Self-extinguishing fine particulate expandable styrene polymers

Self-extinguishing, fine particulate, expandable styrene polymers for the manufacture of molded articles, containing bromine compounds and one synergist. The synergist, referred to the styrene polymer, is at least one hydrocarbon present in amounts from about 0.1 to 3% by weight and forms stable radicals at temperatures above 300.degree. C.

CROSS-REFERENCE TO A RELATED APPLICATION 
Applicants claim priority under 35 USC 119 for application P 29 06 336.3, 
filed Feb. 19, 1979 in the Patent Office of the Federal Republic of 
Germany. 
BACKGROUND OF THE INVENTION 
The field of the invention is self-extinguishing, fine particulate, 
expandable styrene polymers for the preparation of molded articles. The 
present invention is particularly concerned with expandable, particulate 
molding compositions of styrene polymers containing organic halogen 
compounds and a synergist as flame proofing agents. 
The state of the art of expandable polystyrene may be ascertained by 
reference to the Kirk-Othmer, "encyclopedia of Chemical Technology," 2nd 
Edition, Vol. 9 (1966) under the section entitled "Foamed Plastics," pages 
847-884, particularly pages 852, 853 and 855 where polystyrene is 
disclosed, and Vol. 19 (1969) under the section entitled "Styrene 
Plastics," pages 85-134, particularly pages 116-120, where polystyrene 
foams are disclosed and pages 120, 121 where prior art self-extinguishing 
polystyrene foams are disclosed in U.S. Pat. Nos. 3,058,926; 3,058,927; 
3,274,133; 3,389,097; 3,457,204; 3,789,028; 3,897,373 and 3,972,843; the 
disclosures of which are incorporated herein. 
The disclosure of assignee's U.S. Pat. No. 2,954,412 is incorporated herein 
to show the preparation of dibenzylbenzene starting materials useful in 
the present invention. 
U.S. Pat. No. 3,972,843 discloses methods, useful in the present invention, 
for producing particulate molding compositions for the production of 
foamed articles by polymerizing styrene in aqueous suspension. 
It is known to use halogenated materials, especially organic bromine 
compounds, as flame proofing substances for self-extinguishing 
thermoplastic polmers. To achieve a sufficient effect, relatively large 
amounts of the halogenated compounds must be added. This adversely affects 
the processing properties especially as regards expandable polymers. 
Further, it is known that the amount of the halogenated compound needed to 
keep the effect constant can be decreased by adding synergistic 
substances. The following particular synergists are known: organic 
peroxide compounds such as disclosed in U.S. Pat. Nos. 3,058,926 and 
3,058,927 and diazo compounds such as disclosed in U.S. Pat. No. 
3,897,373. Both organic peroxides and diazo compounds suffer from the 
drawback that they, as well as their dissociation products are highly 
toxic in the high concentrations required and that on occasion they 
decompose explosively. 
The use of polymers and oligomers of p-diisopropylbenzene as synergists for 
brominated fireproofing agents as disclosed in U.S. Pat. No. 3,457,204, 
French Pat. No. 14 57 547 and Belgian Pat. No. 704,666 suffers from the 
drawback that these polymers and oligomers are insoluble in styrene and 
furthermore, they are present in the solid aggregate state, whereby it is 
difficult to introduce them into expandable styrene polymers. Furthermore, 
as regards a good effect, concentrations exceeding 1% by weight are 
required. 
The use of the N-nitroso compounds as disclosed in U.S. Pat. No. 3,274,133, 
of triphenylphosphine oxide as disclosed in French Pat. No. 14 10 556 or 
of tetraphenylhydrazine, as disclosed in French Pat. No. 12 45 593 is 
prohibited in practice because these materials or their decomposition 
products are toxic. 
SUMMARY OF THE INVENTION 
Having in mind the limitations of the prior art, it is an object of the 
present invention to prepare molded articles from fine particulate, 
selfextinguishing, expandable styrene polymer molding compositions 
containing organic bromine compounds as flame proofing agents and an 
improved synergist. The synergist of the present invention is used in a 
concentration of 0.1 to 3% by weight referred to the styrene polymer and 
consists of at least one hydrocarbon which forms stable radicals at 
temperatures above 300.degree. C. The organic bromine compound has more 
than 40% by weight bromine and sufficient bromine compound is used to 
provide at least 0.1% but no more than 2% by weight bromine based on the 
weight of styrene polymer. 
By "hydrocarbon which forms stable radicals at temperatures about 
300.degree. C." is meant, the c-c-linkages of said hydrocarbon are labile. 
The bonding strength is strong enough that the c-c bond does not decompose 
under polymerization--or molding temperatures but low enough not to form 
radicals before fire temperatures are reached (above 300.degree. C.). 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Suitable hydrocarbons which form stable radicals at temperatures about 
300.degree. C. are dibenzylbenzenes of the general formula 
##STR1## 
where R.sub.1 through R.sub.6 represent hydrogen or halogen atoms, alkyl, 
cycloalkyl or aryl groups. The dibenzylbenzenes are obtained by the method 
disclosed in U.S. Pat. No. 2,954,412. As a rule, the dibenzylbenzenes 
represent mixtures of isomers which are useful in that form. Further 
suitable hydrocarbons which form stable radicals at temperatures above 
300.degree. C. include, but are not limited to, benzyltoluol, also in the 
form of its isomerous mixture, and especially 
1-phenyl-1,3,3-trimethylindane, which is easily obtained through catalytic 
dimerization of alpha-methylstyrene. Generally speaking, the useful 
hydrocarbons contain at least one aromatic group. 
The synergistic effect of the hydrocarbons which form stable radicals at 
temperatures above 300.degree. C. can be improved if additionally from 
about 0.01 to 0.08% by weight of organic peroxides, referred to the weight 
of styrene polymers, are used where the organic peroxides have a half 
value time of dissociation exceeding two hours at 100.degree. C. Examples 
of these peroxides include, but are not limited to: 
di-tert.-butylperoxide, dicumylperoxide, di-tert.-amylperoxide or 
3,3,6,6,9,9-hexamethyl-1,2,4,5-tetraoxacyclononane, where dicumylperoxide 
is especially preferred. 
It is especially advantageous that the hydrocarbons of the invention be 
present in amounts from about 0.4 to 1% by weight and the peroxides in 
amounts from about 0.04 to 0.06% by weight, all referred to the weight of 
styrene polymer. 
Accordingly, the peroxides are useful in very slight proportions, in which 
as such, they evidence no synergistic effect, and whereby the known 
drawbacks of their application is averted. 
Both the hydrocarbons and the peroxides are soluble in styrene monomer and 
do not decompose under the conventional conditions of polymerization. 
Thereby, a homogeneous distribution is assured in the end product. 
Therefore, the hydrocarbons and peroxides of the invention are 
advantageously added prior to, or at the beginning of the polymerization. 
Because of the use of the economical hydrocarbons of the invention, the 
synergistic effect is not lost even when the polymer end product is stored 
for extended periods of time at fairly high temperatures. 
Polystyrene and copolymers of styrene with up to 50% by weight of 
comonomers are useful as the styrene polymers. The comonomers include, but 
are not limited to alpha-methylstyrene, acrylonitrile as well as esters of 
acrylic acid or methacrylic acid where the esters are of alcohols having 1 
to 8 carbon atoms. 
The styrene polymers contain one or more expanding agents homogeneously 
distributed therein. Suitable expanding agents are, for instance under 
ordinary conditions, gaseous or liquid hydrocarbons or halogen 
hydrocarbons which do not dissolve the styrene polymer and the boiling 
point of which is less than the polymer's softening point. Suitable 
expanding agents include, but are not limited to, propane, butane, 
pentane, cyclopentane or halogen hydrocarbons such as 
dichlorodifluoromethane and methylene chloride. Furthermore, the styrene 
polymers of the invention may contain mixtures of expanding agents. The 
expanding agents as a rule are contained in the styrene polymers in 
amounts from about 3 to 15, especially 5 to 8% by weight referred to the 
weight of styrene polymer. 
The bromine compounds, preferably contain at least 4 carbon atoms. 
Particularly suitable are low-volatility compounds acting only slightly or 
not at all as plasticizers and free of offensive odors, for instance, 
1,2,5,6,9,10-hexabromocyclododecane, ethoxitetrabromooctane, 
tribromo-trichlorocyclohexane and pentabromomonochlorocyclohexane. A 
listing of suitable bromine compounds is found in KUNSTSTOFF-HANDBUCH, 
vol. V, "Polystyrol" (1965), pp. 690. Bromine compounds should contain 
more than 40% by weight of bromine and are applied in sufficient amounts 
that the content in bromine is at least 0.1 but no more than 2% by weight 
referred to the weight of styrene polymer. Preferably, the bromine content 
is from about 0.4 to 1% by weight. 
The styrene polymers of the invention may furthermore contain additives 
such as plasticizers, dyestuffs and fillers. Furthermore, the expandable 
polystyrenes may be surface-coated during prefoaming for instance with 
anti-clumping substances, or against static charging as disclosed in U.S. 
Pat. Nos. 3,389,097 and 3,789,028. 
The expandable styrene polymers are obtained by polymerizing in the 
presence of organic polymerization initiators which, under the influence 
of heat, decompose into polymerization triggering radicals. The following 
substances are typically applicable: peroxides such as benzoylperoxide, 
laurylperoxide or tert.-butylperbenzoate, tert.-butylperoctoate or 
mixtures of these, as well as unstable azo compounds such as 
azobisisobutyronitrile. The initiators as a rule are used in 
concentrations from about 0.01 to 1% by weight referred to the weight of 
the monomers. 
The type of initiator used depends on the temperature of polymerization 
being considered. Advantageously mixtures of initiators are used, the 
temperature of polymerization being adjustable when desired to the 
corresponding half value time of the initiator. As a rule, the temperature 
of polymerization lies between about 60.degree. and 150.degree. C., 
preferably between 80.degree. and 120.degree. C. 
The expandable styrene polymers are usually present in the form of beads or 
in any other useful form, the particles preferably having diameters from 
about 0.3 to 3 mm. 
The self-extinguishing molded articles made from the styrene polymers are 
tested in the following manner: 
One test body 30.times.30.times.120 mm in size is clamped vertically into a 
holder and is made to burn for 5 seconds using a nonluminous bunsen burner 
flame with a flame height of 40 mm. The flame is then evenly removed. The 
time of extinction of the molded article following removal from the flame 
is a measure of its flame-proofing. Molded articles that are 
insufficiently flame-proofed or not flame-proofed at all burn down 
completely after the flame is removed. 
According to the present invention, the following combinations of styrene 
polymers/halogenated compounds/hydrocarbon synergists/peroxides produce 
new and unexpected results where the abbreviations used are: 
______________________________________ 
DBT = dibenzyltoluol 
HBB = hexabromobutene 
isomer mixture 
MBT = benzyltoluol 
isomer mixture 
PMI = 1-phenyl-1,3,3- 
trimethylindane 
DCP = dicumylperoxide 
HBCD = 1,2,5,6,9,10-hexa- 
bromocyclododecane 
ETBO = 1-ethoxi-2,3,7,8- 
tetrabromooctane 
DHI = dehydro-oligomer of 
diisopropylbenzene 
______________________________________ 
HALO- HYDRO- 
GENATED CARBON 
COM- SYNER- PER- 
POLYMER POUND GIST OXIDE in 
from in weight % 
in weight % weight % 
______________________________________ 
Styrene HBCD 0.75 DBT 0.6 -- -- 
Monomer 
Styrene HBCD 0.75 DBT 1.0 -- -- 
Monomer 
Styrene HBCD 0.75 PMI 0.6 -- -- 
Monomer 
Styrene HBCD 0.75 MBT 0.4 DCP 0.05 
Monomer 
Styrene HBCD 0.75 PMI 0.4 DCP 0.04 
Monomer 
Styrene HBCD 1.0 DBT 0.5 DCP 0.04 
Monomer 
Styrene HBCD 1.0 PMI 0.4 DCP 0.04 
Monomer 
Styrene HBCD 1.0 PMI 0.4 DCP 0.04 
Monomer 
Styrene HBCD 1.0 DBT 0.5 DCP 0.04 
Monomer 
Styrene HBCD 1.0 MBT 0.5 DCP 0.04 
Monomer 
Styrene ETBO 1.0 DBT 0.5 -- -- 
Monomer 
Styrene ETBO 1.0 PMI 0.6 -- -- 
Monomer 
Styrene ETBO 1.0 DBT 0.5 DCP 0.04 
Monomer 
Styrene ETBO 1.0 PMI 0.4 DCP 0.04 
Monomer 
Styrene HBB 0.5 PMI 0.6 -- -- 
Monomer 
Styrene HBB 0.5 DBT 0.6 -- -- 
Monomer 
Styrene HBB 0.5 PMI 0.4 DCP 0.04 
Monomer 
Styrene and HBCD 0.75 PMI 0.6 -- -- 
acrylo nitrile 
HBCD 1.0 DBT 0.5 DCP 0.04 
(90:1) 
Styrene and acrylic 
ETBO 1.0 DBT 1.0 -- -- 
acid butylester 
ETBO 1.0 PMI 0.4 DCP 0.04 
(90:1) 
______________________________________

EXAMPLES a-u 
A mixture of 100 parts by weight of tap water, 100 parts by weight of 
styrene, 0.4 parts by weight of benzoylperoxide, 0.1 part by weight of 
tert.-butylperbenzoate and the concentration of additives as listed in 
Table 1 was heated in each example to 90.degree. C. with stirring in a 
stainless steel pressure proof mixing vessel. After two hours at 
90.degree. C., 5 parts by weight of a 2% aqueous solution of polyvinyl 
alcohol were added. After another two hours at 90.degree. C., 7 parts by 
weight of pentane were added. Following another hour at 90.degree. C., the 
mixture was raised to 120.degree. C. and kept at this temperature for 6 
hours. 
The end of the polymerization cycle was followed by cooling and the bead 
polymer was separated from the aqueous phase, dried and sifted. 
The beads were prefoamed in a continuous mixing prefoamer of the Rauscher 
type, using flowing steam, to a bulk weight of 15 g/l, then were 
preliminarily stored for 24 hours and then foamed in a 500 liter block 
mold of the Rauscher type. The set of 5 test panels 30.times.30.times.120 
mm was cut out of the finished block and the flame-proofing was determined 
as indicated above. The results are summarized in Table 1 (concentrations 
are in % by weight referred to styrene). 
TABLE 1 
______________________________________ 
Additives 
Synergists 
Br Compound hydrocarbon 
peroxide 
A- A- A- 
mount mount mount Extinction 
% by % by % by time in 
Ex. Type wt Type wt Type wt seconds 
______________________________________ 
a HBCD 1 -- -- -- -- &gt;20.sup.1 
b HBCD 1 -- -- DCP 0.04 &gt;20.sup.1 
c HBCD 1 -- -- DHI 0.3 10 
d HBCD 1 -- -- DCP 0.3 4 
e HBCD 0.75 DBT 0.6 -- -- 10 
f HBCD 0.75 DBT 1.0 -- -- 8 
g HBCD 0.75 PMI 0.6 -- -- 10 
h HBCD 0.75 MBT 0.4 DCP 0.05 2 
i HBCD 0.75 PMI 0.4 DCP 0.04 1 
j HBCD 1.0 DBT 0.5 DCP 0.04 0.5 
k HBCD 1.0 PMI 0.4 DCP 0.04 0.5 
l HBCD 1.0 PMI 0.4 DCP 0.04 1 
m HBCD 1.0 DBT 0.5 DCP 0.04 2 
n HBCD 1.0 MBT 0.5 DCP 0.04 1 
o ETBO 1.0 DBT 1.0 -- -- 7 
p ETBO 1.0 PMI 0.6 -- -- 8 
q ETBO 1.0 DBT 0.5 DCP 0.04 1 
r ETBO 1.0 PMI 0.4 DCP 0.04 0.5 
s HBB 0.5 PMI 0.6 -- -- 9 
t HBB 0.5 DBT 0.6 -- -- 9 
u HBB 0.5 PMI 0.4 DCP 0.04 1 
______________________________________ 
"a" through "d" are comparison examples; 
"e" through "n" are examples of the invention 
.sup.1 burned down completely 
EXAMPLES v and w 
Examples a-u are repeated using instead 100 parts by weight of styrene 99 
parts by weight of styrene and 1 part by weight of acrylonitrile. The 
results are summarized in Table 2, A. 
EXAMPLES x and y 
Examples a-u are repeated using 99 parts by weight of styrene and 1 part by 
weight of acrylic acid butylester instead 100 parts by weight of styrene. 
The results are summarized in Table 2, B. 
TABLE 2 
______________________________________ 
Additives 
Synergists 
Br Compound hydrocarbon 
peroxide 
A- A- A- Extinc- 
mount mount mount tion 
% by % by % by time in 
Ex. Type wt Type wt Type wt seconds 
______________________________________ 
A v HBCD 0.75 PMI 0.6 -- -- 10 
W HBCD 1.0 DBT 0.5 DCP 0.04 2 
B x ETBO 1.0 DBT 1.0 -- -- 9 
y ETBO 1.0 PMI 0.4 DCP 0.04 0.5 
______________________________________