Cyclic peroxyketal cross-linking/blowing agents for polyethylene

Novel processes and compositions are provided for the preparation of foamed, crosslinked polyethylene utilizing cyclic peroxyketal crosslinking/blowing agents. The novel compositions include esters of thiodipropionic acid as activators.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to certain cyclic peroxyketals useful as 
cross-linking/blowing agents and, in particular, to their use in 
compositions and processes for the preparation of foamed, cross-linked 
polyethylene. 
2. Prior Art 
It is known to form foamed, cross-linked polyethylene using chemical 
blowing agents by heating an expandable mixture comprising a thermoplastic 
resin such as polyethylene, a cross-linking agent and a chemical blowing 
agent. U.S. Pat. No. 3,470,119 teaches a method for manufacturing foamed 
polyethylene by use of a chemical blowing agent. U.S. Pat. No. 3,658,730 
teaches a specific composition for blowing thermoplastic resins. 
Chemical blowing agents (CBAs) are generally solid compounds or 
compositions which decompose at a specific temperature to yield a large 
volume of gas and a solid decomposition residue. Sodium bicarbonate, the 
most widely used inorganic CBA has limited use because it decomposes over 
a broad range of temperatures and because its decomposition point occurs 
at temperatures below those at which most resins, including polyethylene, 
are processed. 
Organic CBA's tend to evolve gas over a more defined temperature range. 
Modern Plastics Encyclopedia 1979-1980, p. 186-188 teaches a group of 
known organic CBAs useful in the production of foamed, cross-linked 
polyethylene. The blowing composition of U.S. Pat. No. 3,658,731 utilizes 
azodicarbonamide, a known organic blowing agent, in conjunction with a 
chromium compound. The use of azobisformamide, 
p,p'-oxy-bis(benzenesulfonyl hydrazide), diazoaminebenzene 
dinitrosopentamethylenetetramine, 4-nitro-benzene sulfonic acid hydrazine, 
.beta.-naphthalene sulfonic acid hydrazide, diphenyl-4,4'-disulfonyl 
azide, and barium azodicarboxylate as blowing agents is taught in U.S. 
Pat. No. 3,470,119. A disadvantage with such azo blowing agents is the 
production of small amounts of ammonia which can corrode equipment. 
The production of crosslinked polyethylene foams generally requires the use 
of cross-linking agents in addition to the blowing agent. An exception to 
the requirement of separate cross-linking and blowing agents is disclosed 
in U.S. Pat. No. 4,129,531 and U.S. Pat. No. 4,101,464 wherein certain azo 
esters function as cross-linking/blowing agents. However, as with other 
azo blowing compounds, small amounts of ammonia are produced. 
Many organic peroxides, including cyclic peroxyketals, are known to be 
effective cross-linking agents for thermoplastic resins. U.S. Application 
Ser. No. 688,874, filed May 21, 1976 teaches nine-membered peroxyketals 
useful as cross-linking agents for polyethylene. 
DESCRIPTION OF THE INVENTION 
This invention relates to the novel use of certain cyclic peroxyketals as 
blowing agents to make foamed, cross-linked polyethylene, to novel 
expansible mixtures of polyethylene blended with both cyclic peroxyketal 
cross-linking/blowing agents and certain antioxidants which operate as 
activators and to novel processes for simultaneously or sequentially 
cross-linking and foaming polyethylene. 
It has now been discovered that certain cyclic peroxyketals heretofore 
thought to be useful only as cross-linking agents can be utilized as 
blowing agents as well. Moreover, the use of the cyclic peroxyketal 
cross-linking/blowing agents in the compositions and processes of the 
present invention results in cross-linked polyethylene foam with good 
color and improved heat stability without the formation of corrosive 
by-products. 
In particular, the present invention relates to the use of cyclic 
peroxyketals which provide the dual function of cross-linking and blowing 
agents. The cross-linking/blowing agents of the present invention are 
organic peroxides of the formula: 
##STR1## 
wherein each of R.sub.2, R.sub.3, R.sub.4 and R.sub.5 is selected from 
alkyl having 1-4 atoms, e.g. methyl, ethyl; each of R and R.sub.1 is 
selected from alkyl, hydroxyalkyl, such as 2-methyl-2-hydroxypropyl, alkyl 
carboxylate ester groups of up to about 10 carbon atoms in which either 
the acid or alcohol moiety, preferably the acid moiety, is bonded to the 
ring carbon atom, 
##STR2## 
wherein n is 0 to 3 and X is lower alkyl or alkoxy of up to 5 carbon 
atoms. The cyclic peroxyketals useful in the present invention are those 
described and prepared in accordance with the teachings of Ser. No. 
688,874, filed May 21, 1976. 
The cyclic peroxyketals of the present invention decompose at temperature 
ranges at which polyethylene is conveniently molded, typically in the 
range of 150.degree. to 250.degree. C., to yield carbon dioxide gas and 
decomposition residues which are compatible with foamed, crosslinked 
polyethylene. The gas yield upon decomposition is sufficient to create a 
foam when the cyclic peroxyketals are utilized as blowing agents according 
to the present invention. The amount of gas evolution is generally 
determined by the temperature and time. 
The decomposition of the cyclic peroxyketal cross-linking/blowing agents of 
the instant invention may be promoted by the addition of certain 
activators. In particular, it has been found that certain known 
antioxidants, such as those described in U.S. Pat. No. 3,876,613, function 
in a dual capacity as activators and antioxidants. 
Novel expansible compositions from which our foamed, cross-linked 
polyethylene is prepared comprise polyethylene, a cyclic organic peroxide 
as described above and an anti-oxidant/activator which is an ester of 
thiodipropionic acid. 
The process of the present invention comprises the steps of providing an 
expansible mixture comprising polyethylene and an effective amount, 
typically 0.10-10% by weight of the polyethylene, of an organic peroxide 
cross-linking/blowing agent; heating said mixture by conventional means to 
crosslink said polyethylene; and expanding said mixture to a volume 
greater than the initial volume of the mixture whereby the density of the 
polyethylene is reduced, typically by about 30 percent or more. 
In one embodiment, the mixture also includes an effective amount, typically 
0.05 to 0.50 weight percent of an ester of thiodipropionic acid which acts 
as both an antioxidant for the foamed, crosslinked polyethylene and as a 
promoter or activator of the cyclic organic peroxide. 
The antioxidants/activators useful in the composition and processes of the 
present invention are esters of thiodipropionic acid having the formula: 
##STR3## 
wherein R.sub.6 and R.sub.7 are selected from the group consisting of 
alkyl, alkenyl, aryl, and cycloalkyl hydrocarbon radicals and combinations 
thereof such as alkaryl, aralkyl and alkylcycloalkyl, having up to 22 
carbon atoms and wherein at least one R has at least 10 carbon atoms per 
molecule. 
Some suitable R radicals include for example, methyl, ethyl, propyl, 
isopropyl, butyl, isobutyl, t-butyl, amyl, isoamyl, n-octyl, isooctyl, 
2-ethyl hexyl, t-octyl, decyl, dodecyl, octadecyl, allyl, hexenyl, 
linoleyl, ricinoleyl, lauryl, stearyl, myristyl, oleyl, phenyl, xylyl, 
tolyl, ethylphenyl, naphthyl, cyclohexyl, benzyl, cyclopentyl, 
methylcyclohexyl, ethylcyclohexyl, and naphthenyl. 
Some examples of suitable thiodipropionic acid esters include, for example, 
butyl stearyl thiodipropionate, diisodecyl thiodipropionate, isodecyl 
phenyl thiodipropionate, benzyl lauryl thiodipropionate, the diester of 
mixed coconut fatty alcohols and thiodipropionic acid, the diester of 
mixed tallow fatty alcohols and thiodipropionic acid, the diester of mixed 
cottonseed oil fatty alcohols and thiodipropionic acid, the diester of 
mixed soybean oil fatty alcohols and thiodipropionic acid. 
A presently preferred group of esters of thiodipropionic acid in which each 
of R.sub.6 and R.sub.7 has 12-20 carbon atoms, more preferably esters in 
which both R.sub.6 and R.sub.7 are the same, include the dilauryl, 
distearyl, dimyristyl, dioleyl and diricinoleyl esters. 
Perferably the amount of the ester is in the range of 0.02-0.5 weight 
percent based on the weight of the solid polymer. More often the amount is 
in the range of 0.05-0.10 weight percent which range includes amounts 
which have been found to give good results. 
Polyethylene foam products having high impact strength at low temperature 
can also be obtained when a phenolic antioxidant is incorporated into the 
polymer in addition to the ester of thiodipropionic acid of the present 
invention. Amounts of the phenolic antioxidant, such as Toponol CA, up to 
about 0.5 percent by weight, preferably up to about 0.1 percent by weight 
can be utilized with good results. 
The esters of thiodipropionic acid useful in the present invention are 
known to be useful as anti-oxidants for polyethylene. To avoid a change of 
properties upon extended exposure to heat, such antioxidants are 
incorporated into the polyethylene composition prior to molding thereby 
stabilizing the molded polyethylene articles during and after the molding 
process. In general, for normal temperature operation many stabilizing 
antioxidants can be used. However, many antioxidants have a negative 
effect upon low temperature impact strength and it is known that good low 
temperature impact strength can be obtained by using the esters of 
thiodipropionic acids herein described. 
However, in addition to acting in their known capacity of antioxidants, 
when utilized according to the present invention the esters of 
thiodipropionic acid serve a second function as activators for the organic 
peroxide crosslinking/blowing agents in that they promote the 
decomposition of such peroxides. 
In accordance with the present invention the cyclic peroxyketal 
crosslinking/blowing agents described are blended with polyethylene. The 
polyethylene useful in the novel compositions and processes of the present 
invention may be low, medium or high density polyethylene as described in 
Modern Plastics Encyclopedia (1978-1979). By high density polyethylene 
(HDPE) is meant substantially linear polyethylene, i.e. having few side 
chains and a density of greater than about 0.958 g/cc. By medium density 
polyethylene (MDPE) is meant polyethylene with short side chains and a 
density of from about 0.940 to about 0.955 g/cc. By low density 
polyethylene is meant branched-chain polyethylene having a density of from 
about 0.910 to about 0.935 g/cc. 
As will be known and understood by those in the art the polyethylene useful 
in the present invention may contain varying quantities of other 
comonomers such as 1-butene, 1-hexene and propylene. 
Incorporation of the cross-linking/blowing agents may be effected by a 
variety of techniques known in the art including dry tumbling, liquid 
dispersion of the organic peroxides and pelletized concentrates of the 
organic peroxides. Each of these techniques is described in more detail in 
Modern Plastics Encyclopedia 1979-1980, page 188. 
Once the mixing of the polyethylene and the cross-linking/blowing agent is 
completed, the mixture is molded by conventional means under conditions 
which allow expansion of the foam, including heating to a temperature 
sufficient to cross-link and foam the polyethylene, usually within a 
preferred range of 150.degree.-250.degree. C. Typically, the mixture is 
heated to a temperature sufficient to effect cross-linking and foaming in 
the absence of applied pressure or substantially at atmospheric pressure 
in a mold having a volume greater than the initial volume of the mixture 
and the mixture expands to fill the mold volume. The cross-linking and 
foaming may occur simultaneously or sequentially. The resultant foamed or 
expanded polyethylene, having increased in volume, will typically have a 
reduction in density of at least 30 percent as compared to the starting 
density of the polyethylene. Where a foamed article of a particular shape 
is desired, the step of mixing the polyethylene and the 
cross-linking/blowing agent may be followed by shaping the mixture into 
the desired form. 
The expansible mixtures of the present invention may be foamed by a variety 
of conventional methods. For example, foamed polyethylene blocks, or 
articles may be prepared by introducing a volume of mixture into a mold 
having a larger total volume and heating the mixture within the mold to at 
least 150.degree. C. whereby the polyethylene is cross-linked and expands 
into and fills the mold. The foamed polyethylene blocks may then be set by 
cooling. In another embodiment the expansible mixture may be introduced 
into a mold of substantially the same volume. The mixture in the mold is 
then heated to at least 150.degree. C. to initiate cross-linking and 
foaming. As the pressure within the mold increases the volume of the mold 
may be increased, as by separating the sides, thereby allowing the foam to 
gradually expand with the mold. Alternatively, the expansible mixture may 
be heated in a mold of substantially the same volume to at least 
150.degree. C. for a period of time sufficient to initiate crosslinking, 
followed by a release of pressure thereby allowing the polyethylene to 
expand. The heating may be carried out under an initially applied pressure 
or the pressure may increase from initially atmospheric pressure 
conditions due to the CO.sub.2 released during the decomposition of the 
cross-linking/blowing agent. In another embodiment sheet like polyethylene 
may be turned into foamed sheet continuously by heating it on a wire-net 
conveyor in a hot air oven. 
The amount of pure cross-linking/blowing agent may vary depending on the 
density of the starting polyethylene, the temperature and the degree of 
foaming, i.e. expansion, desired, but will usually be in the range of from 
about 0.010-10%, more typically 0.50-5.0% by weight of the polyethylene. 
Similarly, as will be known and understood by those skilled in the art the 
process steps followed in the practice of the present invention can be 
varied depending on the type of polyethylene utilized, the density of foam 
desired, and the degree of crosslinking desired. 
In a preferred embodiment the heating for purposes of simultaneously or 
sequentially foaming and cross-linking the polyethylene is applied during 
the procedure known as rotational molding. Rotational molding is a process 
intended primarily for the manufacture of hollow objects. In this process 
the solid or liquid polymer is placed in a mold; the mold is first heated 
and then cooled while being rotated about two perpendicular axes 
simultaneously. During the first portion of the heating stage when molding 
powdered material, a porous skin is formed on the mold surface. This 
gradually melts as the cycle progresses to form a homogenous layer of 
uniform thickness. However, when molding a liquid material, it tends to 
flow and coat the mold surface until the gel temperature of the resin is 
reached, at which time all flow ceases. The mold is then indexed into a 
cooling station, where forced air, water spray or a combination of both 
cool the mold. It is then positioned in a work zone, where the mold is 
opened, the finished part removed and the mold recharged for the following 
cycle. Centrifugal force rather than applied pressure is utilized during 
rotational molding. For more details as to various techniques and 
apparatus used in rotational molding see Kravity and Heck, "Now's The Time 
To Look Into Foam Rotational Molding", Plastics Technology, October 1979, 
p. 63-66. 
The following experimental work is designed to show the satisfactory 
results obtained by the processes and compositions of the present 
invention.

EXPERIMENTAL PROCEDURES 
The resin mixture was prepared by dry blending the peroxide and the 
antioxidant together into 30 g of MDPE powder for about 5 minutes. The 
resin used was Phillips Marlex TR880 with a density of 0.955 and a melt 
index of 18. Platen temperatures on the press were checked with a surface 
pyrometer and were either 200.degree. C. or 240.degree. C. Molding time 
was 15 minutes. 
The resin mixture was spread evenly over the lower platen, which had been 
covered with aluminum foil. Another sheet of aluminum foil was placed on 
top of the resin mixture. The platens were then gently brought together 
(about 4 mm apart) with very little, if any, ram pressure applied. At the 
end of the molding cycle, the ram pressure indicated on the press gauge 
was approximately 1000 lbs. The molded specimen was then released and 
cooled quickly in water. Each molded specimen had the aluminum foil peeled 
off before any evaluations were performed. 
To determine the percent weight gel, approximately 0.3000 g sample was cut 
into 6-7 pieces and placed inside a stainless steel screen pouch. These 
pouches were extracted in 2 liters of boiling xylene containing 10 g of 
Plastanox 2246 antioxidant for 16 hours and then dried in an oven at 
170.degree. C. for 4 hours. 
The %wt gel was calculated by the following formula: 
##EQU1## 
where: W.sub.1 =wt. of sample, g 
W.sub.2 =wt. of sample+pouch, g 
W.sub.3 =wt. of sample+pouch after extraction, g 
0.0036=blank value for resin without peroxide. 
Densities were determined by ASTM 1622-63, "Apparent Density of Rigid 
Cellular Plastics". The procedure is to cut out rectangles of the 
cross-linked foamed specimens and measure as accurately as possible their 
length, width, and thickness with a dial caliper. The volume can then be 
calculated. The density was found by dividing the weight of each rectangle 
by its volume. 
Heat stability tests were done by cutting out 1 cm.times.2 cm rectangles of 
the cross-linked foamed specimens and placing them in an oven at 
140.degree. C. and observing the color change with time. 
The cyclic peroxides listed in Table I were prepared by reacting the 
designated starting ketone with 2,5-dimethyl-2,5-dihydroperoxyhexane 
according to the experimental procedures described in Ser. No. 688,874 
filed May 21, 1976. 
TABLE I 
__________________________________________________________________________ 
PEROXIDES USED TO MAKE CROSSLINKED MDPE FOAMS 
Peroxide 
1. 2,5-Dimethyl-2,5-Di(t-Butyl Peroxy) Hexyne-3 (Hexyne Dialkyl I) 
2. Cyclic Peroxyketals made from 2,5-Dimethyl-2,5-Dihydroperoxy Hexane 
##STR4## 
Cyclic Peroxyketal 
Starting Ketone R.sub.1 Group 
__________________________________________________________________________ 
A Ethyl Acetoacetate 
##STR5## 
B Methyl n-Butyl Ketone 
n-butyl 
C Methyl n-Propyl Ketone 
n-propyl 
D n-Butyl Levulenate 
##STR6## 
E Acetal Acetate 
##STR7## 
F n-Butyl 2-Oxopropyl Carbonate 
##STR8## 
__________________________________________________________________________ 
TABLE II 
__________________________________________________________________________ 
DENSITIES AND PERCENT GELS OF CROSSLINKED MDPE FOAMS 
USING AZODICARBONAMIDE AS THE BLOWING AGENT 
phr Blowing 
Foam Density 
TEST 
Foaming Temp., .degree.C. 
phr Peroxide 
Agent (g/cm.sup.3)* 
% Wt. Gel 
__________________________________________________________________________ 
1. 200 1.5 -- 0.815 98.5 
2. 200 0.5 1.0 0.519 55.5 
3. 200 0.5 5.0 0.576 50.1 
4. 200 1.0 1.0 0.779 95.9 
5. 200 1.0 5.0 0.728 88.9 
6. 200 1.0 10.0 0.742 86.6 
7. 240 1.5 1.0 0.653 97.7 
8. 240 1.5 5.0 0.634 83.0 
SET B - Cyclic Peroxyketal A 
1. 200 1.5 -- 0.477** 
89.2** 
2. 200 1.5 5.0 0.642 5.9 
3. 240 1.5 1.0 0.558 31.7 
4. 240 1.5 5.0 0.504 10.1 
__________________________________________________________________________ 
*The procedure used was ASTM 16226B, "Apparent Density of Rigid Cellular 
Plastics". 
**Average values from 3 tests. 
In the above Tables I and II, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, 
hereinafter referred to as hexyne dialkyl I, is included for comparison 
because it is the preferred commercial peroxide used for preparing 
crosslinked MDPE and HPDE. Table II shows the testing results on foamed, 
cross-linked medium density polyethylene (MDPE) utilizing 
azodicarbonamide, the most commonly used organic chemical blowing agent 
and either hexyne dialkyl I or cyclic peroxide A from Table I as the 
cross-linking agent. The results indicate the use of the combination of 
hexyne dialkyl I/azodicarbonamide is not as effective as cyclic peroxide A 
alone. Moreover, cyclic peroxide A alone produced a foam with higher % wt 
gel and lower density than when used as the cross-linking agent in 
conjunction with the known blowing agent. 
Table III demonstrates the advantageous results obtained with the use of 
esters of thiodipropionic acid as activators compared to the use of other 
known antioxidants. A comparison of Test #1 and Test #4 shows a density 
reduction (enhanced foaming) without any loss in % gel was achieved by the 
use of distearylthiodipropionate (DSTDP) in conjunction with cyclic 
peroxide A than by the use of cyclic peroxide A alone. Other types of 
antioxidants tested results in insignificant or no reduction in density. 
Test #13 demonstrates that DSTDP is not an activator for hexyne dialkyl I. 
The use of zinc oxide (ZnO), a nucleating agent, with cyclic peroxyketal A 
alone or in combination with DSTDP is presented in Table IV. Nucleating 
agents aid in obtaining a foam with a more uniform cell size. The use of 
ZnO in known quantities does not reduce either the foam density or the % 
wt. gel, and thus appears to overpower the activator, DSTDP. As will be 
known and/or understood by those in the art, it is contemplated within the 
scope of the invention that it may nevertheless be useful to incorporate 
small amounts, such as 0-5 parts by weight, of nucleating agents such as 
ZnO. 
Similarly other ingredients which do not adversely affect the molding, or 
the cross-linking or foaming of the polyethylene and which do not impart 
undesirable characteristics to the foam products can be added to the 
mixture. Examples of such materials which may be added under suitable 
conditions and in suitable amounts include pigments, stabilizers, 
anti-static agents, ultra-violet absorbers for light stabilization, 
fillers, reinforcing materials, etc. The only requirement for such 
additives is that they be compatible with the specific composition to 
permit proper molding, crosslinking and foaming to obtain well formed 
products and molded articles having the desired properties. 
TABLE III 
______________________________________ 
DENSITIES AND PERCENT GELS OF CROSSLINKED 
MDPE FOAMS 
Using 1.5 phr Cyclic Peroxyketal A at 200.degree. C. and 15 Minutes 
Molding Time 
Foam 
ANTIOXIDANT Density 
TEST (Activator) phr (g/cm.sup.3) 
% Wt. Gel 
______________________________________ 
1. -- -- 0.477.sup.1 
89.2.sup.1 
2. DSTDP.sup.2 0.05 0.400 93 
3. DSTDP 0.10 0.369.sup.3 
80.4.sup.3 
4..sup.4 DSTDP 0.10 0.340 91.8 
5. DSTDP 0.30 0.411 26.2 
6. DLTDP.sup.5 0.10 0.394 80.8 
7. Mark 328.sup.6 
0.10 0.385 91.1 
8. Topanol CA 0.10 0.440 92.8 
9. Mark 1589.sup.7 
0.10 0.433 93.9 
10. Mark 2112.sup.8 
0.10 0.503 93.0 
11. Santonox R.sup.9 
0.10 0.452.sup.10 
68.5.sup.10 
12. Santonox R 0.20 0.591 37.4 
13. 1.0 phr 
DSTDP 0.10 0.847 98.3 
Hexyne 
Dialkyl I 
______________________________________ 
.sup.1 Average values from three tests 
.sup.2 Distearyl Thiodipropionate 
.sup.3 Average value from four tests 
.sup.4 Mold temperature was 240.degree. C. 
.sup.5 Dilauryl Thiodipropionate 
.sup.6 6 Parts DSTDP to one part Topanol CA (a phenolic type antioxidant) 
.sup.7 A phenolic type antioxidant 
.sup.8 A phosphite type antioxidant 
.sup.9 A thio bis alkylated phenol type antioxidant 
.sup.10 Average values from two tests 
TABLE IV 
__________________________________________________________________________ 
DENSITIES AND PERCENT GELS OF CROSSLINKED MDPE FOAMS 
Using 1.5 phr Cyclic Peroxyketal A at 200.degree. C. and 15 Minutes 
Molding Time 
With Both Activator and Nucleating Agent 
FOAM 
ANTIOXIDANT DENSITY 
TEST 
(Activator) 
phr 
NUCLEATING AGENT 
phr 
(g/cm.sup.3) 
% WT. GEL 
__________________________________________________________________________ 
1. -- -- -- -- 0.477 89.2 
2. DSTDP 0.10 
-- -- 0.369 80.4 
3. -- -- ZnO 5.0 
0.477 90.9 
4. DSTDP 0.10 
LnO 5.0 
0.457 86.4 
__________________________________________________________________________ 
The other cyclic peroxides of Table I were used as crosslinking/blowing 
agents for MDPE. The results are given in Table V and demonstrate utility. 
Moreover, a comparison with Test #2 of Set A in Table II, the best test 
using commercially available products, demonstrates that in several 
instances the results obtained from the compositions of the present 
invention are far superior to those obtained by compositions utilizing the 
known blowing agent. 
In Table VI, heat stabilities of crosslinked polyethylene foams made with 
either cyclic peroxyketal A alone or in combination with examples of the 
preferred antioxidant/activators are compared to non-foamed crosslinked 
polyethylene made with hexyne diakyl I alone on in combination with one of 
the antioxidant systems. Similar results were obtained with both Sets A 
and B. 
TABLE V 
______________________________________ 
DENSITIES AND PERCENT GELS OF CROSSLINKED 
MDPE FOAMS 
Using 1.5 phr Other Cyclic Peroxyketals and 0.1 phr DSTDP 
at 200.degree. C. and 15 Minutes 
FOAM 
DENSITY 
TEST CYCLIC PEROXYKETAL (g/cm.sup.3) 
% WT. GEL 
______________________________________ 
1. B 0.530* 15.3* 
2.** B 0.524 91.6 
3. C 0.524 23.6 
4. D 0.627 2.4 
5. E 0.310 92.6*** 
6.** E 0.402 88.0 
7. F 0.479 93.5*** 
8.** F 0.425 94.4 
______________________________________ 
*Average values from 2 tests. 
**Mold temperature was 240.degree. C. 
***Average values from 2 determinations on the same specimen. 
TABLE VI 
______________________________________ 
HEAT STABILITY TESTS AT 140.degree. C. ON 
SELECTED CROSSLINKED SPECIMENS 
Molded for 15 Minutes at 200.degree. C. 
COLOR AFTER 
AGING AT 140.degree. C.* 
SAMPLE Days 1 2 3 6 8 10 
______________________________________ 
Set A - Made with 1 phr 
Hexyne Dialkyl I (Nonfoamed) 
0.1 phr 
Antioxidant 
1. -- y y dy vdy b b 
2. Mark 328 ly ly y dy dy dy 
______________________________________ 
Set B - Made with 
1.5 phr Cyclic 
Peroxyketal A (Foamed) 
0.1 phr 
Antioxidant 
3. -- y y dy vdy b b 
4. DSTDP w w ly dy b b 
5. Mark 328 w w ly dy dy b 
6. 0.2 phr Mark 328 
w w w ly y y 
______________________________________ 
*Color Legend: 
w = white 
ly = light yellow 
y = yellow 
dy = dark yellow 
vdy = very dark yellow 
b = brown