Polymerization of cyclic dihalophosphazene oligomers

A catalytic method for polymerizing cyclic dihalophosphazene to linear polydihalophosphazene is provided wherein the catalyst is a solid support of silica or alumina containing supported thereon both a transition metal compound and an organometallic compound.

BACKGROUND OF THE INVENTION 
This invention relates to the polymerization of cyclic dihalophosphazenes 
oligomers to higher molecular weight substantially linear 
polydihalophosphazene polymers. The polymerization of cyclic 
dihalophosphazenes such as (NPCl.sub.2).sub.3 or (NPCl.sub.2).sub.4 to 
higher molecular weight linear polydihalophosphazene polymers is well 
known in the art. 
Prior known processes for polymerizing such cyclic dihalophosphazenes 
involved the uncatalyzed or catalyzed thermal polymerization of such 
dihalophosphazenes either in a bulk process or in a solution process 
employing a solvent. Such processes are taught, for example, in U.S. Pat. 
No. 3,370,020 to Allcock et al., issued Feb. 20, 1968; U.S. Pat. No. 
3,515,688 to Rose, issued June 2, 1970; U.S. Pat. No. 4,005,171 to Reynard 
et al., issued Jan. 25, 1977; U.S. Pat. No. 4,123,503 to Snyder et al., 
issued Oct. 31, 1978; U.S. Pat. No. 4,327,064 to Fieldhouse et al., issued 
Apr. 27, 1982; U.S. Pat. No. 3,917,802 to Allcock et al., issued Nov. 4, 
1975; U.S. Pat. No. 4,137,330 to Prichard et al., issued Jan. 30, 1979; 
U.S. Pat. No. 4,242,316 to Sinclair, issued Dec. 30, 1980; PTO Patent 
Specification Publication No. 0004877, published May 12, 1982, to Snyder 
et al.; U.S. Pat. No. 4,225,567 to Halasa et al., issued Sept. 30, 1980; 
U.S. Pat. No. 3,937,790 to Allcock et al., issued Feb. 10, 1976; and U.S. 
Pat. No. 4,226,840 to Fieldhouse et al., issued Oct. 7, 1980. 
The present invention concerns an improvement over all of the prior 
technology by use of a specifically defined supported coordination 
catalyst containing both titanium and aluminum. By this method lower 
temperatures and reaction times are possible and starting materials can be 
employed which are not ultra pure. 
SUMMARY OF THE INVENTION 
In the practice of the present invention, cyclic dihalophosphazenes 
oligomers are polymerized to form polydihalophosphazenes by agitating, 
under an inert gaseous atmosphere, a mixture containing at least one 
cyclic dihalophosphazene and a polar organic solvent for the cyclic 
halophosphazene, in the presence of a catalytic amount of a solid catalyst 
which is composed of a solid support (particulated) selected from the 
group consisting of silica gel or alumina and supported on such support a 
transition metal compound and an organo metallic compound. At least a 
proportion of the transition metal ion has a valence of three or less. The 
agitated mixture is maintained at a temperature of from about 150.degree. 
to about 250.degree. C. for a sufficient period of time to form linear 
polydihalophosphazene and the polydihalophosphazene is recovered. 
DETAILED DESCRIPTION OF THE INVENTION 
The starting material or monomer of the present invention comprises one or 
more cyclic dihalophosphazene oligomers represented by the formula 
(NPX.sub.2).sub.n in which n is from 3 to about 7 and wherein X is a 
halogen selected from the group consisting of chloride, fluoride, and 
bromide ion. X is preferably chloride. The cyclic dihalophosphazene 
oligomers which are employed as starting materials are substantially pure 
oligomers which are obtained by purification of crude cyclic 
dihalophosphazene oligomers. A mixture of these cyclic dihalophosphazenes 
can be employed in the practice of the invention. For example, a mixture 
of tri- and tetracyclic dihalophosphazenes are useful. A variety of 
methods for purification are known in the art and include, for example, 
extraction, crystallization, distillation, saponification, and hydrolysis 
techniques. Cyclic phosphonitrilic chloride trimer or tetramer are 
preferred. One or more of these materials can be employed as the starting 
materials. 
The solvent employed in the practice of the present invention comprises a 
material which is both unreactive to the catalyst and monomer, and 
preferably is a solvent for the monomer and the polymer at the 
polymerization temperatures employed. A polar solvent having a dielectric 
constant high enough to permit cationic polymerization is preferred. 
Examples of suitable solvents include 1,2,4-trichlorobenzene; 
1,2,3-trichlorobenzene; 1,3,5-trichlorobenzene, and mixtures thereof. The 
solvent should preferably be used in an amount which is sufficient to form 
a readily agitated slurry mixture containing the particulate catalyst and 
the monomer. Generally, the solvent should be employed in an amount less 
than about 50 percent by weight of the reaction mixture. 
The process is preferably carried out under an inert, dry atmosphere such 
as nitrogen, helium, or argon. The polymerizations may be conducted under 
a vacuum, atmospheric or elevated pressures. 
The catalysts employed in the present invention comprises a solid support 
of silica gel or alumina containing supported thereon a catalytically 
effective amount of a transition metal compound selected from the group 
consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, 
chromium, molybdenum, tungsten or mixture thereof. Also present on the 
support is an organometallic compound of aluminum or boron, represented by 
the formula R.sub.a MX.sub.b wherein M is either aluminum or boron, a+b is 
equal to the valence of M, X is a halogen such as chloride or bromide, and 
R is a hydrocarbon radical selected from the group consisting of alkyl, 
aryl, cycloalkyl, alkaryl, and arylalkyl, wherein the group contains from 
C.sub.1 to C.sub.20. 
The aluminum atom to transition metal atom mole ratio on the supported 
catalyst is important and should range from about 0.1 to about 100 
aluminum to transition metal, preferably from about 1.0 to about 65, most 
preferably about 3 to about 8. 
The transition metal compound is preferably an alkoxide or a halide such 
as, for example, transition metal-(OR).sub.4 and transition 
metal-(OR).sub.3 wherein R is selected from the group consisting of a 
hydrocarbon or transition metal-X.sub.4 and transition metal-X.sub.3 
wherein X is a halogen. Preferred hydrocarbon groups are isobutyl, 
n-butyl, and isopropyl. The preferred halogen atom is chloride. Preferred 
transition metal compounds include Ti(OCH.sub.2 CH(CH.sub.3).sub.2).sub.4, 
and TiCl.sub.4 and the valence 3 form of these compounds. Preferred 
organometallic compounds are aluminum alkyl halides such as ethylaluminum 
dichloride, diethyl aluminum chloride, ethyl aluminum sesqui chloride and 
mixtures thereof. 
A catalytically sufficient amount of the supported catalyst should be 
present. The catalyst, based on the active transition metal, is provided 
in a molar ratio to "NPCl.sub.2 " unit ranging from about 
1.times.10.sup.-4 :1, to 1.times.10.sup.-2 :1, most preferably 
8.times.10.sup.-4 :1 to 8.times.10.sup.-3 :1. It is preferred to adjust 
the quantity of active catalyst by changing the amount of catalyst on the 
support instead of the amount of support and catalyst. It has been 
discovered that the amount of support in the reaction mixture needs to be 
minimized in order to reduce the formation of gels in the polymer. 
The material employed to support the transition metal compound and 
organometallic compound comprises alumina or silica. These supports can be 
prepared in any convenient manner. The supports should generally be in 
particulate form and range in size from about 60 to about 200 mesh (U.S. 
Standard Sieve Series). The alumina supports can be prepared, for example, 
by the method taught in U.S. Pat. No. 4,428,863, the teachings of which 
are incorporated herein by reference. Silica supports can be prepared, for 
example, by heating silica to about 500.degree. C. under vacuum for about 
5 hours and then cooling under vacuum or nitrogen. Silica supports can 
also be prepared according to the teachings of U.S. Pat. Nos. 4,436,882; 
4,384,086; 4,369,295; 4,434,280 and 4,199,475 the teachings of which are 
incorporated herein by reference. Supporting the transition metal compound 
and organometallic compound on the silica or alumina can likewise be 
accomplished in any manner known in the art. For example, the method 
taught at column 7, line 40 through line 68 of U.S. Pat. No. 4,302,565 can 
be employed. Other techniques can be used. 
Uniform heat distribution throughout the reaction mass should be maintained 
during the polymerization process. Therefore, good mixing is required to 
reduce crosslinking and gel formation. 
The polymerization reaction may be carried out within a temperature range 
of from about 150.degree. to about 250.degree. C. A preferable temperature 
range is from about 200.degree. to about 220.degree. C. 
The polymers produced according to the practice of the present invention 
can range in molecular weight from about 3,500 to 35,000. The molecular 
weight can be controlled by controlling the amount of catalyst present 
during the polymerization reaction. The molecular weight is determined by 
the technique set forth in Examples 19-28. 
The reaction times will vary depending on factors such as polymerization 
temperatures, the amount of catalysts and the like. Polymerization times 
ranging from about 3 to about 6 hours are satisfactory. 
It has been found that the catalyst does not need to be removed from the 
polydihalophosphazene polymer prior to converting the dihalophosphazene to 
a polyorganophosphazene such as taught in U.S. Pat. No. 3,370,020. 
However, if desired the catalyst may be removed from the polymer by 
diluting the polymer in toluene and removing the solid catalyst particles 
by centrifuging the mixture. Other techniques may also be employed.

In the following examples of the invention the following procedure was 
employed to prepare the supported catalyst. A titanium compound was 
reacted with either activated silica gel or alumina at a temperature of 
about 20.degree. to 30.degree. C. in hexane solvent. The silica-titanium 
material is then contacted at a temperature of about 20.degree. to about 
30.degree. C. with an aluminum compound dissolved in toluene. The mixture 
was then heated to reflux for several hours. The solid catalyst was 
recovered by filtration, washed with hexane and then dried under vacuum. 
The silica gel or alumina is activated by known techniques such as heating 
to 400.degree. to 500.degree. C. under vacuum or nitrogen purge for about 
four hours and the solid cooled under vacuum or nitrogen. 
EXAMPLES 1-18 
A catalyst was prepared by the following procedure. 
Silica (60-200 mesh U.S. Standard Sieve Series) was activated and 5.90 
grams slurried in 100 ml of hexane. A solution consisting of 1.00 ml (2.85 
mmoles) of Ti[OCH.sub.2 --CH--(CH.sub.3).sub.2 ].sub.4 and 50 ml of hexane 
was added to the activated silica with vigorous stirring. The solution was 
stirred for one hour at room temperature. The solid was then filtered, 
washed with three 50 ml portions of hexane and dried under vacuum. A 
solution consisting of 10 ml (18 mmoles) of ethylaluminum dichloride in 50 
ml of toluene was prepared and placed in a dropping funnel. The 
silica-supported Ti compound was then slurried in 50 ml of toluene and the 
ethylaluminum dichloride solution was added to the supported Ti slurry 
with vigorous stirring. The slurry was then warmed to reflux for two 
hours, cooled to room temperature and stirred overnight. The solid 
catalyst (brown in color) was then filtered, washed with four 50 ml 
portions of hexane, and dried under vacuum. At least a portion of the Ti 
will be reduced by the aluminum compound to a valence of +3. 
Several other catalysts were prepared employing the foregoing procedure but 
altering the Ti source, mole ratio and support. The catalysts are 
described in the following Table I. 
TABLE I 
______________________________________ 
Composition of Supported Catalysts 
Concen- 
Al/ 
Catalyst # 
Support Ti-Source.sup.1 
Al-Source 
tration.sup.2 
Ti.sup.3 
______________________________________ 
1 Silica Ti(OR).sub.4 
EtAlCl.sub.2 
0.47 6.43 
2 Silica TiCl.sub.4 
EtAlCl.sub.2 
0.26 11.80 
3 Alumina Ti(OR).sub.4 
EtAlCl.sub.2 
0.48 6.35 
______________________________________ 
Notes: 
.sup.1 Ti-Source: R is isobutyl [--CH.sub.2 CH(CH.sub.3).sub.2 ]. 
.sup.2 Concentration: in units of mmoles Ti/gram of support added. 
.sup.3 Al/Ti: the ratio of moles of Al added/moles of Ti added. 
Employing the catalysts identified in Table I, (NPCL.sub.2).sub.3 trimer 
was polymerized in the following manner. The catalyst employed, reaction 
temperature, reaction time, solvent, ratio of Ti to NPCl.sub.2 and yield 
are set forth in the following Table II. 
The polymerization was carried out by mixing the reaction components 
(catalyst, (NPCl.sub.2).sub.3, and solvent) in a 50 ml flask in a dry box. 
The flask was fitted with a reflux condenser and an adaptor with a 2 mm 
stopcock placed on the top of the condenser. The apparatus was then 
removed from the dry box. A tube from a double manifold vacuum/nitrogen 
line was then attached to the adaptor. The tube was evacuated and refilled 
with nitrogen five times. The flask was then opened to the nitrogen line. 
Following this the flask and its contents were placed inside a heating 
mantle and the contents quickly heated to the reflux temperature of the 
solvent and the temperature maintained at reflux until the reaction was 
terminated. To terminate the reaction, the heat source was removed from 
the flask, and the apparatus allowed to cool to room temperature. The 
flask was then removed to the dry box and the polymerization yield was 
determined. 
The contents of the flask after cooling to room temperature were diluted 
with toluene and filtered. The solids, which consisted of catalyst and 
crosslinked polymer (i.e., gel, which is not considered to be a useful 
product of this reaction) were separated from the liquid. The liquid 
portion was then added dropwise to hexane. A solid precipitate was formed 
consisting of the linear polymer. The yield was calculated based on the 
weight of the solids after they were separated and dried. 
The results of these polymerization runs are set forth in the following 
Table II. 
TABLE II 
______________________________________ 
Results of Polymerization 
Runs Using Supported Catalysts 
Example Time Temp % 
No. Catalyst #.sup.3 
Solvent.sup.1 
(hrs) 
(.degree.C.) 
Ratio.sup.2 
Yield 
______________________________________ 
1 1 A 1.0 214 4.9 15 
2 1 A 2.0 214 4.8 53 
3 1 A 3.0 214 4.8 74 
4 1 A 4.0 214 5.0 85 
5 1 A 5.0 214 4.7 88 
6 1 A 6.0 214 4.9 82 
7 1 A 6.0 214 5.0 83 
8 1 A 6.6 214 5.0 76 
9 1 C 3.2 214 5.0 83 
10 1 A 5.7 214 5.0 81 
11 1 A 4.0 214 0.72 54 
12 2 A 5.0 214 5.0 80 
13 2 A 5.0 214 2.8 67 
14 3 A 1.0 214 5.0 25 
15 3 A 2.5 214 5.0 33 
16 3 A 4.0 214 5.1 68 
17 3 A 5.0 214 4.9 73 
18 3 A 6.0 214 5.1 73 
______________________________________ 
Notes: 
.sup.1 Solvent: 
A = 1,2,4trichlorobenzene 
C = 1.0 ml portions of 1,2,4trichlorobenzene were added at the following 
intervals into the reaction: 0.20, 0.92 and 1.25 hours. 
.sup.2 Ratio: The ratio of mmoles Ti/mole NPCl.sub.2 
.sup.3 Catalyst #: The catalyst composition is given in Table I. 
EXAMPLES 19-35 
These Examples were conducted in the same general manner as Examples 1-18 
except that certain process parameters were varied. These variations are 
noted below or in Tables, III, IV and V. 
Silica (60-200 mesh U.S. Standard Sieve Series) was activated prior to use 
by heating to 500.degree. C. in a tube furnace with a slow nitrogen purge 
until no more steam was evolved from the tube. The tube was then evacuated 
for two hours at 500.degree. C., cooled slowly to room temperature, and 
placed into the dry box. (NPCl.sub.2).sub.3 was either used as received, 
recrystallized from hexane, or vacuum sublimed. The purification of this 
reagent appeared to have no effect on the polymerization reactions. 
1,2,4-trichlorobenzene solvent (TCB) was vacuum distilled from barium 
oxide and stored under nitrogen prior to use. All other reagents were used 
as received. 
All of the supported catalysts were prepared in a manner analogous to that 
set forth in the Examples 1-18. 
A slurry of activated silica in hexane was treated with a solution of 
isobutyl titanate in hexane. The solution was stirred vigorously for 
several hours. The solid catalyst was collected by decanting the solvent, 
washing with hexane, and decanting the solvent again. To a slurry of this 
solid in hexane was added a solution of ethyl aluminum dichloride in 
toluene. The reaction mixture was heated to reflux for several hours and 
the slurry was stirred overnight. The solid catalyst was collected and 
dried under vacuum after several wash/decant steps with hexane. Table III 
sets forth the ratios of the reagents used to prepare these catalysts. 
The polymerization reactions were carried out under a variety of 
conditions. The experimental conditions for each run are given in Table 
IV. All runs were performed under nitrogen. 
In a number of Examples reported in Table V, derivatives of 
linear-phosphonitrilic chloride polymer were prepared according to 
standard literature procedures Allcock, H. R., Kugel, R. L., Valen K. J., 
"Inorganic Chemistry", 1966 5 1709. However, the isolation and 
purification of the product differed from previously reported procedures 
in the following respect. Excess sodium alkoxides and/or phenoxides were 
neutralized to pH.ltoreq.3.0 by the dropwise addition of concentrated HCl. 
The polymer was then precipitated by slow addition of the reaction mixture 
to water with vigorous stirring. The water was decanted and the polymer 
was washed with excess water to remove most of the salts and organic 
solvents. The polymer was then washed with n-propanol, then water, and 
finally with n-propanol. The solvent was then decanted from the polymers. 
Toluene was then added and the mixture was heated to boiling. The water 
and n-propanol were removed as the toluene azeotropes. As the boiling 
point of the mixture reached 110.degree. C., the polymer dissolved to form 
a viscous, cloudy solution. The solution was cooled to room temperature, 
poured into centrifuge tubes, and spun at 10,000 rpm for 15 minutes to 
remove insoluble salts and gels. The clear solution was decanted from the 
centrifuge tubes into a beaker. The toluene was evaporated by heating 
under an air purge. The final traces of solvent were removed by placing 
the beaker in a vacuum oven (90.degree. C., 20 mm Hg) until a constant 
weight was obtained. Yields were determined gravimetrically, and are based 
on the moles of (NPCl.sub.2) in the starting reagent (NPCl.sub.2).sub.3. 
Solution viscosity data is reported as the inherent viscosity, 
##EQU1## 
where t is the time for the polymer solution, t.sub.o is the time for the 
pure solvent, and c is the concentration of polymer (grams/deciliter). All 
viscosity data was obtained at 25.degree. C. using a Ubbelohde viscometer. 
Polymer solutions were prepared in either tetrahydrofuran or toluene. 
Determination of the same polymer sample in the two solvents showed less 
than a 5 percent difference in the viscosity values. 
Approximations to Mv, the viscosity average molecular weight, were made 
using the Mark-Houwink equation, 
EQU [n]=K.sup.1 Mv.sup.a 
with the constants K.sup.1 =2.50.times.10.sup.-3 dl.multidot.mole/g.sup.2 
and a=1/2, as reported by Allcock in Allcock, H. R.; Kugel, R. L.; Valen, 
K. J.; "Macromolecules", 1978, 11, 179. 
TABLE III 
______________________________________ 
Catalyst Composition 
Catalyst 
Number (Ti).sup.1 
Al/Ti.sup.2 
______________________________________ 
4 0.474 6.43 
5 0.047 64.5 
6 0.474 6.43 
7 0.479 6.29 
8 0.479 11.0 
______________________________________ 
.sup.1 mmoles Ti/gram silica added 
.sup.2 molar ratio 
TABLE IV 
______________________________________ 
Yield and Viscosity Data 
Example 
Cata- Ra- Sol- Condi- 
Number.sup.1 
lyst Time.sup.2 
tio.sup.3 
vent.sup.4 
tions.sup.5 
Yield.sup.6 
DSV.sup.7 
______________________________________ 
19 4 5.5 5.0 TCB b -- 0.44 
20 4 5.5 5.0 TCB b -- 0.29 
21 4 5.5 5.0 TCB a 66% 0.17 
22 5 4.8 0.5 TCB a 96% 0.15 
23 5 6.4 0.5 TCB c 60% 0.42 
24 6 7.1 0.5 TCB b,c 60% 0.47 
25 6 5.5 0.5 TCB c 29% 0.11 
26 7 6.0 5.0 TCB c 75% 0.31 
27 7 6.0 5.0 TCB b,c 58% 0.39 
28 8 5.0 5.3 TCB c 67% oil 
______________________________________ 
.sup.1 all runs were performed in refluxing solvent (214.degree. C.) 
.sup.2 in hours 
.sup.3 mmoles Ti/mole NPCl.sub.2 
.sup.4 TCB = 1,2,4trichlorobenzene 
.sup.5 Experimental conditions as follows: a = nitrogen pad, 50% (weight) 
solvent; b = solvent addition as needed to keep the viscosity of the 
solution low enough for efficient stirring, up to a maximum of 50% 
(weight) solvent; c = nitrogen purge 
.sup.6 remainder gel 
.sup.7 dilute solution viscosity in deciliters/gram 
TABLE V 
______________________________________ 
Scale-Up Reactions 
Starting 
Example 
Cata- Com- Deriv- Condi- 
Number.sup.1 
lyst pound.sup.2 
Time.sup.3 
ative.sup.4 
Yield.sup.5 
tions.sup.6(a) 
______________________________________ 
29 4 30.sup.6(b) 
5.5 APN 53% a 
30 4 30 5.5 APN 95% a 
31 4 30 5.5 APN .sup. 80%.sup.7 
a 
32 5 30 9.5 APN --.sup.8 
a,b 
33 6 30 7.1 APN &gt;50%.sup.7 
a,b 
34 6 30 5.5 APN 29% b 
35 7 100 6.0 APN 58% a,b 
______________________________________ 
.sup.1 all reactions were performed in refluxing 1,2,4trichlorobenzene 
(214.degree. C.) 
.sup.2 grams of (NPCl.sub.2).sub.3 
.sup.3 in hours 
.sup.4 APN is [NP(OC.sub.6 H.sub.5) (OC.sub.6 H.sub.4 --4C.sub.2 
H.sub.5)].sub.n 
.sup.5 determined as [moles APN/moles (NPCl.sub.2)]*100. Yields were 
determined gravimetrically unless stated otherwise. 
.sup.6(a) experimental conditions as follows: a = solvent addition as 
needed to keep the viscosity of the solution low enough for efficient 
stirring, up to a maximum of 50% (weight) solvent. b = nitrogen purge. 
.sup.6(b) starting mixture was (NPCl.sub.2)m with M = 3, and 4 where rati 
of 3 to 4 was 4:1, respectively. 
.sup.7 polymer was dissolved in toluene and not isolated as a solid. Yiel 
estimated from solution concentration. 
.sup.8 yield not determined