Flame retardant for synthetic resins

Flame retardant for synthetic resins comprising an oligomer having the following structural formula: ##STR1## wherein Y is ##STR2## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are independently H or alkyl of C.sub.1 -C.sub.3, X and X' are independently Br or Cl, A is H or a residue of a terminator selected from the group consisting of phenol, alkylphenol, halo-nucleus-substituted phenol, halo-nucleus-substituted alkylphenol, aniline or halo-nucleus-substituted aniline, B is OH or said residue, m is 1 or 2, and l is integer of from 1 to 10.

BACKGROUND OF THE INVENTION 
This invention relates to a flame retardant for synthetic resins, and 
particularly relates to a flame retardant for synthetic resins comprising 
an oligomer having repeated units of 
##STR3## 
The flame retardant for synthetic resins of the present invention is 
stable to heat, does not substantially impair the properties of the 
synthetic resins and has flame retardance effect. 
Generally, articles made from synthetic resin are flammable. A variety of 
flame retardants for synthetic resins, such as organic halides, and 
organic phosphorus compounds have been proposed in the prior art. However, 
some of the flame retardants of the prior art are unstable to heat. Some 
of the flame retardants which are stable to heat tend to discolor the 
articles made from synthetic resins incorporating the flame retardant and 
to lower the physical properties, such as the mechanical strength of said 
articles. 
A variety of flame retardants have been developed in order to overcome the 
disadvantages of the flame retardants composed of the organic halide 
compounds. For example, in Japanese Public Disclosure No. 49- 131234 (laid 
open), a compound having the formula 
##STR4## 
wherein X is O or S, m is integer of from 2 to 4 and l is integer of from 
1 to 50 disclosed as a flame retardant for a synthetic resin. In Japanese 
Patent Publication No. 47- 44537, the compound having the formula 
##STR5## 
wherein R is H or lower alkyl, m is integer of from 1 to 5 and n is 
integer of from 2 to 10 is disclosed as a flame retardant for a synthetic 
resin. 
However, when these flame retardants are added to a polyester or 
polycarbonate which has flame retardancy property per se they enhance said 
flame retardance effect. However, when they are added to polystyrene, 
high-impact polystyrene or ABS resin which is flammable, they give little 
or no flame retardant property to the resin. 
We have carried out experiments on flame retardancy of the compounds 
disclosed in Japanese Public Disclosure No. 49- 131234 (laid open). In 
high-impact polystyrene (sold under the trade name of "Styrone 492" by 
Asahi Dow Co.) were incorporated 20% by weight of such a compound and 5% 
by weight of antimony trioxide based on the total weight of high-impact 
polystyrene, the flame retardant and antimony trioxide. A molded article 
was formed from the resulting mixture. The flame retardancy of the article 
was tested in accordance with UL 94 test method (Standard for Flammability 
Tests of Plastic Materials for Parts in Devices and Appliance UL 94, Sept. 
1973). The class of the retardancy was 94 v- 2. That is the drippings of 
the resin were observed to fall. This shows that the flame retardancy of 
the compound was not sufficient. 
We have have also carried out an experiment on the flame retardancy of an 
oligomer of tetrabromobisphenol A polycarbonate disclosed in Japanese 
Public Disclosure No. 47- 44537. In polystyrene (sold under the trade name 
of "Styrone 666" by Asahi Dow Co.) were incorporated 20% by weight of said 
oligomer and 5% by weight of antimony trioxide based on the total weight 
of the polystyrene, flame retardant and antimony trioxide. A molded 
article was formed from the resulting mixture. The flame retardancy of the 
article was tested in accordance with Ul 94 Standard. The class of the 
flame retardancy was 94 v- 2. This shows that the flame retardancy of this 
compound, too, is not sufficient. In the above two experiments the class 
of UL 94 v- 2 in the test of UL 94 Standard shows that drippings of the 
resin fall on cotton cloth, thereby burning the cloth. This shows there is 
possibility of causing secondary ignition. Therefore, it was apparent from 
the above two experiments that the flame retardants as disclosed in 
Disclosure No. 49- 131234 and Publication No. 47- 44537 impart poor flame 
retardancy to high-impact polystyrene and polystyrene when incorporated 
therein. Consequently, there is need for a flame retardant for synthetic 
resins having such fire-retardancy effect that in case a resin containing 
the fire retardant burns, drippings of the resin do not fall. 
Also, a tetrabromobisphenol A oligomer terminated with a halo-substituted 
phenol is disclosed in U.S. Pat. No. 3,846,469 as a flame retardant. 
However, it was found from our flaming-test that this oligomer had the 
same flame retardancy as that of an oligomer disclosed in Japanese Patent 
Publication No. 47- 44537. 
SUMMARY OF THE INVENTION 
One object of this invention is to provide a fire retardant for synthetic 
resins which gives an excellent fire retardancy effect when incorporated 
in a flammable resin. 
Another object of this invention is to provide a flame retardant which, 
when incorporated in synthetic resins, does not substantially impair the 
properties of the synthetic resins. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invetion relates to a flame retardant for synthetic resins 
comprising an oligomer having the following structural formula: 
##STR6## 
wherein Y is 
##STR7## 
wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 
independently H or alkyl of C.sub.1 -C.sub.3 ; X.sub.1 and X' are 
independently Br or Cl; A is H or a residue of a terminator selected from 
the group consisting of phenol; alkylphenol, such as p-tert-butylphenol; 
halonucleus-substituted phenol, such as di- or tri-bromophenol; 
halo-nucleus-substituted alkylphenol, such as 
2,6-dibromo-p-tert-butylphenol; aniline or halo-nucleus-substituted 
aniline, such as di- or tri-bromoaniline; B is OH or said residue; m is 1 
or 2; and l is integer of from 1 to 10. Such terminators are well known 
in the art. 
It is preferred that a flame retardant for synthetic resins comprises an 
oligomer having the following structural formula 
##STR8## 
wherein Y is 
##STR9## 
X is Br or Cl, X' is Cl, A is H and B is OH, m is 1 or 2 and l is integer 
of from 1 to 10. 
The oligomer represented by the formula I is prepared by 
dehydrohalogenation reaction of a phosphorus oxyhalide having the formula 
II 
EQU pox.sub.3 ' ii 
wherein X' is Cl or Br, with the halogenated dihydroxy compound having the 
formula III 
##STR10## 
wherein Y is 
##STR11## 
wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are 
independently H or alkyl of C.sub.1 -C.sub.3 X is Cl or Br, and m is 1 or 
2. The above reaction may be effected by a conventional solvent method. 
That is, the halogenated dihydroxy compound represented by Formula III and 
a material, such as sodium hydroxide, may be dissolved in a solvent, such 
as, for example, methylene chloride, chlorobenzene, pyridine, toluene and 
xylene. A solution of the phosphorus oxyhalide represented by formula II 
in methylene chloride is suitably added dropwise to the solution of the 
halogenated dihydroxy compound over a time interval of from about 0.5 hrs 
to about 1.5 hrs at room temperature. The reaction is advantageously 
effected at a temperature ranging from room temperature to the boiling 
point of the solvent to be used for from about 1 hr to about 3 hrs. In the 
above reaction, from about 0.5 mol to about 1.5 mol, preferably from about 
0.8 mol, to about 1 mol of phosphorus a oxyhalide is conveniently employed 
per 1 mol of halogenated dihydroxy compound. 
The equation of the reaction is as follows: 
##STR12## 
wherein Y, X and x' are as defined above, A is H or 
##STR13## 
wherein Z is H or a residue of the terminator and k is integer of from 0 
to 8. 
In the product represented by the above equation, whether A is H or 
##STR14## 
depends on the molar ratio of the reactants, the reaction conditions, and 
the like. 
The residues of terminators represented by Z in the formula 
##STR15## 
include, for example residues of phenol, alkylphenol, 
halo-nucleus-substituted phenol, halo-nucleus-substituted alkylphenol, 
aniline, and halo-nucleus-substituted aniline. 
All of the compounds represented by formula IV are usable as flame 
retardants for synthetic resins of the present invention. 
In general, in the formula IV, the compounds wherein A is 
##STR16## 
are insoluble in the reaction solvent, such as methylene chloride. So, the 
resulting product is formed as a precipitate after completing the 
reaction. In the formula IV, the compounds of lower molecular weight 
wherein A is H are soluble in methylene chloride. 
In formula I, the compounds wherein l is more than 10 have poor 
compatibility with the synthetic resins which will constitute a matrix in 
a mixture of the resin and such a compound. As a result, when such 
compound is incorporated in the resin, it bleeds on the surface of the 
molded product, whereby the appearance of the molded product is noticeably 
impaired. 
The phosphorus-oxyhalides employed in the preparation of the flame 
retardant of the present invention include, for example, phosphorus 
oxytrichloride, phosphorus-oxytribromide, and the like. 
The halogenated dihydroxy compounds having the formula 
##STR17## 
employed in such preparation include, for example, 
bis(4-hydroxy-2-bromophenyl)methane, bis(4-hydroxy-3-bromophenyl)methane, 
bis(4-hydroxy-3-chlorophenyl)methane, 
bis(4-hydroxy-3,5-dibromophenyl)methane, 
bis(4-hydroxy-3,5-dichlorophenyl)methane, 
1,1-bis(4-hydroxy-3-chlorophenyl)ethane, 
1,1-bis(4-hydroxy-3-bromophenyl)ethane, 
1,1-bis(4-hydroxy-3,5-dichlorophenyl)ethane, 
1,1-bis(4-hydroxy-3,5-dibromophenyl)ethane, 
1,2-bis(4-hydroxy-3-chlorophenyl)ethane, 
1,2-bis(4-hydroxy-3-bromophenyl)ethane, 
1,2-bis(4-hydroxy-3,5-dichlorophenyl)ethane, 
1,2-bis(4-hydroxy-3,5-dibromophenyl)ethane, 
2,2-bis(4-hydroxy-2-bromophenyl)propane, 
2,2-bis(4-hydroxy-3-chlorophenyl)propane, 
2,2-bis(4-hydroxy-3-bromophenyl)propane, 
2,2-bis(4-hydroxy-3,5-dibromophenyl)propane, 
2,2-bis(4-hydroxy-3,5-dichlorophenyl)propane, 
1,1-bis(4-hydroxy-3,5-dichlorophenyl)butane, 
1,1-bis(4-hydroxy-3,5-dichlorophenyl)butane, 
1,1-bis(4-hydroxy-3-chlorophenyl)butane, 
1,1-bis(4-hydroxy-3-bromophenyl)butane. Of those compounds 
2,2-bis(4-hydroxy 3,5-dibromophenyl)propane and 
2,2-bis(4-hydroxy-3,5-dichlorophenyl)propane are preferred. 
The synthetic resins to which the flame retardant of the present invention 
is added for imparting flame retardancy to the resin include for example, 
thermoplastic resins, that is, a homopolymer such as polyethylene, 
polypropylene, polystyrene; a copolymer, such as styrenebutadiene 
copolymer; styrene-butadiene-acrylonitrile terpolymer (including ABS 
resin); blending polymer consisting of homopolymer thereof, homopolymer of 
styrene, butadiene or acrylonitrile, and/or copolymer thereof; polyester; 
polycarbonate; polyamide; polyacetal; polyurethane and mixture thereof; 
and a thermosetting resin, such as a phenol resin and an epoxy resin. 
When a resin incorporating the flame retardant of the present invention is 
burnt, the drippings of the resin do not fall. So, the flame retardant of 
the present invention imparts excellent flame retardancy to the resins, 
when incorporated therein. 
The flame retardant of the present invention may be incorporated in the 
synthetic resin alone. Or it may be used in conjunction with a flame 
retardant promotor, such as antimony trioxide, bismuth trioxide, tin 
oxide, zirconium oxide and the like. 
Any conventional process may be used for incorporating the flame retardant 
of the present invention in the synthetic resin including, for example, 
the dry blend method comprising mixing the retardant with resin pellets; 
the wet blend method comprising mixing a solution of the retardant in a 
solvent with molten resin; the immersion method comprising immersing the 
molded product in a solution of the retardant in a solvent; and the 
coating method comprising coating the solution of the retardant on the 
molded product. 
The amount of the flame retardant employed is not critical. The amount 
depends on whether the flame retardant promoter is used or not, the degree 
of flame retardancy desired and the like. More than 5% by weight, 
preferably from about 10 to about 20% by weight of the flame retardant is 
conveniently employed on the basis of total weight of the resin and the 
flame retardant. 
Knonw heat stabilizers, light stabilizers, colorants, inorganic fillers, 
and/or lubricants may be added to the flame retardant-incorporating resin. 
Tests on the flame retardancy effectiveness of the present invention were 
carried out in accordance with UL Standard. 
The term "UL" means Underwriters Laboratories Inc. in the United States. 
The Underwriters Laboratories Inc. is a public safety organization. The 
Underwriter Laboratories Inc. describes the test for flammability of a 
plastic. The standard of the test is UL 94. In UL 94 Test Standard there 
are 4 classes, 94 V-0, 94 V-1, 94 V-2, 94 HB for evaluating the degree of 
flame retardancy.

This invention is further illustrated, but in no way limited, by the 
following Examples. The parts and percent by weight unless otherwise 
specified. 
EXAMPLE 1 
Preparation of flame retardant of this invention. 
In a four necked flask equipped with agitator, cooler, thermometer and 
dropping funnel was charged 0.3 mol of sodium salt of tetrabromo bisphenol 
A namely, 2,2-bis(4-hydroxy-3,5-bromophenyl)propane. To the flask was 
added 200 ml of dry methylene chloride to prepare a suspension of 
tetrabromobisphenol A. A solution of 0.2 mol of phosphorus oxytrichloride 
in 100 ml of dry methylene chloride was added dropwise to the suspension 
from the dropping funnel over 1 hour at room temperature. After the 
dropping step is completed, the mixture was gradually heated to 40.degree. 
C. over 1 hour with stirring. Then 1.0 ml of triethylamine was added to 
the mixture. The agitation of the solution was continued for 5 hours to 
complete the reaction. After the reaction was completed, precipitate 
(referred to as product B) was separated from methylene chloride phase 
dissolving product A through filtration. Product was ground and was boiled 
in boiling water for 1 to 2 hrs., and was washed with methanol to obtain 
120 g of white solid material having melting point of from 225.degree. to 
228.degree. C. (referred to as product B'). Product B' was insoluble in 
methanol or dioxane, was wettable with methylene or tetrahydrofuran and 
was soluble in dimethyl acetamide. The content of phosphorus in product B' 
was 6.2%; and the content of Cl in P-Cl type in product B' was 5.0%. 
Product B' was confirmed through infrared absorption analysis to be the 
reaction product of tetrabromophenol A with phosphorus oxytrichloride. 
The product B' was washed with boiling water. The content of phosphorus in 
treated product B' was 3.3%; and the content of Cl in P-Cl type therein 
was 4.5%. The treated product B' was insoluble in methanol or dioxane, was 
wettable with methylene chloride or tetrahydrofuran and was soluble in 
dimethyl acetamide. Product B' had an intrinsic viscosity of 0.027 when a 
solution of product B' in dimethyl acetamide was measured. This intrinsic 
viscosity value corresponds to a polymerization degree of 4. 
The filtrate (methylene chloride phase containing product A) was poured 
into a large amount of methanol to obtain 30 g of white solid material 
(product A') having melting point of 176.degree. to 178.degree. C. Product 
A' was confirmed to be the reaction product of tetrabromobisphenol A with 
phosphorus oxyrichloride. Molecular weight, content of phosphorus and 
content of Cl in P-Cl type of product A' were measured. 
The results are shown in the following. 
______________________________________ 
Molecular 
Content Content of 
weight of P (%) Cl in P-Cl type (%) 
______________________________________ 
Measured 1156 2.9 3.7 
Theoretical 
1167.5 2.6 3.1 
______________________________________ 
We found from the results that product A' was a compound having the formula 
##STR18## 
EXAMPLE 2 
In a four necked flask equipped with agitator, cooler, thermometer and 
dropping funnel was charged 0.3 mol of tetrabromobisphenol A. 100 Ml of 
dry methylene chloride and 100 ml of pyridine were added to the mixture, 
and 1 mol of NaOH was added thereto. A solution of 0.2 mol of phosphorus 
oxytrichloride in 100 ml of dry methylene chloride was added dropwise to 
the resulting mixture from the dropping funnel over 1 hour at room 
temperature. After the dropping step was completed, the mixture was 
gradually heated to 40.degree. C. over 1 hour with stirring. The reaction 
was continued for an additional 4 hrs. After the reaction was completed, 
the solvent and pyridine were separated from the reaction product by a 
conventional method and treated in the same way as in Example 1 to obtain 
white solid material. The intrinsic viscosity of the solid was 0.047 when 
a solution of the solid in dimethyl acetamide was measured. This intrinsic 
viscosity value corresponds to a polymerizaton degree of 8. 
We found that the solid material is the same as product B' in Example 1. 
EXAMPLE 3 
The procedure of Example 1 was repeated except that tetrachlorobisphenol A, 
namely 2,2-bis(4-hydroxy-3,5-dichlorophenyl)propane was used. As in 
Example 1, a white solid having melting point of from 225.degree. to 
230.degree. C. was obtained. The intrinsic viscosity of the solid was 
0.033 when a solution of the solid in dimethyl acetamide was measured. 
EXAMPLE 4 
Preparation of flame retardant in case POX.sub.3 is POBr.sub.3. 
In a four necked flask equipped with agitator, cooler, thermometer and 
dropping funnel was charged 0.3 mol of tetrabromobisphenol A. 200 Ml of 
dry methylene chloride, 1.0 mol of triethylamine as a catalyst and 0.75 
mol of sodium hydroxide were added to the tetrabromobisphenol A to produce 
a suspension. A solution of 0.2 mol of phosphorus oxytribromide in 100 ml 
of dry methylene chloride was added dropwise to the suspension from the 
dropping funnel over 1 hour at room temperature. After the dropping step 
is completed, 300 ml of water was added to the mixture. Agitation of the 
mixture was continued for an addtional 2 hrs. to obtain 115 gr. of white 
solid precipitate. The precipitate was insoluble in methanol or dioxane, 
was somewhat wettable with methylene chloride or tetrahydrofuran and was 
soluble in dimethyl acetamide. The precipitate was purified and ground in 
the same way as in Example 1 to obtain white solid product having melting 
point of from 225.degree. to 230.degree. C. The product was confirmed 
through infrared absorption analysis to be the reaction product of 
tetrabromobisphenol A with phosphorus oxytribromide. Measured intrinsic 
viscosity of the solid was 0.040 (as dimethylacetamide solution). 
EXAMPLES 5-11 
Product B' prepared in Example 1 was added to each of the resins as shown 
in Table 1. Article 1/3 inch thick, 0.5 inch wide and 5 inches long was 
obtained by molding each of the resins incorporating product B'. The 
flaming-test of the molded articles was conducted in accordance with UL 94 
Standard. The results are shown in Table 1. 
For comparison, the flame retardant of the prior art was added to each of 
the resins as shown in Table 1. The molding step and the combustion test 
were conducted in the above way. The results are shown in Table 1 as 
control tests 1 and 2. 
Table 1 
__________________________________________________________________________ 
Amount 
Amount 
of flame 
of 
Example 
retardant 
Sb.sub.2 O.sub.3 
Resins UL 94 flame 
Drippings 
No. added (%) 
added 
employed 
class of resin 
__________________________________________________________________________ 
5 20 0 polystyrene 
94 V-0 Non 
6 15 5 polystyrene 
94 V-0 Non 
7 20 0 High-impact 
94 V-0 Non 
polystyrene 
8 15 5 High-impact 
94 V-0 Non 
polystyrene 
9 20 0 ABS 94 V-0 Non 
10 15 5 ABS 94 V-0 Non 
11 10 0 poly- 94 V-1 ++ 
carbonate 
Control High-impact 
1 20* 5 polystyrene 
94 V-2 + 
Control 
2 20** 5 polystyrene 
94 V-2 + 
__________________________________________________________________________ 
+: Dripping that ignited the cotton 
++: Dripping, but did not ignited the cotton 
*: Flame retardant of prior art employed in control 1 is the compound 
having the formula 
##STR19## 
**: Flame retardant of prior art employed in control is the compound 
having the formula 
##STR20## 
- 
EXAMPLE 12-15 
The procedure of Examples 5-11 were repeated except that product A' was 
employed in place of product B'. The results are shown in Table 2. 
Table 2 
______________________________________ 
Amount Amount 
of flame of UL 
retardant Sb.sub.2 O.sub.3 
Resins flame Drippings 
No. added (%) added employed class of resin 
______________________________________ 
12 20 0 polystyrene 
94 V-0 
Non 
13 20 0 High-impact 
94 V-0 
Non 
polystyrene 
14 20 5 ABS 94 V-0 
Non 
15 10 0 poly- 94 V-1 
** 
carbonate 
______________________________________ 
** Dripping, but did not ignite the cotton 
EXAMPLE 16 
(a) The product obtained in Example 3 in the amount of 20% by weight or (b) 
said product in the amount of 15% by weight and antimony trioxide in the 
amount of 5% by weight was incorporated in high-impact polystyrene. The 
molding step and the combustion test were effected in the same way as in 
Example 4. The class of all flame retardancy were UL 94 V-0.