Process for Conversion of Elastomeric Phosphazene

This invention relates to polyphosphazene elastomers which are possessed of an exceptional ease of curability and to useful articles produced from said elastomers. More particularly, it is directed to polyphosphazene elastomers of the type described in U.S. Pat. No. 3,702,833 issued Nov. 14, 1972, the disclosure of which is incorporated herin by this reference.

One object of this invention is to provide polyphosphazenes of the type described having curative sites which are not directly attached to the ##EQU2## backbone and which do not detract from the thermal stability of the elastomer and which can be cured by means of sulfur cures, peroxide cures, or radiation cures.

Another object of the invention is to provide novel phosphazene terpolymers and to provide procedures and formulations whereby the raw gums comprising the polyphosphazenes are incorporated into compositions from which useful articles with outstanding properties are obtained.

A further object of the invention is to provide compositions and articles which exhibit excellent solvent resistance, low temperature flexibility and good physical strength over a broad range of service conditions.

The phosphazene polymers of the present invention contain small but significant amounts of unsaturation in the groups attached to the P atoms of the ##EQU3## chain, in addition to aryloxy and/or alkoxy groups (both unsubstituted and substituted) attached to the P atoms, a particularly preferred substituent being an o-allyl phenoxy group. In the preferred embodiment of the invention, 0.1-5% by weight of o-allyl phenol groups are randomly distributed among the groups attached to the ##EQU4## polymer backbone.

Briefly, the invention contemplates the replacement of some of the chlorine atoms in linear (NPCl.sub.2) polymer with a substituent which possesses at least some unsaturation in a side chain not directly attached to the P atoms in the chains.

The following structural formula may be taken as illustrative of the polyphosphazenes of the present invention: ##EQU5## in which Q, Q' and Q" represents monovalent groups randomly distributed along the -P=N- backbone, Q' and Q" being preferably relatively inert or unreactive alkoxy or aryloxy groups of the types described in U.S. Pat. Nos. 3,370,020; 3,515,488; 3,700,629 and 3,702,833 and others of a similar nature, the total of Q and Q' groups being sufficient to replace at least 90% and preferably at least 95% but not more than 99% of the Cl atoms originally present in the linear (NPCl.sub.2) polymer; and the Q" groups being a group with some unsaturation e.g. a group represented by ##SPC1##

in which R includes some unsaturation e.g. an alkenyl group such as vinyl, allyl, crotyl or the like, the number of Q" groups distributed randomly along the -P=N- chain being preferably between 0.1% and 5% of the total of Q, Q' and Q". Q and Q' may be either the same or may differ and each may represent more than one group. Because of the greater reactivity exhibited by the Q" groups, as compared with the Q and Q' groups it is believed that these groups serve as cure sites or as sites for crosslinking and vulcanization.

In particularly preferred copolymers according to the present invention, the groups Q, Q' and Q" comprise the following and are present in the relative proportions indicated:

The elastomers of this invention were prepared as follows: a suitable alcohol or fluoroalcohol or a mixture of alcohols and/or fluoroalcohols, together with o-allyl phenol were slowly added to sodium metal in dried tetrahydrofuran under a nitrogen atmosphere in a 3 neck, 12 liter, round bottom Pyrex flask fitted with a dropping funnel, a dry ice condenser with a H.sub.2 vent line, and a motor driven glass stirrer. The flask was immersed in a thermostatically controlled liquid bath. After the reaction of the alcohols with sodium had proceeded to completion, a solution of linear poly(dichlorophosphazene) in benzene was added rapidly to the mixture of alkoxides and/or fluoroalkoxide(s) and o-allyl phenoxide. The chlorine atoms of the poly(dichlorophosphazene) combined readily with the alkali metal of the alkoxides and as a result, the substituted polyphosphazene derivative was produced. The derivatized product was recovered by washing the reaction mixture free of salt until the test for chloride was negative.

The table above gives other examples of elastomers with unsaturation in the side chains of the groups attached to the P atoms.

Terpolymers or copolymers containing the indicated unsaturation can be readily compounded and cured i.e. vulcanized in much the same way as presently known rubbers, producing useful products possessing an outstanding combination of properties, which are substantially retained over an extreme temperature range from temperatures as low as -80.degree.F to temperatures as high as 400.degree.F, thus permitting use of the vulcanizates in service applications where they will encounter such temperatures.

The presence of the indicated unsaturation results in polymers which can be cured more efficiently with lower levels of peroxide than polymers in which only saturated groups are attached to the polyphosphazene chain, the resulting vulcanizates possess better heat aging properties and better compression set than the corresponding polymers lacking the unsaturated side groups. They are also more amenable to curing than their saturated counterparts and it is possible to use peroxide curing agents in compositions containing carbon black fillers and to use sulfur-accelerated cures as well as radiation cures.

The level of unsaturated groups is quite important and may be varied according to the cure system to be used and according to the properties desired in the cured composition. For example, when the unsaturation is provided as o-allyl phenoxy groups the following is noted:

The properties of several different terpolymer gums and the compounded stock obtained from them are set forth in the tables which follow, compounding having been achieved by simply mixing the several constituents with the polyphosphazene gums in a Banbury, Brabender or other conventional mixer.

Phosphonitrilic fluoroelastomer of the general formula [(CF.sub.3 CH.sub.2 O)(HF.sub.2 C(CF.sub.2).sub.3 CH.sub.2 O)(o-allyl C.sub.6 H.sub.4 O)P=N].sub.n in which the three substituents are randomly distributed along the ##EQU6## backbone is produced by the above described method and is usually a light tan crumb which exhibits no cold flow. It posesses the following properties (average):

The raw gum feels quite tough and exhibits considerable "nerve". It softens readily at high shear rates, as for example when processed on a rubber mill or in an extruder or mixer and it exhibits good green strength and nerve reduction after addition of reinforcing agents such as carbon blacks, silicas or treated clays.

In the preceding tables various tradenames and abbreviations are utilized, the meanings of which are as follows:

Terpolymer (I) is a linear polyphosphazene with three randomly distributed substituents; namely: CF.sub.3 CH.sub.2 O-; HF.sub.2 C(CF.sub.2).sub.3 CH.sub.2 O- and o-allyl phenoxy

Terpolymer (II) is a linear polyphosphazene with three randomly distributed substituents; namely: CF.sub.3 CH.sub.2 O-; CF.sub.3 (CF.sub.2).sub.2 CH.sub.2 O- and o-allyl phenoxy (OAP)

Terpolymer (III) is a linear polyphosphazene with three randomly distributed substituents; namely: C.sub.6 H.sub.5 O-; CH.sub.3 (CH.sub.2).sub.3 CH.sub.2 O- and OAP

Silanox 101 is a silane-coated fumed silica

Stan Mag ELC is MgO

Dicup 40C is dicumyl peroxide (40% on CaCO.sub.3)

Varox is 2,5-bis(t-butylperoxy)-2,5-dimethylhexane (50% on inert carrier)

MBT is mercaptobenzothiazole

Cyclex B is t-Butyl-2-mercaptobenzothiazole sulfenamide

Butyl Zimate is dibutyl dithiocarbamate

Methyl Zimate is dimethyl dithiocarbamate

phr means per hundred parts of polyphosphazene rubber

M is Modulus

DTDM is dithiodimorpholine