CA1080400A - Poly (phosphazene) vulcanizates and foams - Google Patents

Abstract

ABSTRACT
This invention relates to fire-resistant polyphosphazene polymers which exhibit a high degree of flame retardancy, and which do not generate large amounts of smoke or toxic products when ignited or exposed to relatively high temperatures. More specifically, it relates to low density polyphosphazenes as foams and coating materials with outstanding thermal stability and to vulcanizable compositions of poly(phosphazenes) and insulating foams made therefrom. Additionally, the invention provides a process for the preparation of fire retardant, low smoking, thermally stable oil resistant vulcanizates and closed cell foams which are made from the poly(phosphazenes) polymers described above. To process comprises preparing a suitable mixture; milling the mixture;
cutting the product to a preform charge; and either molding said preform charge under heat and pressure to produce a vulcanizate or molding said preform charge to produce a procured slab which is expanded and vulcanized in an oven to pro-duce a foam.

Description

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This application is directed to poly(phosphazene) polymer compositions Eor preparing closea cell foams, the preparation thereof and the products so produced, whereas parent application S.N. 241,205, filed December 8, 1975, is directed to poly(phosphazene) polymer compositions for the preparation of vulcanizates, the preparation thereof and the products so produced.
This invention herein described was made in the course of or under a contract or subcontract with the United States Government.
This invention relates to fire-resistant polyphosphazene polymers which exhibit a high degree of 1ame ret,ardancy, and which do not generate large amounts of smoke or toxic products when ignited or exposed to relatively high temperatures.
More specifically, it relates to low density polyphosphazenes as foams and coating materials with outstanding thermal stability and to vulcanizable compositions of poly(phosphazenes) and insulating foams made therefrom, The polyphosphazenes to which the present invention is applicable include those described in United States Patents 3,515,688, issued June 2, 1970;
3,370,020, issued February 20, 1968; 3,700,629, issued October 24, 1972, and 3,702,822, issued November 14, 1972, and to polyphosphazenes described in '~phosphorus-Nitrogen Compounds", by Allcock, published 1972, and elsewhere in the literature.
It is particularly adapted for use with poly(aryloxyphosphazenes) of the type described in United States Patent No. 3,856,713, issued December 24, 1974, namely copolymers represented by the general formula .,.
R'O\ /OR

~ P - N

, , - 2 -.

:~ ' ~

,: . .: . , , . -' . ' . . . :- . . : . '~` . : -, . ~ , , .- , . :
: , where n is 50 to 50,000 ana in which R and R' represent different aryl grGups.
For purposes of illustration, and not by way of limitation, the invention is described as it applies to poly(aryloxyphosphazenes) of the type described in the above-noted patent application, but it will be readily apparent to others skilled in the art that it is applicable to other polyphosphazenes.
Briefly, the invention comprises the preparation of such polyphospha-zenes as vulcanizable and foamable compositions, and the production o vulcani-zates, foams or oamed coatings from such compositions.
The poly(aryloxyphosphazenes) were prepared in the manner described in United States Patent No. 3,856,713.
For purposes of illustration, the following is a d~scription of the preparation of a phenoxy-4-ethylphenoxyphosphazene copolymer.
Hexachlorophosphazene was purified by distillation (b.p. 120-125 C/
10 mm Hg) and recrystallization (n-heptane), and was polymerized under vacuum at 250 C, generally in the presence of HCl (1 mmole per 2600-2800 g monomer).
The aryloxides were prepared by addition of sodium methoxide (10 mole ~ over P-Cl equivalents) to a dry equimolar (5 mole % excess over sodium methoxide) solution of phenol and ~-ethylphenol in bis(2-methoxyethyl) ether as about 1.5 liter/mole of sodium methoxide. The methanol produced was removed by addition of benzene, followed by azeotropic distillation. Purified CC12PN~
polymer was dissolved in dry benzene (ca. 1 liter solvent/100 ~ polymer), and added slowly over 3 to 5 hours to a refluxing (125C) solution of sodium aryloxides and temperature was maintained at 125 ~ 1 C for 50 to 55 hours.
The reaction mixture was cooled to 80 C or lower, and copolymer was precipitated by addition to twice the total volume of methanol or ethanol/water (lOv/lv).
The copolymer was washed briefly with methanol and stirred well with water/
methanol (or ethanol) (lv/lv) for one to two days. The polymer was thrice dissolved in 8 to 16 liters of -tetrahydrofuran, precipitated into 10 to 15 ~ ` ' ~, ., -, .. . - . - - .. .. . . .

~allons of distilled water and washed ~ith methanol or isopropyl alcohol.
Vulcanizates of the copolymer are prepared by mixing with each 100 parts by weight of copolymer, up to 350 parts by weight of one or more fillers, 20 to 200 parts by weight of silane treated reinforcing filler, 3 to 20 parts by weight of MgO or ZnO, and 1 to 20 parts by weight of curing agent (peroxide).
Other optional ingredients include plasticizers or processing aids in amounts up to 30 parts by weight, and otherwise conventional additives. A coagent such as triallylcyanurate, trimethylolpropane trimethacrylate, e-thylene glycol dimethacrylate, or other compounds with ~lkenyl functionality of two or higher may also be used, in amounts up to 10 parts by weight per 100 parts by weight of copolymer.
Preferred vulcanizates of the copolymer were prepared by mixing copolymer with 20 to 200 parts by weight of reinforcing filler per hundred parts by weight of copolymer, 5 or 6 parts by weight of MgO and several parts by weight of peroxide curing agent.
The vulcanizate mix was milled, calendered, and cut to a preform charge which was molded at 290 to 320F for 15 minutes, and could be further postcured for 24 hours at 212 F.
Tensile strengths up to 2410 psi and ultimate elongations of 50% to 530% were obtained from the resulting vulcanizates, as shown in Table I, which follows.

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~ 8~0 o ~r o o o o ~ ,, ~ Ut o o,,, In ~ ~ I t ~
,, O O O O O h ~ ~ ' V) ~ C~
o ~ 1 ,o, I ~o ~ o~ O

~1 ~ X
O
~ ~J
o ~r o o o o x , ,~ V O
I o o I I I u~ I I u~ I Ei ~ ,E~
V O O

3~`~ .a ~ ~ I I In C~ ~ ~
~r ~) .
~J~ ~ O ~ ~ ~ ,,~ Ul ~ ~ ~ ~ . JJ
~:1 h 1 h n~ --^~ ~ O ~ ~ ~0 ~ 1 o ,o~
CO I ~ ~ ~

O-- ~1 0 _ ~0~

_' U ~ A ~ U ~ U
. - 5 -~' Formulations for the preparation o~ foams are similar to those for the preparation of vulcanizates, but do not have to include the silane treated reinforcing filler, and may include up to 50 parts by weight plasticizer and processing aid, and include in addition about 1 to 70 parts by weight of a chemical blowing agent, and any activator necessary for the blowing agent.
Several preferred formulations are shown in Table II.
Foams were produced from such formulations by confinement of a sample preform in a pressurized, preheated mold to obtain a slight precure, and removal of the hot sample for final expansion and cure in a forced air oven.
The sample preform was the same length and width as the mold, and about 125~ of the aepth. Precure was accomplished by confinement of the sample preform in the mold under pressure for up to 8 minutes at 230F to 260 F.
Final expansion and cure was effected in a forced air oven for 5 to 60 minutes at 285 F to 350 F with a linear expansion of slightly more than double for most samples. A free blown sample (i.e., no premold) also produced a good foam.
The addition of a small amount of zinc stearate (4 to 14 parts by weight per hundred parts of copolymer) resulted in marked improvement of pore size and uniformity.
The foams exhibited excellen-t properties when tested according to the National Bureau of Standards Smoke Test, as may be seen from the physical ; property data in Table II.

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04ao TABLE II
:
NBS Smoke Test on [(C6H5O)2PN-(4-c2H5c6H4O)2pN]n Foam (Flaming Condition)_ Commercial :~
FR Foam _ II II~ IV
DensitY. 3 pounds/ft 6 5.9 4.3 9.4 6.7 Limiting Oxygen Index, % 29 25 31 31 48 max.
T to S=16, minØ2 0.2 0.9 0.9 1.5 R , max rate, m min 1 149 50 40 60 11 HCl, ppm - - 0 0 0 CO2, ppm - 6000 1400 1400 3000 CO, ppm - 800 200 200 100 HCN, ppm - 30 7 7 10 ~oam Formulation Copolymer 100 100 100 100 Calcium Carbonate 40 Hydrated Alumina - 100 100 200 High Activity MgO 5 5 5 5 VAROX* Powder 5 5.7 3 8 Benzoyl Peroxide (wet) 1 1.4 1.6 2 Azodicarbonamide 15 21.2 15 30 Surface Treated Urea 10 14.1 10 20 Zinc Stearate - 4 10 14 Cure, Min/ F 1/2705/2305/230 6/230 Oven Expansion, Min/ F 15/300 60/300 25/285 15/300 Compression resistance at 25% deflection (psi) 0.9 2.2 4.8 2.1 Tensile strength (psi) - 20 60 20 Elongation, % - 80 125 90 * Trade Mark '~' : `~

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.: , - - . : . . , : : ::: : : : . . , . . . ;

Foams with densities as low as 3.4 lbs/f-t have been produced, and foams of lower density are possible. The pore si~e and closed cell structure appeared quite uniform under microscopic examination.
The L(C6H50) 2PN-(4-C2H5C6H40)2PN~n foam5 aged in a static air oven at 300 F were compared to commercially availa~le fire-retardant thermal insulation for changes in density and compression resistance at 25~ de~lection. Changes in density with time shown in Table III show very little change in the ~C6H50)2PN--(4-C2H5C6H~o)2PN~ foam density as compared with up to 80% gain in density for a commercial foam after 408 hours at 300-F.
Compression resistance at 2% deflection of ~(C6H50)2PN-(4-C2H5C6H40)2-PN~n foam was unchanged after 168 hours and was reasonably low (12.5 psi) after 600 hours at 300 F. Commercial fire-retardant foam sheets became rigid after 24 hours and crumbled when tested at 96 hours. Compression resistance at 25%
deflection ranged from 0.9 to 4.8 psi for all L(C6H5G)2PN-(4-C2H5C6H4o)2PN3 foams tested.
Tensile strengths of 20 to 35 psi were obtained for t(C6H50)2PN-(4--C2H5C6H40)2PN~ foams in the desired density range, with tensile strengths of up to 82 psi for higher density foams. Ultimate elongations ranged from 80 to 175%.
While the invention has been described with particular reference to a copolymer in which phenoxy and 4-ethylphenoxy groups are present in the copolymer in substantially equimolar proportions, similar Eire resistant foams have been produced from ~(CH30)2PN-(4-Clc6H40)2PN]n~ L(C6H5 )2 P 4 9 6 4 2 n Outstanding thermal stability of the low density ~(C6H50)2PN-(4--C2H5C6H40)2PN~ foams as compared to other commercial fire-resistant thermal insulations has been demonstrated in isothermal aging tests at 300F. Poly(aryl-oxyphosphazene) samples remained flexible after 408 hours with little change in density, while other foam materials shrank and embrittled, as evidenced by the results in Table III. - 8 -,, : : :

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TABLE I I I
Density (lbs/ft ) of Foams After Isothermal Aging at 300 F

Commercial Commercial [~C ~50)2pN-(4_ Foam A Foam B -C2~5C6H40) 2P ~ n (Hr/300 F) FR Tube BlackPhosphazene Foam 0 5.2 6.0 6.2 24 7.0 11.57.2 48 7.6 10.37.8 144 7.0 10.1 7.9 168 6.6 10.4 7.0 408 - 10.8 7.1 Percent Gain After 408 hours - 80 lS
All samples except the phosphazene foam were rigid after 24 hours at 300 F.

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~(c6H5o)2PN (m CH3C6H4)2PN~(-~CH3C6H40)2PN~n and ~(n-cH3c6H4o)2PN-(p-cH3c6H4o)2-PN] and can be produced from any of the poly~aryloxyphosphazenes) described in our sritish Patent No. 1,413,784, dated June 10, 1974, or more broadly from polymers having a degree of polymerization between about 50 and 50,000 and consisting of repeating units randomly distributed along a -P=N- backbone and represented by at least one o the general formulae:
R~R2 ~Rl --P=N--, --I--1~--, --I=1~--, --l=N--, RJ~ Rl/f~\R2 RlJ~2 R~R2 O
P - ~T - ~- P N -O Q

` 1~2 ~2 in which Rl represents hydrogen, bromine, chlorine, alkyl radicals selected from the group of primary alkyls with 1 to 12 carbon atoms, secondary alkyls with 4 to 12 carbon atoms and cx,c~-dimethyl tertiary alkyls with 4 to 14 carbon atoms, R2 is alkyl as defined for Rl, with the proviso that Rl when alkyl or halogen, and R2 when substituted on an aryl ring, are substituted at the meta or para position, and the Rl's and R2's need not all be the same.

. , : ' '~' ;-: `'` .,, : ' " ~; ' ,' ' :

:: :

4(~al In addition, for cure enhancement, a small amount (0.1 to 5 mole ~) of an alkenyloxy or an alkenyl substi-tuted aryloxy such as one derived from vinyl phenol, allyl phenol, isoeugenol or eugenol may be present on the phosphorus atom.
It will be readily appreciated that other peroxides may be used in place of dicumyl or benzoyl peroxide, other plasticiæers may be used in place of zinc stearate and other fillers may be used in place of those disclosed without departing from the intended scope of the invention which is defined - in the appended claims.
The present invention provides a process for the preparation of fire retardant, low smoking, thermally stable oil resistant vulcanizates, and closed cell foams which are made from the poly(phosphazene) polymers described above.
The process comprises:
preparing a suitable mixture;
milling the mixture;
cutting the product to a preform charge; and either molding said preform charge under heat and pressure to produce a vulcanizate, or molding said preform charge to produce a precured ~' slab which is expanded and vulcanized in an oven to produce a foam.
` 20 ~, : ', .

,. ,

Claims (12)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A composition suitable for the preparation of a fire retardant, low-smoking, non-dripping, oil-resistant closed cell foam, comprising for each 100 parts of poly(phosphazene) polymer:
up to 350 parts by weight of hydrated alumina;
3 to 20 parts by weight of MgO or ZnO;
up to about 50 parts by weight of a plasticizer and processing aid;
up to 10 parts by weight of coagent consisting of compounds with alkenyl functionality of two or higher;
between about 1 and 70 parts by weight of a chemical blowing agent and any necessary activator for said blowing agent;
between about 1 and 15 parts by weight of at least one organic peroxide curing agent;
the phosphazene polymer having a degree of polymerization of 50 to 50,000 and consisting of repeating units randomly distributed along a -P=N-backbone, and represented by at least one of the general formulae:

, , , , , , in which R1 represents hydrogen, bromine, chlorine, alkyl radicals selected from the group of primary alkyls with 1 to 12 carbon atoms, secondary alkyls with 4 to 12 carbon atoms and .alpha.,.alpha.-dimethyl tertiary alkyls with 4 to 14 carbon atoms, R2 is alkyl as defined for R1 with the proviso that R1 when alkyl or halogen, and R2 when substituted on an aryl ring, are substituted at the meta or para position, and the R1's and R2's need not all be the same.

2. The composition of claim 1, wherein the blowing agent is azodicarbon-amide.

3. The composition of claim 1, wherein the plasticizer is a metallic stearate.

4. The composition of claim 1, wherein the organic peroxide curing agent comprises a mixture of a first peroxide effective at a relatively low tempera-ture, and a second peroxide effective at a higher temperature.

5. The composition of claim 4, wherein the peroxides are benzoyl peroxide and dicumyl peroxide.

6. The composition of claim 4, wherein the peroxides are benzoyl peroxide and 2,5-bis(tert-butylperoxy)2,5-dimethyl hexane.

7. A process for producing a fire retardant, low-smoking, non-dripping, oil-resistant closed cell foam which comprises:
preparing a mixture consisting of the composition of claim 1;

milling and then calendering said mixture, preparing a preform from the resulting product, precuring said material in a mold under pressure, then expanding and vulcanizing said material in an oven.

8. A process for producing a fire retardant, low-smoking, non-dripping, oil-resistant closed cell foam which comprises:
preparing a mixture consisting of the composition of claim 1;
milling and then calendering said mixture, preparing a preform from the resulting product, and expanding and vulcanizing said material in an oven.

9. The process of claim 7, including in addition the step of post curing the material for up to 24 hours at 200 to 300 F.

10. Foamed poly(phosphazene) polymers with a degree of polymerization of 50 to 50,000, consisting of repeating units randomly distributed along a -P=N-backbone, and represented by at least one of the general formulae:

, , , , ,, in which R1 represents hydrogen, bromine, chlorine, alkyl radicals selected from the group of primary alkyls with 1 to 12 carbon atoms, secondary alkyls with 4 to 12 carbon atoms and .alpha.,.alpha.-dimethyl tertiary alkyls with 4 to 14 carbon atoms, R2 is alkyl as defined for R1 with the proviso that R1 when alkyl or halogen, and R2 when substituted on an aryl ring, are substituted at the meta or para position, and the R1's and R2's need not all be the same, when prepared by the process of claim 8.

11. An article covered with the foam of claim 10.

12. A composition which produces a low-smoking, low-flame spread index closed cell foam, comprising:
100 parts by weight of [(C6H5O)2PN-(4-C2H5C6H4O)2PN] copolymer;
200 parts by weight of hydrated alumina;
5 parts by weight of magnesium oxide;
8 parts by weight of a 50% active blend of 2,5-bis(tert-butylperoxy)--2,5-dimethyl hexane on inert mineral filler;
2 parts by weight of wet benzoyl peroxide;
30 parts by weight azodicarbonamide;
14 parts by weight zinc stearate; and 20 parts by weight surface treated urea.