Note: Descriptions are shown in the official language in which they were submitted.
1079027 ~
This invention relates to improvements in the separation of linear
poly NPCl2 from cyclic oligomers of poly NPCl2.
The preparation of useful polyphosphazenes by derivatization of linear
(NPC12) is described in several recently issued patents including the follow-
ing:
Allcock et al. - 3,370,020 - issued February 20, 1968
Rose - 3,515,688 - issued June 2, 1970
Reynard et al. - 3,700,629 - issued October 24, 1972
Rose - 3,702,833 - issued November 14, 1972
and elsewhere in the published literature.
The procedures known in the prior art involve (1) preparation of low
molecular weight polydichlorophosphazene (NPC12) by reaction of NH4Cl with
PC15 to yield as product (NPC12) in which n is generally less than 7, usually
3 or 4, followed by (2) purification of the product to recover pure trimer
(n=3) or mixtures of trimer and tetramer (n=3 or 4).
The next step in the known prior art procedure is to thermally
polymerize the purified trimer, to a polydichlorophosphazene, e.g. as described
in Allcock et al., United States Patent 3,370,020.
The product is then reacted to replace the Cl in the P-Cl groups
with groups which are hydrolytically stable. When such replacement reactions
are effected, e.g. by a reaction such as ~PNC12t-- ~ 2nNaOR-~ ~PN(OR ~ +
2nNaCl, a large amount of the reagent NaOR is wasted because its reaction
with cyclic oligomers of poly (NPC12) do not yield products with properties
such as those possessed by the reaction products when NaOR is reacted with
linear (NPC12)n.
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In general, the thermal polymerization of (NPC12) proceeds
to from 50-70~ conversion to linear poly NPC12 without the formation of
objectionable amounts of gel or the occurrence of large amounts of cross-
linking, provided the thermal polymerization is conducted at carefully
controlled temperatures.
As described in United States Patent 3,755,537, issued to Tate et al.
on August 28, 1973, it is considered desirable to separate the cyclic oligomers
from the linear polydichlorophosphazene before the derivatization step,
if such separation can be effected economically. In United States Patent
3,755,537, a rather complex separation procedure is described in which the
linear polymer is separated from the cyclic oligomers after both have been
dissolved. A principal object of the present invention is to provide a
simpler and more economically attractive process for achieving the separation
of linear poly NPC12 from cyclic poly NPC12.
Various methods have been suggested in the prior art for effecting
separation of the desired linear poly NPC12 from the unpolymerized starting
; materials and from the cyclic oligomers produced by polymerization of some
of the starting materials.
The approaches which have been described in the literature
include sublimation, extraction with solvents and other "physical"
methods of separation.
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One typical sublimation procedure described in the prior art is
found in J. Polymer Science 36 C130~ pages 195-203. In this procedure,
the recovered polymer is gelled and is insoluble in benzene, probably as a
result of the high temperatures at which the sublimation was completed.
In a large scale commercial plant high temperatures would be used with large
batches because of the mass of material and heat transfer through such solids
is relatively slow and inefficient. These disadvantages are avoided by the
present invention, which uses less expensive equipment and is readily
controlled.
Solvent extraction of low molecular weight polymeric dichlorophos-
phazene from a mixture of trimer, tetramer, low molecular weight polymer
and iinear ionics, using light petrol, is described in Redfarn, United States
Patent 2,866,773. This, of course, gives no indication of the result which
might be obtained when high molecular weight polydichlorophospha~ene is
present in the mixture to be subjected to solvent extraction.
Solvent extraction has been reported on a laboratory scale, utilizing
pentane as the solvent [see J. Macromol. Chem. 1, 187 (1966)~. However, the
very low boiling point (39 C) of this solvent makes the process extremely hazar-
; dous, especially in case of any leakage. The solvents used in carrying out the
present invention are hexane (boiling point 69 C) and higher boiling point
; liquid aliphatic hydrocarbons such as heptane, octane, isooctane, cyclohexane,
and other aliphatic hydrocarbons. Further, this reference reports the detection
by infrared of residual PC12, POH, P=O or POP bonds in the polymers after reac-
tion vf the extracted chloropolymers with alkoxides or alcohols. Applicants
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normally do not find these groups in their polymers.
The present invention provides a process for separating linear
polydichlorophosphazene from cyclic polydichlorophosphazene oligomers which
comprises
(1) charging at least one low molecular weight polydichlorophosphazene
represented by the formula (NPC12) in which m is between 3 and 7, and mixtures
thereof into a polymerization vesseli
(2) thermally polymerizing said polydichlorophosphazene to produce
a product consisting of a mixture of linear polydichlorophosphazenes and cyclic
polydichlorophosphazenes;
(3) contacting said product with a high boiling point aliphatic
hydrocarbon solvent or aliphatic hydrocarbon solvent mixture by mixing said -
product with said solvent; and
(4) separating the resulting solution of said cyclic polyphosphazene
oligomers from the insoluble linear polydichlorophosphazenes.
Thus, by the present invention, the non-linear (cyclic) low molecular
weight poly NPC12 is s~parated from the linear NPC12 and in a preferred
embodiment is recycled to be thermally polymerized to the desired linear species.
Preferably, the amount of solvent used is 2 to 6 times the weight of
the product of the thermal polymerization.
Briefly, a preferred procedure followed in the present invention is as
follows:
(1) (NPC12)m trimer, tetramer or mixture of oligomers tm = 3 to 7)
produced by hexane extraction of the reaction product produced
by FeactiOn of NH4
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with PC15 in the classical preparation of polydichlorophospha-
zenes, is charged into a polymerization apparatus and thermally
polymerized to a mixture of linear polydichlorophosphazenes
and cyclic polydichlorophosphazenes.
(2) The resulting product is extracted with hexane or other solvent
or solvent mixture in which trimer oligomers and "unreacted"
dichlorophosphazene is soluble; the extraction being performed
by mixing the raw polymerization product with solvent in a
vessel equipped with a stirrer.
(3) After a suitable interval (e.g. 20-24 hours), the stirring
was halted and the contents of the vessel were decanted.
(4) A second addition of solvent was made. Stirring was resumed
and a further extraction was effected.
(5) A second decantation was made.~
(6) The solid residue was then taken into solution in benzene
with stirring conducted for 3 to 7 days.
(7) The product, soluble in benzene, was obtained.
The results are summarized in the following table
(all parts are by weight):
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10790Z7
A _ C D
Original Polymerizate 26 35.2 27 21.5
1st Solvent
Hexane (hr.) 106(21)155(19) 85(16) 46(67)
1st Decant
(% solids) 113(10.7) 166(9.7) 90(10.8) 47
2nd Solvent
addition (hr.) 75(7)40(8) _ ~ _
2nd Decant
10 (% solids) 77(1.8) 41(4.5)
Residue 17 23 22 20.5
Benzene
(~ solids) 157(6.3) 150(7.2) 200(7.7) 208(6.3)
Stir Days 7 4 3 3
Recovered Polymer 11 12.5 15.514.3
Recovered Oligomers 13.4 18.1 9.7 3.9
Recovered by Sublimation
(comparison)
Polymer 14.2 16 17.316.4
20 Oligomers 11.8 19 9.45.1
From Runs A-D, it will be seen that the amount o extractant should
be between about 2 to about 4 or 5 times the weight of the polymerizate,
but even more extractant may be used if the ratio of polymer to "unreacted"
oligomer is higher than in the samples extracted above. It wil~ also be seen
that with polymerizate rich in high MW polymer and lean in trimer and oligomers,
only a single extraction may be required, the length of the extraction being
shorter if either the ratio of solvent is increased or the polymerizate is
leaner in trimer and oligomers.
The unpolymerized material is recovered from the accompanying solvent
and is returned to a subsequent polymerization run. The recovered solvent is
purified, if necessary, and is then ready for reuse. -
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It will be seen that there has been provided in a preferred embodiment
of the invention an improved process for producing substantially linear poly-
phosphaæenes represented by the general formula
OR
P - N
OR
in which n is between 50 and 20,000 and each R represents a group selected
from alkyl, particularly fluoroalkyl, aryl, and arylalkyl, and at least some
of the R groups possess unsaturation, e.g. some are alkenyl substituted aryl
groups, which process consists of:
(1) Thermally polymerizing at least one low molecular weight
polydichlorophosphazene represented by the formula (Npcl2)
in which m is between 3 and 7, to produce a product which
contains linear (NPC12) in which q is greater than 7 and cyclic
oligomers of (NPC12) in which m is less than 7;
(2) Extracting the cyclic oligomers from said product with a high
boiling aliphatic hydrocarbon solvent having a boiling point
of at least 65 C to produce a solution of said oligomers and a
solid residue of linear polyphosphazenes;
(3) Recovering said residue and derivatizing the same to produce
the desired
OR
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OR
product;
(4) Removing said hydrocarbon solvent from said solution, leaving
a residue of cyclic oligomers; and
(5) Returning said cyclic oligomers to the thermal polymerization
step to be thermally polymerized.
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