Extraction resistant polyolefin stabilizer

An extraction resistant, smoke resistant linear polymeric phenolic antioxidant containing sulfonic acid groups or salts thereof in at least a portion of the recurring phenolic ring groups.

BACKGROUND OF THE INVENTION 
It is well known to stabilize plastics, e.g. olefin polymers, against 
degradation due to heat and oxidation by incorporating into the polymers a 
stabilizing amount of hindered phenolic antioxidants. However, such 
antioxidant stabilizers have not proved entirely satisfactory for many end 
uses. This is true because of the relative ease with which they can be 
extracted from the polymers by nongaseous fluids. For example, a plurality 
of individual plastic insulated wire are encased in plastic tubing to form 
underground cables. The void spaces within the tubing are filled with a 
very high viscosity liquid such as petrolatum or petroleum jelly. A 
serious disadvantage to the use of plastic materials as insulators for 
this application has been the fact that at least a portion of the 
stabilizing amount of the antioxidants incorporated into the plastic 
insulation is extracted into the petrolatum. This causes a rapid 
deterioration of the insulation due to the combined effects of heat and 
oxidation. 
A prior art solution to this extraction problem involves the use of novolac 
resins of high molecular weight as primary antioxidants. These 
thermoplastic resins, which are condensation products of a phenol with an 
aldehyde, do exhibit much greater extraction resistance than non-polymeric 
phenolic antioxidant or novolacs of relatively low molecular weight, e.g. 
those having on the average 20 or less phenolic ring groups in the 
molecular structure. However, commercialization of these high molecular 
weight novolacs as stabilizers have not been altogether successful. One 
reason therefor is that resins stabilized with novolacs in general tend to 
smoke excessively and even seriously degrade at temperatures often 
encountered in extrusion of the resin, e.g. in the extrusion of wire or 
cable coatings. 
Another serious disadvantage to the use of plastic materials, e.g. 
polyolefin resins, as insulation for wire and cables is the fact that the 
degradation of the polymer is accelerated by the presence of copper and 
alloys of copper. Prior art methods to solve this problem have resulted in 
a combination of the polyolefin resin with the primary hindered phenolic 
antioxidant and a copper deactivator of chelating agent such as organic 
hydrazide or hydrazine compounds. However, these methods do not solve the 
problem when the resulting compositions are contacted with petrolatum. In 
fact, test results have indicated that the deactivation due to copper is 
often accelerated even further after the polymeric material has been 
subjected to extraction with petrolatum. 
It is therefore a primary objective of this invention to provide a novel 
hindered phenolic antioxidant compound which exhibits resistance to 
extraction with hydrocarbons such as petrolatum. 
It is another object of the invention to provide a novel extraction 
resistant stabilized polyolefin composition. 
It is a further object to provide a polyolefin composition useful in 
underground wire and cable applications. 
Other objects of the invention will become apparent from the detailed 
description and appended claims. 
THE INVENTION 
It has now been found that excellent extraction resistance can be obtained 
without the aforementioned attending problem of excessive smoking and 
deterioration, when a polyolefin is stabilized with the novel polymeric 
phenolic antioxidant described hereinafter. Thus, in accordance with the 
present invention there is provided a linear polymer which comprises: 
0-99 mole percent of the recurring groups A of the formula 
##STR1## 
1-100 mole percent of the recurring groups B of the formula 
##STR2## 
wherein X can be 
##STR3## 
and wherein R.sub.1 and R.sub.2 is an isomeric alkyl, cycloalkyl, alkaryl 
or an aryl group of 3 to 20 carbon atoms, R.sub.3 is a sulfonic acid group 
- SO.sub.3 H or a salt thereof, R.sub.4 and R.sub.5 is hydrogen, or an 
alkyl, cycloalkyl, alkaryl or an aryl group of 1 to 20 carbon atoms. 
The polymer is suitably prepared by first sulfonating at least one para 
substituted phenol under conventional sulfonation conditions, which 
involves reaction with a concentrated sulfuric acid, oleum, sulfur 
trioxide or any other known sulfonating agent. The aforementioned para 
substituted phenol should be one wherein a group R.sub.2 as defined above 
is located in the para position with respect to the hydroxyl group in the 
ring structure. Examples of suitable phenols include isopropyl phenol, 
p-t-butyl phenol, p-t-amyl phenol, p-t-octyl phenol, p-t-dodecyl phenol, 
p-phenyl phenol and the like. 
The sulfonated phenol is then reacted with a reactant such as an aldehyde, 
a ketone, sulfur monochloride or sulfur dichloride. Examples of suitable 
aldehydes and ketones include formaldehyde, acetaldehyde, 
propionylaldehyde, butylaldehyde, benzaldehyde, tolualdehydes, 
furfuraldehyde, acetone, methyl ethyl ketone, methyl propyl ketone, 
diethyl ketone, etc. This second reaction can be carried out optionally in 
the presence of one or more unsulfonated para substituted phenols. The 
latter may be the same or different from the para substituted phenol or 
phenols used in preparing the sulfonated phenolic reactant. The reaction 
is a condensation reaction, resulting in the formation of a linear polymer 
(novolac) and, depending on the reactant used, either water or hydrogen as 
by-products. 
When the desired final reaction product is one containing a proportion of 
unsulfonated para substituted phenol groups and the sulfonated phenol is 
derived from the same species of unsulfonated phenol, the first reaction 
is suitably carried out by sulfonation with less than a stoichiometric 
amount of sulfonation agent to obtain a mixture of unsulfonated and 
sulfonated phenol in the desired proportions. 
The reactants are supplied to the second reaction such that the molar ratio 
of the phenol linking reactant (i.e., aldehyde, ketone, etc.) to the total 
phenols (sulfonated and unsulfonated) is at least 0.7:1 and preferably 
between about 0.9:1 to 1.5:1. With low ratios there results a polymer of 
relatively low molecular weight, while relatively high molecular weight 
polymers are obtained at the high ratios. Theoretically, in an ideal 
reaction system a 1:1 ratio of reactants should be sufficient to produce a 
polymer of very high chain lengths. In practice, however, some of the 
linking reactant may not enter into the reaction, e.g. it may be lost or 
entrapped in the equipment due to high volatility, or may undergo side 
reactions. Therefore, when high molecular weight products are desired, a 
ratio of above 1:1 may be required, although the ratio can vary 
considerably depending upon the efficiency of the particular reaction 
system used. 
Inasmuch as the sulfonated phenol in itself provides the acidity necessary 
to catalyze the reaction, no further addition of acid catalyst is 
necessary. The reaction is suitably carried out at ambient pressure and at 
moderate temperatures, e.g. in the range of about 80.degree.-130.degree. C 
after which the by-product water or hydrogen chloride is removed by 
distillation at higher temperatures such as 200.degree.-250.degree. C and 
preferably at subatmospheric pressure. 
If desired, the sulfonic acid groups of the polymer product can be 
partially or completely neutralized with an inorganic or organic base, 
such as an amine, ammonia or a hydroxide, carbonate or bicarbonate of an 
alkali metal or alkaline earth metal. Examples of suitable bases in 
addition to ammonia include dimethyl amine, trimethyl amine, diethyl 
amine, triethyl amine, diphenyl amine, triphenyl amine, sodium hydroxide, 
potassium hydroxide, calcium hydroxide, lithium hydroxide, sodium 
carbonate, potassium carbonate, sodium bicarbonate, and many others. The 
resulting salts are preferably prepared by treating the sulfonated 
condensation polymer with any of the aforementioned bases after the 
distillation step to remove the condensation reaction by-products and 
unreacted compounds. However, it is entirely feasible, especially when 
only partial salts are to be prepared, to carry out the partial 
neutralization after the sulfonation step but prior to the condensation 
step, whereby the acidity needed to catalyze the reaction is provided by 
the remaining non-neutralized sulfonic acid groups. It is, of course, also 
possible to completely neutralize the sulfonated phenol and then carry out 
the condensation reaction in the presence of added acid catalyst. 
The degree of polymerization, i.e. the average number of phenolic rings in 
the molecule chain, have little, if any, significance in the invention, 
i.e. both increased extraction resistance and smoke resistance are 
obtained regardless of molecular weight of the compounds of the invention. 
The degree of improvement in extraction resistance is more pronounced, 
however, with the sulfonated low molecular weight compounds than with high 
molecular weight compounds, as considerable extraction resistance is 
already a feature of the unsulfonated high molecular weight compounds due 
to bulkiness of the molecules. Since it was surprisingly found that the 
presence of only a very small proportion of sulfonic acid groups or 
sulfonic acid salt groups is necessary to significantly improve the 
extraction resistance over that of a similar unsulfonated compound, and 
since this proportion does not materially change the molecular weight, the 
improvement cannot be explained by reason of increase in size of the 
molecule by the modifying groups. Whatever the actual reason for the 
improvement may be, e.g. the ionic nature of the modifying groups, the 
fact still remains the extraction resistance and smoke resistance are 
increased considerably. In addition, compositions stabilized with the 
antioxidants of this invention have excellent dielectric properties. 
The polyolefin base resin to be stabilized with the primary antioxidant of 
this invention comprises solid, substantially crystalline polyolefins 
including homopolymers and copolymers of .alpha.-olefins having 2 to 8 
carbon atoms and blends thereof. Among the preferred polyolefins are the 
polypropylene based resins containing at least 60 percent by weight 
preferably at least 75 percent polymerized propylene groups. Especially 
preferred resins are the ethylene-propylene polymer resins, such as random 
or block copolymers of ethylene and propylene, blends of homopolymers of 
propylene and ethylene, and various combinations thereof, wherein the 
ethylene in either homo-or copolymerized state accounts for from about 2 
to about 25 percent by weight of the total resin and more preferably from 
about 3 to about 15 percent. 
Generally, the hindered phenolic antioxidant of this invention is added in 
quantities of about 0.01 to about 5 percent by weight based on the weight 
of the polyolefin. 
When the stabilized polyolefin composition is to be used to insulate copper 
and copper alloy wires it is customary also, to include a metal 
deactivator or chelating agent often referred to as a secondary 
stabilizer. Preferably, the secondary stabilizer should be one of the well 
known organic hydrazide or hydrazine compounds commonly used for this 
specific purpose, e.g. the compounds disclosed in U.S. Pat. Nos. 
3,438,935; 3,484,285; 3,660,438; 3,752,865 and 3,772,245, all incorporated 
herein by reference. When used, the secondary stabilizers are added in 
quantities sufficient to provide a concentration of from about 0.01 to 
about 5 percent based on the weight of the polyolefin. 
It is also contemplated to incorporate a thioester synergist such as 
dilauryl thiodipropionate (DLTDP) or distearylthiodipropionate (DSTDP) 
into the polyolefin composition, usually in amounts not exceeding 1.5 
percent, preferably in the range of about 0.5 to 1.3 percent based on the 
total weight of the composition. 
In addition, the compositions of this invention can also contain other 
optional ingredients such as ultraviolet stabilizers, pigments, 
delustrants, plasticizers, flame retardant materials, anti-static agents, 
processing aids, and any other additive which is known in the art to 
impart a particular property to the composition for a particular 
application.

In order to provide a better understanding of the invention, reference is 
had to the following examples, which are to be considered only as 
illustrative but not a limitation of the invention. 
EXAMPLES 1-3 
Two antioxidants (A and B) according to the invention and one control 
composition (C) were prepared as follows: 
103 grams of tertiary para octyl phenol was partially sulfonated by heating 
to 95.degree. C with 0.2 grams concentrated sulfuric acid (98%) under an 
atmosphere of nitrogen with agitation. 40.6 grams of formalin solution 
(37%) was then added and the mixture was refluxed for 2 hours. After 
addition of 100 cc of xylene, a water-xylene azeotropic was distilled from 
the mixture at a temperature up to 140.degree. C and at ambient pressure. 
The pressure was then gradually reduced to 1.5 torr, and the stripping 
continued up to a temperature of 225.degree. C. The mixture was then 
cooled to obtain a solid novolac product (Composition A). 
Composition B was prepared following the above procedure and then heating 
the resulting product to 190.degree. C and adding 0.3 grams triethylamine 
with agitation. Heating and stirring was then continued under reflux for 
15 minutes with the temperature rising to 230.degree. C, and the resulting 
trialkylamine salt product was then cooled. 
Control Composition C was made according to the procedure for making 
Composition A except that the sulfonation step was omitted, i.e. the 
aqueous formalin solution was now added to the tertiary para octyl phenol 
prior to the addition of the sulfuric acid, which in this case acts merely 
as the catalyst for the reaction. 
EXAMPLE 4-6 
97 parts by weight of an ethylene-propylene copolymer containing 11.3 wt.% 
ethylene was compounded in a Brabender at 190.degree. C for 5 minutes with 
2 parts of Composition A and 1 part of N-salicylidene, N'-salicyl 
hydrazide, a metal chelating agent. 
Two other blends were made as above except that Composition A was omitted 
and Compositions B and C were respectively added instead. 
Each of the blends were then compression molded into 6 .times. 6 inches 
.times. 10 mil. plaques at 400.degree. F and 25,000 psig for 60 seconds. 
The plaques were rapidly cooled at high pressure and cut into 11/2 .times. 
11/2 inches .times. 10 mil. strips. One set of strips was submerged in 
U.S.P. Grade petrolatum at 86.degree. .+-. 1.degree. C for 18 hours. The 
strips were removed from the petrolatum, wiped clean tested using 
differential scanning calorimetry (DSC). This analysis provides an 
extremely effective method for obtaining accelerated aging data which can 
be extrapolated to periods of decades at ambient temperatures. 
The DSC test procedure set forth below was followed: 
A small sample of the 10 mil. film strip prepared in the compression mold 
having a diameter of approximately 0.25 inches is placed on a copper test 
pan in a Perkin-Elmer differential scanning calorimeter (DSC). The pan is 
then covered and heated from room temperature at a linear programmed rate 
of 10.degree. C/min. in the presence of nitrogen flowing through the DSC 
at a rate of 0.08 cu. ft. per hour. When the temperature in the DSC 
reaches 200.degree. C, the nitrogen is automatically stopped and oxygen 
flowing at the same rate is passed through the DSC. The temperature is 
maintained at 200.degree. C until the oxidation peak has occurred and the 
induction period is measured in minutes from the time the oxygen is added 
until the oxidative degradation occurs. 
The test results are shown in Table I. 
TABLE I 
______________________________________ 
DSC Stability 
DSC - Minutes 
Before After % Retention 
Examples 
Primary Stab. Extr. Extr. of Stability 
______________________________________ 
4 A (sulfonated) 
47 42 89 
5 B (sulfonated salt) 
43 37 86 
6 C (unsulfonated) 
42 9 21 
______________________________________ 
As seen from the above data, incorporation of the antioxidants of this 
invention containing small amounts of either sulfonic acid or sulfonic 
acid salt groups increases the extraction resistance to over 400 percent 
of that obtained with an unsulfonated antioxidant. 
EXAMPLES 7-9 
To evaluate the smoke resistance of Composition A and B a thermal 
gravimetric analysis (TGA) method was followed in which weighed samples of 
each of these compositions were heated at a rate of 10.degree. C per 
minute to 260.degree. C in a nitrogen atmosphere and then maintained at 
260.degree. C for 30 minutes. The weight loss of each sample was 
determined during the heating period at 100, 150, 200 and 260.degree. C 
and thereafter at 15 minute intervals. 
As control, a test was also made with a commercially available unsulfonated 
t-butyl-t-octyl phenol acetaldehyde novolac resin of about the same 
extraction resistance as that of Compositions A and B. 
The results of the tests are shown in Table II. 
TABLE II 
______________________________________ 
Thermal Gravimetric Analysis - % Weight Loss 
Ex- Com- 
am- posi- 260.degree. C 
260.degree. C 
ple tion 100.degree. C 
150.degree. C 
200.degree. C 
260.degree. C 
15' 30' 
______________________________________ 
7 A 0 0 0 0.05 0.98 1.50 
8 B 0 0 0 0.17 1.10 1.63 
9 Con- -- 0.46 2.44 1.18 38.0 49.0 
trol 
______________________________________ 
The presence of sulfonic acid or sulfonic acid salt group in the novolac 
antioxidants has the effect of almost completely retarding the smoking and 
degradation of the compositions, while the control lost about 50% of its 
weight evolving heavy smoke fumes. 
EXAMPLES 10-12 
The stabilized propylene copolymer compositions of Examples 4 and 5 were 
tested using ASTM D-150-64T and found to have the properties set forth in 
Table III: 
TABLE III 
______________________________________ 
Electrical Properties 
Unstabilized 
Propylene 
Resin Copolymer Example 4 Example 5 
______________________________________ 
Dielectric Constant at: 
100 cps 2.10 2.10 2.14 
1000 cps 2.09 2.10 2.13 
1,000,000 cps 2.10 2.10 2.14 
Dissipation Factor at: 
100 cps 0.00055 0.00068 0.00060 
1000 cps 0.00058 0.00071 0.00060 
1,000,000 cps 0.00040 0.00060 0.00040 
______________________________________ 
The conclusion that incorporation of either one of stabilizers A or B into 
the propylene copolymer has no significant effect on the electrical 
properties is an especially important factor in wire and cable 
applications. 
It is obvious to those skilled in the art that many variations and 
modifications can be made to the compositions of this invention. All such 
departures from the foregoing specification are considered within the 
scope of this invention as defined by this specification and appended 
claims.