CA1110503A - Encapsulation process employing phase transfer catalysts - Google Patents

Abstract

IN THE UNITED STATES PATENT AND TRADEMARK OFFICE

IMPROVED ENCAPSULATION PROCESS
EMPLOYING PHASE TRANSFER CATALYSTS

Abstract of the Disclosure An improved encapsulation process to prepare en-capsulated water-immiscible material employing an or-ganic polyisocyanate intermediate to form discrete polyurea capsule enclosures around a water-immiscible material dispersed in an aqueous continuous phase said improvement comprising the addition of a catalytic amount of a phase transfer catalyst.

Description

BACRGl~(~UND OF THE INVENTION

This invention relates to encapsulation and par-ticu].arly to the produc~ion of small or minute capsules constituted by a skin or a thin wall of organic CompQSitiOn enclosing a body of material such as a liquid. The process of this inve~tion is directed to the production of such cap-sules which may be produced to a predetermined size, and in a convenient and rapid method by chemical reaction in situ, wherein a suspension or a collection of discrete spheres or capsular spheroids is formed in a body of liquid which then may be readily separated or re~ained and used in said liquid~
Capsules of this na~ure and description have a variety of uses, such as for contaîning dyes, inks~ ch~mical reagents, pharmaceuticals, flavoring materials, fungicides, bactericides, pesticides, such as herbicidesg insecticides and the like, which substances can be dissolved, suspended or otherwise dispersed in or as the ma~erial ~o be enclosed by the capsule. The material to be encapsulated can be employed in the initial dispersion at a temperature above its melting point, or dissolved or dispersed in suitable wa~er-immiscible organic solvent. The nature of the water-immiscible material to be encapsulated can be organic or inorganic in origin.
- Once encapsulated, the liquid or other form is preserved until it is r leased by ~ome mean~ or instrumentality that breaks, crushes, melts, dissolves or otherwise removes the capsule skin, or until release by diffusion is effected under suitable conditionsc An important spe ific aspect of this invention, together with other ~eatures and advantages contemplated by the invention, is the procedure ~or polymerization involv nc the reaction between polyisocyanate monomers, to produce a capsular skin of polyurea1 ~

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A variet~ of techniques have been hereto,ore used or descri~ed for encapsula~ion purposes. r~mong these is the method, wherein the enclosing ilm is deposited b~ condensation and other procedures which involve polymerizing a substance contained in droplats or in a surrounding continuous liquid phase, so as to de-posit the resulting polymer at the surace of such droplets.
Another method involves the shooting of droplets through a falling film of liquid capsule-wall rnaterial which then solidifies around the individual drople~s. Various me~hods of encapsulation by interfacial condensation between direct-acting~ complimentary reactants are Icnown. Within these methods are reactions for producing various types of polymers as the capsule walls. Man~J
of such reactions to produce the coating substance occur between ~ -an amine which must be of at least difunctional character and a second reactant intermediate of acid or~ more accurately, acid~
derived nature, which for producing a polyamide is a difunctional or polyfunctional acid chloride. The amines chiefly used or proposed in these methods are typified by ethylene diamine or the like, havin~ at least two primary amino groups.

For many processes of encapsulation, there is a fi.nal requirement of separa~ion of the encapsulated materials from the forming mediaO During the sepaxation process, ~he capsule wall material is subjected to great mechanical stress.
For this reason~ the highly desirable thin sl~n or cell wall is greatly restricted in the prior art methods. A particular object of the present invention is to provide a new and im proved encapsulation process which is rapid and effective and .

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which avoids the necessity of separa~ion of the encapsulated material. ~ special advantage, therefore, is the permissible formation of extremely thin skin or cellular wall in conjunc-tion with the capsules Interfacial polymerization generally involves bring-ing together two immiscible heterogeneous liquids, e.g., water and organic solvent, respectively, containing complimentary, direct-acting, organic intermediates ~hat will react with each other to establish a solid polycondensate~ Such polyconden-sates, such as a polyamide, polyester, polyurethane, polyurea, or like su~stances, can be formed from resin in~ermediates or monomers. It has also been proposed to spxay drople~s of or-ganic sol~ent containing a diacid chloride into an aqueous liquid containing, for instance, ethylene glycol with the ob-ject of encapsulating the organic liquid or oil in polyester capsules. These ef~orts have allen short of a practical value in various respects. For example, special appara~us is required for this technique. Further, various experiments have indicated the di~ficulty in establishing the desired capsules in dis-crete form whereby coalescense of the partially f~rmed capsules into a heterogeneous mass of materials lacking distinct cap~
sule formation will result. Control of capsule size or uni-ormity is troublesome in the prior ar~ method~ The processes appear limited in ~ypes of reactions a~d prod~lcts involved.
One particular method of encapsulation by interfacial polycondensation is disclosed in U.S. Patent 3,577,515, issued May 4, 1971~ This patent describes a continuous or batch method which requixes a first reac~ant and a second rea tant compli-mentary to the first reactant with each reactant in separate phases, such that ~he first and second rea~tant rea t at the S~3 , . .
interface between the droplets to form encapsulated droplets. As will berome apparent hereinafter, the instant invention eliminates ~he necessity or a second reactant wherein it has been found that a polyurea type encapsulation body can be formed ~ith great ease and provides special advanta~es.
Reference is made to French Patent 1,415,039 which dis~
closes a multifacit technology employing various polymer systems or encapsulation, however, with no description of the instant invention.
That is, there is no teaching of the use of phase transfer catalysts in any encapsulation process.
Reerence is made to Belgian Patent No. 796,746, assigned to Stauf~er Chemical Company, published September 14, 1973. The aforementioned pa~ent describes a method for encapsulating various water-immiscible materials employing an organic isocyanate intermediate to form a polyurea capsule enclosure around a water-i~miscible ma-terial dispersed in an aqueous continuous phase.
SUMM~RY OF THE INVE~rION
This invention relates to encapsulation and particularly to the method of production of small of minute capsules con~tituted by a skin or a thin wall of organic polymer composition enclosing a water-lmmiscible material, such as an organic li~uid. ~lore pa~
ticularly, this invention relates to an improved method for production of discrete polyurea microcapsules containing various core materials by the addition of a phase transfer catalyst to the organic phase.
In contradi~tinction to the prior art and in accor-dance with the preferred practice of the present inventicn, ;t has been discovered that effective encapsulation by interfacial polymerization of an organic isocyanate intermediate can be effectively enhanced by the addition of a phase transfer catalyst in the process which utilizes ~wo su~stantially heterogeneous immiscible liquids, one termed an a~ueous phase and the other P5~3 termed an organic phase, and which comprises establishing a physical d~spers~on of the organic phase in the aqueous phase, said organic phase containing the organic isocyanate inter-mediate for th~ polyurea capsule skin or enclosure. The inter-facial polymerization of the present invention to form the capsul~r wall involves hydrolysis of an isocyanate monomer in the presence of a catalytic amount of phase transfer catalyst to form an amine which in turn reacts with another isocyanate ~onomer to form the polyurea enclosure. The addition of no lQ other reactant is required once the dispersion establishing dxoplets of the or~anic phase within a continuous liquid phase, i.e., aqueous phase, has been accomplished. Thereafter, and preferafily with moderate agitation of the dispersion, the for-mation of the polyurea capsule skin or enclosure around the dispersed organic droplets is enhanced by the catalytic action of an agent known as a phase transfer catalyst capable of increas-ing the rate or isocyanate hydrolysis, thereby effecting the desired condensation ~eaction at the interface between the or-ganic droplets and the continuous phase without external heating 2Q of the dispersion.
Thus/ in accordance with the present teachings, a process is provided for the pxeparation of encapsulated water-immiscihle material within discrete shells of polyurea without external heating. There is provided in an aqueous phase a solution comprising water, a surfactant and a protective colloid and the pH of the aqueous phase is adjusted to about 2 to about 8 and added to the adjusted pH aqueous phase is a water-immiscible phase comprising the water-immiscible material which is to be encapsulated, an organic polyisocyanate and a catalytic amount of 3Q an organic quarternary salt phase transfer catalyst. The water immiscihle phase is dispersed in the aqueous phase to establish droplets of the ~ater-immiscible phase in the aqueous phase and 5~3 , the pH of the dispersion is adjusted to between about p~ 8 to ~hout pH 12 whereupon discrete pol~urea capsular enclosure ~orm around the water-immisci~le material.
~ n this fashion, fully satisfactory, discrete capsules ~re formed having a skin consisting of the polyurea produced the reaction and containing the encapsulated water-lmmisci~le material. Within the process of the invention the xeaction which forms the skin or enclosure for the capsule generally is complete, such that essentially no unreacted poly-lQ isoc~anate remains. ~t is not necessary to separate the cap-~ules ~or desired utllization, i.e., the encapsulated material ma~ he directly usable, depending of course upon the intended ut~lization. Howe~er, such separation prior to utilization may -6a-~ pS1~3 be carried out by any-of the normal separation processes in-volving, for example, settling, filtration or skimmillg of the collected capsules, washing and~ if desired, drying. The pro-duct from the process of this invention is particularly suitable 5 for direct agricultural pesticidal applications, additional agents can be added such as thickeners, biocides, surfactants and dispersants to improve storage stability and ease of appli-cation. The initial dispersion of the organic phase in the aqueous phase may be assisted with an appropriate emulsifying or dispersing agent and the control of the size and uni~ormity of the ultimate capsules is readily effected by any convenient method to disperse one liquid into another.

DETAILE~ DESCRI~PTION OF THE INVENTIO~
In all cases, within the practice o the present in-vention, the effective procedure involves first, producing, as by simple agitation, a solution of water, a suitable surfactant and protective colloid. These three ingredients comprise the aqueous phase or continuous phase of the process. The aqueous or continuous phase is essentially free of any components that will react with the material therein or any of such groups of materials. The surfactant and protective colloid in the aqueous phase do not enter into the polycondensation reaction by which the capsule wall is formed.
By way of ~urther exemplification, the surfactan s in the aqueous or continuous phase can be described as nonionic or anionic surfactants in the XLB (hydrophile-lipcphile balance) range from about 12 to about 16. There are many surfactants which satisfy this HLB range requirement. Among the acceptable surfactants are th~ compounds known as sodium isopropyl naphthalene sulfonate, polyoxyethylenesorbitol oleate --7~

laurate, etho~ylated nonylphenols, however, the preferred sur-factan~ is of the class polyethylene glycol ethers of linear alcohols. ~7hereas the surfactant is described herein as placed in the aqueous phase, it can also be placed in the organic phase.
Without speciic reference to the phase in which the surfactant is placed, ~here wîll be a partitioning and dis~ribution of the surfactant between each phase upon the mixing o~ the phases de~
pending upon the reIative solubility therein. Use of a surfac-tant may be omitted provided that a sufficiently high shear rate is employed to form the dispersion. In the preferred embodiment of this invention a surfactant is employed.~ The range o~ sur-factant concentration found most acceptable in this system is from about 0.01 per rent to about 3.0 per cent by weight based on the aqueous phase. Higher concentration of surfactant may be used witho~t increased ease of dispersibility~
Also present in the aqueous or continuous phase is a protective colloid which ca~ be selected from a wide range of such materials. The usa~le protective colloids can be exempli-fied by ~he foll~wing: Polyacrylates, methyl cellulose, poly-vinyl alcohol, polyacrylamide and poly(methylvinyl ether/maleic anhydride)~ The amount of colloid employed will depend upon various ~actors such as moleculæ weight, type and effectiveness within the media, compat~bil;ty and the ~ke. It has been ound that the protective colloid can be added to the aqueous phase prior to addition of the organic phase to the aqueous phase.
Alternatively, the protective colloid can be added to the sy~tem following the addition of the organic phase or following the ~ispersion thereof. As another alternative, the protective colloid can be added partially prior to addition of the org~nic phase and partially after the dispersion step. Generally, from , ~ 5~3 about 0.1 per cent to about 5.0 per cent by weight based on the aqueous phase is used.
A second phase, known as the organic phase, comprises the material to be encapsulated, a polyisocynate and phase S transfer ca~alyst. The material to be encapsula~ed can b~
used in a concentrated form or in a solution of a water-immis-cible solvent. The material to be encapsulated can be used as the solven~ for the polyisocyanate and phase transfer catalys~.
HGwever, to achieve a desired concentration o active material in the final product, a water-immiscible organic solvent can be used to dissolve the material to be encapsulated, polyisocyanate and phase transfer catalyst. The ma~erial ~o be encapsulated and the polyisocyanate are added simultaneously to the aqueous phase. Whereas, the mater~al to be encapsulated and the poly-isocyanate may be added separately with sl~w agitation in the reactor for a time suficient to cause a homogeneous organic solution~ ~he preferred method of simultan20us addition of the compone~ts of the organic phase is in à pre-mixed stateO That is, the material to be encapsulated and the polyisocyanate are pxe-mixed to obtain a homogeneous phase before addition ~o and mixing with the aqueous phase. The amount of the organic phase may vary rom about 1 per cent to about 75 per cent by volume of the aqueouR phase present in the raction vessel~ The con-centrations in the lower end of the range are relatively unde-sirable since they result in a very dilute suspension of capsules.
The preferred amount of organic phase îs about 25 per cent to about 50 per cen~ by ~olume.
The nature of the organic polyisocyanate determines the release properties of the capsule formed by this process.

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The polyisocyanates also determine the structural physical strength o the capsular wall. The organic polyisocyanates employed in this process include those members of the aromatic polyisocyanate class which includes the aroma~ic diisocyanates, the aliphatic diisocyanates and the isocyanate pre-polymers.
Representative of the aromatic and aliphatic diisocyanates and other polyisocyanates are the following:

l-Chloro-2,4-phenylene diisocyanate m-Phenylene diisocyanate p-Phenylene diisocyanate 4,4l-Methylenebis (phenyl isocyanate)

2,4-Tolyene diisocyanate Tolyene diisocyanate (60% 2,4-isomer, 40% 2,6-isomer) 2 a 6-Tolylene diisocyanate

3,3'-Dimethyl-4,4'-biphenylene diisocyanate

4,4'-Methylenebis (2-methylphenyl isocyanate) 3,3'-Dimethoxy-4,4'-biphenylene diisocyanate 2,2',5.5'-Tetramethyl-4,4'~biphenylene diisocyanate 80% 2,4- and 20% 2,6-isomer of tolylene diisocyanate Polymethylene polyphenylisocyanate (PAPI) Hexamethylene diisocyanate (HMDI) It is highly desirable to use combinations of the above-mentioned organic polyisocyanates. Such combinations as, for example, polymethylene polyphenylisocyanate and tolylene diisocyanate, containing 80% 2,4~ and 20% 2,6-isomers, produce excellent cap-sular enclosures with exceptional controlled release properties, The use of a phase transfer catalyst allows the use of aliphatic isocyanates, such as hexamethylene diisocyanate for capsule wall formation at 25C or ambient temperatures.

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Without a phase transfer catalyst ~he aliphatic diisocyanates react too slowly even at elevated temperatures. This permits favorable blending of aliphatic and aromatic isocyanates and thereby modify the permeability of the microcapsule wall.
The amount of organic polyisocyanate used in the process will determine the wall content of the capsules formed therein. Generally, based o~ the organic phase, there will be greater than about 2 per cent by weight organic polyisocya-nate present. However, this is by no means limiting and a grea~er am~unt can be used that is approaching about 100 per cent. Clearly, 100 per cent would not be entirely desirable since this would result in a product wiSh no encapsulated ma-terial, The preferred range is from abQut 2.0 per cent to about 75.0 per cent by weight of organic polyisocyanate, thereby orming an encapsula~ed product having a corxesponding wall content9 i.e., about 2.0 per cent to about 75,0 per cent.
More particularly, the preferred range i~ from about 5.0 per cent to ab~ut 50O0 per cent wall content~ -In accordance with preferxed practice ~f the present invention, the foll~wing general steps camprise the proces~
which utilizes the two substantially immiscible phases describe~
above. In essence~ the process comprises establishing a physi-cal disper~ion o ~he organic phase (cuntaining a ~ataly~ic amount of phase transfer catalyst) in the aqueous or ~ntinuous phase, such dispersion thereby establishing droplets of de~
sired size in the aqueous phase~ Thereaftex, by adjusting the pH of the resulting mixture, the desired condensation sl~

reaction is effected at the interfaces between the droplets and the continuous phase. Certain vaxiations in the sequence of steps be~ween adjustment of the pH and addition of a phase txansfer catalyst wall be apparent in the following discussion and examples, The temperatures oE the ~wo-phase mixture, that is, the dispers*on of the organic phase in the aqueous phase, does not require external heating. The temperature range or the condensation reaction within the present invention in the pre~sen~e of the phase transfer catalyst is between about 20C
to about 25C~ Whereas~ heating is required to initiate the reaction o this process without the phase transfer catalyst no heating is required when the phase transfer catalyst is present.
Ambient temperature conditions are usable in this process. The rate of reaction is ex~remely rapid upon increasing the pH of the dispersion to about pH 8 to about pH 12. In an alternative procedure, the adjustment of the pH is performed after the dis-persion is accomplished and the pX is maintained within the limits to be discussed ~el~w.
Within the improvement of the present invention, it has been found that a catalyst~ known as a phase transfer cata lyst, ls capable of increasing the rate of isocyanate hydrolysis.
Addition of the phase transfer catalyst is made to the organic phase prior to the initiation of the desired condensation reac-tion at the interface to form the capsules. There is no need to increase the temperature of the sys~em when ~ phase transfer catalyst is employed as described herein. The catalyst in such a procedurP i~ added preferably to th~ organic phase and is added to the system at the time of mlxing o the aqueous and organic phases. Various catalysts of the phase transfcr type ~12-~ 5Q ~

ha~e been ound acceptable, their selection will depend upon factors easily determinable by one skilled in the art~
The term "phase transfer catalyst'l is used herein to represent any catalyst ~hich can effectively facilitate ~he transfer of ions or other reactive or fullctional chemical spe~ies or groups across the phase interface be~ween one dïs-tinct liquid phase and a second distlnct liquid phase, as in a heterogeneous system. In the majority of cases, one of the reactants is located in an aqueous phase and the other reactant in an organic phase.
Certain organic quarternary salts of Group VA o the Periodic Table of the Elements have been found effective as "phase ~ransfer catalyst" use~ul in the rapid formation of mlcrocapsules according to the present invention.
Examples of su~h catalysts are quarternary salts having the ~ormula ~R3R4R5R6M~ ~ X
wherein R3, R4, R5 and R6 are hydrocarbon radicals having a total sum of 18 to 70 carbon at~ms selected independently from the group consi ting of allcyl, alkenyl, aryl, alkaryl~ aralkyl a~d cycloalkyl radicals; M is a pentavale~t ion selec~ed from the group consisting of nitrogen, phosphorus, ars~nic, antimony, and bismu~h, preferably nitrogen or phosphorus, and X is an anio~ which will dissociate from the cation in an aqueous en-viro~ment, preferably a halide ion or a hydrogyl ion, most pr~ferably chloride or bromide. The number of carbon atoms in the hydrocarbon substituents may vary considerably so as to contain from l to about 25 or more carbon atoms in each instance~

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As used in the description of R3, R4, R5, and R6 above:
The term "alkyl" reers to a monovalent straight or branched chain saturated aliphatic hy~rocarbon group of 1 to 25 carbon atoms, inclusive, e~g " methyl, ethyl, propyl, i-propyl, n-butyl, s-butyl, t bu~yl, n-octyl, 2-methyloctyl, decyl, 6-methylundecyl, dodecyl, and the like;
the term "alkenyl" refers to a monovalent strai~ht or branched chain aliphatic hydrocarbon o 2 to 25 carbon atoms, O inclusive, and containin~ at least one double bond, e.g., allyl, butenyl, butadienyl, and the like;
the term "aryl" refers to a monovalent monocyclic or bicyclic aromatic hydrocarbon group, i.e., phenyl and naphtlyl;
the term l'alkaryl" refers to an aryl groups as de-fined above, in which at least one hydrogen atom is substituted by an alkyl group as defined above, e~g., tolyl, xylylg mesityl, ethylphenyl, and the like;
the term "aralkyl" refers to an alkyl group as de-fined above, in which a hydrogen atom is substituted by an 0 aryl or alkaryl gr~p as defined above, e.g., benzyl, phenethyl, methylbenzyl, naphthylmethyl, and the l;ke; and the term "cycloalkyl" refers to a monovalent cyclical saturated hydrocarbon group of 4 to 8 carbon atoms, inclusive~
i.e., cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl.
Mixtures of such quarternary salts may be likewise utilized in the practice of this invention. Double or multi-~unctiona~ quaternary salts in whîch the general foxmula ..

~ ~ 5~ 3 (R3R4RSR6M) ~ X is repeated a plurality of times with the same or different sub~tituen~ combinations 9 can also be utilized effectively.
The preferred phase transfer catalysts are tetra-i n-butyl phosphonium chloride, tri-n-butyl n-cetyl phosphonium brom~de, hexadecyl tributyl phosphonium bromide, benzyl tri-ethyl ammol~um chloride, benzyl triethyl ammonium bromide, trioctyl ethyl ammonium bromQde~ tetraheptyl ammonium iodide, triphenyl decyl phosphomium iodide, tribenzyl decyl arsonium ) chloride, tetranonylammonium hydroxide, tricaprylyl methyl ammonium chloride, and dimethyl dicoco ammonium chloride~
The latter two catalysts are manufactured by General Mills Co., Chemical Division~ Kankakee, Illinois, and are alternatively designated by the names "Aliquat 336" and "Aliquat 221'1, re-spectively.
The term "catalytic amount" is used herein to repre-sent any amount o phase transfer catalyst (quarternary salt) which will enhance the progress of the reaction. The amount o~ catalyst normally used will range from about 0.05 weight 0 percent to about 5~0 weight percent based on the organic phase, preferably from about 0.2 weight percent to about 2.0 weight percent based on ~he organic phaseO
The terms catalytic activity and catalysis as they are here used are intended to mean that a finite i~crease in the extent to which, or the rate at which, ~he reactants in the several phases react with each other is caused to occur by the presence in the system of the quarternary salt. Thus, there may or may not be an economic advantage to conducting the cata-lysis in the case of a particular reactiona but, as will be 0 hereinafter shown in microencapsulation technology involving ' heterogeneous ionic reactions, a striking improvement in xe-activity is realized which makes the heterogeneous or mulki phase en~ironment a much more attractive route by which to produce microcapsules than any method heretofore available.
It is satlsactory to prepare the aqueous phase as described above, While stirring the aqueous phase, the organic phase ls added, preferably in a pre-mixed state. Upon addition of the organie phase to the aqueous phase, a suitable dis-persing means to disperse one liquid in~o the other is employed.
Any hi~h shear device can be used conv~niently to obtain the desired droplet size within the range of from about 0.5 microns to about 4,000 microns. The actual range will depend upon the desired end use. As an example, the pre-Eerred range for most pesticidal applications is from about 1 micron to about 100 microns. The actual range will depend upon the de~ired end use. The instant process is applicable`to preparing widely varied but u~iform sized capsules. Once the proper droplet size is obtained, the dispersion means employed to establish the desired droplet size i5 discontinued. Only mild agitation is required for the balance of the process.
The process of the instant invention is capable of - satisfactury performance and production of encapsulated ma~
terial with easy adjustment of pH to facilitate the reaction.
At a low pH value (about 2 to about 5), the rate of wall formation is slow even with a phase transfer catalyst present~

~ 3 This is advantageous to allow time ox dispersion of th~
organic phase. ~owever, satisfac~ory disper~ion can take place in the pH range o from about 2 to abQut 8. When properly dispersed to the desired particle size, the pH is raised to about pH ~ to about pH 12 preferably pH 10, at which ~alue the wall forming reaction for the microcapsules takes place rapidly. In an alternative procedure~ the en-capsulation process can be achieved by initially adjusting the pH of the aqueous phase to abou~ 5 to about 10, without further pH adjustment after dispersion. In most instances the reaction is about t~o-thirds complete in the initial 5 minutes ater raising the pH value to about 10 at ambient tempera~ure or abou~ 25C. This is to be directly compared to the situa~ion occurring in the absence of the phase trans-fer catalyst~ Without a phase transfer catalyst present only about one-half completion is achieved in 60 minutes at 25C depending upon the type of diisocyanate and material to be encapsulated~
The encapsulaticn process will proceed most satis-factory a~ a pH value of between about 8 to about 14, more preferabl~ between abou~ 8 to about 12. The desirabilit~ of ~ny adjustment of pH to a particular value wlll depend upon ~he nature of the systems components, such ~s gurfactant 9 colloid3 catalyst~ temperature, material to be encapsulated and the like. The pH i~ adjus~ed after dispersio~ and main tained at that value for the remainder of the condensation reaction, The adjustment of ~he pH takes place in the aqueous phase following the dispersion therein of the organic phaseO
The adjustmen~ and maintenance of a particular pH throughout the reaction ~an be accomplished with variou~ water soluble bases or acids nonreactive with the polyisocyanate inter-mediate. Preferably, sodium hydroxide (10% solution), po-tassium hydroxide, hydrochloric acid and the like can be used The desired conden~ation reaction at the in~er~ace between the droplets and the continuous phase occurs ex~remely rapidly in the presence of a phase tr~nsfer catalyst, The majority of the reaction is complete within the first five to ten minu~es of reaction time. There is no need to con-tinue ~he reaction conditions for an ~xtended period of time to insure completion o~ the reac~ionO Under properly adJ~s~ed pH conditions and with a phase transfer catalyst~ ~he reaction time is shortened. At the end of this short time, the forma-tion of a capsule wall has been completed, thereby encapsulat-ing the organi~ matexial within the skin of a polycondensate, and there exists a usable encapsulated product. A specific feature of the present invention~ which is highly desirable, reside~ in the fact that for certain intended applications, no further separation or handling of the encapsulated material is requiredg i.e., the product is directly usable. The en-capsulated m~terial c~n be used ~or various direct applications at this point or indirectly ~y incorporating the material into othe~ products.
The thickness or chemical composition of the capsule-wall can be selected or controlled in various ways. For ex-ample~ these properties can be affected by con~rol of the reaction conditiong by chemical selection~ especially in the creation of cross-linkage which is determined by the function~
ality of the polyisocyanate in accordance with the technology.
The thic~ness of the capsule skin can also be altered by 1~-

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varying the amounts of reactants within the organic phase.
One convenient mode of controlling the size of the capsule is adjustment of the speed o agitation, that is, in bringing about the original dispersion of the organic phase 3 smaller capsules can be obtained with higher speeds o~ agitaticn re~
sul~ing in a greater sheaxing force.
Tests have indicated that capsules produ~ed in accordance with the present invention can be utilized in the same manner as products of other encapsulatian procedures.
Thus, for example, encapsulated herb;cides or insecticides can be embodled in dispersions for applica~ion purposes, for controlled release of the encapsulated material at the desired locality. Special utility is noted for the encapsulation of various volatile or unstable insecticides and herbicides.
By encapsulation, premature volatilization or other deteriora-tion of the material is avoided; such encapsulation can also serve the purpose o~ retardi~g or delaying ac~ion to ~he tîme when desired. Controlled release of these materials is im-portant for environmental protection and the proper efect on the organism to be controlled, as well as decreased toxicity on beneficial organisms.
The present invention may be pr~cticed in a batch or bateh-like form or in a continuous or continucus-like form.
When the invention ls practiced in a manner resembling a batch process, all the various liquids and vaxious reæ tants will be brought together and various steps determined by the proper : time sequence into a single body of liquid~ The batch process may be altered by using the suitable reactors such that a continuous or continuous-like form of the encapsulation process ~19- ~

5~3 is achieved.
Due to the extremely xapid rate of capsule wall formation in the presence of a phase transfex catalyst a con-tiM~ous process is part of this invention. In the continuous S form of the inventive process, continuous dispersion and agi-tation o~ the reæ~ing phases may be practiced at a proper rate to continuously form a suitable dispersion of droplets in the aqueous phase and such that a continuously supplied portion of the dispersion of droplets in an aqueous phase is O added to a reactor in which the pH can be adjusted to promote the interfæ ial condensation. Within the continuous system~
the proper rate for reaction may be obtained by selecting the appropriate conditions. Both the batch and continuous aspects of the present invention are highly desirable, and choice ~here between will rest solely with the desired ma~ufacturing conditions.

EXAMPT~ I
Water (279g.), containing 2.0% of neutralized poly(methyl vinyl ether/maleic anhydride) protective colloid (Gantrez AN 119), 0.22% polyvinyl alcohol, protective colloid ' (Vinol 205) and 0.3% lineax alcohol ethoxylate emulsifier ;~ (Terglt~l 15-5 7) is placed into an open reartor vessel~ The pH is adjusted to about 4.3 with sodium hydroxlde sol~tion.
In a separate container 340g. of S-ethyl diisobutyL thiocarba-ma~e (an herbicide), 14.2g. of N,N-diallyl dichloroacetamid~
~5 (an herbicide antidote)~ 15.8g. polymethylene polyphenyliso-cyanate (PAPI) 9 12.9g. tolylene diisocyanate (TDI) and 2.3g.
tricaprylyl methyl ammonium chloride (a phase transfer cata~
~) lyst, also known as l'Aliquat 336") are mQxed together.

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~ 5~ 3 This ~ixture ls then added to the reactor vessel and emulsified with a high shear stirrer. The resulting par-ticle size is ln the range of from about S microns ~u) to about 40 microns ~). Only mild agitation is required for the remaindex o~ the reaction, No heating is required. The pH o the resulting mixture is adjusted to about 10.0 wî~h a 20% sodium hydroxide solution~ At pH about 10.0 the micro-capsule wall formation is about 93.2% complete ln about ~wo (2) minutes, Well formed, discrete microcapsules are observed LO under a microscope.
In contras~,conventional polyurea microcapsule for-mation as described~ without the phase transfer catalyst, re-quires about 3 hours at 50C.
EXAMPLE II
.
In a simil~r procedure as described in Example I, to 471.7g. of water containing 2.0% neutralized poly (methyl-vinyl ether/maleic anhydride) protective colloid' (Gantre~ AN
llg) 0,22% polyvinyl alcohol protective colloid (Vinol 2053 and 0.3% linear alcohol ethoxylate emulsi~ier (Tergitol 15-5 73 in an open vessel i5 added the mixture of 170g. S~ethyl diiso-butylthiocarbamate (an herbicide), 7.lg. N,N-diallyl dichloro-acetamide (an herbicide antidote)~ 7.9g. polymethylene poly-phenylisocyanate (PAPI), 6.45g. hexamethylene diis~cyanate (HMDI) and 1.29g~ tricaprylyl methyl ammonium chloride. The particle size is established in the range of about 5 ~u to ~5 about 40 ~. The pH of the reaction mixture was adjusted to about 10.0 with sodium hydroxide solution. In about 2 minutes the formation of microcapsules in the dispersion ~s 50% com-plete. Continued stirring will increase the decimal degree ~21-:
. ~

.. . .~

of completion, The degree of completion is judged by sodium hydroxide consumption, Discrete well-formed partieles are observed under a microscope, EXAMPL~. III
In a ~imilar procedure as described in EXAMPLE I, to 1710g, o~ water containing 2.0% neutralized poly (methyl vinyl ether/maleic anhydride) protective colloid (Gantrez AN 119), 0,22% polyvinyl alcohol protective colloid (Vinol~
205) and 0.3 linear alcohol ethoxylate emulsifier (Tergitol 15-5-7~ in an open vessel is added the mixture of 1700g.
S-ethyl hexahydro ~lH-azepine-l-carbothioate (an herbicide), 92.0g, polymethylene polyphenylisocyanate(p~pI)~ 46.0g. toly~
lene diisocyanate (TDI) and ll.Og. tricaprylyl methyl ammonium chloride (a phase transfer catalyst o "Ali~uat 336"), The particle size i9 established as described above in the range i from about 5 ~ to about 40 ~. The pH i~ initially adjusted to 4.5 then raised to about 10,0 where ~he capsulP. formation takes place. After stirring for about 20 mi~utes 3 discrete well-formed capsules are obtained in good yield, EXAMPLE IV
. ~ ~
In a similar procedure as described in EXAMPLE I, 3 to 378g~ of wa~er containing 2.0% polyvinyl alcohol pro~ec~ive ~3 colloid (Vinol 205) and 0,3% linear alcohol ethoxylate emul- .
~3 sifier (Tergitol 150507) in an cpen vessel is added the mixture of 317g. 0,0-dimethyl 0-p-nitrophenyl phosphorothioate (an herbicide3, 19,3g. polymethylene polyphenylisocyan~te (PAPI), :j 6.4g. tolylene diisocyanate (TDI) and 2.lg. tricaprylyl methyl ammonium chloride (Aliquat 336)o Emulsification i~ carried out as previously described. At this point, the pH is about -22~

~ 3 5.8,the par~icle si~e is established at about 5 ~ to about 40 ~. Mild agitation is continued for one hour with the temperature at about 25C. At the end o this time well-ormed discrete microcapsules are obtained, To react any uMwanted resid~al isocy~na~e 12.5g. of 28% ammonia solution is added.
The inal pH adjustment to about pH 7 is made with con~entrated hydrochloric acid.
EX~MPLE V
In a similar procedure as described in EX~PLE I, to 509g, of water containing 2,0% polyvinyl alcohol protectiwe cclloid (Vinol 205) and 0.3% linear alcohol ethoxylate emNl-sifier (Tergitol 15-5-7) is added 165g. S-ethyl diisobutyl thiocarbamate (an herbicide), 7.3g. polymethylene polyphenyl-isocyanate, 6~0g. tolylene diisocyanate and l.Og. tri n-butyl n-cetyl phosphonium bromide (a phase transfer catalyst). There is ~o initial pH adjustment. Emulsification is carried out as previously described. The particle size is established at about 5Jl to about 40JU~ At this point the pH is adjusted to about 10.0 with sodium hydroxide solution. In about ~ix

(6) minutes the formation of microcapsules is about 56.5%
complete. Stirring is continued until the desired degree of completion is achieved as determined by sodium hydroxide con-sumption.
Discrete well~formed microcapsules are observed with a microscope.
As p~eviously mentioned and illustrated by the ex-amples herein, the improved process for encapsulation of the instant invention employing a phase transfer catalyst provides capsules capable of c~ntrol:Ling release of epcapsulated organic ~2~-5~3 ::

material. Representative and especially of importa~ce are the process and capsules comprising as a constituent in the organic phase herbicides of the class thiocarbamate such as S-ethyl diisobutylthiocarbamate; S-ethyl dipropylthiocarba-mate; S-ethyl hexahydro-l-H-azepine-l-carbothioate; S-propyl hexahydro-l-H-azepine-l-carbothioate; S-propyl dipropylthio-carbamate; S-ethyl ethylcyclohexyl thiocarbamate; S-4-chloro- : :
benzyl diethyl thiocarbamate; S-propyl butylethyl thiocarba-mate; organo phosphorus insecticides of the class organo phosphoro and phosphorothioates and dithioates such as O-ethyl S-phenyl ethylphosphorodithioate, S-[(p-chlorophenylthio)methyl]
O,O-dimethyl phosphorodithioateg S-[(p-chlorophenylthio)methyl3 O,O-diethylpho~phorodiethi.oate, O,O~dimethyl O-p-nitrophenyl phosphorothioate, O,O-diethyl O-p-nitrophenyl phosphorothioate~
and insect hormones and mimics such as:
Cecropia - Juveni le Hormone - I
1-(4'~ethyl)phenoxy-3,7-dimethyl-7,7- :
epoxy-trans-2-octene 1-(3',4-methylendioxy)pehnoxy-3,7- :
dimethyl-6,7-epoxy-trans-2-nonene Ethyl 3,7,11-trimethyldodeca-2,4-dienoate Isopropyl 11 methoxy-3,7,11-trimethyl-dodeca-2,4-dienoate Capsules of compounds useful for plant disease con-trol provide a route ~o long ~erm control of disease using com~ -. .
. pounds generally regarded to have only short term effectiveness.
-:~ Similarly, herbicides, romplementary herbicide antidotes, nemato-cides, insecticides9 rodenticides and soil nutrients can be en-capsulated with useful results. Chemicals USPd for see~ treatment ) are also readily encapsulated by the process of the inYention. ~ther biological products can be encapsulated including: Anthelmintics, ~3 .

, ~ 3 lamphrey and slime control agents, algicides, swlmming pool chemicals, miticides, acaracides~ animal attractants, antisep-tics, deodorants, disinlectants, mildewicides~ and the like.
The material to be encapsulated utilizing the im-proved process of the instant invention can be of any type which is water-immiscible. The material need not consist o~
onlq one type, but may be a combination of two or more various types of water-immiscible materials. For example, employing an appropriate water-immiscible material, such a combination is an active herbicide and an active insecticide. Also contem-plated is a water-immiscible material to be encapsulated which comprises an active ingredient, such as an herbicide and an inactive ingredient such as a solvent or adjuvant. Encapsu-lation of a solid ma~erial can be accomplished by this method by forming a solution of the solid material in an appropriate solvent; thereby, normally solid water-immiscible material can be e~capsulated~ For example, the insecticide ~-(mercapto-methyl) phthalimide S-(0~0-dimethyl phosphorodithioate), m.p.
72C,~ can be encapsulated by first dissolving the solid in an appropriate solvent, such as heavy aromatic naphtha solvent.

In addition other representative and especially o~ importance are the process and capsules comprîsing as con-stituents in the organic phase herbicides of the class acetanilide or substituted acetanilide herbicides, particularly the type substituted chloroacetanilide herbicides such as: N-~3'-methoxy propyl-(2))-2-methyl-6-ethyl chloroacetanilide, N-(2' metho~y~
ethyl)-2,6-dimethyl chloroacetanilide, 2-chloro-2',6'-diethyl-N-~methoxymethyl) acetanilide~ 2 chloro-2',6'-diethyl-N-(methyl-carbethoxy) ac~tanilide, 2-chloro-N-isopropylacetanilide, and the like; and 2,4-dichloro and 2; 4, 5-trichloro phe~ogy acetic acid, esters and salts thereof.
As important constituents in the organic phase either alone or in combination wi~h complimentary herbicides are the class of agents known as herbicide antidotes can be used with herbicides as mentioned above. Classes o antidotes include N,N-disubstituted haloacetamides, sulfon2mldes, oxazoli-dines and thîazolidines, various halogenated esters, halogenated ketones, disul~ides, thiuronium salts, a tetrazolium salt and certain imidazolines, certain carbamates, thiocarbamates and dithiocarbamates, cyanomethyl ether of phenyl glyoxylonitrie oxime and substituted pryidyloxy alkanoic acid amides.

,, ~

.

Claims

WHAT IS CLAIMED IS:

1. A process for the preparation of encapsulated water immiscible material within discrete shells of polyurea without external heating which comprises (a) providing in an aqueous phase a solution comprising water, a surfactant and a protective colloid;
(b) adjusting the pH of said aqueous phase to about 2 to about 8;
(c) adding to said pH adjusted aqueous phase a water-immiscible phase comprising the water-immiscible material to be encapsulated, an organic polyisocyanate and a catalytic amount of an organic quarternary salt phase trans-fer catalyst;
(d) dispersing said water-immiscible phase in said aqueous phase to establish droplets of the water-immis-cible phase in said aqueous phase;
(e) adjusting the pH of the dispersion to between about pH 8 and about pH 12; whereupon discrete polyurea cap-sular enclosure form around the water-immiscible material.
2. The process of Claim 1 in which said organic quarternary salt phase transfer catalyst has the formula wherein R3, R4, R5 and R6 are hydroearbon radicals independ-ently selected from the group consisting of alkyl, alkenyl, aryl, alkaryl, aralkyl, and cycloalkyl radicals; M is a mem-ber selested from the group consisting of nitrogen, phospho rus, axsenic, antimony, and bismuth; and X is an anion selectPd from a halide ion or a hydroxyl ion which will dissociate from the cation in an aqueous environment.

3. The process of Claim 2 in which M is nitrogen.
4. The process of Claim 2 in which X is a halide.
5. The process of Claim 3 in which X is chlorine or bromine.
6. The process of Claim 2 in which M is phospho-rus.
7. The process of Claim 5 in which X is a halide.
8. The process as described in Claim 2 in which the organic quarternary salt is selected from the group con-sisting of tetra-n-butyl phosphonium chloride, tri-n-butyl n-cetyl phosphonium bromide, hexadecyl tributyl phosphonium bromide, benzyl triethyl ammonium chloride, benzyl triethyl ammonium bromide, tricaprylyl methyl ammonium chloride, and dimethyl dicoco ammonium chloride.
10. The process of Claim 1 in which said water-immiscible material is a water-immiscible organic material.
11. The process of Claim 1 wherein the organic phase contains organic polyisocyanate within the range of about 20 per cent to about 75.0 per cent by weight.
12. The process of Claim 11 wherein said organic polyisocyanate is an aromatic diisocyanate.
13. The process of Claim 12 wherein said aromatic diisocyanate is about 80 per cent 2,4- and about 20 per cent 2,6-isomer of tolylene diisocyanate.
14. The process of Claim 12 wherein said organic polyiscocyanate is aromatic polyisocyanate.

15. The process of Claim 14 wherein said aromatic polyisocyanate is polymethylene polyphenylisocyanate.
16. The process of Claim 11 wherein said organic polyisocyanate is an aliphatic diisocyanate.
17. The process of Claim 16 wherein said allphatic diisocyanate is hexamethylene dlisocyanate.
18. The process of Claim 11 wherein said organic polyisocyanate is a combination of aromatic isocyanate and aliphatic polyisocyanates.
19. The process of Claim 18 wherein said aro-matic polyisocyanate is polymethylene polyphenylisocyanate and said aliphatic polyisocyanate is hexamethylene dilsocyanate.
20. The process of Claim 10 for encapsulating water-immiscible organic material wherein the organic phase added to the aqueous phase is a combination of organic poly-isocyanates, per cent to about 75 per cent by weight.
21. The process of Claim 20 wherein said combi-nation of organic polyisocyanates consist of polymethylene polyphenylisocyanate and 80 per cent 2,4- and 20 per cent 2,6-isomers of tolylene diisocyanate.
22. The process o Claim 1 wherein said water-immis-cible organic material is a thiocarbamate herbicide whereupon said thiocarbamate herbicide is encapsulated within a polyurea capsular enclosure.
23. The process of Claim 22 for encapsulating water-immiscible organic material within a polyurea capsule wherein said thiocarbamate herbicide is S-ethyl diisobutyl thiocarbamate.

24. The process of Claim 22 for encapsulating a water-immiscible organic material within a polyurea capsule wherein said thiocarbamate herbicide is S-ethyl dipropylthio-carbamate.
25. The process of Claim 22 for encapsulating a water-immiscible organic material within a polyurea capsule wherein said thiocarbamate herbicide is S-ethyl hexahydro-l-H-aæepine-l-carbothioate.
26. The process of Claim 22 for encapsulating a water-immiscible organic material within a polyurea capsule wherein said thiocarbamate herbicide is S-propyl dipropylthio-carbamate.
27. The process of Claim 22 for encapsulating a water-immiscible organic material within a polyurea capsule wherein said thiocarbamate herbicide is S-ethyl ethylcyclo-hexylthiocarbamate.
28. The process of Claim 22 for encapsulating a water-immiscible organic material within a polyurea capsule wherein said thiocarbamate herbicide is S-propyl butylethyl-thiocarbamate.
29. The process of Claim 22 for encapsulating a water-immiscible organic material within a polyurea capsule wherein said thiocarbamate herbicide is S-propyl hexahydro-l-H-azepine-l-carbothioate.
30. The process of Claim 1 wherein said water-immiscible organic material is an organophosphorus insecticide and whereupon said organophosphorus insecticide is en apsulated within a polyurea capsular enclosure.

31. The process of Claim 30 for encapsulating a water-immiscible organic material within a polyurea capsule wherein said organophosphorus insecticide is O-ethyl S-phenyl ethylphosphonodithioate.
32. The process of Claim 30 for encapsulating a water-immiscible organic material within a polyurea capsule wherein said organophosphorus insecticide is O,O-dimethyl O-p-nitrophenyl phosphorothioate.
33. The process of Claim 30 for encapsulating a water immiscible organic material within a polyurea capsule wherein said organophosphorus insecticide is O,O-diethyl O-p-nitrophenyl phosphorothioate.
34. The process of Claim 30 for encapsulating a water-immiscible organic material within a polyurea capsule wherein said organophosphorus insecticide is S[(p-chlorophenyl-thio)methyl] O,O-dimethyl phosphorodithioate.
35. The process of Claim 30 for encapsulating a water-immiscible organic material within a polyurea capsule wherein said organophosphorus insecticide is S[(p-chlorophenyl-thio)methyl] O,O-diethyl phosphorodithioate.
36. The process of Claim 1 wherein said water-immis-cible organic material is an insect hormone mimic whereupon said insect hormone mimic is encapsulated within a polyurea capsular enclosure.
37. The process of Claim 36 for encapsulating a water-immiscible organic material within a polyurea capsule wherein said insect hormone mimic is 1-(4'ethyl)phenoxy-3,7-dimethyl-6,7-epoxy-trans-2-octene.

38. The process as described in Claim 1 used to encapsulate a mixture of an herbicide and a complimentary antidote therefore.
39. The process of Claim 38 in which the herbicide is S-ethyl diisobutyl thiocarbamate and the complimentary antidote is N,N-diallyl dichloroacetamide.
40. The process of Claim 38 in which the herbi-cide is S-ethyl dipropylthiocarbamate and the complimentary antidote is N,N-diallyl dichloroacetamide.
41. The process of Claim 38 in which the herbi-cide is S-propyl dipropylthiocarbamate and the complimentary antidote is N,N-diallyl dichloroacetamide.
42. A process for the preparation of encapsulated water-immiscible material within discrete shells of polyurea without external heating which comprises (a) providing in an aqueous phase a solution comprising water, a surfactant and a protective colloid;
(b) adjusting the pH of said aqueous phase to about 5 to about 10;
(c) adding to said pH adjusted aqueous phase a water-immiscible phase comprising the water-immiscible material to be encapsulated, an organic polyisocyanate and a cata-lytic amount of an organic quarternary salt phase transfer catalyst;
(d) dispersing said water-immiscible phase in said aqueous phase to establish droplets of the water-immis-cible phase in said aqueous phase; whereupon discrete polyurea capsular enclosure form around the water-immiscible material.

43. The process of Claim 42 in which said organic quarternary salt phase transfer catalyst has the formula (R3R4R5R6M) + X-wherein R3, R4, R5 and R6 are hydrocarbon radicals independ-ently selected from the group consisting of alkyl, alkenyl, axyl, alkaryl, aralkyl and cycloalkyl radicals; M is a mem-ber selected from the group consisting of nitrogen, phospho-rus, arsenic, antimony and bismuth; and X is an anion selected from a halide ion or a hydroxyl ion which will dissociate from the cation in an aqueous environment.
44. The process as described in Claim 43 in which the organic quarternary salt is selected from the group con-sisting o tetra-n-butyl phosphonium chloride, tri-n-butyl n-cetyl phosphonium bromide, hexadecyl tributyl phosphonium bromide, benzyl triethyl ammonium chloride, benzyl triethyl ammonium bromide, tricaprylyl methyl ammonium chloride, and dimethyl dicoco ammonium chloride.
45. The process of Claim 42 wherein the organic phase contains organic polyisocyanate within the range of about 20 per cent to about 75,0 per cent by weight.
46. The process of Claim 42 wherein said water-immis-cible organic material is a thiocarbamate herbicide whereupon saîd thiocarbamate herbicide is encapsulated within a polyurea capsular enclosure.
47. The process of Claim 42 wherein said water-immiscible organic material is an organophosphorus insecticide and whereupon said organophosphorus insecticide is encapsulated within a polyurea capsular enclosure.

48. The process of Claim 42 wherein said water-immiscible organic material is an insect hormone mimic whereupon said insect hormone mimic is encapsulated within a polyurea capsular enclosure.