A PROCESS FOR THERMALLY POLYMERIZING CYCLIC PHOSPHAZENES

Abstract: Thermal polymerization of (NPCI₂) 3,4 is improved by conducting the polymerization in the presence of Ziegler type catalysts, namely compounds of the transition metals: Ti, Zr, Hf, V, Nb, Ta, Cr, Mo or W, with or without the presence of compounds of B or Al as cocatalysts.

Description: CATALYSIS OF PHOSPHAZENE CYCLICS TO POLYMER, USING ZIEGLER TYPE CATALYSTS BACKGROUND OF THE INVENTION This invention relates to improvements in the conversion of low molecular weight cyclopolydichlorophosphazenes to higher molecular weight linear polydichlorophosphazenes. More particularly, it relates to the use of suitable catalysts in order to improve the above polymerization by increasing the rate of polymerization, while decreasing or entirely eliminating the formation of gel and by permitting better control of the molecular weight and other physical properties of the polymer produced. Thermal polymerization of (NPC12)n where n is a small integer such as 3 or 4 are described in Allcock et al, United States Patent 3,370,020 issued February 20, 1968 and in Rose, United States Patent 3,515,688 issued June 2, 1970 and elsewhere in the literature. In scaling-up such methods of thermal polymerization from laboratory size glass apparatus to pilot plant and semi-works installations, the polymerization vessels have been fabricated from stainless steels because of the relatively high temperatures utilized in the polymerization. An undesired consequence of the use of stainless steel equipment has been the contamination of the polymerization mixture with small amounts of metals such as chromium, nickel and iron which have significant but unpredictable effects on the manner in which the polymerization proceeds. These and other-objects of the invention will be pointed out or will be apparent from the description which follows. It has been found that the desired polymerization of cyclic dichlorophosphazenes to linear polydichlorophosphazenes can be effected at lower temperatures and at a more rapid rate by the use-of Ziegler type compounds of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo or W as catalysts. It has also been found that the catalyzed polymerizations in glass or in stainless steel vessels proceed without the formation of gel, and that the molecular weight of the product can be controlled conveniently by varying the concentration of catalyst. It has further been found that some control over the molecular weight distribution of the resulting polymer can be achieved by incremental addition of the catalyst and/or of the cyclic oligomers to the polymerization apparatus. Ziegler type catalysts suitable for the present invention are generally produced by preparing suitable compounds of one or more transition elements of Groups IV, V or VI, particularly metal halides, metal hydrides or metal alkyls of the transition element. It appears that transition elements which form compounds with incomplete d-shells and are in the lower valence states can associate metal alkyls to form complexes with highly polarized bonds. Particularly preferred catalysts for the present invention are compounds of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W wherein at least some of the metal is present in a valence state of 3 or below, or is associated with a sufficient amount of a reducing agent, capable of lowering the valence of such metal to the lower valence state. Metals, metal hydrides, metal alkyls or aryls and Grignard reagents are examples of the reducing agents which may be present to lower the valence of the transition metal in the compound which is to act as a catalyst. The transition metal compounds which serve as catalysts or from which the catalyst is prepared may be inorganic compounds such as a halide, oxyhalide, or other complex halide, or oxide or may be organic compounds such as an alcoholate, acetate, phenol ate, or the like. The following compounds are illustrative of preferred Ziegler type catalysts which may be used in the practice of the present invention. Metal halogen compounds of metals of Groups IVB, VB, and VIB of the Periodic Table represented by the formula M'Y'c in which c is the valence of the metal M; and Y is anionic, e.g. a halogen such as chlorine. Particularly preferred metals are titanium, zirconium, vanadium and chromium. TiC13, TiC14, ZrC14, VCl5 and CrCl3 are such compounds. Combinations of such compounds with organometallic compounds of aluminum or boron represented by the formula RaMXb in which M is either Al or B having a valence of a+b; X is anionic, e.g. a halogen such as chlorine and R is a hydrocarbon selected from the group consisting of alkyl, aryl, cycloalkyl, alkaryl and arylalkyl. The invention will be more fully understood from the Examples which follow and which are intended to illustrate and not to limit the invention. Twenty (20) grams of cyclic trimer (NPCl2)3 and the indicated additive were charged into small, clean, dry, glass tubes in a dry box. The tubes were then evacuated to a vacuum of 0.1 mm Hg or less and sealed while connected to the vacuum line. The sealed tubes and their contents were placed in a forced air oven maintained at the desired temperature and polymerized for the times shown in Table I. The polymerizates are then removed from the glass tubes and unreacted trimer was removed by sublimation. Unsublimed material is the polymer which can then be dissolved in benzene or toluene and reacted with alkoxides as described in United States Patents 3,370,020 or 3,515,688 noted above. A control without the additive was also run at the same time. Tables I and II illustrate the results obtained with different starting materials. TABLE I Time Percent Additive Amount Hrs. Temperature Polymer IA None None 24 2500C 46 1B TiC14 .04 ml 22.5 2500C 90 (Neat) 2A None None 32.6 250 C 21.9 2B ZrC14 .29 g 8.75 2280C 82 TABLE II g Catalyst/ Polymerization Conver Catalyst g Trimer TOC Hrs. sion DSV 1. ZrC14 0.0033 270 4 89 0.31 2. ZrC14 0.0033 250 8 90 0.33 3. ZrCl4 0.033 250 4 95 0.25 4. ZrCl4 + BCl3 0.0067+0.005 200 10 90 0.16 As indicated in Table II above, catalysts may comprise the compounds of metals of Groups IVB, VB, and VIB of the Periodic Table or combinations of such catalysts with cocatalysts such as compounds of'B or Al. This is further shown in the following table. The triethyl aluminum was used as 20% solution in toluene, and the vanadium acetylacetonate as a 0.1 molar solution. TABLE III Polymerization Catalyst Amount Catalyst/20g Trimer T C Hrs %Conversion DSV 1. None - 220 30.0 9.2 2.46 2. TiCl3 0.1g 220 12.0 28.9 0.74 5 3. TiCl3+EtAl 0.1g+3 drops 20% soln* 220 12.0 50.0 0.23 4. Ti(OBu)4+Et3Al 3 drops + 6 drops 20% soln* 220 12.0 30.7 0.52 5. CrO2Cl2+Et3Al 3 drops + 12 drops 20% soln* 220 19.5 49.7 0.58 6. Vacac**+Et3Al 4 drops 0.1 M soln. + 4 drops 220 21.0 71.0 0.31 20% soln* 10 7. CrO2Cl2+Et3Al 0.08Mm + 0,013mM** 170 90.0 26.2 N.D.*** *Et3Al in toluene **acac = acetylacetonate ***mM = Millimoles ****Not Determined The product can be recovered in any of several ways. A preferred method is to permit the reactor to cool sufficiently whereupon the polydichiorophosphazene can be dissolved in a solvent or solvent mixture and the product can be flushed out of the reactor. Although the invention has been described with specific reference to dichlorophosphazenes it is also applicable to the polymerization of dibromophosphazene and difluorophosphazene oligomers. Having now described preferred embodiments of the invention, it is not intended that it be limited except as may be required by the appended claims.

Claims: CLAIMS: 1. In a process for thermally polymerizing cyclic phosphazenes represented by the general formula (NPHal2)n in which Hal is a halogen selected from the group consisting of C1, F and Br and n is a small integer between 3 and 7 comprising heating said cyclic phosphazenes to a temperature in the range between 150 and 3000C for a time sufficient to produce a linear polydichalophosphazehe wherein the degree of polymerization is between 20 and 50,000, the improvement which comprises conducting said heating to thermally polymerize said cyclic phosphazene in the present of a catalytically effective amount of a Ziegler type catalyst, said catalyst comprising a compound of a transition metal selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W. 2. The process of Claim 1 wherein Hal is C1 and n is 3,4 or mixtures of 3 and 4. 3. The process of Claim 1 wherein the catalyst includes a cocatalyst which is a compound of Al or B. 4. The process of Claim 1 in which the amount of catalyst present is between about 0.1 millimoles and 20.0 millimoles/mole of cyclic phosphazene. 5. The process of Claim 1 in which the catalyst is a metal halogen compound. 6. The process of Claim 1 in which the catalyst is a Ti compound. 7. The process of Claim 1 in which the catalyst is TiC13 or TiC14. 8. The process of Claim 1 in which the catalyst is ZrCl4. 9. The process of Claim 1 in which a cocatalyst is present in addition to the catalyst and the cocatalyst is an organometallic compound RaAlXb, in which R is an organic radical such as alkyl, aryl, cycloalkyl, arylalkyl or alkylary and a and-b are small integers totalling the valence of Al and X is anionic. 10. The process of Claim 1 in which the catalyst further contains an aluminum alkyl compound.

Inventors: FIELDHOUSE, JOHN WILLIAM, KANG, JUNG WONG, SNYDER, DENNIS LAVERNE
Applicants: THE FIRESTONE TIRE & RUBBER COMPANY
Application year: 1979
Main classification: C08G79
IPC codes: C01B21