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Polyvinyl chloride resin compositions used for the manufacture of rigid
articles such as pipe and siding for buildings are processed nowadays by
extrusion in multi-screw extruders. Multi-screw extruders differ from the
older single-screw extruders, calenders and blow-molding machines in
retaining the polyvinyl chloride resin composition being processed for a
much shorter period of time. The polyvinyl chloride resin compositions
that are being extruded are highly lubricated, by virtue of the addition
of substantial amounts of lubricants such as calcium stearate, so that,
due to the positive displacement pumping action of the multi-screw
extruder, they can be processed at any desired rate. Thus, the polyvinyl
chloride resin compositions may not be subjected to the rather elevated
temperatures, of the order of 375.degree. F. and higher, required to bring
the composition to an extrudable, softened condition for much longer than
thirty minutes, and frequently only for as little as five to ten minutes.
Conventional heat stabilizers are not suitable for use with the rigid
polyvinyl chloride resin compositions especially formulated for extrusion
in such machines. Such stabilizers are formulated to impart long term heat
stability, but these compositions do not require stabilization against
long heating times at 375.degree. F. What is required, particularly for
light colored compositions, is a resistance to the development of
significant discoloration during the first five to ten or twenty minutes
of heating. Such discoloration is referred to as "early yellowing". Long
term heat stabilizers are tailored to inhibit the development of dark
discoloration after forty minutes of heating, and more. An early
discoloration can be tolerated, since some discoloration is expected, if
only the color after long term heating is not much worse, and the
degradation in physical properties can be avoided.
Unfortunately, the highly lubricated formulations that have been developed
for extrusion in these machines contain substantial quantities of
lubricants, such as calcium stearate; frequently, more lubricant than
stabilizer. Typically from 0.6 to 1 part per hundred, and sometimes as
much as two parts per hundred, of lubricant are used, with from 0.3 to 0.5
part per hundred of an organotin stabilizer containing 12% tin or less.
Such proportions are to be contrasted with the proportions used in
conventional extrudable compositions for use with single-screw extruders,
where from 1 to 1.5 parts per hundred of stabilizers containing 18% tin or
21 to 26% tin is used, with a maximum of about 0.5 part per hundred of the
lubricant.
Since the most popular lubricant has been calcium stearate, the change in
relative proportions has meant a considerable change in the tin/calcium
ratio. Moreover, since calcium stearate has a tendency to impart an
initial yellow discoloration on its own, which tends to worsen as heating
continues, the prevention of early yellowing in such highly lubricated
extrudable formulations has become correspondingly more difficult.
The organotin mercaptocarboxylic acid esters are widely recognized as the
most effective organotin stabilizers, having a tin content of about 18%
Sn. The position of the organotin mercaptocarboxylic acid esters has been
challenged in recent years by the provision of stabilizers containing a
higher proportion of tin, from about 21 to about 26% Sn, referred to as
the "high efficiency" organotins. The latter are exemplified by the
organotin mercaptocarboxylic acid ester sulfides of U.S. Pat. Nos.
3,565,930, 3,565,931, and 3,817,915 (see later discussion). However, a
high tin content is not a determinative factor in preventing the
development of early discoloration, as exemplified by the organotin
sulfides, which offer the highest tin and sulfur content per organotin
group, and yet are not the most effective in this respect, affording a
poor initial color, particularly.
The organotin mercaptocarboxylic acid esters are described in U.S. Pat.
Nos. 3,753,325 to Leistner et al, issued June 26, 1956, U.S. Pat. No.
2,641,596 to Leistner et al, issued June 9, 1953 and U.S. Pat. No.
2,648,650 to Weinberg et al, issued Aug. 11, 1953.
Variations on these have also been proposed, derived from 2-hydroxyethyl
and 2-acyloxyethylmercaptans, also referred to as 2-mercaptoethanol and
2-mercaptoethylcarboxylate esters, including Stefl et al U.S. Pat. No.
2,731,440, Best U.S. Pat. No. 2,731,484, Ramsden et al U.S. Pat. No.
2,790,785, Mack et al U.S. Pat. No. 2,809,956, Ramsden et al U.S. Pat. No.
2,830,067, Leistner U.S. Pat. Nos. 2,870,119, 2,870,182, 2,872,468 and
2,883,363, Ramsden U.S. Pat. No. 2,885,415 and British Pat. No. 759,382,
Molt U.S. Pat. No. 3,931,263 and German Offenlegungsschrift No. 2,503,554.
These have not, however, been found to be as satisfactory as the organotin
mercaptocarboxylic acid esters, and none has ever received much attention
commercially.
Stefl U.S. Pat. No. 2,731,440 patented Jan. 17, 1956 proposed monoorganotin
trimercaptides of the formula:
##STR1##
in which formula:
R.sub.1 independently in each occurrence represents an organic radical
consisting of from one to twenty-two carbon atoms, hydrogen, carbon-carbon
single bonds, carbon-hydrogen bonds, (optionally) aromatic ring
carbon-carbon double bonds and (also optionally) a maximum total of four
innocuous structures such as carbon-carbon triple bonds, aliphatic
carbon-carbon double bonds, ether linkages, thioether linkages, carboxylic
ester groups bonded to carbon atoms, fluorine atoms linked to carbon
atoms, and halogen atoms bonded to aromatic ring carbon atoms; and
R.sub.2 independently in each occurrence represents an organic radical
consisting of from one to twenty-two carbon atoms, hydrogen, carbon-carbon
single bonds, carbon-hydrogen bonds, (optionally) aromatic ring
carbon-carbon double bonds, and (also optionally) a maximum total of four
innocuous structures such as carbon-carbon triple bonds, aliphatic
carbon-carbon double bonds, hydroxyl groups bonded to carbon, sulfhydryl
groups bonded to carbon, ether linkages, thioether linkages, carboxylic
ester groups bonded to carbon atoms, carboxylic amide groups bonded to
carbon atoms, fluorine atoms bonded to carbon atoms, halogen atoms bonded
to aromatic ring carbon atoms, and groups of the formula
##STR2##
under the same notation.
In the above formulae, the atoms in the groups R.sub.1 and R.sub.2 attached
to the sulfur and tin atoms must always be carbon atoms. It will also be
understood that the innocuous groups mentioned as optional constituents of
the radicals R.sub.1 or R.sub.2 need not all be identical in any given
radical R.sub.1 or R.sub.2, but their total number, enumerated without
distinction as to kind of innocuous group, must not exceed four in any
given radical R.sub.1 or R.sub.2.
These stabilizers are said to be effective in stabilizing vinyl chloride
resins at temperatures of from 315.degree. to 350.degree. F. for extended
periods of time, such as thirty to sixty minutes. There is no reference to
resistance to the development of early discoloration.
Best U.S. Pat. No. 2,731,484 patented Jan. 17, 1956 proposed diorganotin
dimercaptides of the formula:
##STR3##
in which formula
R.sub.1 independently in each occurrence represents an organic radical
consisting of from one to twenty-two carbon atoms, hydrogen, carbon-carbon
single bonds, carbon-hydrogen bonds, (optionally) aromatic ring
carbon-carbon double bonds, and (also optionally) a maximum total of four
innocuous structures such as carbon-carbon triple bonds, aliphatic
carbon-carbon double bonds, hydroxyl groups bonded to carbon, sulfhydryl
groups bonded to carbon, ether linkages, thioether linkages, carboxylic
ester groups bonded to carbon atoms, carboxylic amine groups bonded to
carbon atoms, fluorine atoms bonded to carbon atoms, halogen atoms bonded
to aromatic ring carbon atoms and groups of the formula:
##STR4##
under the same notation, and
R.sub.2 independently in each occurrence represents and organic radical
consisting of from one to twenty-two carbon atoms, carbon, hydrogen,
carbon-carbon single bonds, carbon-hydrogen bonds, (optionally) aromatic
ring carbon-carbon double bonds and (also optionally) a maximum total of
four innocuous structures such as carbon-carbon triple bonds, aliphatic
carbon-carbon double bonds, ether linkages, thioether linkages, carboxylic
ester groups bonded to carbon atoms, fluorine atoms bonded to carbon
atoms, and halogen atoms bonded to aromatic ring carbon atoms.
In the above and all following formulae, the atoms in the groups R.sub.1
and R.sub.2 attached to the sulfur and tin atoms must always be carbon
atoms.
Ramsden, Weinberg and Tomka U.S. Pat. No. 2,790,785 patented Apr. 30, 1957
proposed hydrocarbontin mercapto alcohol esters having the formula:
R.sub.n Sn(SR'OX).sub.4-n
where
R is an alkyl, aryl, aralkyl group and R' is an alkylene or arylene group,
X is a residue of an oxygen-containing acid less an hydroxyl group, and n
is an integer in the order of 1, 2 or 3. In these compounds, all valences
of Sn not satisfied by R groups are joined to S atoms.
These compounds were proposed as antioxidants for natural and synthetic
rubbers.
Mack and Parker U.S. Pat. No. 2,809,956 patented Oct. 15, 1957 proposed
organotin compounds in polymeric form of the types:
##STR5##
In these formulae, R and R' are monovalent hydrocarbon radicals. They may
be different but will be in most cases identical when the dihydrocarbon
tin halides or oxides available in commerce are used as starting materials
for the synthesis of the compounds; R and R.sup.1 may be aliphatic,
aromatic, or alicyclic groups, such as methyl, ethyl, propyl, butyl, amyl,
hexyl, octyl, lauryl, allyl, benzyl, phenyl, tolyl, cyclohexyl.
SX and SX.sup.1 are radicals of a mercapto compound, which are bound
through the S atom to a terminal Sn atom. Suitable mercapto compounds are,
for instance, mercaptans, mercapto alcohols, and esters thereof, and
esters of mercapto acids.
Ramsden and Weinberg U.S. Pat. No. 2,830,067 patented Apr. 8, 1958 proposed
a group of sulfur-containing organostannate stabilizers which are the
reaction product of an alcohol or alcohols, a dibasic acid, a bifunctional
tin oxide, and a mercaptoalkanol derivative. At least a portion of the
organotin or all of the organotin is present as a "six-fold coordinate
organostannate anion" of the type:
##STR6##
wherein
R=alkyl, aryl or aralkyl, Y=coordination groups, coordinated through O or
S, and b is a varying charge dependent upon the nature of the Y's.
Leistner and Hecker U.S. Pat. Nos. 2,870,119 and 2,870,182 both patented
Jan. 20, 1959 proposed organotin mercapto alcohol monocarboxylic acid
esters of the type:
R.sub.n --Sn--X.sub.4-n
wherein
R stands for a radical selected from the group consisting of alkyl, aryl,
oxyalkyl and oxyaryl, the furfuryl and tetrahydrofurfuryl radicals, X for
the radical of an ester of a mercapto alcohol having from two to four
carbon atoms, and having its sulfur atom linked to Sn, and n for an
integral number from 1 to 3.
The mercaptoalcohol can be esterified with an aliphatic acid or
cycloaliphatic acid having from six to twelve carbon atoms. Exemplary
products are:
(1) C.sub.4 H.sub.9 Sn(S CH.sub.2 CH.sub.2 OCOC.sub.11 H.sub.23).sub.3
(2) (C.sub.4 H.sub.9).sub.2 Sn(S CH.sub.2 CH.sub.2 OCOC.sub.11
H.sub.23).sub.2
(3) (C.sub.4 H.sub.9).sub.3 Sn S CH.sub.2 CH.sub.2 OCOC.sub.11 H.sub.23
Leistner and Hecker U.S. Pat. Nos. 2,872,468 patented Feb. 3, 1959 and
2,883,363 patented Apr. 21, 1959 proposed organotin compounds of the type:
R.sub.n n --Sn--X.sub.4-n
wherein
R stands for a radical selected from the group consisting of alkyl, aryl,
hydroaromatic or heterocyclic radicals, X for the radical of an ester of a
mercapto alcohol having from two to four carbon atoms with an aliphatic
aromatic or hydroaromatic dibasic acid containing from six to twelve
carbon atoms, and n for an integral number from 1 to 3.
In this case, the alcohol can be esterified with a dicarboxylic acid,
producing products having the type formulae:
##STR7##
Ramsden U.S. Pat. No. 2,885,415 patented May 5, 1969 suggested organotin
compounds derived from mercaptoalcohols in which each mercaptyl hydrogen
is replaced by a bond to an organotin group, the hydroxyl hydrogen either
remaining intact or also being replaced by bonds to the same or other
organotin groups. These compounds are defined by the formula:
##STR8##
wherein
n is 1, 2 or 3; R is a radical selected from the group consisting of alkyl,
alkenyl, alkynyl, aryl and aralkyl groups; R' is selected from the group
consisting of aliphatic and aromatic radicals, and m is a number from 0 to
4-n. R' may be derived from any mercaptoalcohol wherein the mercapto group
is not inactivated by molecular configuration, such as
beta-mercaptoethanol; 3-mercaptopropanol-1; 2-mercaptopropanol-1;
1-mercaptopropanol-2; 2 (or 3 or 4) mercapto-n-butanol-1; o-(or m- or p-)
mercaptobenzyl alcohol; etc.
Dorfelt and Lorz U.S. Pat. No. 3,442,852 patented May 6, 1969 proposed
organotin stabilizers obtained by reacting an organotin halide having one
hydrocarbon group with a mixture of an alkali metal sulfide and an
aliphatic alkali metal mercaptide, or an alkali metal salt of a saturated
or unsaturated mono or polycarboxylic acid. The products are complex
mixtures composed of one or more of the following materials:
##STR9##
Products with three and more tin atoms linked by sulfur bridges may also
form, for example, compounds of the formula:
##STR10##
In the above formula R means the hydrocarbon radical which is directly
bound to the tin atom via a carbon atom and R' is the alkyl radical of the
mercaptan. Analogous compounds in which --S--R' of the above formulae is
replaced by --O--CO--R' are obtained by reacting alkyltin halide, alkali
metal sulfide and alkali metal salts of carboxylic acids.
Molt U.S. Pat. No. 3,931,263 patented Jan. 6, 1976 proposed a new method of
preparing organotin mercaptides based on the reaction of organotin
sulfides with active organic halides in the presence of water. A complex
series of reactions is described as follows:
##STR11##
wherein:
R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, and R.sub.6 are alkyl, usually
of one to twenty carbon atoms, cycloalkyl, usually of five to six carbon
atoms in the ring, alkenyl, usually of two to twenty or more, frequently
three to eighteen carbon atoms, aryl, usually phenyl or alkyl phenyl
having one to four carbon atoms in the alkyl group, or aralkyl, usually of
seven carbon atoms (R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, and
R.sub.6 preferably are methyl);
##STR12##
where R.sub.14 is hydrogen or methyl;
R.sub.11 is defined as R.sub.1 ;
R.sub.7 is alkyl usually of one to twenty carbon atoms, cycloalkyl usually
having five to six carbon atoms in the ring, alkenyl, usually of two to
twenty carbon atoms, more commonly three to eighteen carbon atoms, or
aralkyl, usually of seven carbon atoms:
R.sub.12 is alkyl, usually of one to nineteen carbon atoms, or alkenyl
usually of two to seventeen carbon atoms;
X is a halogen of atomic weight 35 to 80, i.e., chlorine or bromine;
n is an integer of 1 or 2; and
m is an integer of 2 to 3.
Molt acknowledges that many of the products prepared by this process are
old. Thus, Leistner U.S. Pat. No. 2,641,596 discloses some of the
nonchlorine-containing compounds prepared by reaction (3). Brecker U.S.
Pat. No. 3,595,931 shows many compounds which can be prepared from the
compounds made by reaction (1). Hoye U.S. Pat. No. 3,542,825 discloses
many compounds prepared by reactions (2) and (4) as does the similar
British Pat. No. 1,117,652. Wowk U.S. Pat. No. 3,665,025 and British Pat.
No. 1,297,550 disclose some of the compounds prepared by reaction (4) as
well as compounds somewhat similar to those prepared in reaction (1).
German Offenlegungsschrift No. 2,503,554 published Sept. 11, 1975 describes
the preparation of various methyltin thioethers including methyltin
thioglycolates and thioglycolate sulfides.
British Pat. No. 759,382 published Oct. 17, 1956 describes condensation
products of hydrocarbontin compounds with mercapto alcohol esters, defined
by the formula:
R.sub.n Sn(SR.sup.1 OR.sup.11).sub.4-n
wherein
n is 1, 2 or 3;
R is an alkyl, alkenyl, alkynyl, aryl or aralkyl radical;
R.sup.1 is an alkylene or arylene radical, and R.sup.11 is an acyl group.
All the valences of Sn not satisfied by R groups are joined to S atoms.
The organotin sulfides are described in U.S. Pat. No. 2,746,946 to Weinberg
et al, dated May 22, 1956. Polymeric organotin sulfides having a high
proportion of tin and sulfur by weight have also been suggested. Examples
of such materials are given in U.S. Pat. No. 3,021,302 to Frey, dated Feb.
13, 1962, which discloses polymeric condensation products of hydrocarbon
stannonic acid, hydrocarbon thiostannonic acid and co-condensation
products of these materials. However, all of these materials have suffered
from one or another failing, which until now has prevented their coming
into general commercial use.
Dutch Pat. No. 6700014, published July 4, 1967, and referring to U.S.
applications Ser. Nos. 517,967 filed Jan. 3, 1966, and 531,805 filed Mar.
2, 1966, describes combinations of monoalkyltin sulfides with
trisubstituted hindered phenols, and optionally, in addition, with
organotin mercapto carboxylic acids, mercapto carboxylic acid esters, or
mercaptides. The purpose of the addition of the phenol is evidently to
avoid the deleterious properties of the organotin sulfide, and the further
addition of the organotin mercaptide, mercapto acid or mercapto acid ester
supplements the effect of the phenol and of the organotin sulfide in this
regard.
Similar disclosures of polymeric organotin compounds, which generally
include a chain of tin atoms connected through oxygen or sulfur atoms, are
set out in U.S. Pats. No. 2,597,920, dated Apr. 15, 1962; No. 2,626,953,
dated Jan. 27, 1953; No. 2,628,211, dated Feb. 10, 1953; No. 2,746,946,
dated May 22, 1956; No. 3,184,430, dated May 18, 1965; and No. 2,938,013,
dated May 24, 1960.
U.S. Pat. Nos. 3,078,390, 3,196,129 and 3,217,004 describe a series of
thioacetal and thioketal organotin carboxylate salt stabilizers which can
be prepared in situ by the reaction of thioacetal and thioketal carboxylic
acids with dihydrocarbontin oxides or sulfides, or the corresponding
monohydrocarbon or trihydrocarbontin compounds.
U.S. Pat. Nos. 3,565,930 and 3,565,931, both patented Feb. 23, 1971, and
No. 3,817,915, patented June 18, 1974, have suggested that the organotin
mercaptocarboxylic acid esters are the recognized standard for judging
other organotin stabilizers, and considered that the way to improve upon
these stabilizers was to increase the amount of tin and sulfur in the
molecule. Accordingly, organotin mercaptocarboxylic acid ester sulfides
were proposed, having a relatively high concentration of tin, within the
range from about 18 to about 35% tin, and from about 10 to about 25%
sulfur.
These organotin mercapto acid ester sulfides are defined as organotin
compounds having organic radicals linked to tin only through carbon,
mercapto sulfur, and sulfide sulfur groups, and have the general formula:
##STR13##
n is an integer from one to two. m is the number of COOR.sub.1 groups, and
is an integer from one to four.
x is an integer from zero to one.
R is a hydrocarbon radical having from about one to about eighteen carbon
atoms, and preferably from four to eight carbon atoms.
R.sub.1 is an organic group derived from a monohydric or polyhydric alcohol
of the formula R(OH).sub.n4, where n.sub.4 is an integer from one to about
four, but is preferably one or two.
R.sub.2 is R or S (COOR.sub.1).sub.m.
is a bivalent alkylene radical carrying the S group in a position alpha
or beta to a COOR.sub.1 group, and can contain additional free carboxylic
acid, carboxylic ester, or carboxylic acid salt groups, and mercapto
groups. The radical has from one to about five carbon atoms.
Kauder, U.S. Pat. No. 3,632,538, patented Jan. 4, 1972, provides
particularly effective polyvinyl chloride resin stabilizer compositions
having a relatively high concentration of tin, within the range from about
20 to about 35% Sn, and a relatively high concentration of sulfur, within
the range from about 10 to about 25% S, and comprising (a) an organotin
.alpha.- or .beta.-mercapto carboxylic acid ester, and (b) an organotin
sulfide.
The organotin sulfides contain groups linked to tin only through carbon,
and a sulfide sulfur group, .dbd.S, wherein the sulfide sulfur valences
are linked to the same tin atom or to different tin atoms. Each compound
contains per tin atom one or two hydrocarbon or heterocyclic groups linked
to tin through carbon. For best results, Kauder states, and to obtain a
synergistic stabilizing effectiveness, at least one of the compounds of
the combination of this invention should contain only one hydrocarbon
group per tin atom, linked to tin through a carbon atom. This combination
generally improves the initial color of a resin composition during
heating, i.e., during the first thirty minutes of a heat test, and can
also improve the long-term stability before final charring.
It has also been suggested that combinations of monoalkyltin and dialkyltin
mercapto compounds are superior to the mono- or the dialkyltin mercapto
compounds alone. Weisfeld U.S. Pat. Nos. 3,640,950 and 3,925,309 and
Brecker U.S. Pat. No. 3,787,357 disclose various combinations of this
type, but they are not however as effective in inhibiting the development
of an early discoloration during the first fifteen minutes of heating.
Kugele, U.S. Pat. No. 4,062,881, patented Dec. 13, 1977, provides
monoorganotin and/or diorganotin mercaptoalkyl carboxylate monosulfides
and/or poly sulfides useful as stabilizers for improving the resistance to
deterioration of vinyl chloride polymers (e.g., vinyl chloride resins)
when heated at 350.degree. F. having at least two tin atoms linked
together only through sulfide sulfur and having tin atoms linked to said
tin atoms one to two hydrocarbon groups (e.g., alkyl, aryl, cycloalkyl,
aralkyl or alkenyl having from one to twenty carbon atoms), and linked to
the tin through carbon, at least one mercaptoalkyl carboxylic acid ester
group linked to tin through the sulfur of the mercaptoalkyl group, the
organotin compound having an amount of tin within the range from 10 to 42%
by weight and an amount of sulfur within the range from 8 to 42% by
weight.
The compounds are said to have the formula:
##STR14##
where
R is hydrocarbyl, e.g., alkyl, aryl, cycloalkyl, aralkyl or alkenyl and R
usually has one to twenty carbon atoms, R.sub.19 is R or
##STR15##
where
Z is a polyvalent alkylene or hydroxyalkylene radical of at least two
carbon atoms and usually not over twenty carbon atoms, the valence of Z
being m+1, R.sub.10 is hydrogen, alkyl, aryl, aralkyl, cycloalkyl,
aralkenyl, alkenyl having up to 3 ethylenic double bonds, hydroxy-alkyl,
hydroxy-alkenyl or --R.sub.14 COOR.sub.23, where R.sub.14 is
(CH.sub.2).sub.p, phenylene or --CH.dbd.CH-- where p is 0 or an integer up
to 8 and R.sub.23 is alkyl of one to twenty carbon atoms, cycloalkyl of
five to six carbon atoms, alkenyl of two to twenty carbon atoms, aryl,
e.g., phenyl or tolyl or benzyl. R.sub.10 can have one to nineteen carbon
atoms or more when it is a hydrocarbon or hydroxy-hydrocarbon group, m is
the number of OOCR.sub.10 groups, m is an integer of 1 to 3, n is an
integer of 1 to 2 and x is 1 to 10, usually 1 to 4.
In addition to these compounds, there can also be employed overbased tin
compounds by reacting a compound of the formula:
##STR16##
where
R.sub.24 is defined as R.sub.9 in an amount of up to 2 moles per available
carboxyl group with such tin sulfides. The "overbased" product can be
obtained simply by dissolving the dihydrocarbyltin oxide in the tin
mercaptoalkyl carboxylic acid ester sulfide, for example.
In preparing these compounds, numerous processes can be employed. The
reaction can be carried out at room temperature to 100.degree. C., usually
at 25.degree. to 50.degree. C. The reaction is usually carried out with
water as a solvent, regardless of the procedure employed. There can also
be employed water-immiscible organic solvents, e.g., aliphatic and
aromatic hydrocarbons, e.g., hexane, octane, benzene, toluene, xylene,
aliphatic carboxylic acid esters, e.g., butyl acetate, propyl propionate,
methyl valerate. The proportions of solvent are not critical and can vary
widely.
Illustrative procedures include:
PROCEDURE 1
This follows the general procedure of Kauder and Brecker, Pat. Nos.
3,565,930 and 3,565,931, except that sodium monosulfide, sodium disulfide,
sodium trisulfide, sodium tetrasulfide, ammonium monosulfide, ammonium
disulfide, ammonium trisulfide or ammonium tetrasulfide is reacted with
the appropriate tin compound and appropriate --SH containing compound or
compounds as indicated above, for example.
PROCEDURE 2
In this procedure, the sodium mono or polysulfide (or potassium mono or
polysulfide), water, mercapto containing ester, hydrocarbon if desired and
ammonium hydroxide are charged into a reactor and an aqueous solution of
an alkyltin halide slowly added, e.g., at 25.degree. to 35.degree. C. The
mixture is then heated, e.g., to 50.degree. C., the layers separated, and
the product is washed and dried.
PROCEDURE 3
In this method the mercapto containing ester, water, organic solvent and
ammonium hydroxide are charged into a flask and then two solutions (A)
alkyltin chloride and (B) alkali metal mono or polysulfide are added
simultaneously. The product is then separated, washed and stripped.
PROCEDURE 4
This is the same procedure as Procedure 3 except that NaHCO.sub.3 is
substituted in the same molar amount for the ammonium hydroxide.
PROCEDURE 5
In this procedure the alkyltin chloride, water and ammonium hydroxide are
charged into a flask and then there are added simultaneously the mercapto
containing ester and alkali metal mono or polysulfide.
PROCEDURE 6
This method comprises charging the mercapto containing ester, water and
ammonium hydroxide into a reactor and then adding an alkyltin chloride
followed by an alkali metal polysulfide or monosulfide slowly at
30.degree. C. After heating to 45.degree. C., the product was separated,
washed and stripped.
In accordance with this invention, stabilizer mixtures for extrudable rigid
polyvinyl chloride resin compositions are provided, composed of a mixture
of a monoalkyltin 2-acyloxyethylmercaptide, of a dialkyltin
2-acyloxyethylmercaptide, or both, with a dialkyltin and/or monoalkyltin
sulfide. These stabilizer mixtures are remarkably effective in inhibiting
the development of early discoloration when the composition is heated at
375.degree. F. during the first five or ten minutes up to approximately
twenty or even thirty minutes of heating, even in the presence of
substantial proportions of lubricating metal carboxylate salts, such as
calcium stearate. This effect is particularly remarkable in view of the
fact that such lubricants and particularly calcium stearate impart a
yellow discoloration initially to the resin composition, even before
heating is begun. In the presence of the stabilizer systems of the
invention, however, this initial yellow discoloration does not appear, and
the development of such discoloration is inhibited for at least the first
ten to twenty minutes of heating.
The monoalkyltin 2-acyloxyethylmercaptides are defined by the formula:
R.sub.1 Sn--(SCH.sub.2 CH.sub.2 OR.sub.4).sub.3. 1.
The dialkyltin 2-acyloxyethylmercaptides are defined by the formula:
(R.sub.1).sub.2 Sn--(SCH.sub.2 CH.sub.2 OR.sub.4).sub.2. 11.
In these formulae R.sub.1 is an aliphatic hydrocarbon group having from one
to about twenty-six carbon atoms in a straight or branched chain.
R.sub.4 is H or
##STR17##
not more than one R.sub.4 being H.
R.sub.2 and R.sub.3 are a hydrogen atom or an aliphatic hydrocarbon group
which can be either saturated or ethylenically unsaturated, and has from
about one to about twenty carbon atoms. It is apparent from formulae I and
II that the esterifying carboxylic acid in the 2-acyloxyethylmercaptide
group has an unsubstituted or monosubstituted .alpha.-carbon, and
branching can occur in the R.sub.2 group. Aliphatic acids having two
substituents on the .alpha.-carbon and aromatic acids do not readily
esterify the alcohol hydroxyl of the 2-mercaptoethanol groups --SCH.sub.2
CH.sub.2 O--.
If a mixture of monoalkyltin and dialkyltin 2-acyloxyethylmercaptides is
used, the relative proportions thereof are important to stabilizing
effectiveness. This proportion is expressed as tin content of the total
tin present in the mixture. From about 30 to about 90%, and preferably
from about 45 to about 75%, of the total tin should be monoalkyltin
2-acyloxyethylmercaptide, while the remainder, from about 10 to about 70%,
and preferably from about 25 to about 55%, of the total tin is dialkyltin
2-acyloxyethylmercaptide.
The monoalkyltin and dialkyltin 2-acyloxyethylmercaptides are known
compounds, and can be prepared using known procedures. From the standpoint
of ease of preparation, it is convenient if R.sub.1 and R.sub.2 are the
same in monoalkyltin and dialkyltin 2-acyloxyethylmercaptides, since in
this event, mixtures of the monoalkyltin trihalide and dialkyltin
dihalide, such as RSnCl.sub.3 and R.sub.2 SnCl.sub.2, the intermediates
used in the preparation of the stabilizer, can easily be made in a single
reaction step, either from stannic tetrachloride and excess dimethyltin
dichloride to give monomethyltin trichloride and dimethyltin dichloride,
or from tetraalkyltin R.sub.2 Sn (where R is an alkyl higher than methyl)
to give monoalkyltin trichloride mixed with dialkyltin dichloride.
The alkyltin sulfides useful in combination with these organotin
2-acyloxyethylmercaptides contain one or two alkyl groups linked to tin
through carbon, and a sulfide sulfur group, .dbd.S, wherein the sulfide
sulfur valences are linked to the same tin atom or to different tin atoms.
Each compound contains per tin atom one or two hydrocarbon groups linked
to tin through carbon.
One type of dialkyltin sulfides useful in this invention can be defined by
the formula:
R.sub.2 SnS 111
wherein
R is an alkyl group linked to tin through carbon, and containing from one
to about eight carbon atoms. The atomic ratio of sulfur to tin is 1:1.
Another group of organotin sulfides of this invention are polymers which
can be illustrated by the formulae:
##STR18##
in which
R is alkyl as above and each tin atom is linked to three sulfur atoms and
each sulfur is linked to two tin atoms, and x is a number from one to
about 100.
Another type has the recurring group
##STR19##
where n is the number of units in the chain, and ranges up to 100 and
more.
Another way of defining the R.sub.2 SnS type is:
##STR20##
The R's are as defined above. The above formulae are not intended to limit
the structure of the compound in any way. The structures can be straight
chain, branched chain, cyclic, or any combination thereof.
The R alkyl groups in the above formulae have from one to eight carbon
atoms. The preferred R groups are alkyl groups having from four to eight
carbon atoms.
These organotin sulfides are well known and can be prepared by a number of
procedures described in earlier references which are known to the art. For
example, hydrogen sulfide can be bubbled at about 40.degree. C. into a
slurry of hydrocarbontin oxide in water or an organic solvent (such as
methanol, acetone, or toluene). The insoluble oxide is converted to a
solution or dispersion of the sulfide and the reaction is terminated when
the entire system is liquefied.
Another useful technique is the displacement of hydrocarbontin halide (e.g.
Bu.sub.2 SCl.sub.2) by an aqueous alkali metal sulfide or ammonium
sulfide. Hydrocarbontin sulfides also can be prepared from the interaction
of hydrocarbontin halide with other sulfur compounds than sulfides, such
as sodium thiosulfite and ammonium polysulfide. These reactions provide
unstable intermediates that decompose to the hydrocarbontin sulfide plus
another product characteristic of the particular starting materials, e.g.
alkali metal sulfide or free sulfur.
All the above preparative methods can be summarized in the transformations
below, where the n-butyltin compounds shown are representative of the
entire class of organotin compounds:
(Bu.sub.2 SnO).sub.m +mH.sub.2 S.fwdarw.m/n (Bu.sub.2 SnS).sub.n +mH.sub.2
O
Bu.sub.2 SnCl.sub.2 +Na.sub.2 S.fwdarw.1/n (Bu.sub.2 SnS).sub.n +NaCl
2BuSnCl.sub.3 +3Na.sub.2 S.fwdarw.1/x ((BuSn).sub.2 S.sub.3).sub.x +6NaCl
Bu.sub.2 SnCl.sub.2 +Na.sub.2 S.sub.2 O.sub.3 +NaOH.fwdarw.1/n (Bu.sub.2
SnS).sub.n +2NaCl+NaHSO.sub.3
Bu.sub.2 SnCl.sub.3 +(NH.sub.4).sub.2 S.sub.4 .fwdarw.1/n (BuSnS).sub.n
+2NH.sub.4 Cl+2S
When these preparations are carried out in an aqueous medium, a small
proportion of the sulfur atoms in the hydrocarbontin sulfides are replaced
by oxygen atoms, resulting in sulfur-deficient products having average
compositions represented by the empirical formulae:
(R.sub.2 SnS.sub.p O.sub.1-p)
and ((RSn).sub.2 S.sub.r O.sub.2-r).sub.x, where p is at least 0.85 and r
is at least 1.5.
In the stabilizer composition of this invention these sulfides are fully as
effective as the pure oxygen-free sulfides, and wherever alkyltin sulfides
are mentioned the term is intended to include both the pure compounds and
the sulfur-deficient preparations.
There are many other procedures for the preparation of these compounds. The
above list of procedures is not intended to be exhaustive. Alkyltin
sulfides prepared by any other procedure would also be useful in the
present combination.
The R alkyl groups linked to tin through carbon can, for example, be
methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tert-butyl,
sec-butyl, amyl, hexyl, octyl, 2-ethylhexyl and isooctyl.
Preferred examples of organotin sulfides are dipropyltin sulfide,
dibutyltin sulfide, di-n-pentyltin sulfide, dihexyltin sulfide,
di-2-ethylhexyltin sulfide, di-(isobutyl)tin sulfide,
di-(octyltin)sulfide, dimethyltin sulfide, di-(isoamyl)tin sulfide,
diisohexyltin sulfide, and 2-ethyl butyltin sulfide; butyltin
sesquisulfide ((BuSn).sub.2 S.sub.3).sub.x (x=from 1 to 100 or higher),
hexyltin sesquisulfide, isooctyltin sesquisulfide, heptyltin
sesquisulfide, n-octyltin sesquisulfide, sec-butyltin sesquisulfide,
propyltin sesquisulfide, isoamyltin sesquisulfide, and 2-ethylhexyltin
sesquisulfide.
The above compounds can have any degree of polymerization falling within
the above formula.
Components of these stabilizer compositions can be selected so as to have a
relatively high concentration of tin, up to about 35% Sn, and a relatively
high concentration of sulfur, up to about 25% S. Since these stabilizer
compositions are remarkably effective in low concentrations, i.e., working
with modest quantities of tin and sulfur relative to vinyl chloride
polymer being stabilized, it is also possible to formulate stabilizer
compositions having modest tin and sulfur concentrations as low as about
6% tin and 4% sulfur by selection of active components and inert diluents
where necessary.
The following mixtures of alkyltin 2-acyloxyethylmercaptides and alkyltin
sulfides are typical of those coming within the invention:
__________________________________________________________________________
Alkyltin 2-acyloxyethylmercaptide Dialkyltin Sulfide
__________________________________________________________________________
1. iso-C.sub.4 H.sub.9Sn[SCH.sub.2 CH.sub.2OOCC.sub.2 H.sub.5 ].sub.3
(n-C.sub.4 H.sub.9).sub.2 Sn | | |
