Note: Descriptions are shown in the official language in which they were submitted.
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ALKYL-THIO-GLYCOLATE PVC STABILIZERS
] WITH ADDED AROMATIC ETHER ALCOHOL TO PREVENT
PRECIPITATION
The present invention relates to liquid
stabilizer systems for vinyl halide resin compositions,
to resinous compositions stabilized therewith, and to
methods of preparation of such products. More
particularly, it relates to liquid stabilizer systems
including a tin-organo sulfur compound and an additive
therefor.
It is well known that vinyl halide resins
undergo undesirable changes when they are exposed to
heat or to light, and that these changes lead to
discoloration and to deterioration of the mechanical
properties of compositions containing such resins.
Since elevated temperatures are required f_or the
processing and/or formulation of compositions containing
these resins, and since the resins are exposed to heat,
to light, or both, when they are subsequently used, it
is necessary to incorporate in the vinyl halide
compositions stabilizers that will inhibit or prevent
discoloration, or loss of physical integrity, when they
are exposed to such conditions.
Organo tin compounds that contain sulfur have
long been recognized as highly effective heat
stabilizers for vinyl halide resin compositions.
Examples include organo tin ethanol mercaptides such as
those disclosed in U.S. Patent No. 4,059,562; and
monomeric tetra-functional organotin mono- or di-alkyl
di- or tri- (alkyl thioglycolate) or (mercapto alkyl
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carboxylate) compounds such as disclosed in U.S. Patent
1
No. 5,032,634.
A thorough historical review of organotin and organotin-sulfur compounds in
stabilizing polyvinyl
chloride compositions appears in the "Plastics Additives
and Modifiers Handbook" (J. Edenbaum, Van Nostrand
Reinhold, 1992, at pp. 309-326, Chapter 19: Dworkin,
"Polyvinyl chloride processing stabilizers: tin and its
derivatives".
Compounds of the formula (2)
(R')aSn(-SCH,,COOR2)4_d (2)
wherein the substituents R' and R 2 and the subscript a
are as defined herein, are useful liquid stabilizers for
vinyl halide resins, but have long been known to exhibit
a tendency to form precipitates on standing. The
precipitates generally have a higher tin content than
the liquid product, but are considerably less effective
as stabilizers. Thus, the formation of the precipitates
represents an undesirable economic loss, in the
stabilization efficiency which is lost, in the cost of
the product which is lost to the precipiatate, as well
as in the input of material and energy necessary to
attempt to redissolve or otherwise handle the
precipitates. There thus remains a need to formulate
liquid stabilizers for vinyl halide compositions,
including one or more components of the above mentioned
formula (2), which do not exhibit a tendency to form
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1 precipitates and yet which otherwise can be formulated
effectively into vinyl halide resin compositions.
The present invention is directed to a liquid
stabilizer composition for poly(vinyl halide)
compositions which exhibits a reduced tendency to form
precipitate on standing, comprising
(a) a water-insoluble aromatic ether alcohol
of formula (1)
Ar-O- (CHZCH(X)O)nH (1)
wherein Ar is aryl containing 6 to 10 carbon atoms;
X independently at each occurrence is
-H or -CH3; and
n is i to 5; provided that when X at each
occurrence is -H, then n is 1; and
(b) one or more thioglycolates of formula (2)
(R')aSn(-SCH1COOR2)4_a (2)
wherein R' independently at each occurrence is straight
or branched alkyl containing 1 to 4 carbon atoms;
a is 1 to 2;
R' independently at each occurrence is straight
or branched alkyl containing 7 to 16 carbon atoms;
optionally admixed with one or more tin compounds
selected from the group consisting of monoalkyl tin
sulfides, dialkyl tin sulfides, monoalkyl tin
carboxylates, and dialkyl tin carboxylates, in which
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1 group each alkyl substituent independently is straight
or branched and contains 1 to 4 carbon atoms.
The components (a) and (b) are present in such
amounts relative to each other that the composition
containing those components is a liquid which is stable
against formation of precipitates on standing, even
prolonged standing.
The present invention is further directed to
vinyl halide resin compositions containing such a
stabilizer composition in an amount thereof effective to
impart to the vinyl halide resin increased stability
against heat-mediated degradation of the polymer
composition.
Still further, the present invention is
directed to a method of prolonging the stability against
precipitate formation of a liquid stabilizer composition
which comprises one or more thioglycolates of the
foregoing formula (2), comprising admixing into said
composition one or more compounds of the foregoing
formula (1) in an amount thereof effective to prolong
the stability against precipitate formation of said
admixture.
One of the essential components of the liquid
stabilizer compositions of the present invention is one
or more compounds corresponding to formula (2), which
compounds are generally ternied thioglycolates. While
the advantages of the present invention can be realized
in compositions containing but one compound
corresponding to formula (2), the advantages are quite
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evident in compositions containing more than one
thioglycolate of the formula (2) in the stabilizer
= composition.
Referring to formula (2), the group R' is
= straight or branched alkyl containing 1 to 4 carbon
atoms. R' is preferably methyl or n-butyl. The group RZ
is straight or branched alkyl containing 7 to 16 carbon
atoms, and preferably straight or branched alkyl
containing 8 to 10 carbon atoms. Particularly preferred
R2 groups include ethylhexyl such as 2-ethylhexyl, and
more generally isooctyl.
In formula (2), a is 1 or 2. However,
compounds wherein a is 1 and compounds wherein a is 2
are believed to have somewhat different effects on
polymer compositions into which they are compounded;
that is, compounds wherein a is 1 are believed to
improve early color stability but to exhibit shorter
longer-term stability, whereas compounds wherein a is 2
conversely exhibit better longer-term stability. Thus,
it is preferred to use stabilizers which contain blends
of two or more thioglycolates of the formula (2), such
that the average value of a, the number of alkyl
(preferably methyl) substituents, is between 1 and 2,
corresponding to about 19:1 to 1:19 by weight. As will
be pointed out below, the blends are advantageously
prepared by suitable adjustment of the e.g. alkyl tin
chloride and thioglycolate reactants.
The liquid stabilizer compositions can, and
preferably do, contain one or more alkyl tin sulfides,
particularly monoalkyl tin sulfide, dialkyl tin sulfide,
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or both, and can contain one or more monoalkyl tin
1
carboxylates alone or with any mono-or dialkyl tin
sulfide. The alkyl moiety can be straight or branched
and contains 1 to 4 carbon atoms. Preferably the alkyl
moiety is methyl, or n-butyl. More preferably, the
liquid stabilizer composition contains both monoalkyl
tin sulfide and dialkyl tin sulfide.
The monoalkyl tin sulfide, dialkyl tin
sulfide, or both, and/or the monoalkyl and/or dialkyl
tin carboxylate, as the case may be, when present, are
in admixture with the one or more thioglycolates of
formula (2). By "admixture" is meant any combination
regardless of whether the components are present as an
exclusively physical mixture devoid of chemical (i.e.
covalent or ionic) bonding therebetween, or are
completely chemically bonded (i.e. covalently and/or
ionically) amongst each other; or exist partially as a
physical mixture and partially as chemically bonded
species. The determining criterion is simply whether
the various moieties correspond to the empirical
formulas and relationships set forth herein.
Dialkyltin sulfides can be represented by the
formula (R') SnS. Dialkyltin carboxylates can be
represented by the formula (R') ,Sn (OOCR') ,. Monoalkyltin
sulfides can be represented by the formula (R'Sn)2S3.
Monoalkyltin carboxylates can be represented by the
formula (R' ) Sn (OOCR2),. In these formulas each
occurrence of R' is as defined above.
In blends including one or more thioglycolates
of formula (2) and a dialkyltin sulfide and/or
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1 monoalkyltin sulfide, the ratio of equivalents of
thioglycolate to equivalents of sulfide can range from
4:1 to 1:2, preferably from 2:1 to 1:1. In blends
including one or more thioglycolates and a dialkyltin
carboxylate and/or monoalkyltin carboxylate, the ratio
of equivalents of thioglycolate to equivalents of
carboxylate can range from 19:1 to 1:2, preferably from
2:1 to 1:1.
Such blends can be prepared by blending the
individual components prepared by conventional methods.
It is frequently convenient to prepare the components of
a blend simultaneously in the same reaction vessel
starting from a mixture of alkyltin precursors, which
are usually alkyltin halides such as dialkyltin
dihalides and monoalkyltin trihalides.
In general, compounds of-the formula (2) can
be prepared by reacting monoalkyltin trihalide and/or
dialkyl tin dihalide, in the presence of water with an
alkaline solution such as ammonium hydroxide, potassium
hydroxide, or sodium hydroxide solution, and reacting
this intermediate mixture with the alkyl thioglycolate,
recovering the product as a hydrophobic liquid phase
separating from an aqueous brine phase in a decanting
vessel such as a separatory funnel, and stripping and
filtering undesirable side products.
Similarly, a blend including one or more
thioglycolates and a monoalkyltin sulfide and/or
dialkyltin sulfide can be prepared by reacting
monoalkyltin trihalide and/or dialkyltin dihalide in the
presence of water with an alkaline solution such as
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ammonium hydroxide, potassium hydroxide, or sodium
hydroxide solution, and reacting this intermediate
mixture with an amount of the alkyl thioglycolate less
than sufficient to convert all the monoalkyltin
trihalide and/or dialkyltin dihalide charged and then
adding a so)ution of a sulfide such as sodium sulfide in
water to convert remaining monoalkyltin trihalide and/or
dialkyltin dihalide to monoalkyltin sulfide and/or
dialkyltin sulfide, and recovering the product as a
hydrophobic liquid phase separating from an aqueous
brine phase in a decanting vessel such as a separatory
funnel. A blend including one or more thioglycolates
and a moiioalkyltin and/or dialkyltin carboxylate can be
prepared by reacting monoalkyltin trihalide and/or
dialkyltin dihalide in the presence of water with an
alkaline solution such as ammonium hydroxide, potassium
hydroxide, or sodium hydroxide solution, and reacting
this intermediate mixture with an amount of the alkyl
thioglycolate less than sufficient to convert all the
monoalkyltin trihalide and/or dialkyltin dihalide
charged, and adding a carboxylic acid and additional
alkaline solution as required to convert remaining
monoalkyltin trihalide and/or dialkyltin dihalide to
monoalkyltin and/or dialkyltin carboxylate, recovering
the product as a hydrophobic liquid phase separating
from an aqueous brine phase in a decanting vessel such
as a separatory funnel.
While the desired final liquid stabilizer
component can be formed by mixing this product with the
aromatic ether alcohol of formula (1), it is preferred
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1 to incorporate the aromatic ether alcohol of formula (1)
during the synthesis of the thioglycolate or
thioglycolate/sulfide admixture.
Preferably, the liquid stabilizer composition
of the present invention is made by adding the aromatic
ether alcohol at the point after the alkyl tin halide
and alkyl thioglycolate components have been added to
the alkaline solution.
In the component of the formula (1)
Ar-O- (CH,CH(X)O)RH (1)
the group Ar can be a monocyclic or bicyclic aryl group
containing 6 to 10 carbons atoms. Preferably, Ar is
phenyl. This compound of formula (1) contains 1 to 5
repeating alkoxy units, and preferably 1 to 2 repeating
alkoxy units. As can be seen, each occurrence of the
substituent X can be hydrogen or methyl, although it is
preferred that each occurrence of the substituent X in a
given compound is the same. The compound of the formula
(1) should be water-insoluble, by which is meant that it
exhibits a solubility of less than 3 grams per 100
milliliters of water.
Compounds of formula (1) can be synthesized in
a straightforward manner by reaction of the
corresponding aryloxy precursor, e.g. phenol, and
alkylene oxide such as ethylene oxide or propylene oxide
whereby the aryl group is attached to one end thereof.
Compounds of the formula (1) which exhibit satisfactory
performance in the compositions of the present invention
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are also commercially available. For instance, ethylene
1
glycol phenyl ether (having the formula C6H5OCZH40H) and
propylene glycol phenyl ether (also termed
1-phenoxy-2-propanol, having the formula C6H5OC3H6OH) are
commercially available as, respectively, "Dowanol EPh"
and "Dowanol PPh" from Dow Chemical Company.
Preferably, the one or more thioglycolates of
the formula (2) and the one or more aromatic ether
alcohols of the formula (1) are present in the liquid
stabilizer composition in amounts such that the ratio by
weight of thioglycolate(s) to aromatic ether alcohol(s)
is from 99:1 to 4:1 and preferably from 30:1 to 7:1.
Satisfactory ratios of aromatic ether
alcohol(s) to thioglycolate(s) in the composition can be
ascertained for any particular formula of the alcohol(s)
and thioglycolate(s) being employed, by formulating a
given composition and assessing its storability, that
is, its tendency to form precipitates upon standing for
a given length of time at a specified temperature.
Without intending to be bound by any
particular explanation of the operation of the
invention, the invention has been observed to exhibit
behavior consistent with the proposition that since the
aromatic ether alcohol is essentially water insoluble,
this insolubility assists in retaining the thioglycolate
component in the stabilizer-product. This behavior
retains the full stabilization capability of the
thioglycolate and simultaneously avoids contamination of
waste water streams generated during the synthesis of
the thioglycolate. In addition, the aromatic ether _
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alcohol appears to contribute uniformity to the organic
phase that is formed, while solubilizing the various
species of the stabilizer composition to form a
homogeneous liquid product. The aromatic ether alcohol
also reduces the water content in the organic phase,
5.thus effectively reducing the time and the severity of
the conditions (e.g. temperature) necessary to dry (e.g.
remove water from) the product. Being able to dry the
product without having to raise its temperature unduly
has the beneficial effect of reducing the extent of
hydrolysis of esters present. Also, notably, the
aromatic ether alcohol contributes long term shelf
stability to the liquid stabilizer product.
Synthesis of the liquid stabilizer composition
in accordance with the present invention exhibits rapid
phase separation, thereby facilitating synthesis and
minimizing the need to remove entrained water. Thus,
the organic (lower) phase formed in the synthesis
generally contains a surprisingly reduced amount of
water on the order of 1 to 3.5%, or less.
The liquid stabilizer compositions of the
present invention are preferably used to advantage in
combination with vinyl halide resins, preferably
polyvinyl chloride resins. The term "polyvinyl
chloride" as used herein is inclusive of any polymer
formed at least in part of the recurring group
(-CHCl-CX,-)P and having a chlorine content in excess of
40%. In this formula, each of the X groups can be
either hydrogen or chlorine, and p is the number of
units in each polymer chain. In polyvinyl chloride
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homopolymers, each of the X groups is hydrogen. Thus,
1
the terms "PVC" and "polyvinyl chloride" include not
only polyvinyl chloride homopolymers but also after
chlorinated polyvinyl chlorides, as well as copolymers
of vinyl chloride in a major proportion with other
copolymerizable monomers in moderate proportion such as
copolymers of vinyl chloride and vinyl acetate,
copolymers of vinyl chloride with maleic or fumaric
acids or esters, and copolymers of vinyl chloride with
styrene. The stabilizer compositions are effective also
with mixtures of polyvinyl chloride in major proportion
with a minor proportion of other synthetic resins such
as chlorinated polyethylene or copolymers of
acrylonitrile, butylene and styrene.
Stabilizer compositions of the present
invention can be used with plasticized polyvinyl
chloride resin compositions of conventional formulation.
Conventional plasticizers well known to those skilled in
the art can be employed such as, for example, dioctyl
phthalate, octyl diphenylphospate, and epoxidized
soybean oil. Particularly useful plasticizers are the
epoxidized esters having from 20 to 150 carbon atoms.
The stabilizer compositions of the present
invention are used in small but effective amounts to
impart heat stability, that is, enhanced resistance to
heat-mediated deterioration of the PVC or other
polyvinyl chloride resin. That is, "heat-mediated
deterioration" includes deterioration which is due to
exposure to excessive heat, as well as deterioration
which is initiated or accelerated by exposure to heat.
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Effective heat stability is afforded generally by adding
about 0.5 to about 5 phr (parts by weight per hundred
parts by weight of resin) of the stabilizer composition.
Preferred amounts of the stabilizer are generally in the
range of about 1 to about 4 phr. The liquid stabilizer
can be compounded into the resin formulation in
accordance with conventional compounding techniques
abundantly familiar to one of ordinary skill in this
art.
The stabilized polyvinyl chloride resin
composition comprising these components can also contain
conventional additional additives such as antioxidants,
lubricity agents, flame retardants, fillers, pigments,
and the like, in relative amounts effective to fulfill
the desired functions of each such ingredient. These
ingredients can be added, if desired, prior to, during,
or subsequent to the step in which the heat stabilizer
composition of the present invention is compounded into
the polyvinyl chloride composition.
Liquid stabilizer compositions prepared in
accordance with the teachings of the present invention
have been found to exhibit little or no precipitation
upon standing at ambient temperature for a year or
longer.
In addition, polyvinyl chloride formulations
prepared with the liquid stabilizer compositions of the
present invention have been found to exhibit not only
notable heat stability, but also superior whiteness
color hold, and long-term dynamic stability.
~
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The invention will be described further in the
following examples, which are intended for illustration
and should not be deemed limiting of the scope of the
present invention.
EXAMPLE 1
Into a 2-liter beaker were charged 154.2 g of
a 75:25 (weight) mixture of monomethyl tin trichloride
and dimethyl tin dichloride, an additional 36.4 g of
dimethyl tin dichloride (the aggregate thus
corresponding to a monomethyl:dimethyl ratio of 60:40)
and 200.0 grams of water.
Then, 265.9 grams of a 20 wt.% sodium
hydroxide solution (1.329 moles NaOH) was added at 60-
65 C followed by 274.5 grams (1.329 moles) of 2-
ethylhexyl thioglycolate (99%). This mixture was
agitated for 30 minutes, following which 27.5 grams of
"Dowanol PPh" propylene glycol phenyl ether was added,
followed by a solution of 51.8 grams (0.3988 moles) of
Na,S(60%) in 200 grams of water. The final aliquot was
added carefully to a final pH of 7Ø The mixture was
transferred to a separatory funnel and allowed to sett_le
for 1-2 hours. The liquid stabilizer formed as a liquid
product beneath the aqueous phase in the separatory
funnel. It was recovered from the funnel and was found
to weigh 431.0 grams. This product was transferred to a
3-neck flask and stripped (of water) at 20 mm pressure
and 105 C. The weight of the product remaining after
the stripping step was 423.1 grams. This corresponds to
a moisture content of 1.9% in the product prior to
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stripping. The stripped product was filtered through a
1
celluosic filter medium and the final product weighed
406.4 grams.
The tin and sulfur contents of this product,
based on the reactants, were 23.1W tin, 10.4% mercaptan
sulfur, and 3.0% sulfide sulfur (i.e. on an equivalents
basis, a ratio of SH:S of about 1.66:1).
EXAMPLE 2
The procedure employed in Example 1 was
carried out with 129.6 grams of a 75:25 (weight) mixture
of monomethyltin trichloride and dimethyl tin
dichloride, an additional 67.1 grams of dimethyl tin
dichloride (bringing the aggregate monomethyl:dimethyl
ratio to 50:50), and 200.0 grams of water, followed by
212.7 grams (1.0635 moles) of sodium hydroxide (20%
solution), 219.6 grams (1.0635 moles) of 2-ethylhexyl
thioglycolate, 27.5 grams of propylene glycol phenyl
ether, and a solution of 69.1 grams (0.5318 moles) of
Na,S in 300.0 grams of water.
The weight of the recovered product was 384.0
grams; the weight following the stripping of water was
377.0 grams. This corresponded to a moisture content of
1.9W in the product before stripping. The final product
obtained after filtration weighed 356.7 grams.
The tin and sulfur contents of this product,
based on the amounts of the reactants, were 26.9% tin,
9.3g mercaptan sulfur, and 4.5W sulfide sulfur (i.e. on
an equivalents basis, a ratio of SH:S of about 1:1).
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EXAMPLES 3-8
Additional compositions containing alkyl tin
thioglycolate, methyl tin sulfides, and 4.0-5.0%
propylene glycol phenyl ether, were made using
procedures similar to that in Example 1. The
compositions, the contents based on reactant amounts,
and the moisture content after settling 1-2 hours
(before stripping of water) were as follows:
Moisture
Monomethyl: SH:S content
Ex. Dimethyl ratio (equiv.) Sn% SH% S%- (1-2hrs.)
3 75:25 1.66:1 22.3 10.6 3.1 1.8
4 50:50 1.66:1 23.7 10.3 3.0 1.8
5 40:60 1.66:1 24.3 10.1 2.95 3.4
6 75:25 1:1 25.4 9.6 4.7 2.4
7 60.40 1:1 26.4 9.5 4.6 1.0
8 40:60 1:1 27.5 9.1 4.4 1.7
Synthesis of these or similar stabilizers, but
omitting any aryl ether alcohol, has been found to
result in products containing 5-10% moisture.
EXAMPLES 9-12
The stability against precipitate formation of
various compositions was evaluated by accelerated aging
tests carried out at 140-150 F. The results are set
forth in the following table:
Ex. Stabilizer composition Observation
9 Dimethyltin bis(2-ethylhexyl
thioglycolate ) ( 80 2 0 ) /
Monomethyltin tris (2-ethylhexyl
thioglycolate) (20 2%)
(A) without additive Precipitate
after 7 days
(B) with 5% propylene Clear without
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glycol phenyl ether precipitate
after 3 weeks
Monomethyltin tris (2-ethylhexyl
thioglycolate) / dimethyltin
bis (2-ethylhexyl thioglycolate)/
monomethyl tin sulfide/dimethyl tin
5 sulfide(approx. 3:1 (wt.)
monomethyltin: dimethyltin and 1:1
(equivs.) 2-ethylhexyl
thioglycolate:sulfide)
(A) without additive Precipitate
after 3
10 months
(B) with approx. 7%- propylene Clear without
glycol phenyl ether precipitate
after 3
months
11 Dibutyl tin bis(2-ethylhexyl
thioglycolate)
(A) without additive Precipitate
after 7 days
(B) with 5% propylene glycol Clear without
phenyl ether precipitate
after 3 weeks
12 Dibutyl tin bis(2-ethylhexyl
thioglycolate) (50%)/dibutyl
tin dilaurate (50%)
(A) without additive Precipitate
after 2
weeks
(B) with 2.5% propylene Precipitate
glycol phenyl ether after 32
days
These results demonstrate that the presence of
the aryl ether alcohol in the stabilizer compositions
substantially reduces the tendency of the composition to
form precipitates.
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EXAMPLES 13
PVC formulations containing various stabilizers
were made in accordance with the following compositions, and
were tested for color stability in a "dynamic Brabender"
procedure wherein the PVC formulation was heated in a
continuous mixer and torque rheometer and periodically
sampled to monitor color changes and melt viscosity.
Siding Formulation
PVC homopolymer 100.0 (all in parts
by wt.)
("*Geon 27", Geon Corp)
Acrylic copolymer processing aids
("K-125", Rohn & Haas) 0.4
("*K-175", Rohn & Haas) 1.0
Acrylic polymer blend, impact
modifier 7.0
("KM-334", Rohn & Haas)
Calcium stearate 1.2
Paraffin wax (m.p. approx. 165 F) 1.0
Titanium dioxide 10.0
Stabilizer 1.5
*Trade-mark
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Clear PVC Formulation
PVC homopolymer ("*Oxy 225", Oxy Chemical Corp.) 100.0
Diisooctyl phthalate 5.0
Acrylic copolymer processing aid
("*K-120N", Rohn & Haas) 1.5
Oxidized polyethylene ("*AC 629A", Allied-Signal) 0.2
Stabilizer 1.5
Samples of the siding and clear formulations
containing, in turn, each of the stabilizers described in
Examples 1, 2, 4, 5, 7 and 8 were found to be equivalent or
superior to the formulations containing different
stabilizers (not containing the aryl ether alcohols) in
whiteness, color hold and long-term dynamic stability.
Thus, it can be seen that the compositions of the present
invention are effective stabilizers in addition to their
virtues in exhibiting a reduced tendency to form precipitate
on standing.
30
*Trade-mark
