WO1991009066A1 - High carbon resins and foams - Google Patents

Abstract

High carbon resins and methods for preparing such resins, including foaming compositions that include (a) a foaming agent, (b) an aromatic polyacetylenically unsaturated prepolymer, and (c) a viscosity modifier modifying the flow properties of the prepolymer, viscosity modifier having one or more acetylenic groups available for reacting with the prepolymer. The foaming agent, prepolymer, and viscosity modifier are chosen such that at the decomposition temperature of the foaming agent, the viscosity of the composition is sufficient to permit molding and foaming. The acetylenic groups of the viscosity modifier react with the residual acetylenic groups of the prepolymer during molding so that the viscosity modifier becomes part of the final foam, does not have to be removed following, and will not leach out of the foam or impair its chemical or physical properties. Following molding, the foam may be carbonized to produce a carbon foam useful for electrical applications.

Description

HIGH CARBON RESINS AND FOAMS Field of the Invention The invention relates to high carbon resins. Background of the Invention High carbon resins may be prepared from acetylenic starting materials (i.e. materials containing C^ groups). The resins are prepared in two steps. The first step is a catalytic polycyclotrimerization or co-polycyclotrimerization reaction in which the C^C groups of the starting material react with each other to form benzene rings. The reaction product is a soluble ^' and fusible prepolymer. At least one of the reactants must be a polyfunctional acetylene (i.e. containing two or more C=C groups) in order to yield a polymer. The prepolymer thus formed can then be molded and cured in a high temperature step to form the thermoset resin.

Summary of the Invention In general, the invention features a foaming composition that includes (a) a foaming agent; (b) an aromatic polyacetylenically unsaturated prepolymer; and (c) a viscosity modifier for modifying the flow properties of said prepolymer having one or more acetylenic groups available for reacting with the prepolymer. The foaming agent, prepolymer, and viscosity modifier are chosen such that at the decomposition temperature of the foaming agent, the viscosity of the composition is sufficient to permit molding and foaming.

In preferred embodiments, the amount of viscosity modifier is no greater than 20% by weight, more preferably between 8 and 20% by weight. The viscosity modifier has a softening point less than 150°C. Preferred viscosity modifiers include diacetylenic aromatic compounds (e.g., diphenylbutadiyne, bis(ethynylphenyl)ether, or ,4'-diethynyldiphenylmethane) ; diacetylenic aliphatic compounds having the formula HC=C-CH -C=CH where n is an integer between 2 and 12, inclusive (e.g., 1,4-pentadiyn.e) ; and monoacetylenic aromatic compounds (e.g., biphenyl acetylene or naphthyl acetylene). Also preferred are oligomers having a lower degree of polymerization than the prepolymer. These oligomers may also have the same chemical composition as the prepolyme .

Preferred prepoly erε include the cyclotrimerized product of an aromatic diacetylene (e.g., diethynylbenzene, bis(ethynylphenyl)ether, or bis(ethynylphenyi)ether) and an aryl or alkyl monoacetylene (e.g., phenylacetylene) or acetylene. Also preferred are prepolymers which are the . cyclotrimerized products of a) an aliphatic diacetylene having the formula HC~C-CH -C=CH where n is an integer between 2 and 10, inclusive (e.g., 1,4-pentadiyne) and an aryl or alkyl monoacetylene (e.g., phenylacetylene) or acetylene; b) diacetylene and an aryl or alkyl monoacetylene (e.g., phenylacetylene) or acetylene, and c) an aromatic diacetylene (e.g., diethynylbenzene, 4, '-diethynyldiphenylmethane, or bis(ethynylphenyl)ether) or aliphatic diacetylene (as recited above, e.g., 1,4-pentadiyne) and an aryl or alkyl nitrile (e.g., benzonitrile, dicyanobenzene, cyanopyridine, cyanothiophene, perfluorocyanobenzene, dicyanomethane, or cyanoacetamide) .

Preferred foaming agents include azodicarbona ide, p-toluenesulfonyl hydrazide, and 4,4'-oxybisbenzenesulfonyl hydrazide. Particularly preferred foaming compositions ^• include those in which the foaming agent is azodicarbonamide, the prepolymer is the cyclotrimerized product of diethynylbenzene and phenylacetylene, and the viscosity modifier is diphenylbutadiyne; those in which the foaming agent is azodicarbonamide, the prepolymer is the cyclotrimerized product of diethynylbenzene and phenylacetylene, and the viscosity modifier is 4,4 '-diethynyldiphenylmethane; and those in which the foaming agent is azodicarbonamide, the prepolymer is the cyclotrimerized product of diethynylbenzene and phenylacetylene, and the viscosity modifier is bis(ethynylphenyl)methane.

The invention also features a process for . preparing a foam that includes taking the above-described foaming-composition and molding it to form a shaped article under-reaction conditions, including^" temperature and pressure, sufficient to decompose the foaming agent, thereby causing foaming of the composition, and to cause the acetylenic groups of the viscosity modifier to react with the prepolymer.

Following molding, the foam may be carbonized. The foaming composition is preferably formed by ball milling the foaming agent, prepolymer, and viscosity modifier to form a homogeneous powder. The molding step preferably takes place at a temperature below about

250°C.

Foams preferred from the foaming compositions

3 preferably have densities less than 0.2 g/cm (more preferably between 0.01 and 0.2 g/cm , more preferably

3 ^■ between 0.05 and 0.14 g/cm ) . The compressive strength of the foam preferably is at least 100 psi in the temperature range 0 - 500°F. The compressive strength preferably does not vary by more than 5% upon exposure to moisture. The foams are lightweight, chemically inert, and thermally stable (below 600°F in air). They are also moisture resistant and thus dimensionally stable, even at elevated temperatures. Similarly, they exhibit good compressive strength, even at elevated temperatures. They are also readily prepared at relatively low temperatures; thus, crosslinking of the prepolymer to form an infusible solid is avoided. The invention also features novel polyacetylenically unsaturated prepolymers and thermoset resins prepared from them, and processes for preparing these materials, including cyclotrimerization catalysts. Controlling the molecular weight of the^' product through selection of the proper solvent and the discovery of catalysts whose activity is not highly sensitive to monomer concentration enables steady. state (and thus continuous) polymerization. Moreover, soluble oligomers that result during preparation of the prepolymer can be recycled and used to prepare more prepolymer.

Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof, and from the claims. Description of the Preferred Embodiments We now describe preferred embodiments of the invention. Foams

Thermally stable, chemically inert, low density foams are prepared from a foaming composition that includes a) a foaming agent, b) an aromatic (e.g., containing one or more aromatic rings) polyacetylenically unsaturated prepolymer, and c) a viscosity modifier (present in an amount between 8 and 20% by weight). The particular materials are chosen such that at the decomposition temperature of the foaming agent (i.e. the temperature at which it decomposes to form a gas that causes foaming) , the viscosity of the composition is sufficient to permit molding and foaming.

The viscosity modifier is generally a solid at room temperature that softens or melts in the range of the decomposition temperature of the foaming agent. At this temperature, however, the prepolymer is normally present as a solid or highly viscous liquid; thus, it cannot be efficiently molded or foamed at this temperature. At higher temperatures, however, the prepolymer cures, forming an insoluble, infusible solid that cannot be shaped. The purpose of the viscosity modifier is to soften the prepolymer and reduce-its viscosity to the point where it can flow and fill the mold at the decomposition temperature of the foaming - agent. -The reduced viscosity also allows the gas released by the foaming agent to be trapped in the curing prepolymer, thereby resulting in uniform foaming throughout the prepolymer (as opposed to escaping from the interior of the prepolymer). The acetylenic groups of the viscosity modifier also react with the residual acetylenic groups of the prepolymer during molding so that the viscosity modifier becomes part of the final foam; thus, it does not have to be removed following molding, nor will it leach out of the foam or impair the foam's chemical and physical properties in use. The foaming agent may be conveniently introduced as a thermally unstable powder, uniformly mixed into the prepolymer and viscocity modifier. Generally, particulate sizes of the foaming agent powder are small to affect a uniform evolution of gas during the cure and hence, a uniformly foamed product. By controlling the amount of the foaming agent, the density of the foams is controlled. The first step in preparing the foams involves preparation of the prepolymer. Various prepolymers may be synthesized and used to produce foams having advantageous properties as will be discussed further below. Next, the prepolymer, viscosity modifier, and foaming agent are intimately mixed, for example, in a ball mill to form a homogeneous powder. Finally, the mixture is discharged into a mold and heated. Generally, the heating step includes heating for a period of time at a temperature below the optimum cure temperature, but high enough such that the viscosity modifier softens and reduces the viscosity of the mixture, e.g., about 130°C. This initial heating forms a uniform mixture of lower viscosity. The mixture is then brought to a higher temperature, e.g., about about 200°.C at which the foaming agent decomposes and the in.al foam. roduct i-s. formed.

Subsequently., the foam may be carbonized by a high temperature cure (e.g., at 1000°C) to form a hard, glassy, carbon foam for electrical applications.

The foams are useful in a variety of applications, including composite structures where a combination of low density and dimensional stability at elevated temperatures are needed. The following examples are illustrative of the formation of foams.

Example 1 The following example illustrates preparation of a foam forming composition in the form of a powder. Into a 000 ball mill jar was placed 23.00 g of a prepolymer prepared according to Example 8, below, 2.68 g of diphenylbutadiyne (viscosity modifier), and 1.07 g of azodicarbonamide (foaming agent). To the mixture was added stainless steel media to fill the jar 2/3 full. The jar was capped and turned on a roller mill at 180 rpm for 18 hrs. The mixture was removed from the jar and the resin was scraped from the wall of the jar and ground in a mortar with a pestle. The fine powder was transferred to a bottle, affording 24.34 g of recovered foaming composition.

Into a small ball mill jar was placed 16.31 g of the foaming composition above and enough media to fill the jar 1/2 full. The jar was rolled at 180 rpm for 5hrs. The powder was then scraped from the side of the jar and the contents were milled for an additional 9 hrs. The media were poured from the jar and the resin was scraped from the jar and ground with a mortor and ■ pestle, A total of 15.26 g of foaming composition was recovered.

Example 2 The^'- following example illustrates preparation of a^'foaming^"composition in^' the form of a powder.

Into a 000 ceramic ball mill jar was placed 18.09 g of a prepolymer prepared according to Example 8, 2.12 g of diethynyldiphenyl methane (viscosity modifier), and .85 g of azodicarbonamide (foaming agent). Enough stainless steel media were placed in the jar to fill the jar 2/3 full. The capped jar was turned on a roller mill at 180 rpm. The sides of the jar were scraped down after 1 hour, 4 hours, and 20 hours. The jar was turned a total of 28 hours.

The media were separated from the foaming composition with a 15 mesh sieve and the composition was ground with a mortar and pestle. A total of 16.36 g of foaming composition was recovered. The foaming composition included 85.9% prepolymer, 10.1% viscosity modifier, and 4.0% foaming agent (all percentages given as weight percentages). Example 3 The following example illustrates the formation of foam using the foaming composition discussed in Example 1. A 1" x 3" compression mold was sprayed with mold release agent. A 1" x 3" piece of 3 mil porous glass-Teflon cloth was then placed in the mold, followed by 2.63 g of foaming composition and a 1" x 3" piece of non-porous glass-Teflon cloth. The top half of the mold was placed in the cavity and the mold was placed in preheated carver press and pressurized in the range of 10,000 to 0 psi. The top half of the mold served to compact the mixture to a uniform thickness. When the mold reached 121°C, the top was removed and the nonporous cloth was removed. The taffy-like mixture was then compacted with a spatula, after which the moid -(with- a flat steel plate cover) was returned to the press- -and- eheated to a mold temperature of 127°C. For the final heating, the steel cover and a sheet of porous teflon-glass cloth were placed over the mold cavity and the mold was placed into a carver press preheated to around 200°C. The mold was then heated to 219°C over 28 minutes. The sample was removed from the mold while hot after 28 minutes. The resulting product had a density of 0.1416 g/cm³.

Example 4 The following illustrates formation of a foam using the foaming composition of Example 1.

A 1" x 3" compression mold was sprayed with mold release agent and a 1" x 3" piece of 3 mil porous Teflon cloth was placed in the mold, followed by 2.37 g of foaming composition according to Example 1 and a 1" x 3" piece of non-porous glass-teflon cloth. The mold was assembled and heated to 127°C - 8 minutes. The mold was then removed from the press, the upper half of the mold ^• removed, and the nonporous cloth peeled off the softened and consolidated resin. The flat lower half of the mold was then returned to the press and heated to 126°C; the resin was then compacted with a spatula to force more resin into the corners and edges prior to foaming. Next, a 3" x 4" piece of porous Teflon-glass cloth was placed over the opening. A steel plate was then placed in the mold and the mold was placed in a Carver Press with its platen preheated to 210°C. The temperature was increased to 215°C over 32 minutes, at the end of which the foam was removed. The resulting foam had a density of 0.1241 g/cm³.

Example 5 The procedure of Example 3 was followed using

2__60 g. of .foaming composition. After seven minutes of heating, the mold was removed from the press, the nonporous cloth was peeled off the resin, and the resin was compacted toward the corner with a spatula. The mold was again heated in the press to 127°C, removed, and the molten foaming composition compacted with a spatula to even out the coverage. Afterwards, the cavity was covered with a 3" x 4" piece of porous Teflon-glass cloth and a piece of steel plate was placed over the mold before it was placed in a Carver Press with platen preheated to 210°C. The mold was heated to 219°C over 48 minutes, after which the foam was removed. The resulting foam had a density of 0.136 g/cm . Example 6

The following illustrates the preparation of a foam using the foaming composition of Example 2.

A 1" x 3" compression mold was sprayed with Teflon mold release agent before a 1" x 3" piece of porous glass-Teflon cloth was placed in the bottom of the mold. The mold was then charged with 2.66 g of foaming composition. A piece of 1" x 3" non-porous glass-Teflon cloth was placed on the lower half. The mold was placed in a Carver Press with preheated platens. After 5 minutes, the mold temperature was

120°C. The mold was then disassembled and the nonporous cloth removed. The mixture was then returned to the press and reheated. When the mold temperature reached

128°C, the mold was transferred to a press with platens heated to 212°C. After 67 minutes, the sample was removed from the hot mold. The resulting foam had a

₃ density of .134 g/cm .- The compressive strength of this foam remained at 180 - 200^' psi in the temperature range between room temperature and 600^CF. Foaming Agents

Examples of suitable foaming agents include azodicarbonomide, p-toluensulfonyl hydrazide, and 4, 4'- oxybisbenzenesulfόήyl hydrazide. Viscosity Modifiers Acetylenically substituted compounds that can be used to modify the viscosity of the prepolymer and are reactive (copolymerizable) with the prepolymer can be any mono- or polyacetylenically substituted compound, which can be the same of different from the compound used to prepare the prepolymer, provided that this acetylenically substituted compound softens at about the temperature at which the foaming agent decomposes. It may be aromatic (e.g., containing one or aromatic rings) or aliphatic having the general formula HC^C-CH -C≡CH where n is an integer between 2 and 12, inclusive. Preferred examples of aromatic compounds include diphenylbutadiyne, 4, 4'- diethynyldiphenyl methane, and bis(ethynylphenyl)ether. Preferred examples of aliphatic compounds include 1,4-pentadiyne. Also suitable are oligomers having a lower degree of polymerization (and thus a lower molecular weight and softening temperature) than the prepolymer. These oligomers may also have the same chemical composition as the prepolymer.

Other suitable examples of viscosity modifiers can be found in U.S. Patent No. 4,097,400 to Jabloner, entitled "Polyarylacetylenes and Thermoset Resins Therefrom", the entire contents of which are hereby incorporated by reference. They include betanaphthylacetylene, biphenylacetylene, 4-ethynyltrans-azobenzene, diphenylacetylene, di-m-tolylacetylene, di-o-tolylacetylene, bis(4-ethylphenyl) cetylene, bis(4-chlorophenyl)acetylene, phenylbenzoylacetylene, be anaphthylphenylacetylene, di( lpha-naphthyl)acetylene, 1,4-diethynylnaphthalene, 9, lO-diethynyl-anth-r-acene, 4,4'-di-ethynylbiphenyl, 9,10-diethynylphenanthrene, 4, '-diethynyl-transazobenzene, 4,4'-diethynyldiphenylether, 2,3,5,6-tetrachloro-l,4-diethynylbenzene, dibenzyldiacetylene, 2,2'-dichlorodiphenyl diacetylene, 3,3'-dichlorodiphenyl diacetylene, di(alpha-naphthyl) iacetylene, and diethynyldiphenyl butadiyne.

The following example illustrates the preparation of an oligomeric viscosity modifier.

Example 7 A 12 liter, 4-neck round bottom flask was equipped with a mechanical stirrer, a thermometer, a subsurface oxygen inlet, and an air cooled condenser. To the flask was added 648 g of crude concentrate of the soluble portion from the preparation of the prepolymer prepared in Example 8, described below. Analysis of the concentrate indicated it contained 193 g of phenylacetylene, 59 g of diethynylbenzene, and 210 g of hexanes-soluble, low molecular weight oligomer. To the flask, was also added 115 g of phenylacetylene, 150 g of diethynylbenzene, 10 g of the prepolymer prepared in

Example 8, 501 g of pepidine, 5 liters of acetone, and 90 g of copper(I)chloride. The green mixture was stirred while oxygen was bubbled through the liquid. A gentle exotherm was observed during the first five hours. The reaction was stirred overnight before the solids were removed by filtration. The filtrate was concentrated on a rotary evaporator (< 60°C), affording a thick, black oil with particuiates. The oil was diluted with 300 ml acetone, 1200 ml toluene, and then filtered. The filtrate was rinsed twice with 1 liter of water, twice with 1 liter of 1 N HCL, 1 liter of saturated^"sodium^"bicarbonate, and twice with 750 ml of brine. ^"The resulting dark brown liquid was filtered through a glass fiber filter to remove some finely suspended solids before mixing with 100 g of anhydrous magnesium sulfate and 20 g of norite. Filtration through celite afforded a dark brown solution which was concentrated under vacuum, initially at 60°C and 20 mm Hg and finally at 75°C for 30 minutes at 0.5 mm. A total of 525 g of the oligomeric product was obtained as a dark brown oil. Prepolymers

The prepolymers are fusible aromatic polymers having unreacted acetylene groups; these acetylene groups may be internal or external. They generally have a number average molecular weight less than about 15,000. The prepolymers are synthesized by cyclotrimerization of various acetylenic species in the presence of a catalyst. Suitable prepolymers for the formation of foams include those synthesized by reaction of an aromatic diacetylene (e.g., diethynylbenzene and phenylacetylene) or aliphatic diacetylene (e.g., 1, -pentadiyne) and an aryl or alkyl monoacetylene (e.g., phenylacetylene or l-decyne), diacetylene and an aryl or alkyl monoacetylene (e.g., phenylacetylene), an aromatic diacetylene (e.g., diethynylbenzene) and an aryl or alkyl nitrile (e.g., benzonitrile) , or by reaction of various functionalized starting materials to produce functionalized prepolymers having various properties, all of which are further discussed below, along with specific examples. Acetylene itself may also be used instead of the aliphatic or aromatic monoacetylene. Also suitable are the prepolymers described in

Jabloner, U.S. Pat. No. 4,097,460, discussed above. Examples of polyacetylenically substituted aromatic compounds useful- in- preparing the prepolymers include m- and p-diethynylbenzenes; diethynyl toluenes; diethynylxylenes; 9,10-diethynylphenanthrene;

4, '-diethynyl-trans-azobenzene; di(ethynylphenyl)ether; 2,3,5,6-tetrachloro-l,4-diethynylbenzene; diphenyl-diacetylene (i.e., diphenylbutadiyne); dibenzyl-diacetylene; di-p-tolyldiacetylene; di-α-naphthyldiacetylene; l-chloro-2,5-diethynylbenzene; 2,2'-dichlorodiphenyldiacetylene; 4,4 '-dichlorodiphenyldiacetylene; 4,4'-dibro odiphenyldiacetylene; l,4-bis(-phenylethynyl)benzene; 1,3-bis(pheny1ethyny1)benzene; 9,10-bis(phenylethynyl)anthracene; l,3,5-tris-(phenylethynyl)-2,4,6-triphenylbenzene; 1,2,4-tris-(phenylethynyl)-3,5,6-triphenylbenzene; and t is(ethynyl-phenyl)benzene. Suitable monoacetylenically substituted aromatic compounds as set forth in Jabloner include phenylacetylene and biphenylacetylene. Prepolymer Synthesis

The following examples illustrate the preparation of a prepolymer by eyelotrimerizing diethynylbenzene and phenylacetylene.

Example 8 A 2 liter reactor.equipped with a mechanical stirrer, a dry ice condenser, a thermometer, an addition funnel, and a vacuum take-off was purged with argon before 600 ml of deoxygenated hexanes was added. Argon was bubbled through the solvent overnight. In a separate flask, a solution of 31.01 g (.304 moles) of phenylacetylene, 19.59 g (.155 moles) of I,^"3-diethynylbenzene, -and ^"3.78 g (.0315 moles) of mesit-ylene in 150 ml hexanes was deoxygenated with argon overnight before it was charged into the addition funnel. The catalyst was prepared in another flask by charging 0.156 g (0.61 mmol) of nickel acetylacetonate and 0.739 g (2.42 mmol) of tri-o-tolylphosphine into 20 ml of toluene. The solution was deoxygenated overnight with argon. In all cases, the overnight deoxygenations were done to expedite start-up the next day.

The hexanes in the reactor were treated with 1.6 mmol of diisobutylaluminum hydride in hexanes and the reactor was placed under reduced pressure (82 mm Hg) and held constant. The hexanes cooled to 8°C. To the hexanes was added 10% of the acetylene mixture. The catalyst solution was activated by adding 2.42 mmol of diisobutylaluminum hydride in hexanes and after five minutes one half of the catalyst mixture was added to the reactor. During the next 30 minutes the remaining monomers were slowly added, followed by the remaining catalyst. The reaction was maintained at reduced pressure for 6 1/2 hours before it was returned to atmospheric pressure by introducing argon into the reactor. The mixture was stirred for an additional 17 1/2 hours before the product was collected by filtration, rinsed with 100 ml hexanes, and dried under reduced pressure (60°C at 25 mm Hg with air bleed) to yield the final prepolymer. Example 9

Into a 200 gallon reactor was charged 115 gal of dry, deoxygenated hexanes and 1.325 liter of a 1 M solution of diisobutylaluminum hydride in hexanes. The reactor was cooled to 0-15°C. In a separate container was prepared a deoxygenated solution of 18.5 kg"of phenylacetylene and 11.66 kg of 1,3-diethynylbenzene in 17.94-kg of toluene. In a third container was prepared -a- solution of- 97.7 g of -anhydrous nickel acetylacetonate, 440 g of tri-o-tolylphosphine, and 10.6 liters of toluens. The solution was stirred, cooled to 15°C, and deoxygenated for 4 hours with argon. To thenickel-phosphine solution was added 1.460 liter of diisobutylaluminum hydride while maintaining the temperature below 25°C. Ten percent of the acetylene mixture was transferred to the 200 gallon reactor, followed by half of the catalyst mixture. The remaining acetylene mixture was added over a two hour period while maintaining the reaction temperature below 10°C. The second half of the catalyst mixture was added an hour later when the exotherm began to subside. The reaction was monitored by gas chromatography periodically throughout the addition of the reagents and thereafte . When the consumption of diethynylbenzene was between 80-90% and that of phenylacetylene between 50-60% (24 hours), the reaction was quenched with 200 g of acetic acid in 200 g of methanol. The heterogeneous mixture was stirred for 1 hour prior to filtration. The precipitate was rinsed with hexanes an air dried to a fine, yellow powder. Vacuum drying (60°C, 20 in. Hg, 48 5 hr. ) reduced the weight of the solid an additional 5%, affording 8.56 lbs of the prepolymer. Upon standing, the combined supernatant and exane rinse afforded additional product which was purified from contaminants by dissolving it in four times its weight of toluene, 0 filtering while hot, and re-precipitating it from four times the solution's volume of hexanes. An additional 7.8 lbs of vacuum dried prepolymer was obtained. Elemental analysis indicated the following composition: C-94.55, H-4.98, Ni-0.049, P-0.039, Al-0.095. 5 In addition to the above-described syntheses

■ and those described -in- abloner, we have discovered the following synthetic routes to the prepolymers.

Synthesis with Metal Halide Type Catalysts

We have identified a number of transition metal 0 halides which, either alone or in combination with a trialkylalane or dialkylaluminum halide, effect the cyclotrimerization of phenylacetylene. We have also discovered certain lanthanide elements with similar ability. By controlling the reaction time and 5 temperature, the reaction medium, ratio of feedstocks, and catalyst composition, a broad range of prepolymer types are available due to changes in molecular weight, residual ethynyl group content, and variation in the 1,2,4- versus 1,3,5-isomer distribution of the 0 cyclotrimerization. With many of these catalysts no linear oligomerization of the acetylene occurs. We have found that in conjunction with diethylaluminum chloride, the following metal halides will cyclotrimerize phenylacetylene: nickel fluoride, 5 cobalt chloride, chromium chloride, molybdenum chloride, tungsten chloride, vanadium trichloride, niobium pentachloride, bis(cyclopentadienyl) niobium dichloride, tantalum pentachlo ide, titanium tetrachloride, cyclopentadienyltitanium trichloride, bis(cyclopentadienyl)titanium dichloride, zirconium tetrachloride, bis(cyclopentadienyl)zirconium dichloride, and bis(cyclopentadienyl)hafnium dichloride. The selectivity for cyclotrimer vs. linear- oligomer varies from one catalyst to another as well as the selectivity for 1,2,4- versus 1,3,5-triphenylbenzene.

Niobium and tantalum pentachloride both are also active cyclotrimerization catalysts for phenylacetylene but in the presence of diethyl.aluminum chloride, a different catalyst is present as indicated by the differing 1,2,4- to 1,3,5-selectivity ratios produced. ^" Furthermore, niobium and tantalum pentahalides can be modified by the addition of alkoxides, phenoxides, or mercaptides. Niobium tetrachloride and niobium trichloride have also been shown to be active catalysts. Preferred catalysts include niobium pentachloride modified with lithium tert-butyl ercaptide, titanium tetrachloride-diethylaluminum chloride, and cyclopentadienyltitanium trichloride-diethylaluminum chloride.

The application of a number of these catalyst systems to the preparation of polyphenylene prepolymers from mixtures of phenylacetylene and diethynylbenzene has afforded polymers with a wide spread of properties. For example, polymers with molecular weights over 10 AMU and with essentially no residual ethynyl groups have been prepared using titanium tetrachloride and diethylaluminum chloride. Lower molecular weight resins, i.e., with average molecular weight < 2,000 and with large amounts of residual ethynyl groups can be prepared for example using cyclopentandienyl titanium trichloride and diethylaluminum chloride. Low molecular weight (<5,000 AMU) polymers with moderate ethynyl group content (DSC cure energies >100 J/g and <400 J/g) are often particularly desirable due to the ease of processing such material- as thermally stable and chemically inert thermoset resins. When these polycyclotri erizations are run in aliphatic hydrocarbons as solvent, the molecular weight and ethynyl group content can be controlled by precipitation of the resins at the appropriate time as will be further discussed below. Synthesis with Transition Metal Carbonyl

Catalysts

-We have also discovered a general method to convert-Group IV through Group VIII transition metals into active cyclotrimerization catalysts for arylacetylenes. Alkylacetylenes and diaryldiacetylenes may also be used to prepare prepolymers from a mixture of alkyl and/or arylacetylenes and polyacetylenically substituted aromatics. The very high selectivity for cyclotrimerization exhibited by these catalysts enables the synthesis of polymers containing only minor amounts of linear oligomers (i.e. vinyl protons) under mild conditions and can be used to prepare polycyclotrimerized polyphenylene polymers. The catalysts involve the reduction of transition metal salts of 1,3-dicarbonyl compounds with aluminum hydrides. The activity and selectivity of the catalysts is, in general, dependent on the metal, added ligands, and reaction conditions. With some metals, other reductants such as sodium naphthalide or triisobutylaluminum may be used. The catalyst systems make polyphenylene polymers which contain residual ethynyl groups.

The catalysts are prepared by reducing the transition metal compound with a dialkylaluminum hydride or trialkyl aluminum compound. The transition metal compounds usually contain 1,3 dicarbonyl anionic ligandε such as acetylacetonates . When nickel(II)acetylacetonate is reduced in the presence of a triaryl phosphine with two molar equivalents of diisobutylaluminum hydride at or below room temperature, an active catalyst for the cyclotrimerization of acetylenes is obtained. The catalyst activity is a function of the phosphine chosen, with ortho-substituted phosphines often providing the highest activity and selectivity. Thus, aryl phosphines substituted at the ^■-ortho position with methyl or methoxy groups are more active than unsubstituted phosphines, which are more active than arylphosphites, which are more active than alkylphosphines. For example, the catalyst prepared at -20°C from one molar equivalent of nickel acetylacetonate, two molar equivalents of diisobutylaluminum hydride, and four molar equivalents of tri-o-tolylphosphine will catalytically cyclotrimerize phenylacetylenes to a mixture of 1,2,4- and 1,3,5-triphenylbenzene in which the former isomer predominates 45 to 1. Only trace amounts of dimer and linear trimer are produced. Catalysts prepared with the less active phosphorous ligands require higher reaction temperatures and afford products of lower isometric purity and lower selectivity for cyclotrimer compared to the linear oligomer.

Using this method to prepare catalysts, polyphenylene resins from phenyl acetylene and diethynylbenzene with only trace amounts linear oligomer have been made. Another advantage of preparing cyclotrimerization catalysts as above is that the active catalyst is stable in the absence of acetylenes and that the highly exothermic cyclotrimerization can therefore be readily controlled by acetylene addition.

A broad range of prepolymer types can be prepared by controlling the- reaction time and temperatures, the amount and type of ligands, the reaction medium, and the order and ratio of feedstock addition.

For example, prepolymers of low molecular weight with cure energies of about 100-300 J/g can be selectively produced. Aliphatic hydrocarbons or alcoholic solvents can be used for controlling properties since the polyphenylene resins can be - precipitated from the reaction media at the appropriate- conversion.' - Prepolymer processability is also a -function of the isomer selectivity of the cyclotrimerization catalyst. Since the relative amounts of 1,2,4- and 1,3,5-isomers can be varied by changing the reaction temperature, catalyst metal and the ligands around the catalyst, this provides an additional tunable variable to optimize resin properties and processability. Catalysts which afford particularly high selectivity for cyclotrimerization compared to linear oligomerization for preparing prepolymers from phenylacetylene and diethynylbenzene include the following:

1. Nickel acetylacetonates reduced with diisobutylaluminum hydride or triisobutylaluminum in the presence of phosphines of phosphites.

2. Cobalt acetylacetonate reduced with diisobutylaluminum hydride or triisobutylaluminum either in the presence or absence of phosphines or tolane. 3. Iron acetylacetonates or iron ^'dibenzoylmethanates reduced with diisobutylaluminum hydride or triisobutylaluminum.

4. Manganese acetylacetonates reduced with diisobutylaluminum hydride either in the presence of ^■ absence of tolane.

5. Chromium acetylacetonates reduced with diisobutylaluminum hydride or triisobutylaluminum in the presence of absence of tolane. 6. Vanadium acetylacetonate reduced with diisobutylaluminum hydride or triisobutylaluminum.

7. Titanocene dichloride reduced with diisobutylaluminum hydride.

8. Zirconium tetrachloride reduced with triisobutylaluminum.

Synthesis with Niobium Catalyst Additionally^", we have found that niobium-based compounds catalyze the co-cyclotrimerization of diacetylene and phenylacetylenes into a useful prepolymer resin.

The catalysts can be used without prior treatment, by introducing them into the reaction vessel under an inert atmosphere, such as argon, either directly as solids, or solutions in aromatic solvents, such a toluene, followed by the introduction of the acetylene compounds to be polymerized. Besides co-cyclotrimerized products of phenylacetylene with diacetylene, the same reaction is extendable to diacetylene and acetylene and to other mono-substituted acetylenes besides phenylacetylene, and to other diacetylene molecules (i.e., in which two acetylenic functions are linked by an organic fragment). The catalyst is also expected to exhibit some activity in the similar reaction of disubstituted acetylenes and diacetylenes. The reaction proceeds at room temperature or below. The products are very clean, containing little, if any, linear polymer. They do contain sufficient amounts of terminal acetylenes to provide enough cure so that shape retention is possible upon molding. Curing occurs at about 150-170°C, preceded and accompanied by softening and melting.

Functionalized Polyphenylene Prepolymers Functionalized acetylenes and diacetylenes may be reacted to yield functionalized prepolymers

(polycyclotrimerization) that yield final polymers with modified properties. These functionalized polymers can contain residual, unreacted ethynyl groups and can be used as thermoset resins. By appropriate reactions and modifications, the functional groups can be the point of attachment of other molecules, including polymers, to prepare a wide spectrum of graft polymers. Such systems could provide better strength, thermal stability, chemical inertness to the^' grafted polymers, and improved composite properties.

We have cocyclotrimerized diethynylbenzene and phenylacetylene mixtures with a variety of functionalized acetylenes including propargyl alcohol, 3-methylbut-3-en-l-yne, alkylacetylenes, 3-carboethoxyphenylacetylene, diethynylsilanes, and diphenylbutadiyne. There is very little, if any, detectable linear oligomer in the polymers. The residual ethynyl group content and polymer molecular weight can be adjusted by varying the catalyst feed stocks, reaction solvent, temperature and reaction time. The polymers are soluble in a number of organic solvents allowing one to further modify the functional groups via standard organic reactions. For example, the polymer prepared from diethynylbenzene, phenylacetylene and 3-methyl-3-buten-l-yne contains isopropenyl groups off the aromatic backbones which can be involved in olefin polymerizations with substrates such as ethylene, styrene, butadiene, etc. The prepolymer may also be modified with a variety of electrophilic agents such as peracids, halogens, ozone, etc., allowing grafting of a wide variety of substrates to the functionalized polyphenylene resin. Likewise, polyphenylene polymers containing carboethoxy groups can be converted to acids, acid halides, amides, or alcohols, or transesterified. Additional functional groups can be introduced through the incorporation of mono or polyethynyl silanes where the other substituents attached to the silicon atom contain the functionality. The silanes could be - polymeric and. other metals or metalloids could be substituted for silicon.

The above mentioned polymers (either before or after grafting) can be used, for example, as thermosets, adhesives, potting compounds, and dielectrics. The following are illustrative examples.

Example 10 The following illustrates preparation of carboxy and functionalized branched polyphenylene prepolymers by cyclotrimerization.

A mixture of phenylacetylene (10 parts), 3-ethynylmethylbenzoate (10 parts), 1,3-diethynylbenzene (20 parts) and toluene (360 parts) are mixed in a reaction vessel. The mixture is catalytically cyclotrimerized to yield a mixture of branched polyphenylene prepolymers containing methoxy carbonyl substituents.

Example 11 The following illustrates a preparation of 2-hydroxyethoxycarbonyl functionalized branched polyphenylene prepolymer. The branched polyphenylene prepolymers containing methoxy carbonyl groups (as prepared in Example 10) are stirred with excess ethylene glycol and 0.05 parts sodium methoxide at about 110°C. Methyl alcohol distills off, and the reaction is worked up to yield a mixture of branched polyphenylene prepolymers containing 2-hydroxyethoxyca^'rbonyl substituents.

Example 12 The following illustrates preparation of 3-amino-propylamino carbonyl functionalized branched polyphenylene preopolymers.

The branched polyphenylene prepolymers containing methoxycarbonyl groups (1 part, prepared as in Example 10) are stirred with excess l,^'3-diaminopropynyl solvent. Methyl alcohol distills off, and the reaction is worked up to yield a mixture of branched^' polyphenylene prepolymers containing 3-aminopropylaminocarbonyl substituents.

Example 13 The following illustrates the preparation of sodium carboxylate functionalized branched polyphenylene prepolymers by hydrolysis of the corresponding ester.

A carboxy ester-functionalized branched polyphenylene prepolymer (prepared, for example, as in Example 12), is dissolved in a solvent and treated with excess sodium hydroxide and a phase transfer catalyst. The reaction is worked up to yield a mixture of branched polyphenylene prepolymers containing sodium carboxylate substituents. Example 14

The following illustrates the preparation of branched polyphenylene prepolymers containing hydroxy methyl substituents. The branched polyphenylene prepolymers containing methoxycarbonyl groups are reacted with lithium aluminum hydride in tetrahydrofuran solvent. The reaction mixture is worked up to yield branched polyphenylene prepolymers containing hydroxymethyl substituents.

Example 15 The following illustrates preparation of branched polyphenylene prepolymers containing hydroxy substituents.

Phenylacetylene (10 parts), 3-acetoxyphenylacetylene (10 parts),

1,3-diethynylbenzene (20 parts); and toluene (360 parts) are mixed in a reactor vessel. The mixture is catalytically cyclotrimerized to yield branched ■ polyphenylene prepolymers containing acetoxy substituents. This material is then treated with aqueous caustic and phase transfer catalyst, and branched polyphenylene prepolymers containing hydroxy groups are isolated.

Example 16 The following illustrates preparation of branched polyphenylene prepolymers containing glycidylether substitutents . Branched polyphenylene- prepolymers containing hydroxy substituents (for example, as prepared in Example 15), are treated with excess epichlorohydrin, and worked up to yield branched polyphenylene prepolymers containing glycidylether substituents. Pyridyl Polyphenylene Prepolymers

The prepolymers may be prepared by polycyclotrimerizing a diacetylene with an aryl or alkyl nitrile. In general, the prepolymers are more basic and polar than the polyphenylene polymers and should be useful where these properties are desired. The polyphenylene polymers include pyridyl rings and can be prepared with residual unreacted ethynyl groups. These polymers can also be used to form thermoset resins having excellent thermal and chemical stability and are 5 particularly useful for composites, adhesives, membrane materials, and thin film barriers.

We have found that. cobalt catalysts can be used to prepare pyridyl containing polyphenylene polymers by cocyclotrimerizing bis(ethynyl)-compounds with aryl and

10. alkyl nitriles. To control the residual ethynyl group content, the degree of crosslinking, the pyridine content, and the processability of the polymer, a monoacetylene, such as phenylacetylene, may also be added to the monomer feed. Cure energies greater than

15 100 J/g can easily be achieved when preparing these polymers. For pr.eparation of resins, when the polymers- are compression molded at 200°C and thermally post cured in an inert atmosphere at 350°C, materials which are thermally stable in air below 550°F are obtained.

20 Polymers may be prepared from nitrile containing monomers such as cyanobenzene, dicyanobenzene, cyanopyridine, cyanothiophene, perfluorocyanobenzene, dicyanomethane, and cyanoacetamide. The diethynyl components include diethynylbenzene and

25 bis(ethynylphenyl) ether. The following examples are illustrative.

Example 17 The following is^' illustrative of the preparation of a pyridine containing prepolymer. Minor

30 variations to the synthesis described below may be made to accomodate the reactivity and solubility of the various monomers shown in the table I.

Into a 1 L four-necked, round bottom flask was added 46.68 g (453 mmol) of benzonitrile, 3.77 g of 5 n-dodecane, and 300 ml of m-xylene. An addition funnel was charged with 55.72 g (442 mmol) of 1,3-diethynylbenzene, 50 ml of m-xylene, and 3.82 g of n-tetradecane. The contents of the flask and addition funnel were thoroughly purged with argon and the reaction was run under strictly anaerobic conditions. The contents of the flask were stirred and warmed to reflux. At 100°C, 20 ml of the diethynylbenzene solution was added to the pot. Five minutes later the pot temperature had reached 110°C and 2.00 ml (,8.76 mmol) of cyclopentadienyl cobalt dicarbonyl was added.

The remaining contents of the addition funnel were added over a 2 hour period. Upon completion of the addition, 29% of the diethynylbenzene and 12% of the benzonitrile had been consumed. Two hours later the consumptions were 60 and 15%, respectively, and the catalyst Was inactive. The reaction was allowed to cool to room temperature overnight and was reheated the next morning. A second charge of 2.00 ml of catalyst was then added. An hour later the catalyst was inactive. Consumption of diethynylbenzene was 84% and benzonitrile was 18%. The reaction solution was cooled and dripped into 1500 ml of methanol. The yellow precipitate was rinsed twice with 300 ml of methanol before it was vacuum dried at 45°C for 16 hours to afford 52.66 g of yellow powder.

An analysis of the powder showed it to consist of polymer in the 1000 to 95,000 molecular weight range. Elemental analysis showed 92.03% C; 4.94% H; 2.37% N; .91% Co. NMR analysis of the resin showed a ratio of ethynyl protons centered at 3.0 to aromatic protons centered at 7.3 to be .036. The powder, when heated in an inert atmosphere at 10°/min, exhibited a 182 J/g exotherm between 190 and 240°C. At the same heating rate, the resin lost 5% of its weight at 580°C and 56% of it remained at 1000°C. To form a resin, the prepolymer was compression molded by applying 670 lbs/in pressure to the powder in a mold and electrically heating the mold to 280°C. At 100°C the pressure had dropped to zero. At 160°C the pressure was re-applied to 330 lbs/in . After the mold reached 280°C, it was allowed to cool to 250°C under pressure before the.sample was removed hot. The coupon was then post-cured at 325°C for 17 hr under an , inert atmosphere. TGA analysis of a 120-170 mesh sample in air (50 ml/min) showed a %/hr weight loss at 316°C. Dynamic mechanical analysis showed a flexural modulus of 580 kpεi -at 50°C dropping to 410 dpsi at 325°C when heated at 5°/min under an inert atmosphere.

Other examples of pyridyl prepolymers prepared as described above are given in table I.

TABLE I

^aThe number in parenthesis is the molar parts of the monomer mixed in the reaction.

^bThe molecular weights were determined by HPLC relative to polystyrene.

^cNitrogen content of the dry resin by combustion analysis. The cure energy of the dry resin as determined by differential scanning calorimetry in sealed pans under the inert atmosphere. Curing generally occured between 150°C and 220°C at a heating rate of 10°/min.

^eThe temperatures reported are where the resin lost 5% of its weight under a 50 ml/min flow of argon with a heating rate of lOVmin.

PA=phenylacetylene; DB=1,3-diethynylbenzene; DEE=di-p-ethynylphenyl ether

Oxidative Coupling

A two-stage process for prepolymer formation involving polycyclotrimerization followed by oxi.dative^' coupling may also be used to produce prepolymers which contain manageable residual acetylene content.

In general, the process calls for first preparing a resin with pendant acetylene groups via a cyclotrimerization polymerization. The pendant acetylene groups are then oxidatively coupled either to each other or to other monomers, either mono- or difunctional, to give a higher molecular weight prepolymer (normally 10,000 to 100,000 AMW), which retains the acetylene content of the initial prepolymer and has desirable properties such as excellent crosslinking and high solubility.

In the invention, difunctional acetylenes (e.g., diethynyl benzene), are polymerized via cyclotrimerization to a moderate extent, either alone or with added monofunctional acetylenes (e.g., acetylene, phenylacetylene). This moderate polyme ization may give, for example, a product with an average molecular weight of from ~350 to over 20,000 and with a pendant acetylene content of from < 0.5% to ~20%. The cyclotrimerized polymer is then oxidatively coupled using a copper catalyst in the presence of a weak base (e.g., pyridine) and an oxidant (e.g., air, H₂0₂) to give a higher molecular weight species which contains the same acetylene content. Varying amounts of monofunctional acetylenes (e.g., acetylene, phenylacetylene) may also be added as capping agents to limit the final molecular weight.

Further, difunctional acetylenes (e.g., diethynyl benzene) may be added to increase the average acetylene content or heteroatom containing difunctional acetylenes (e.g., diethynyl dipy idyl ether) to strengthen, toughen, stiffen, etc., the final resin. These difunctional acetylenes may be added with or without monofunctional acetylenes.

The final prepolymer is solvent processable and melt processable. The high molecular weight (from -1000 to > 500,000) prepolymer contains a higher acetylene content per molecule than is available through a simple cyclotrimerization process and yet a manageable acetylene content, below the limit for uncontrolled cure. The following examples are illustrative.

Example 18 The following illustrates the preparation of an oxidation coupled resin. To a 250 mL, 3-necked, round-bottomed flask equipped with thermometer, magnetic stir bar, condenser and oxygen inlet dip tube was charged: 20 g of resin (024-49) [Describe the resin], 100 mL of methylene chloride, 10 mL of pyridine, and 0.10g of cuprous chloride.

The resulting solution was heated to reflux and oxygen was bubbled through the solution. Methylene chloride was added as necessary to maintain a constant reaction volume. The reaction was monitored by NMR and was determined to be complete when the acetylenic proton peak disappeared. When the reaction was complete, the solution was cooled to room temperature and an additional 100 ml of methylene chloride was added. The solution was washed with 3 x 167 mL of saturated aqueous ammonium chloride followed by 3 x 167 mL of 2N hydrochloric acid. Each aqueous layer was back extracted in succession with 2 x 75 mL of methylene chloride. The methylene chloride layers were combined, dried (Na.30,), filtered and concentrated on a rotary evaporator. The residue was dissolved in 60 ml of toluene and then added to 600 ml of methanol dropwise. The precipitate was stirred for one hour, filtered, washed with methanol and dried at 50°C in vacuo to give 8.67 g of a prepolymer. Example 19

The following is an example of the preparation of an oxidatively coupled resin with phenylacetylene modification. This procedure is run virtually identically to the procedure in Example 18 with the difference being that an amount of phenylacetylene equal in weight to the weight of low molecular weight resin is added dropwise to the oxidation mixture during the first hour of reaction. Thus, 7.5 g of prepolymer resin prepared from diethynylbenzene and phenylacetylene and 7.5 g of phenylacetylene are oxidatively coupled. The work-up, which is entirely analogous to the example described proviously, afforded 8.88 g of prepolymer product.

Solvent In any of the above-described syntheses, a polymerization solvent may be used in which the monomer is soluble but the polymer is not in order to control polymer molecular weight. In general, the solvent or mixture of solvents has the property that the monomers are soluble and the polymer of desired molecular weight is insoluble. When the polymer has grown to the desired size, it precipitates from solution, removing it from the polymerization process. Monomer remaining in solution may continue to react. With this invention the molecular weight can be controlled but the extent of monomer consumption can be held at any level desired. In this way, polymerization- reactions may be run continuously. Soluble oligomers that result during preparation of the prepolymer can be recycled and used to prepare more prepolymer. Because catalyst may be occluded in the precipated prepolymer, make-up catalyst may have to be added.

The molecular weight o^'f the polymer obtained is due solely to the polarity of the solvent used and not - on the extent of reaction. In order for the process to function efficiently, the solvent may be less polar than the polymer or more polar than the polymer . A suitable less polar solvent would be a saturated hydrocarbon such as hexane, cyclohexane, octane or methylcyclohexane, or a mixture of a hydrocarbon and an aromatic solvent such as hexane and benzene or perfluorinated hydrocarbon. A suitable solvent which is more polar than .the polymer might be lower ketones such as methyl ethyl ketone; other examples include ethyl acetate, alcohols such as methanol, ethanol, isopropanol; other examples are acetic acid or water or mixtures of these solvents either with each other or with a less polar solvent such as toluene. Intermediate less polar solvents can be prepared by mixing these non-polar solvents with solvents which dissolve the polymers such as aromatic hydrocarbons, chlorinated solvents and oxygenated solvents.

Controlling the molecular weight of the polymer also enables control of the residual acetylene content of the resin. In general, the higher the molecular weight of the resin, the lower the residual acetylene content. The residual acetylene content is important in a thermoset resin in that it determines the degree of crosslinking in the final thermoset object which is produced and hence the physical and mechanical properties of the object. The process of the invention affords control over the residual acetylene content without sacrificing the extent of monomer consumption in the resin preparation reaction. Functional acetylenes may be polymerized either alone or with added monofunctional acetates. Very low molecular weight polymers may be recycled along with fresh difunctional acetylenes either with or without added monofunctional acetylenes. These polymerizations are conducted in a solvent or a mixture of solvents in which a polymer of desired molecular weight and therefore-corresponding desired residual acetylene content is insoluble.

The following examples are illustrative. Example 20

The following illustrates a prepolymer synthesis with a selected solvent. To a 2000 ml, jacketed resin flask equipped with bottom-outlet valve, condenser, mechanical stirrer, addition funnel and septum stopper was charged 1400 ml of methylcyclohexane. Nitrogen was then bubbled through the solvent with stirring for ~15 minutes. At this point, 0.545 g (2.12 mmol) of Ni(acac)₂ and 2.581 g (8.48 mmol) of tri-o-tolyphosphine was added and degassing with nitrogen was continued for another 1/2 hour while the mixture was cooled to +1 to +2°C by means of a circulating pump circulating cooling fluid through a copper coiled in a dry-ice/isopropanol bath. While the reaction mixture was cooling, 86.6 g (0.0848 mole) of phenylacetylene , 53.5 g (0.424 mole) of NOT FURNISHED UPON FILING

The ethylcyclohexane solution from the first filtration was evaporated to give 91.9 g of an oil. It was calculated that the methylcyclohexane distillate contained 8 g of phenylacetylene and 5 g of diethynylbenzene. It was also calculated that the residue contained 9 g of phenylacetylene, 6 g of diethynylbenzene, and 54 g of a very low molecular weight polymer. The balance of the oil was solvent. Both recovered solvent and residual oil were recycled to a second batch of polymer along with 61.3 g of fresh phenylacetylene and 47.6 g of fresh diethynylbenzene. The total charge of polymer producing materials was 180 g-

The polymerization was run exactly as described above. The prepolymer which precipitated from methylcyclohexane turned sticky upon warming to room temperature so it^'was immediately dissolved in 350 ml of tolueneN The toluene solution of polymer was added over ~30 seconds to 3000 ml of methanol at room temperature with stirring. The mixture was stirred over a weekend and the polymer was then collected by filtration to afford 57.26 g of product after vacuum drying at room temperature.

The methylcyclohexane mother liquor was evaporated to give 113 g of an oil. This oil was dissolved in 226 ml of toluene and added dropwise over ~l/2 hour to 3390 ml of hexanes. The hexane slurry was stirred for 10 minutes and then filtered. Vacuum drying afforded a second crop of prepolymer which weighed 26.35 g.

GPC showed the molecular weights of these two prepolymers to be almost identical.

Other embodiments are within the following claims.

Claims

1. A foaming composition comprising

(a) a foaming agent;

(b) an aromatic polyacetylenically unsaturated prepolymer; and

(c) a viscosity modifier for modifying the flow properties of said prepolymer having one or more acetylenic groups available for reacting with said prepolymer, said foaming agent, prepolymer, and viscosity modifier being chosen such, that at the decomposition temperature of said foaming agent, the viscosity of said composition is sufficient to permit molding and foaming.

2. The composition of claim 1 wherein the amount of said viscosity modifier is no greater than 20% . by weight.

3. The foaming composition of claim 2 wherein the amount of said viscosity modifier is between 8 and 20% by weight.

4. The foaming composition of claim 1 wherein the softening point of said viscosity modifier is less than 150°C.

5. The foaming composition of claim 1 wherein said viscosity modifier comprises a diacetylenic aromatic compound.

6. The foaming composition of claim 5 wherein said viscosity modifier is diphenylbutadiyne.

7. The foaming composition of claim 5 wherein said viscosity modifier is 4,4 '-diethynyldiphenylmethane.

8. The foaming composition of claim 5 wherein said viscosity modifier is bis(ethynylphenyl)ether.

9. The foaming composition of claim 1 wherein said viscosity modifier comprises a diacetylenic aliphatic compound having the formula HC=C-CH -C=CH where n is an integer between 2 and 12, inclusive.

10. The foaming composition of claim 9 wherein said viscosity modifier is 1,4-pentadiyne.

11. The foaming composition of claim 1.wherein said viscosity modifier comprises a monoacetylenic aromatic compound.

12. The foaming composition of claim 11 wherein said viscosity modifier is chosen from the group consisting of biphenyl acetylene and naphthyl acetylene.

13. The foaming composition of claim 1 wherein said viscosity modifier comprises an oligomer having a lower degree of polymerization than said prepolymer.

14. The foaming composition of claim 13 wherein said oligomer has the same chemical composition as said prepolymer.

15. The foaming composition of claim 1 wherein said prepolymer comprises the cyclotrimerized product of an aromatic diacetylene and an aryl or alkyl monoacetylene, or acetylene.

16. The foaming composition of claim 15 wherein said aromatic diacetylene is chosen from the group consisting of diethynylbenzene, bis(ethynylphenyl)ether, and 4,4'-diethynyldiphenylmethane.

17. The foaming composition of claim 16 wherein said monoacetylene is phenylacetylene.

18. The foaming composition of claim 1 wherein said prepolymer is the cyclotrimerized product of an aliphatic diacetylene having the formula HC^C-CH -C=CH where n is an integer between 2- and 12, inclusive, . and an aryl or alkyl monoacetylene, or acetylene.

19. The foaming composition of claim 18 wherein said aliphatic diacetylene is 1,4-pentadiyne.

20. The foaming composition of claim 18 wherein said monoacetylene is phenylacetylene.

21. The foaming composition of claim 1 wherein said prepolymer comprises the cyclotrimerized product of diacetylene and an aryl or alkyl monoacetylene, or acetylene.

22. The foaming composition of claim 21 wherein said prepolymer comprises the cyclotrimerized product of diacetylene and phenyl acetylene.

23. The foaming composition of claim 1 wherein said prepolymer comprises the cyclotrimerized product of an aromatic diacetylene and an aryl or alkyl nitrile.

24. The foaming composition of claim 23 wherein said aromatic diacetylene is chosen from the group consisting of diethynylbenzene, bis(ethynylphenyl)ether, and 4,4'-diethynyldiphenylmethane.

25. The foaming composition of claim 24 wherein said aryl or alkyl nitrile is chosen from the group consisting of benzonitrile, dicyanobenzene, cyanopyridine, cyanothiophene, perfluorocyanobenzene, dicyanomethane, and cyanoacetamide.

26. The foaming composition of claim 1 wherein said prepolymer comprises the cyclotrimerized product of an aliphatic diacetylene having the formula

HC=C-CH -C=CH where n is an integer between 2 and 12, inclusive, and an aryl or alkyl nitrile.

27. The foaming composition of claim 26 wherein said aryl or alkyl nitrile is chosen from the group consisting of benzonitrile, dicyanobenzene, cyanopyridine, cyanothiophene, perfluorocyanobenzene, dicyanomethane, and cyanoacetamide.

28. The foaming composition of claim 1 wherein said foaming agent is selected from the group consisting of azodicarbonamide, p-toluenesulfonyl hydrazide, and 4,4'-oxybisbenzenesulfonyl hydrazide.

29. The foaming composition of claim 1 wherein said foaming agent is azocarbonamide, said prepolymer is the cyclotrimerized product of diethynyl benzene and phenyl acetylene, and said viscosity modifier is diphenylbutadiyne.

30. The foaming composition of claim 1 wherein said foaming agent is azodicarbonamide, said prepolymer is the cyclotrimerized product of diethynyl benzene and phenyl acetylene, and said viscosity modifier is 4,4 '-diethynyldiphenylmethane.

31. The foaming composition of claim 1 wherein said foaming agent is azodicarbonamide, said prepolymer is the cyclotrimerized product of diethynyl benzene and phenyl acetylene, and said viscosity modifier is bis(ethynylphenyl)ether.

32. A method for preparing a foam comprising the steps of preparing a foaming composition by blending (a) a foaming agent; (b) an aromatic polyacetylenically unsaturated prepolymer; and

(c) a viscosity modifier for modifying the flow properties of said prepolymer having one or more acetylenic groups available for reacting with said prepolymer, said foaming agent, prepolymer, and viscosity modifier being chosen such that at the decomposition temperature of said foaming agent, the viscosity of said composition is sufficient to permit molding and foaming; and molding said foaming composition to form a shaped article under reaction conditions, including temperature and pressure, sufficient to decompose said foaming agent, thereby causing foaming of said composition, and to cause the acetylenic groups of said viscosity modifier to react with said prepolymer.

33. The process of claim 32 further comprising carbonizing said foam subsequent to said molding step.

34. The process of claim 32 wherein said blending step comprises ball-milling said foaming agent, prepolymer, and viscosity modifier to form a fine, homogeneous powder.

35. The process of claim 32 wherein said molding step takes place at a temperature below 250°C.

36. A foam prepared according to the process of claims 32 or 33.

37. The foam of claim 36 wherein the compressive strength of said foam is at least 100 psi in the temperature range of 0 - 500°F.

38. The foam of claim 36 wherein the density

3 of said foam is no greater than 0.2 g/cm .

39. The foam of claim 38 wherein the density

3 of said foam is between 0.01 and 0.2 g/cm .

40. The foam of claim 38 wherein the density of said foam is between 0.05 and 0.14 g/cm .

41. The foam of claim 36 wherein the compressive strength of said foam does not vary by more than 5% upon exposure to moisture.