Pentaerythrityl diphosphonate-ammonium polyphosphate combinations as flame retardants for olefin polymers

Self-extinguishing, non-dripping polyolefin polymer compositions are prepared from a mixture of certain pentaerythrityl diphosphonates and ammonium phosphate. Dicyanopentaerythrityl diphosphonate, a new compound, is useful herein without the polyphosphate.

The present invention relates in general to flame retardant polyolefin 
compositions and, in particular, to flame retardant polyolefin 
compositions containing effective flame retarding amounts of a combination 
of a pentaerythrityl diphosphonate and ammonium polyphosphate. 
The production of compositions which are flame retardant is of considerable 
commercial importance in that many articles such as castings, moldings, 
and laminates are required to be flame resistant. At least as important as 
the ability to resist burning is the resistance of such compositions to 
drip flaming particles when they do burn, in order to prevent ignition of 
surrounding combustible materials, such as carpeting, draperies, or 
upholstery. Thus, polyolefin compositions need to be both 
self-extinguishing and nondripping. 
The present invention is directed to polyolefin compositions, particularly 
polypropylene compositions, which are rendered flame retardant (i.e., both 
self-extinguishing and nondripping) by the incorporation therein of a 
flame retardant amount of a combination of a pentaerythrityl diphosphonate 
and ammonium polyphosphate. 
The pentaerythrityl diphosphonate used herein may be represented by the 
formula: 
##STR1## 
where R is methyl, phenyl, benzyl, or cyano. 
Pentaerythrityl diphosphonates represented by the above formula where R is 
alkyl of 1 to 18 carbon atoms are disclosed by U.S. Pat. No. 3,141,032. 
The disclosure states that compounds where R is alkyl of at least 8 carbon 
atoms are preferred and that the compounds are useful as flame retardants 
for polyolefins. 
A broader genus of pentaerythrityl diphosphonates, useful as flame 
retardants for polyesters, is disclosed in German Offenleg. No. 2,630,693 
wherein, in the above formula, R is selected from alkyl of 1 to 10 carbon 
atoms, cycloalkyl of 5 to 7 carbon atoms, haloalkyl of 1 to 3 carbon 
atoms, alkenyl of 2 to 10 carbon atoms, phenyl or halogen-substituted 
phenyl, phenylalkyl (or ring halogen-substituted phenylalkyl) of 7 to 9 
carbon atoms or phenylalkenyl (a ring halogen-substituted phenylalkenyl) 
of 8 to 10 carbon atoms. 
The diphosphonates have not been found to be useful by themselves in 
polyolefins to provide self-extinguishing, nondripping compositions. The 
compositions of the present invention, to the contrary, provide 
self-extinguishing, non-dripping polyolefin compositions, particularly 
polypropylene, whereas structurally closely related compositions do not. 
The pentaerythrityl diphosphonate compounds may be readily prepared by 
known procedures. The methyl and phenyl derivatives may be prepared by 
reacting, respectively, methylphosphonic dichloride and phenylphosphonic 
dichloride with pentaerythritol in methylene chloride or dioxane solvent 
at about 50.degree. C., or in the absence of a solvent. 
The compounds in general may be prepared via an Arbuzov-type rearrangement, 
in the presence or absence of a solvent, e.g. dioxane, by reacting an 
appropriate active halogen compound, e.g. benzyl chloride (bromide), with 
a suitable dialkyl pentaerythrityl diphosphite, e.g. diethyl 
pentaerythrityl diphosphite: 
##STR2## 
In addition to a pentaerythrityl diphosphonate compound, the flame 
retardant compositions further contain ammonium polyphosphate which may be 
prepared as described in U.S. Pat. Nos. 3,423,343 and 3,513,114. The 
ammonium polyphosphates are generally substantially water-insoluble and 
possess a plurality of P-O-P type linkages. Ammonium polyphosphate is 
available as Phos-chek P/30 from Monsanto Chemical Co. and has about 30% 
phosphorus. 
The pentaerythrityl diphosphonate and the ammonium polyphosphate 
combination is useful as a flame retardant when incorporated into 
polyolefins, especially polypropylene, in a flame retarding amount, i.e., 
from about 20 to about 40 percent by weight, based on the weight of the 
polymer. The ratio of pentaerythrityl diphosphonate to ammonium 
polyphosphate preferably ranges from about 3:1 to 1:2 to provide the 
self-extinguishing, nondripping formulations of the present invention. 
In order to further improve on the nondripping characteristics of the 
combination of pentaerythrityl diphosphonate and ammonium polyphosphate, 
it has been found that the addition of various oxides and/or carbonates 
may be especially useful. 
The oxides or carbonates may be added to the polyolefin in an amount 
ranging from about 0.25 to 5 percent by weight, based on the weight of the 
polymer. Useful compounds include alkali metal carbonates, such as sodium 
carbonate, potassium carbonate, etc.; alkaline earth metal oxides, such as 
barium oxide, magnesium oxide, etc.; alkaline earth metal carbonates, such 
as magnesium carbonate, calcium carbonate, etc.; Group IV-A metal oxides, 
such as silicon dioxide, stannic oxide, etc.; titanium dioxide, zinc 
oxide, aluminum oxide, antimony oxide, and the like. 
The polyolefins to be flame retarded herein include homopolymers and 
copolymers of olefins, preferably having about 2-4 carbon atoms, and 
particularly propylene polymers,, especially homopolypropylene. Copolymers 
of propylene with ethylene, butylene, and isobutylene, containing 50-90 
percent propylene by weight, may also be flame retarded with this 
invention. 
The flame retardant combination may be added to the polymer as such, or as 
individual components, by any standard method, such as by milling the 
polymer and the components on, for example, a two-roll mill, in a Banbury 
mixer, by molding the components and the polymer simultaneously, or by 
extruding the polymer and components, or by merely blending all the 
ingredients together in powder form and thereafter forming the desired 
ultimate product. Additionally, the flame retardant components or 
combination may be added during the production of the polymer, i.e. during 
polymerization, provided the catalyst, conditions, and other ingredients 
of the polymerization are inert thereto. 
It is also within the scope of this invention to incorporate such common 
ingredients as plasticizers, dyes, pigments, heat and light stabilizers, 
antioxidants, antistatic agents, photochromic materials, and the like, 
into the polymer composition.

EXAMPLE 1 
Preparation of Dimethyl Pentaerythrityl Diphosphonate 
Methylphosphonic dichloride (53.2 grams, 0.4 mole) was reacted with 
pentaerythritol (27.2 grams, 0.2 mole) at 55.degree.-60.degree. C. under a 
nitrogen atmosphere. The desired product was obtained in 48 percent yield; 
m.p. 217.degree. C. 
EXAMPLE 2 
Preparation of Diphenyl Pentaerythrityl Diphosphonate 
To one liter of dioxane was added 68 grams (0.5 mole) of pentaerythritol 
and then 174 grams (2.2 moles) of pyridine was added. Then 195 grams (1.0 
mole) of phenylphosphonic dichloride was added slowly. The mixture along 
with all the solid precipitate was refluxed overnight with stirring. The 
solids were filtered and washed with cold dioxane, then slurried in one 
liter of water and filtered (three times), vacuum dried at 100.degree. C., 
then recrystallized from dimethylformamide. Yield 140 grams (74%), m.p. 
260.degree.-262.degree. C. 
Theory for P.sub.2 O.sub.6 C.sub.17 H.sub.18 : C, 53.8; H, 4.79; P, 16.35. 
Found: C, 53.31; H, 4.78; P. 16.11. 
Example 3 
Preparation of Dibenzyl Pentaerythrityl Diphosphonate 
Diethyl pentaerythrityl diphosphite (0.1 mole) was reacted with benzyl 
chloride (0.3 mole) under a nitrogen atmosphere at 165.degree. C. The 
product had a melting point of 248.degree. C., 42% yield. 
EXAMPLE 4 
Preparation of Dicyano Pentaerythrityl Diphosphonate 
Cyanogen bromide (0.2 mole) was reacted with diethyl pentaerythrityl 
diphosphite (0.1 mole) in 150 ml of dioxane at 15.degree. C. under a 
nitrogen atmosphere to give the desired compound in 43% yield; m.p. 
300.degree. C. (dec.). 
EXAMPLES 5-11 
Following the basic procedure of Example 4, except that the solvent was 
omitted, diethyl pentaerythrityl diphosphite was reacted with the 
appropriate halide at the indicated temperatures to give compounds having 
the following structure wherein the R groups are as shown in Table I: 
##STR3## 
TABLE I 
______________________________________ 
Example 
R T.degree.C. 
M.P. .degree.C. 
Yield, % 
______________________________________ 
120 240 76 
6 
##STR4## 120 196 69 
7 
##STR5## 145 155 82 
8 
##STR6## 170 207 69 
9 
##STR7## 147 220 59 
10 
##STR8## 120 257 71 
11 CH.sub.2CHCH.sub.2 
95 150 52 
______________________________________ 
EXAMPLES 12-15 
To evaluate the effectiveness of the flame retardant compositions of the 
present invention, the specified diphosphonate (15 parts by weight) and 
ammonium polyphosphate (15 parts by weight) were dry blended with 70 parts 
by weight of polypropylene powder (Profax.RTM. 6401 of Hercules). The 
blends were extruded thru a Melt Index Apparatus (described in ASTM 
D-1238) at 250.degree. C. to give cylindrical polymer samples 5" in length 
and 0.25" diameter. Two samples of each composition were subjected to the 
flammability procedure, Underwriters Laboratories Test UL 94, Vertical 
Test Method, as described in Paragraphs 3.10-3.15, September, 1973. 
Each sample, held in a vertical position, was ignited with a 3/4" blue 
flame for 10 seconds. The flame was withdrawn and the duration of the 
flaming before extinguishment was recorded. When flaming ceased, the test 
flame was reapplied for 10 seconds. After removal of the flame, the 
flaming duration was again recorded. 
The following were recorded: 
(1) Duration of time to extinguishment for each application 
(2) Whether or not the specimen dripped flaming particles which ignited a 
cotton swatch placed 12 inches below the specimen 
If a sample burned for more than 30 seconds after either application, it 
was considered as failing the test. The results are summarized in Table II 
below. 
TABLE II 
______________________________________ 
Time to Flame 
Example R Extinguishment 
Melt Dripping 
______________________________________ 
12 Methyl 0 None 
13 Phenyl 12 None 
14 Benzyl 0 None 
15 Cyano 0 None 
______________________________________ 
EXAMPLES 16-33 
The procedure of Examples 12-15 was repeated using the additives in the 
concentrations indicated in Table III. The results are also summarized in 
the Table. 
The results clearly show that the individual additives when used alone, 
with the exception of dicyano pentaerythrityl diphosphonate, are 
ineffective in producing self-extinguishing, non-dripping compositions. 
In addition, in the preferred formulation utilizing 12 percent 
diphosphonate, 17 percent ammonium polyphosphate, and 1 percent titanium 
dioxide per 70 percent of polypropylene, only the four diphosphonates of 
the present invention yielded self-extinguishing, non-dripping 
compositions. The two preferred compounds of U.S. Pat. No. 3,141,032 (See 
Examples 32 and 33) failed to produce self-extinguishing, non-dripping 
compositions. 
TABLE III 
__________________________________________________________________________ 
Evaluation of Flammability 
% % Ammonium 
% Titanium 
Time to Flame 
Melt 
Example 
Diphosphonate 
Polyphosphate 
Dioxide 
Extinguishment 
Dripping 
__________________________________________________________________________ 
16 Methyl 
30 0 0 7 Dripped 
17 Phenyl 
30 0 0 8 Dripped 
18 Benzyl 
30 0 0 4 Dripped 
19 Cyano 30 0 0 0 None 
20 -- 0 30 0 &gt;60 Failed 
21 Methyl 
12 17 1 0 None 
22 Phenyl 
12 17 1 0 None 
23 Benzyl 
12 17 1 2 None 
24 Cyano 12 17 1 23 None 
25 p-methyl- 
12 17 1 6 Dripped 
benzyl 
26 2,4-di- 
12 17 1 5 Dripped* 
methylben- 
zyl 
27 2,4,6-tri- 
12 17 1 13 Dripped* 
methylben- 
zyl 
28 Naphthyl- 
12 17 1 &gt;60 Failed 
methyl 
29 p-chloro- 
12 17 1 15 Dripped* 
benzyl 
30 p-Bromo- 
12 17 1 2 Dripped* 
benzyl 
31 Allyl 12 17 1 &gt;60 Dripped* 
32 n-Decyl** 
12 17 1 24 Dripped* 
33 n-Octo- 
12 17 1 &gt;60 Dripped* 
decyl** 
__________________________________________________________________________ 
*Ignited cotton 
**Preferred compounds iof U. S. 3,141,032 (Exaples 6 and 1, respectively)