect attack, greater than the coating materials using unencapsulated pyrethrins or packaging materials which have been sprayed with natural solutions of unencapsulated pyrethrins. Attempts to formulate microencapsulated natural pyrethrins according to Vandegaer's methods, or according to processes where the rate of addition of the amine compound has not been controlled, and hence where it is evident that the resulting microcapsules are sticky and agglomerate , have resulted in insecticides which are relatively unsuitable for coating materials. Thus, the present invention fulfills a long-felt need to obtain microencapsulated natural pyrethrins for coating compositions of food packaging materials and for other purposes.

EXAMPLE 1: Comparison Example

An organic mixture comprising 50 g of natural synergized pyrethrin (6.1 / active with 10 times the amount of piperonyl butoxide), 2.37 g of sebacoyl chloride (95%) and 2.65 g of PAPI (methylene- polyphenylisocyanate "PAPI" from Upjohn) was emulsified in 140 ml of a 0.5% solution of Gelvatol (a partially hydrolyzed polyvinyl alcohol, available from Monsanto Co). This dispersion was obtained in a 400 ml glass vessel fitted with a faucet valve at the base using a Kraft disperser at position # 6. After 30 seconds emulsification the dispersion was transferred through the tap into a 400 ml beaker. To this dispersion was added

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An aqueous solution containing 1.19 g of ethylenediamine, 1.6 g of 50% NaOH solution and 10 g water is added once. The concentration of quasi 5000ppm free amine was lowered as the reaction took place, but not before the microcapsules thus formed agglomerated immediately after their formation and could not pass through a 50 mesh screen. The product was not suitable for the formulation of insecticidal compositions and could not be used as a constituent of packaging of food packaging.

EXAMPLE 2

The organic mixture from Example 1 was emulsified in an aqueous solution of Elvanol / a using the disperser at the

6.5 for one minute. The resulting dispersion was transferred to a 400 ml beaker and 1.6 g of 50% NaOH in IC50 water was added under stirring. 1.19 g of ethylenediamine was dropped dropwise over a period of at least 30 minutes, while the emulsion was mechanically stirred, not exceeding 400 ppm the unreacted amine concentration. After stirring for an additional hour, the emulsion was neutralized to approximately neutral pH with HCl. The suspension could easily pass through a 50 mesh screen. Microscopic observation revealed natural spherical capsules of microencapsulated natural pyrethrin with a mean capsule diameter of about 30 microns to about 35 microns,

EXAMPLE 3

The procedure of Example 2 was repeated except that 1.36 g of diethylene triamine was further mixed with ethylenediamine in aqueous solution. The mixed amines were added dropwise as in Example 2, keeping the amine unreacted at a concentration of 950 ppm or below. Encapsulation without encapsulation was obtained and the suspension was easily passed through the 50 mesh screen.

EXAMPLE 4

The encapsulation of pyrethrin was performed exactly as in Example 2 except for mixing

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(2,6-di-tert-butyl-4-methylphenol, 0.0346 g) and a UV stabilizer (TINUVIN 328, trademark of Ceiba-Geigy, 334 g). The maximum amount of unreacted amine was maintained below 1000 ppm based on the weight of the mixture. The suspension thus prepared was calculated to give approximately 1.5% active pyrethrin based on the weight of the suspension and found to be well prepared and not agglomerated.

EXAMPLE 5

The procedure of Example 2 was reproduced on a tenfold scale. An organic mixture comprising 500 g of synergized natural pyrethrin (6.0 / active with 10 times more quinoa of piperonyl butoxide), 26.5 PAPI and 23.7 g of sebacoyl chloride was emulsified in 1.4 liters solution of 0.5% Elvanol aqueous solution. The dispersion was carried out in a 3 liter faucet resin flask employing a Kraft disperser for 30 seconds at the & 6 position. The dispersion was blended with a standard stirrer while 16 g of a 50% NaOH solution were added, . An aqueous mixture comprising 25 ml of water, 11.9 g of ethylenediamine and 13.6 g of diethylene triamine was slowly added at a rate of approximately one drop per second for about 50 seconds and then increased to 2 drops per second until complete reaction. This rate of addition kept the amine concentration at levels below about 1000 ppm throughout the amine addition phase. The actual mixture was neutralized with dilute hydrochloric acid to about pH 6-6.5. The suspension was passed through the 50 mesh screen and was characterized by having approximately normal, free-moving, spherical material, the product was analyzed and contained about 1.7 / of natural active pyrethrin and the average size of the capsules was of about 34 microns. To improve the stability of the capsule suspension, 0.35 wt.% Kelzan (a xanthan gum produced by Kelco Com pany) was added. This dispersion thus thicker showed excellent insecticidal properties and good persistence.

EXAMPLE 6

The efficiency and persistence of natural pyrethrins

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croencapsulated, according to this invention, are demonstrated by this example.

Cards were sprayed with insecticidal compositions referred to and infested with flies during certain periods. A pej? cent of fly mortability was determined 24 hours after the flies were placed on the treated surfaces.

The results are presented in the following Table:

TABLE I

SAMPLE 1 3 DAY, / OF DEAD 22 29 7 10 15 Control - No active ingredient .......... 13 0 1 0 0 0 0 Synergized natural pyrethrin (unbound, 6 / active with 10 times piperonyl butoxide) ....... 100 72 6 13 0 0 0 Synthetic pyrethrin (Resmethrin - SB Penick Co.) .......... 84 22 0 6 0 0 0 Material of Example 2. 100 100 100 100 99 100 100

The superiority of microencapsulated natural pyrethrins with respect to either unencapsulated natural pyrethrins or unencapsulated resmethrin is well demonstrated. An attempt was made to spray the material of Example 1 but without success and therefore its efficiency was not evaluated.

Claims

A process for micro-encapsulating naturally occurring pyrethrins with a polyamide-polyurea film by interfacial conditioning of intermediates forming complementary, organic, di- or polyfunctional polycondensates, reacting to form a polyamide-polyurea condensate, comprising: a) formation of a suspension in an aqueous emulsion;

(i) naturally occurring pyrethrin, to be microencapsulated;

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(ii) at least one isocyanate, and

(iii) of at least one acylhalide; at least one of said isocyanate and said polyfunctional acylhalide; and

b) the subsequent addition to the aqueous emulsion of (a), under agitation during the reaction, of at least one amine at an addition rate such as to maintain the unreacted amine concentration below 1000 parts per million of the total weight of (a) ) and (b), to obtain substantially unagglomerated, free-moving microcapsules of said pyrethrin with a mantle. polyamide-polyurea.

Process according to claim 1, at where in the (i) to said pyrethrin was mixed with at least an pyre- trine syntactic. A process according to claim 1, at where in the

(ii) said isocyanate is selected from the group consisting of isocyanates consisting essentially of para-phenylene diisocyanate; meta-phenylene diisocyanate; naphthalene-1,5-diisocyanate; tetra-chloro-m-phenylene diisocyanate; 2,4-toluene diisocyanate; 2,6-toluene diisocyanate; 4,4-diphenyl diisocyanate; dichloro-diphenylmethane diisocyanate; bibenzyl diisocyanate; bitolylene diisocyanate; diphenyl ester diisocyanate; dimethyldiphenyl diisocyanate polymethylene polyphenylisocyanate; triphenylmethane-4,4,4'-triisocyanate; and isopropylbenzene-alpha-diisocyanate.

A process as claimed in claim 1, wherein in (a) (iii) said acylhalide is selected from the group consisting of methyl acyclic esters consisting essentially of sebacoyl chloride; ethylene-bis-chloroformate; phosgene; azelaoyl chloride; adipoyl chloride; terephthaloyl chloride; acid chloride dodecane dioic acid chloride dimeroj 1,3-benzenesulfonyl chloride trimesoyl chloride; 1,3,5-benzene-trisulfonyl-1,2,4,5-benzenetetrahydric chloride; trimeric acid chloride; citric acid chloride; and 1,3,5-benzene-tris-chloroformate.

A process according to claim 1 wherein in (b)

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said amine is chosen from the group of amines consisting essentially of ethylenediamine; phenylenediamine; toluene diamine; hexamethylenediamine; diethylenetriamine; triethylenetetramine; piperidine, 1,3,5-benzenetriamine trihydrochloride; 2,4,6-triaminotoluene-trihydrate; tetraethylenepentamine; pentaethylenehexamine; polyethyleneamine; 1,3,6-triamino-naphthalene; 3,4,5-triamino-1,2,4-triazole; melamine; and 1,4,5,8-tetraaminoanthraquinone,

A process according to claim 1, wherein said amine is maintained at a concentration below 400 ppm,

7. An insecticide preparation process wherein the natural eirp was microencapsulated according to the process of claim 1,

8. The insecticide preparation process of claim 7 wherein said pyrethrin has been singled out,

The insecticide preparation process of claim 7, wherein said pyrethrin has been mixed with at least one synthetic pyrethrin.

10. The insecticide preparation process of claim 9, wherein said pyrethrin has been synergized.