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Description  |
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This invention relates to methods and compositions for the controlled
release of bioactive agents and, more particularly, to the controlled
release of pesticides, such as insecticides.
The utilization of bioactive agents such as pesticides, e.g., insecticides,
herbicides and fungicides has become an important fact of life. However,
these materials are generally effective only as long as they persist on
the substrate to which they are applied.
The basic motivation underlying the modern development of controlled
release pesticidal materials has been to extend the duration between
applications and thus increase the efficiency and hence economy of
control. Controlled release of pesticides permits extended time intervals
between treatments and reduction of the dosage, thus reducing
environmental impact. Thus, from an ecological standpoint, controlled
release of pesticides enhances the lifetime of a non-persistent agent at
the site of treatment while maintaining the preferred property of rapid
detoxification in the environment surrounding the controlled release
pesticide.
The desired controlled release of pesticides has previously been achieved
by their incorporation within a polymeric matrix, e.g., encapsulation
wherein a pest control agent is surrounded by an enveloping polymeric wall
that permits loss through diffusion, permeation or degradation; dispersion
of the pesticide in an elastomer or a plastic wherein the pesticide is
released through leaching or diffusion; and the chemical combination of
the pesticide with a polymer in such a manner that the appended pesticide
slowly breaks off the polymeric backbone upon exposure to the pest
infected environment. However, the prior art approaches fall short of the
desired goal in that there is not adequate provision for the adhesion of
the pesticide within the polymeric matrix to the substrate. This permits
the removal or transfer of the material from the substrate as a result of
physical contact, wind, rain or other atmospheric conditions.
One object of the present invention is to provide a process for the
controlled release of bioactive agents such as pesticides.
Another object of the present invention is to improve the adhesion of such
an agent of suitable substrates and thus to increase its effective
lifetime.
Another object of the present invention is to provide stable compositions
which after application to a suitable substrate and exposure to the
atmosphere, undergo in situ chemical reaction resulting in adherent
insecticides with controlled release characteristics.
A further object of the present invention is to provide novel compositions
containing reactive polysiloxanes, adhesion promoting, crosslinking
reactive silanes and insecticides.
These and other objects of the present invention are achieved by using a
mixture consisting of (a) an organopolysiloxane containing hydroxyl groups
or functional groups which are hydrolyzable to hydroxyl groups, (b) a
hydrolyzable silane selected from the group consisting of (1) a
hydrocarbon substituted hydrolyzable silane, (2) an organopolysiloxane
containing hydrolyzable silane groups, and (3) a partial hydrolyzate of
(1) and/or (2), and (c) an insecticide.
The organopolysiloxanes suitable for use in the practice of the present
invention are well known in the art and contain the structural unit
##STR1##
wherein X is a hydroxyl radical or a hydrolyzable radical such as alkoxy,
acyloxy, hydrogen, halogen and the like and R and R' are oxygen (i.e., the
group --O--) or non-hydrolyzable hydrocarbon, substituted hydrocarbon or
heterocyclic radicals and are the same or different. When R and R' are
hydrocarbon radicals, they may be acyclic or cyclic, saturated or
unsaturated and include aliphatic radicals such as methyl, ethyl, vinyl,
propyl, allyl, butyl, crotyl, hexyl, decyl, dodecyl, hexadecyl, octadecyl,
octadecenyl radicals and the like as well as halogenated or other
substituted aliphatic radicals, aromatic radicals such as phenyl,
biphenyl, phenoxyphenyl and naphthyl radicals as well as halogenated and
other substituted aromatic radicals, aralkyl radicals such as benzyl and
phenylethyl radicals, alkylaryl radicals such as tolyl and xylyl radicals,
cycloaliphatic radicals such as cyclopropyl, cyclopentyl, cyclopentenyl,
cyclohexyl and cyclohexenyl radicals and heterocyclic radicals such as
furfuryl radicals.
The organopolysiloxanes may be linear, branched or both linear and branched
and the X radicals may be terminal end groups or may be situated at other
sites in the polysiloxane chain. The number of X radicals may range from
one radical per polysiloxane molecule up to 30 weight percent of the total
organopolysiloxane molecular weight.
The polysiloxane may be predominantly a monoorganopolysiloxane, a
diorganopolysiloxane, a copolymer containing monoorganosiloxane units and
diorganosiloxane units, a copolymer containing triorganosiloxane units and
SiO.sub.2 units and the like. Notwithstanding the predominant structure,
the organopolysiloxane may contain varying amounts of the other structural
units in addition to hydroxyl radicals or radicals hydrolyzable thereto.
The polysiloxanes suitable for use in the practice of the present invention
are well known in the art and may be prepared by various procedures
including controlled hydrolysis of appropriate precursors as well as ring
opening polymerization of cyclic organopolysiloxanes.
The controlled hydrolysis and cohydrolysis of RSiX.sub.3, R.sub.2
SiX.sub.2, R.sub.3 SiX and SiX.sub.4, where X is a hydrolyzable radical as
previously defined, yields organopolysiloxanes containing
monoorganosiloxane, diorganosiloxane, triorganosiloxane and SiO.sub.2
units, respectively. The relative proportions of said units in the
organopolysiloxane are determined by employing the appropriate ratios of
hydrolyzable precursors. In order to be useful in the practice of the
present invention, the resultant organopolysiloxane must be readily
soluble or dispersible in organic solvents and contain residual hydroxyl
or hydrolyzable radicals.
The polymerization of cyclic organopolysiloxanes provides another route to
the preparation of organopolysiloxanes containing hydroxyl or hydrolyzable
radicals which may be employed in the practice of the present invention.
These and other methods of preparation are set forth in K. A. Andrianov,
"Metalorganic Polymers", Interscience Publishers, New York, 1965, Chapter
III, pages 109-275, the disclosures of which are incorporated herein by
reference.
Polysiloxanes which are at an intermediate stage of polymerization in that
they contain hydroxyl radicals which, upon application of heat, may
undergo condensation to a more advanced stage of polymerization or in that
they contain hydrolyzable groups which upon further hydrolysis may proceed
to a more advanced stage of polymerization are suitable for use in the
practice of the present invention if they have not been rendered insoluble
in organic solvents.
The organopolysiloxanes may be fluids of low or high viscosity or even
solids. The physical appearance of the polysiloxane is dependent upon the
nature of the R and R' radicals, the presence of linear or branched
structures as well as the molecular weight. Notwithstanding the physical
appearance of the polysiloxane, the important requirement for utility in
the practice of the present invention is the presence of hydroxyl radicals
or radicals hydrolyzable thereto. Mixtures of such polysiloxanes are
suitable for use in the present invention.
The hydrolyzable silanes suitable for use in the practice of the present
invention have the formula:
R.sub.n SiX.sub.4-n
where R is a monovalent hydrocarbon radical, X is a hydrolyzable group such
as halogen, alkoxy, acyloxy, hydrogen and the like, and n is an integer
from 0 to 2, inclusive. When X is an alkoxy group, OR', or an acyloxy
group, OCOR', R' may be methyl, ethyl, propyl, isopropyl, butyl, isobutyl,
secondary butyl, 2-ethylhexyl or other aliphatic hydrocarbon radical of
less than 10 carbon atoms. Preferably R' is a lower alkyl radical of no
more than 4 carbon atoms. All of the X's may be the same or they may be
different. The hydrocarbon radical R may be cyclic or acyclic, saturated
or unsaturated, aliphatic or aromatic and include the alkyl, aryl,
alkenyl, aralkenyl, cycloalkyl, cycloalkenyl and heterocyclic radicals
such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, secondary
butyl, tertiary butyl, amyl, hexyl, vinyl, allyl, chloroallyl, methallyl,
crotyl, butadienyl, phenyl, dichlorophenyl, pentachlorophenyl, xylyl,
benzyl, styryl, cinnamyl, furfuryl, cyclohexyl, cyclopentadienyl,
cyclopentenyl, pyridyl, etc. radicals. The hydrocarbon R may also be a
substituted alkyl R"(CH.sub.2).sub.x where x is an integer from 1 to 20
inclusive and R" is a polar and/or reactive functionality such as
acryloxy, methacryloxy, glycidoxy, epoxycyclohexyl, mercapto, amino,
ureido, halo, etc. radicals. There are numerous commercial materials of
this type which are commonly known as organofunctional silane coupling
agents or adhesion promoters.
The monomeric hydrolyzable silanes may be subjected to partial hydrolysis
to promote the formation of condensation products which are still
hydrolyzable silanes and are suitable for use in the practice of the
present invention.
The organopolysiloxanes containing pendant or terminal hydrolyzable silane
radicals, suitable for use in the practice of the present invention, have
the formula:
P-(SiX.sub.n).sub.m
where P is an organopolysiloxane as hereinafter defined, X is a
hydrolyzable group such as halogen, alkoxy, acyloxy, hydrogen, and the
like, n is an integer from 2 to 3 and m is an integer from 1 to 20. When X
is an alkoxy group OR' or an acyloxy group OCOR', R' may be methyl, ethyl,
propyl, isopropyl, butyl, isobutyl, secondary butyl, 2-ethylhexyl or other
aliphatic hydrocarbon radical of less than 10 carbon atoms. Preferably, R'
is a lower alkyl radical of no more than 4 carbon atoms. All the X's may
be the same or they may be different.
The organopolysiloxanes are well known in the art and contain the
structural unit:
##STR2##
where R'" and R"" are oxygen (i.e., the group --O--) or non-hydrolyzable
hydrocarbon, substituted hydrocarbon or heterocyclic radicals and are the
same or different. When R'" and R"" are hydrocarbon radicals, they may be
acyclic or cyclic, saturated or unsaturated and include aliphatic radicals
such as methyl, ethyl, vinyl, propyl, allyl, butyl, crotyl, hexyl, decyl,
dodecyl, hexadecyl, octadecyl, octadecenyl radicals and the like as well
as halogenated or other substituted aliphatic radicals, aromatic radicals
such as phenyl, biphenyl, phenoxyphenyl and naphthyl radicals as well as
halogenated and other substituted aromatic radicals, aralkyl radicals such
as benzyl and phenylethyl radicals, alkylaryl radicals such as tolyl and
xylyl radicals, cycloaliphatic radicals such as cyclopropyl, cyclopentyl,
cyclopentenyl, cyclohexyl and cyclohexenyl radicals and heterocyclic
radicals such as furfuryl radicals.
The organopolysiloxanes may be linear, branched or both linear and
branched. The polysiloxane may be predominantly a monoorganopolysiloxane,
a diorganopolysiloxane, a copolymer containing monoorganosiloxane units
and diorganosiloxane units, a copolymer containing triorganosiloxane units
and SiO.sub.2 units and the like. Notwithstanding the predominant
structure, the organopolysiloxane may contain varying amounts of other
structural units, in addition to hydrolyzable silane radicals.
The polysiloxanes containing hydrolyzable silane radicals, suitable for use
in the practice of the present invention, may be prepared from
organopolysiloxanes which are well known in the art. The latter may be
prepared by various procedures including controlled hydrolysis of
appropriate precursors as well as ring opening polymerization of cyclic
organopolysiloxanes.
The controlled hydrolysis and cohydrolysis of RSiX.sub.3, R.sub.2
SiX.sub.2, R.sub.3 SiX and SiX.sub.4, where X is a hydrolyzable radical as
previously defined, yields organopolysiloxanes containing
monoorganosiloxane, diorganosiloxane, triorganosiloxane and SiO.sub.2
units, respectively. The relative proportions of said units in the
organopolysiloxane are determined by employing the appropriate proportions
of hydrolyzable precursors. In order to be useful in the preparation of
polysiloxanes containing hydrolyzable silane radicals, the precursor
organopolysiloxanes must be readily soluble or dispersible in organic
solvents and contain residual reactive radicals such as hydroxyl, alkoxyl,
acyloxyl, halogen, hydrogen, vinyl, allyl and the like.
The polymerization of cyclic organopolysiloxanes provides another route to
the preparation of organopolysiloxanes containing reactive radicals which
may be employed in the preparation of the organopolysiloxanes containing
hydrolyzable silane radicals which are suitable for use in the practice of
the present invention. These and other methods of preparation are set
forth in K. A. Andrianov, "Metalorganic Polymers", Interscience
Publishers, New York, 1965, Chapter III, pages 109-275, the disclosures of
which are incorporated herein by reference.
Polysiloxanes which are at an intermediate stage of polymerization in that
they contain hydroxyl radicals which, upon application of heat, may
undergo condensation to a more advanced stage of polymerization or in that
they contain hydrolyzable groups which upon further hydrolysis may proceed
to a more advanced stage of polymerization, if they have not been rendered
insoluble in organic solvents, are suitable precursors for the preparation
of the organopolysiloxanes containing hydrolyzable silanes which may be
used in the practice of the present invention.
The organopolysiloxanes containing hydrolyzable silanes may be prepared by
reactions well known in the art. Thus, reaction of an organopolysiloxane
containing hydroxyl groups with excess silicon tetraacetate yields the
triacetoxysilane as shown by the following reaction:
##STR3##
wherein P is as previously defined. Similarly, reaction with an alkyl or
aryltriacetoxysilane yields the corresponding diacetoxysilane as disclosed
in U.S. Pat. No. 3,035,016, the disclosure of which is incorporated herein
by reference. This reaction is shown below:
##STR4##
wherein P and R'" are the same as previously defined.
The reaction of an organopolysiloxane containing SiH units, e.g., as
prepared by hydrolysis and cohydrolysis of a dichlorosilane with an
unsaturated trialkoxysilane or triacyloxysilane in the presence of
chloroplatinic acid, yields an organopolysiloxane containing hydrolyzable
radicals, suitable for use in the practice of the present invention as
shown by the following reaction:
##STR5##
wherein P and R'" are the same as previously defined.
Organopolysiloxanes containing vinyl unsaturation, e.g., as prepared by
cohydrolysis of mixtures of various chlorosilanes including
vinylalkylchlorosilanes, may be reacted with trialkoxysilane to yield
organopolysiloxanes containing hydrolyzable silane radicals suitable for
use in the present invention as shown by the following equation:
P--CH.dbd.CH.sub.2 +HSi(OR'").sub.3 .fwdarw.P--CH.sub.2 CH.sub.2
Si(OR'").sub.3
wherein P and R'" are the same as previously described.
Alternative methods of preparing organopolysiloxanes suitable for use in
the practice of the present invention will be obvious to those skilled in
the art. Notwithstanding the method of preparation, the presence of
SiX.sub.2-3 radicals as pendant or terminal units in an organopolysiloxane
renders it suitable for use in the present invention.
The organopolysiloxanes containing hydrolyzable silane radicals may be
fluids of low or high viscosity or even solids. The physical appearance of
the polysiloxane is dependent upon the nature of the R'" and R"" radicals,
the presence of linear or branched structures as well as the molecular
weight. Notwithstanding the physical appearance of the polysiloxane, the
important requirement for utility in the practice of the present invention
is the presence of hydrolyzable silane radicals. Mixtures of such
polysiloxanes are suitable for use in the present invention.
The preferred compositions of the present invention contain
organopolysiloxanes containing hydroxyl groups and hydrolyzable silanes in
weight ratios from 10/90 to 95/5.
While hydrolyzability is a general characteristic of the silanes which may
be used in the practice of the present invention, the rate of hydrolysis
is a function of the nature of the hydrocarbon substituent in the
hydrolyzable group. Thus, the presence of methyl radicals results in rapid
hydrolysis while higher alkyl radicals result in slower hydrolysis. In the
latter case, it is possible to use water as a diluent or dispersing medium
during the preparation and handling of the active compositions, and as the
hydrolyzing reaction as the composition is applied or after it is applied
to the substrate.
Insecticides which may be used in the practice of this invention include
any of the compounds well known in the art for use as insecticides such as
those set forth in Chemical Week, June 21, 1972, pages 39-64; Chemical
Week, July 16, 1972, pages 19-41; and Commercial and Experimental Organic
Insecticides (1974 Revision), Entomological Society of America, Special
Publication 74-1, October 1974. Some common insecticides which may be used
include the following:
1-naphthyl methylcarbamate (SEVIN)--pyrethrins
malathion--parathoin
methylparathion--phorate
toxaphene--chlordane
Dursban--Baygon
Ddt--diazinon
The insecticides which may be used in the practice of this invention also
include bacterial insecticides such as Bacillus popilliae and Bacillus
thuringiensis and viral insecticides such as the Heliothis virus. These
have been described in Chemical & Engineering News, 35, No. 30, 18 (July
28, 1975), the disclosures of which are incorporated herein by reference.
The insecticide is included in the composition in an amount sufficient to
exert an insecticidal action on the immediate environment surrounding the
substrate. The amount of insecticide will be dependent upon several
factors such as the composition and thickness of the cured polymeric
matrix, the nature of the insecticide, i.e., liquid or solid, the presence
of active hydrogen functionality, the duration of insecticidal action
desired, etc. The optimum amount of insecticide to be included may readily
be determined by those skilled in the art. Generally, from about 1 part by
weight of insecticide to 0.5 to 1000 parts of the combined weight of
polysiloxane and silane is satisfactory.
The compositions of this invention may include volatile diluents such as
aliphatic or aromatic hydrocarbons, e.g., Stoddard Solvent, mineral
spirits, B&P naphtha, cyclohexane, petroleum ether, benzene, toluene,
xylene, etc., chlorinated hydrocarbons such as perchloroethylene or
volatile fluid polysiloxanes such as dimethylpolysiloxane fluids. The
compositions may be prepared by merely admixing the various components.
Before admixing, the components may be dispersed or dissolved in a diluent
such as previously described. The compositions may also be prepared in
aqueous media when slowly hydrolyzing and/or stable components are
present.
The compositions of this invention may be applied to a large number of
substrates. The substrate should be one which contains active hydrogen
atoms which provide sites for coupling with the polysiloxane-silane
system, e.g., hydroxyl groups, amino groups, etc. Thus, various plants
such as ornamental bushes, trees, flowers, greenhouse plants, lawns,
crops, (e.g., wheat, corn, soy beans, barley, oats, cotton, jute, sisle),
fruits, vegetables, berry bushes, nut trees, olive trees, fig trees, grape
vines; various animals such as household pets (e.g., cats, dogs), farm
animals such as dairy cattle, beef cattle, horses, sheep, chickens,
turkeys, swine, goats, zoo animals, etc. Non-plant and animal uses include
spraying surfaces of structures such as buildings and various rooms in
buildings, such as kitchens, bathrooms, closets including wood or plaster
board walls and floor tile to protect against roaches, termites, flying
insects, rug insects, ants, etc. Various containers such as bags and
cardboard or wooden boxes may also serve as substrates in accordance with
the practice of this invention.
The compositions of this invention may be applied to the substrate by
brushing, spraying, dipping or any other known technique for applying a
fluid composition to a solid substrate. It may be applied in the form of
an aerosol mist or fog, propelled by conventional pressurized volatile
halohydrocarbon, hydrocarbon or compressed gas propellants, an air
propelled mist blower, a fog generator, or other suitable means.
Although this invention should not be limited thereby, it is believed that
upon application of the compositions of this invention to a suitable
substrate in an ambient atmosphere, evaporation of the volatile diluent,
if any is present, and exposure to atmospheric moisture results in the
hydrolysis of the hydrolyzable silane, followed by condensation of the
Si(OH).sub.x groups generated thereby with the SiOH groups present or
generated by hydrolysis on the organopolysiloxane to form a crosslinked
polysiloxane matrix containing entrapped or occluded insecticide.
Simultaneously, the Si(OH).sub.x groups promote the adhesion of the
polymeric matrix and the insecticide entrapped or occluded therein to the
substrate. Adhesion to the substrate is due at least in part to the fact
that the polysiloxane matrix is coupled to the substrate by reaction
through active hydrogen atoms on the substrate. In this manner, the
insecticide is held on the substrate to such an extent that it cannot be
physically brushed off, blown off or washed off by rain. Further, as a
result of its entrapped condition the rapid evaporation, sublimation or
extraction of the insecticide is retarded. However, due to the
permeability of the polysiloxane to organic compounds, said evaporation or
sublimation is not completely inhibited, resulting in controlled release
of the insecticide.
When water is present in the compositions of this invention, said water is
generally added shortly before application of the composition to a
suitable substrate, and hydrolysis of the silane may begin before or
during application to said substrate. However, hydrolysis continues after
said application and is followed by condensation of the SiOH groups
generated thereby with the SiOH groups present or generated by hydrolysis
on the organopolysiloxane.
The rate of crosslinking of the hydrolyzable silane, after moisture induced
hydrolysis, may be increased by the use of catalysts, such as tin soaps
including stannous octoate and dibutyl tin dilaurate. Thus, the volatility
of a low viscosity, low molecular weight alkoxysilane such as methyl
triethoxysilane or tetraethyl orthosilicate, may result in loss by
evaporation before sufficient hydrolysis followed by condensation can
increase the viscosity and retard evaporation. The rate of condensation is
increased in the presence of a catalyst, resulting in a rapid viscosity
increase and decreased volatility.
The rate of release may be controlled by adjusting the extent of
crosslinking, e.g., by adjusting the polysiloxane/silane ratio, the
thickness of the polysiloxane coating, e.g., by modifying the composition
and concentration of reactive components in the solution thereof, or by
adding a non-volatile, non-reactive extender for the crosslinked
polysiloxane. The latter acts in a manner analogous to the behavior of the
hydrocarbon oil in a vulcanized oil-extended hydrocarbon rubber. The
extender may be a compatible non-siloxane compound, e.g., a hydrocarbon
oil, or may be an alkyl or arylpolysiloxane fluid having a viscosity
ranging from 5 to 100,000 centistokes at 25.degree. C.
In addition to or in lieu of the solvents which function to reduce the
viscosity of the compositions of this invention as well as control the
thickness of the polysiloxane coating, volatile alcohols such as ethanol,
isopropanol, butanol and the like may be included in the composition to
prevent premature hydrolysis of the hydrolyzable crosslinking agent with
resultant gelation and precipitation.
Other additives which may be incorporated into the compositions of this
invention include stabilizers against environmental degradation, such as
antioxidants and ultraviolet stabilizers, odor masking compounds and
perfumes, dyes, pigments, fillers, etc.
The following examples illustrate the best modes for carrying out this
invention. Examples I to III illustrate the improved adhesion of the
compositions of this invention to a substrate. In the tables in these
examples, the numbers refer to the amount of materials in parts by weight.
EXAMPLE I
Solutions cntaining 50 weight-% of one or more of the following components
were prepared in anhydrous isooctane: (a) methyltriethoxysilane designated
as A-162 by Union Carbide Corporation, (b) a linear dimethylpolysiloxane
fluid containing 3 weight-% hydroxyl groups and having a viscosity of 80
centistokes at 25.degree. C., designated as F1-3563 by the Dow Corning
Corp., and (c) a dimethylpolysiloxane fluid, designated as a DC-200 fluid
by the Dow Corning Corp., having a viscosity of 1000 centistokes at
25.degree. C. (DC-200/1000).
The 50% solutions of alkoxysilane, silanol and/or polysiloxane fluid in
isooctane were mixed with a pyrethroid composition as follows:
0.1 g. pyrethroids
0.5 g. piperonyl butoxide
0.4 g. petroleum distillate
5.0 g. 50% solution of A-162, F1-3563 and/or DC-200/1000 in isooctane
The 50% pyrethroid-containing solutions were diluted to 10 weight-% with
isooctane and 10-20 drops were placed on a weighed glass slide. A glass
rod was rolled over the solution to spread the material uniformly over the
lower four fifths of the slide. The coated slide was air dried for 4 hours
and then placed in a 50% relative humidity chamber for 18 hours. The slide
was then weighed to determine the weight of the coating which ranged from
2-5 mg. covering an area of 15 sq. cm. The coated slide was inserted into
a slit rubber stopper and mounted over the center of a Waring Blender. The
coated slide faced the moving water which completely covered the coating.
The blender was operated at its highest speed for 5 minutes. The slide was
air dried overnight and then weighed to deter | | |
