CA1042150A - Process for foaming ionic copolymers and the products thereof - Google Patents

Abstract

ABSTRACT

This invention relates to a novel process for preparing novel foamed polymeric products having uniform cell structure which comprises mixing a non-volatile polar substance, a foaming agent and an ionic polymer, said non-volatile polar substance being a preferential plasticizer for said ionic polymer and said foaming agent characterized as being sparingly soluble in said ionic polymer, subjecting said mixture to an elevated temperature and pressure whereby said foaming agent and said non-volatile polar substance are impregnated into said ionic polymer, and foaming said impregnated ionic polymer. Preferably the ionic polymer comprises from about .2 to 20 mole %
pendant ionic groups, especially sulfonate groups. In a preferred embodiment of the instant invention a sulfonated polystyrene polymer is admixed with a non-volatile polar compound and a foaming agent which is characterized as having a solubility parameter of less than 7.9 and a boiling point of less than 100°C, under elevated pressure and temperature whereby said foaming agent and said non-volatile polar compound are impregnated into said sulfonated polystyrene polymer and the resultant mixture foamed at atmospheric pressure ant at a temperature of at least 105°C. Upon cooling, a low to moderate density foam of uniform cell structure is formed which can be reprocessed by admixing with a low boiling solvent for polystyrene and a non-volatile polar substance, removing said low boiling solvent and repeating the above foaming process.

Description

1o~i ~ 15 0 This invention relates to a novel process for preparing novel foamed polymeric products having uniform cell structure which comprises mixing a polar substance (it is to be understood that the term "polar substance" and "polar compound" as used herein are meant to include only non-volatile polar substances or compounds), a foaming agent and an ionic polymer, said polar substance being a pref-erential plasticizer for said ionic polymer and said foaming agent characterized as being sparingly soluble in said ionic polymer, subjecting said mixture to an elevated temperature and pressure whereby said foaming agent and said polar sub-stance sre impregnated into said ionic polymer, and foaming said impregnated ionic polymer. Preferably the ionic polymer comprises from about .2 to 20 mole % pendant ionic groups,es-pecially sulfonate groups. In a preferred embodiment of the instant invention a sulfonated polystyrene polymer is admixed with a polar compound and a foaming agent which is character-ized as having a solubility parameter of less than 7.9 and a boiling point of less than 100C., under elevated pressure and temperature whereby said foaming agent and said polar com-pound are impregnated into said sulfonated polystyrene polymer and the resultant mixture foamed at atmospheric pressure and at a temperature of at least 105C. Upon cooling, a low to moderate density foam of uniform cell structure is formed which can be reprocessed by admixing with a low boiling sol-vent for polystyrene and a polflr substance, removing said low boiling solvent and repeating the above foaming process.
There are essentially only two major flexible foam products now available in large volume. They are polyure-thane foam and plasticized poly(vinylchloride) foam. At thistime, semiflexible foamed ~Jolyolefins are being commercialized ~ -2-1 ~4 ~ ~ 5 ~

for special applications; however, these do not repre~ent large volume products.
Flexible polyurethane foams are prepared by a resc-tion wherein the polymer is formed, expanded and crocs-linked.

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1 It is evident that after achieving a cured polyurethsne foam,

2 the process is irreversible. Therefore, if the resulting prod-

3 uct does not meet specifications, it i8 of little or no value.

4 Foamed polyvinylchloride (PVC) can be suitably plas-ticized to yield a flexible cellular product.
6 U.S. Patent 3,322,734 teaches that ionic polymers, 7 for example, partially ~ulfonated polystyrene and partially 8 carboxylated polystyrene, can be employed as plastics for 9 molding ob~ects and utilized to prepare foams. The present invention differs from that patent on a number of very impor-11 tant points. U.S. Patent 3,322,734 teaches that the presence 12 of a modest amount of carboxyl or sulfonic acid groups, if 13 neutralized to a critical degree, permits processability by 14 conventional plastic processes at elevated temperatures, and yet retains ionic associations at ambient temperature. The 16 neutralization process simply involves reaction of the acid 17 moiety with a suitable metal salt, metal oxide, metal hydrox-18 ide, etc. to ~ suitable extent. That art teaches that the 19 acid form should not be completely neutralized -- preferably the neutralization should be only 80a complete (i.e., the 21 metal hydroxide or other compound should be added in an amount 22 correspondin~ to 80% of the stoichio~metric amount of acid pres-23 ent), and in no csse should exceed 90% of the stoichiometric 24 equivalence. (Similarly that patent teaches that a minimum fraction of the acid groups must be neutralized9 i.e., 10%).
26 Thus, it is emphasized clearly in the prior art that incom-27 plete neutralization of the acid moiety is essential in order 28 that the resulting products be fabricable.
29 Thus, tho8e products are similar to conventional plastic systems in that they respond to elevated temper~tures 31 and shear such that the ionic associations are diminished or 32 virtually eliminated. Consequently flow occurs and the prod-`V

1 ucts can be molded or foamed much like conventional thenmo-2 plasticc, such as polystyrene or polyethylene. Similarly, if 3 one creates a foam from these ionic polymers, and exposes it 4 to elevated temperatures (for example, lO0 to 150C.) the ionic interactions are diminished and flow occurs -- that is, 6 the foam collapses. The dimensional stability of such m2te-7 rials at elevated temperatures is inherently poor.
8 The present invention differs from the ionic polymer 9 foams disclo~ed in the prior art in the following critical lo ar2as: -(a) The products of the present invention are pref-l2 erably neutralized completely.
13 (b) The neutralized compositions of this invention 14 are not readily processed by plastics processing equipment even at very high temperatures because, in the absence of a l6 suitable additive, the ionic groups are very strongly associ-17 ated, i.e., the composition is characterized as having ionic 18 domains di~persed in a continuous nonionic phase.
19 (c) The products, as described here, due to their strong associations, exhibit very little flow, even at very 21 high temperatures, msnifesting unusual and valuable dimension-22 al stability.
23 (d) The associations of these ionic polymers are 24 weakened by the addition of suitable plasticizing sgents which disrupt the ionic domains and penmit the foaming process.
26 (e) In the absence of suitable plasticizing agents 27 for the domains, these products are not foamed into desirable 28 products under practical conditions because the strong ionic 29 associations preclude formation of a low density foam of uni-form cell structure.
31 It is evident from this earlier discussion that chem-32 icAlly cross-linked foams possess resistance to flow at ele-vated temperatures, but at the cost of inability to reuse scrap, inability to refoam defective parts, etc.
~ n the other hand, conventional thenmoplastic foams po~sess the virtues of easy processability, reuse of scrap, and simplicity of the foaming operation, but lack dimensional stability at elevated temperature.
The present invention provides nearly all of the ad-vantages of thermoplastic foams and yet retains in the foamed product many of the virtues of the chemically cross-linked o foam.
It has now been unexpectedly discovered that novel foamed polymeric products may be prepared by foaming a mixture comprising an ionic polymer and a polar substance which acts as a plasticizer for ionic groups present in said ionic poly-mer. The polar substance may be a liquid, gas or solid at room temperature, and will have a dipolar moment of greater than 0.9 debyes, preferably from 1.2 to 5.5 debyes. In more detail, a mixture comprising an ionic polymer,said ionic poly-mer comprising about .2 to about 20 mole percent pendantionic groups, and a polar substance is impregnated with a foaming agent at a temperature of at least 40C., preferably from 60-300C. and then foamed. The impregnation step iB carried out at the above temperatures because the foaming agent is chosen 80 as to be sparingly soluble in said ionic polymer. The _ ~ _ 1 foaming agent will have a solubility parameter of less than 2 7.9 (C~lorle~) , preferably from about 4.5 to 7.7. To facil-3 itate impregnation, the foam~ng agent is mixed with said poly-4 mer at elevated temperatures and pressures and/or shear. If the mixture is fluid under the conditions of impregnation, 6 shear forces are helpful in facilitating incorporation. Pref-7 erably the foaming agent is incorporated in said ionic polymer 8 in the presence of the above-described polar substance, e.g., 9 the foaming sgent may be impregnated simultaneously with said polar gubstance or sequentially with the polar compound being 11 incorporated fir~t. The polar substance is further character-l2 ized as being a preferential plasticizer for said pendant ion-13 ic groups. The polar substance acts to weaken the physical 14 associations of the ionic polymer and thereby facilitates flow of the polymer during the foaming process. The amount of polar l6 substance employed should be enough to disrupt the ionic do- -17 mains of the polymer but not 80 much that the excess will alter 8 the desirable foam properties. Generally the amount willnor- ~
19 mally be in the range of from about 0.1 to about 50, preferab~ -from about 0.2 to 20 moles plasticizer per mole of pendant ion 21 ic groups. This process is useful for forming foamed polymeric 22 products in any of the forms known in the prior art and, unli~e 23 the prior art foaming processes involving chemical crosslink-24 ing, allows the reuse of scrap foamed polymers; that i8, the foamed polymers of the instant invention may be reprocessed.
26 The reprocessing of the scrap foamed polymers may be 27 accomplished in several ways -- for example, by dissolving the 28 polymer in a solvent mixture comprised of a solvent for the 29 polymer backbone and a polar substance, such a8 an alcohol, for the ionic domains. This solution may be precipitated to 31 yield the bulk polymer which can then be formulated with proper 32 foaming agents and polar substance. Alternatively the scrap 1 foamed polymer can be combined with a suitable volstile polar 2 compound and then proce~sed using thermoplastic techniques 3 and subsequently combined with additional unprocessed polymer.
4 The resulting blends can be formulated with the foaming agent

5 and additional polar substance , and subsequently refoamed.

6 This advantage of reproces3ing scrap foamed polymer

7 results from the fact that the foamed products of the instant

8 invention have physical cross-link6 and not the chemical cross-

9 links known in the prior art. Physical cross-links result from the interactions of the pendant ionic groups. The addition of sufficient amounts of a liquid polar substance weaken~ these l2 interactions, thus the foam flows readily at elevated tempera-13 tures and it can be readily digsolved in appropriate solvents.
14 After foaming, the polar substance may be removed if it iB
substantially volatile at temperatures below which the ionic 16 polymer degrades, thus leaving behind the strong and tempera-17 ture resistant physical cross-links. In the case of a solid 8 polar substance, after foaming some of the polar substance may 19 phase separate from the polymer and thereby increase the strength of the physical cross-lin~s.
21 This process is a~mirably suited to the preparation 22 of foamed sheet (for example, in extrusion) foamed pellets 23 and foamed molded samples. Furthe re, due to the excellent 24 high temperature dimensional stability of the foamed plastic products, these can be heated subsequent to the foaming proc~s 26 and stamped or forged into complex foamed articles simply by 27 a stamping and cooling cycle. The cooling of the plastic 28 fo~med article below its softening temperature permits the 2g retention of complex configurations.
The foaming agents which may be used in the process 31 of the instant invention are low boiling liquids which are con-32 verted into gaseous form by heating.

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1 The low boiling liquids which c~n be utilized are 2 tho~e which boil at a suitably low tempersture to sllow for 3 convenient foaming. For exsmple, these liquids must volatil-4 ize at a temperature where the polymer flows. When preparing a plsstic foam, the boiling point of the liquids can be ex-6 tremely low, even below room temperature, because if they are7 suitably dispersed in a solid plastic polymer they will not 8 readily vaporize until the polymer reaches a temperature at 9 which it flows. Examples of such suitable liquids are the 4 to 6 carbon alkanes, e.g., butane, pentane and hexane, and 11 the 1 to 2 carbon fluorocarbons or fluorochlorocarbons, e.g., l2 dichlorodifluoro methane, chlorodifluoro methane, trifluoro-13 chloro methane, 1,1,2-trichlorofluoro ethane, and the like.
1~ Similar materials which are gase~ at room temperature may be employed including carbon dioxide and nitrogen. Of course, I6 the low boiling liquids should be only sparingly soluble in 17 the ionic polymer.
18 As discussed above, the foaming agent should have a 19 solubility parameter of less than 7.9, preferably from 4.5 to 7.7. The foaming agent is incorporated into the lonic poly-21 mer in the absence of significant amounts of ~olvents for the22 polymer backbone chain which boil below the temperature of 23 foaming, at elevated temperature and pre~sure, and in the 24 presence of the polar substance. Preferably, the temperature of incorporation of the blowing agent should be greater than 26 40C. and the pressure should be more than 6 psi above atmos-27 pheric pressure. Preferably the pressure will vary from 14 28 to 5000 psi. The amount of foaming agent which is incorpo-29 rated into the ionic polymer will preferably be from l to 300 by weight Df the ionic polymer.
31 A sufficient amount of foaming agent must be used to provide 32 a foam of the proper density.

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1 Ionic polymers which are sub~ect to the process of 2 the instant invention are generally plastic polymers. Specif-3 ic polymers include sulfonsted polystyrene, sulfonated t-butyl 4 styrene, sulfonated polyethylene, sulfonated polypropylene, s sulfonated ~tyrene/acrylonitrile copolymers, sulfonated sty-6 rene/methyl methacrylate copolymer~, sulfonated block copoly-7 mers of styrene/ethylene oxide9 acrylic acid copolymer~ with 8 styrene, and copolymers of any of the above. Tbe ionic poly-9 mers of the invention also include backbone pla~ticized com-position~ of the above; for example, a pla~tic ionic polymer 11 which, when foamed according to the process of the instant 12 invention will give a rigid foam, may be suitably backbone 13 pla6ticized prior to foaming to give a flexible foam.
1~ The ionic polymers of the instant invention prefer-ably comprise from about 0.2 to 20 mole % pendant ionic groups.
16 More preferably, ionic polymers comprise from about .5 to lO
17 le percent pendant ionic groups. These pendant ionic groups 18 include carboxyl groups, carboxylate groups, sulfonate groups 19 and phosphonate groups, most preferred are sulfonate groups.
In accordance with the above, the most preferred ionic polymers 21 for utilization in the instant invention to prepare rigid plas-22 tic foams comprise partially sulfonated polystyrene and poly-23 styrene derivative8,e.g., t-butyl styrene.
24 The ionic groups present in the ionic polymers of the instant invention sre derived from substantially completely 26 neutralized acid or other moieties. For example, if a ~ulfonic 27 acid derivative is employed as the intermediate, sufficient 28 metal hydroxide i~ added to neutralize at least 90% of the acid 29 groups. Even thst residual 10% of unneutralized acid groups 30 can have a deleterious influence on the strength of the physi-31 cal cro6s-links derived from the ionic association. For that 32 reason, it is preferred that greater than 98% of the acidic intermediate species be neutralized, and it is most preferred that essentially all of the pendant ionic groups be neutralized. It is also posslble to add sufficient basic metal hydroxide or oxide to over-neutralize without any specific benefit other than to insure complete neutralization. From a practi-cal viewpoint, it is preferred that this excess of base be kept to no more than S0 mole percent beyond the stoichiometric equivalence of the pendant ionic groups. The neutrali~ing agents are selected from the group consisting of alkaline salts of Groups IA, IIA, IB, and II~ of the Periodic Table of the Elements, e.g., sodium hydroxide, potassium hydroxide, calcium hydroxide, and magnesium hydroxide; or from salts of lead, tin, antimony and aluminum.
Ammonia and amines can also be employed to neutralize these acidic inter-mediates to provide ionic products, e.g., Cl to C30 amines, preferably Cl to C10 amines.
The choice of the polar substance within the scope of the parameters disclosed above is also illimitable. The polar substance can be a liquid, gas, or solid at room temperature, and it should have a dipole moment of greater than 0.9 debyes, and preferably from 1.2 to 5.5 debyes. If the polar substance is a liquid or solid (in a powder form) at room temperature, it can be mixed with powdered polymer and then be exposed to elevated temperature and shear (such as by molding) so as to disperse the polar substance more uniformly in the polymer. The foaming agent is then incorporated into the polymer at elevated temperature and pressure. Alternatively, both the polar substance and the foaming agent can be incorporated into the ionic polymer simultaneously at elevated temperature and pressure.
The polar substance must be sufficiently compatible with the ionic polymer so that it can be fairly uniformly dispersed in the polymer under the influence of elevated temperature and pressure. The amount of polar substance used can vary over a wide range depending on the exact nature of the substance and the degree to which it is desired to weaken the physical associations of the ionic groups of the ionic polymer. However, generally .

the amount of polar substance will be in the range of from 0.1 to 50 moles of polar substance per mole of ionic groups of the polymer.
Preferred polar substances are compounds containing hydroxyl, carboxyl, thiol and amino groups. Most preferred are organic compounds con-taining hydroxyl, carboxyl and amino functional groups, and having no more than 30, preferably no more than 10, carbons per functional group. Examples of the most preferred polar substances include methanol, ethanol, propanol, butanol, hexanol, decanol, benzyl alcohol, phenethanol, triphenyl methanol, ethylene glycol, 1,2-pentane diol, glycerol, l,l,l-tris(hydroxymethyl)-ethane, pentaerythritol, acetic acid, lauric acid, decanoic acid, p-toluic acid, alpha pehnyl-o-toluic acid, 2-bibenzyl carboxylic acid, 3,4-dimethyl benzoic acid, adipic acid, sebacic acid, ethylene diamine, 1,6-hexane diamine, 1,2-diamino propane, 1,4,7,10-tetrazadecane, tris(2-aminoethyl)-amine, iso-hexamethyl triethylenetetra amine, and symmetrical cyclotetramethyl tetra-ethylene tetra amine. Polar substances which are solid at room temperature, e.g. pentaerythritol; decanoic acid; p-toluic acid; 3,4-dimethyl benzoic acid; etc., are also useful for making foams having densities above 10 lbs./
ft. , up to near bulk density of the polymer. Higher density foams (above

10 lbs./ft ) are desirable in some applications which require the foam to bear an appreciable load -- such as structural applications. Of course, when high density foams are desired, lesser amounts of foaming agent are generally used than for lower density foams. Preferably the polar substance will have a molecular weight of less than 2,000, more preferably less than 1,000. As disclosed above, the ionic polymers of the instant invention include polymers in which the nonionic phase is plasticized by a nonvolatile solvent for that phase. This type plasticizer will be referred to as a backbone plasticizer since it solvates the polymer chain backbone. The purpose of these type plasticizers is to convert those polymers which would normally result in rigid foams into foams which are flexible and semi-elastomeric. The use of such backbone plasticizers is limited to compounds which solvate the polymer chain and which have a boiling point of at least150 C. and preferably at least 200 C. The backbone plasticizer chouLd ~l~o have a boiling point in excess of the temperature of the foaming process so that it will not be lost during the foaming, nor should it boil at or near any temperature at which the foamed products will be used. The backbone plasticizer may affect cell structure, so the amount of backbone plasticizer which can be added without causing poor cell structure must be determined.
Specific backbone plasticizers which can be used with the preferred sulfonated polystyrene polymers include di-n-hexyl adipate, dicapryl adipate, di-(2-ethyl hexyl) adipate, dibutoxy-ethyl adipate, benzyl octyl adipate, tricyclohexyl citrate, butyl phthalyl butyl glycolate, butyl laurate, n-propyl oleate, n-butyl palmitate, dibutyl phthalate, dihexyl phthalate, dioctyl phthalate, tributyl phosphate, dioctyl sebacate, and mixtures thereof.
The process of the instant invention provides novel foamed products.
The novel foamed products may have a density of less than 10 lbs. per cubic foot, preferably from 1.5 lbs. per cubic foot to 7.5 lbs. per cubic foot, and include both rigid and flexible foams. The novel foams produced by this 1~3L~
invention may have average cell volumes of less than 0.3 x 10-3 cm3 with less than 5% of the foam volume occupied by cells of volumes greater than 0.5 x 10-2 cm3. Usually the foam structures are closed cell, but open cell foams can also be made.
These foams are novel in that they may be repro-cessed unlike the cros~-lin~ed foams known in the prior srt.
Reprocessing may be easily carried out by dissolving the foamed polymer in a suitable solvent; that is, a solution of lo a low boiling solvent for the backbone and a polar substance which will plasticize the pendant ionic groups. The polar substance may be the same one utilized in forming the original product or may be different.
Although the foams of the instant invention can be reprocessed, they have relatively good dimensional stability at temperstures above 100C., as compared with the prior art polystyrene foam. Also, as compared with polystyrene, foams prepared by this process from lightly sulfonated polystyrene have improved resistance to several common solvents, for in-stsnce, toluene and acetone, and can be foamed with good-re-sults over a temperature range of more than 50C. In addi-tion, the instant foams can be shaped or formed at tempera-tures between 115 and 150C. without foam collapse.
Very often in the preparation of commercisl fo~m samples, nuclesting agents are employed as additives to create 1 a very uniform and small cell structure. These nucleating 2 agents are well known to those versed in the art. Sy~tems 3 such a8 sodium bicarbonate and citric acid or calcium silicate 4 are often employed. TheRe additives can al80 be utilized in the foams produced in this invention. However, in general, 6 the process of the instant invention gives foams which are of 7 low density and uniform cell ~ize, without the use of nucleat-8 ing agents.
9 The preferred ionic copolymers for use in the in-stant invention, i.e., sulfonatet polystyrene and substitutet

11 derivatives thereof, may be prepared by the follow~ng proce-l2 dures:
13 I. Copolymerization with Sulfonate Containin~ Monomers 14 For example, alkali metal salts of styrene sulfonic acid can be copolymerized using free radical initiators with l6 a variety of thermoplastic forming monomers such as styrene, 17 t-butyl styrene, chlorostyrene, and the like.
18 II. Direct Sulfonation of HomoPolYmers 19 Sulfonic acid groups can be introduced into aromatic homopolymers such as polystyrene, polyvinyl toluene, poly-21 alpha-methyl styrene, poly-t-butyl styrene, and the like by 22 tirect reaction with a sulfonating agent. Sulfonating agents 23 such a~ sulfuric acid and chlorosulfonic acid can be used.
24 Preferret sulfonating agents are acetyl sulfate, i.e., the mixet anhytride of acetic acid and sulfuric acid (CH3COOS03H), 26 and sulfur trioxide complexes with dioxane, tetrahydrofuran, 27 and trialkyl phosphates. Of the trialkyl phosphate complexes, 28 those congigting of trialkyl phosphate/S03, ratios of about 29 1.0 are most preferred. The resulting polymer now contains sulfonic acid groups which can be neutralized tirectly with 31 metal oxite, metal hydroxide, or metal salts to achieve the 32 desiret metal sulfonate containing polymer. Alternatively, 1 the sulfonic acld contain~ng polymer can be isolated by pre-2 cipitation and neutralized e~ther in bulk or by redissolving 3 the polymer.
4 III. Dlrect SulfsnatiGn of Modified Polymers Where desirable~ homopolymers cannot be directly re-6 scted to produce sulfonate containing materials, it is possi-7 ble to introduce9 by copolymerization, functional groups cap-8 able of reacting with sulfonating agents. The two most desir-9 able functional groups for this purpose are double bonds and aromatic groups9 especially phenyl groups~ see U.S. Patent 11 3,642,728 for methods of sul-l2 fonating polymers containing olefinic unsaturation. Again, 13 the polymers are neutralized as described hbove.
14 A. Copolymers of Aromatic Monomers Copolymerization of vinyl monomers and relatively l6 small amounts of styrene or other vinyl aromatics reac-17 ~ive to sulfonating agents produces copolymers with 18 essentially homopolymeric properties cspable of being 19 sulfonated. Illustrative examples of such copolymers ~re chlorostyrene=styrene, styrene-acrylonitrile, styrene-21 vinyl acetate, etc. In non-vinylic polymer systems an 22 aromatic group can be introduced into the polymer through 23 the use of an aromatic containing monomer, e.g., phenyl 2~ glycidyl ether copolymerized with propylene oxide. The reagents suitsble for introducing sulfonic acid groups 26 directly are the same 8S those described for the direct 27 sulfonation of homopolymers (II). The polymers are neu-28 tralized as descrlbed above.
29 B. Polvmers Containin~ Unsaturation Although unsaturation may be introduced into homo-31 polymers in a number of ways9 copolymerization with a con-32 ~ugated diolefin generally can be relied on to produce th~rmoplastic materials containing small amounts of unsaturation.
Suitable co-monomers for the incorporation of unsaturation ln vinyl polymers are conjugated diolefins, such as butadiene, isoprene, dimethyl butadiene, piperylene and non-conjugated diolefins, such as allyl styrene. Copolymers can be made by using any of the applicable initiating systems, i.e., free radical, cationic, anionic, or coordinated anionic. In polyethers, unsaturation can be intro-duced by copolymerization with unsaturated epoxides, e.g., allyl glycidyl ether.
The reagents which are suitable for the direct introduction of sulfonic acid groups into unsaturated thermoplastics are the complexes of SO3 with reagents such as dioxane, tetrahydrofuran, trialkyl phosphates, carboxylic acids, trialkylamines, pyridine, etc. Especially suitable are the trialkyl phosphate complexes, and the most preferred are the 1/1 complexes of S03/triethyl phosphate.
The polymers are neutralized as described above.
IV. Oxidation of Sulfur Containing Functional Groups Polymers which contain sulfinic acid groups can be readily air oxidized to sulfonic acids. Polymers containing mercaptan groups can be easily converted to the sulfonic aaid groups through oxidation of the mercaptan groups with a variety of oxidizing agents, such as hydrogen peroxide, potassium permanganate, sodium dichro-mate, etc.
Ionic polymers utilized in the instant invention would generally have an average molecular weight greater than 5,000, more preferably the molecular weight will range from 10,000 to 500,000, most preferably from 20,000 to 250,000.
In general, the process of the instant invention 1 comprises mixing an ionic polymer, which compri~es from about 2 0.2 to 20 mole percent pendant ionic groups, with 8 polar sub-3 stance which is a preferential pla6ticizer for said ionic 4 groups and ~ foaming agent, said foaming agent having a 801u-bility parameter of less than 7.9, heating said mixture to a 6 temperature at which the foaming agent is converted into a 7 gaseous form, and cooling to recover the novel foamed products 8 of the instant invention. The ionic groups described above 9 are neutr~!lized to a degree of at least 90%, preferably 98%, 0 and more preferably 100%. The above mixture will comprise 11 from 20 to 99 weight % of the ionic polymer and having O.l to l2 50 moles of volatile polar substance per mole of pendant ionic 13 group. A low boiling liquid is utilized as the foaming agent, its weight ranging from 1 to 300% of sa~d ionic polymer. The foaming agent is incorporated in said mixture in the presence l6 of said polsr substance. The mixture is generally heated to 17 a temperature of at least 60C., preferably greater ~han 105~, 18 to initiate foaming. Hesting the mixture may be carried out 19 by processe~ known in the art, for example, in a forced air oven, in a hot oil bsth, or in conventional polymer fabrica-21 tion equipment such as a heated extruder. The foaming may be 22 carried out from about ~ second or less to 15 minutes depend-23 ing on the heating method used. After the foaming agent is 24 substantially completely converted to the gaseous form, the foamed product is cooled below its softening temperature to 26 room temperature for subsequent use.
27 The novel foamed products of the instant invention 28 may be reprocessed by dissolving in a mixture of fl solvent 29 for the nonionic (backbone) portion of the ionic polymer, and a polar substance, if needed. The solvent msy be removed by 31 hesting or by precipitation of the polymer, and the ionic 32 polymer reformulated with a foaming agent, and the above ,t~

1 foaming process repeated.
2 The following are specific embodiments of the in-3 stant invention. There is no intention to be limited to the 4 disclosure which said specific embodiments repre~ent.
ExamPle 1 6 A powder of lightly sulfonated polystyrene having 7 approximately 3 mole percent sulfonation, with sodium as the 8 counter ion, was mixed with phenethanol, with 0.3 ml alcohol 9 per gram of polymer. (The sulfonate groups were 100% neu-A lo tralized.) A pad 0.052 inches thick WAS molded from this mix-11 ture at 190C. The pad was immersed in Freon 12 in a pres~ure l2 vessel at 58~C. for one day and at 73C. for 6 day~. Then -the 13 pad was removed and foamed by immersion in silicone oil for 14 about 15 seconds at 175C. A foam having good quality cell structure was produced having an average density of 3.51 pcf.
16 The average cell diameter was approximately 15 microns, which ; 17 is unusually small for polymer foams. For instance, 150 mi-18 crons is a typical diameter for a polystyrene foam; so, 1000 19 of the 15 micron diameter cells could fit in a single cell of 150 microns in diameter. The unusually small cell size and 21 correspontingly thin cell walls result in a foam which is 22 softer and more flexible than foams of the same density having 23 larger cells and thicker cell walls. Foams of such small cell 24 size are advantageous for packing delicate ob~ects, thermal insulation, and other applications.
26 Example 2 27 One hundred parts of a powder of lightly sulfonated 28 polyatyrene having approximately 3 mole percent sulfonation 29 with sodium as the counter ion was mixed with one phr of a fine powder of pentaerythritol (100% neutralized). A pad 31 of 0.054 inches thick was molded from this mixture at 260C.
32 The pad was immersed in Freon 12 in a pressure vessel at 58C.

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l for one day and flt 73C. for 6 days. Then the pad was removed 2 and foamed in silicone oil at 217C. A foam having good qual-3 ity cell ~tructure o~ microscopic cell size was produced, hav-4 ing an average density of 1.91 pcf.
ExamPle 3 6 A psd 0.040 inches thick was molded at 260C. from 7 a powder of lightly sulfonated polystyrene having about 7 mole 8 percent sulfonate content with sodium as the counter ion ~00%
9 neutralized). The pad was put in a pre~sure vessel in a solu-tion of 0.7 ml methanol and 10 ml Freon 12 (dichlorodifluoro-1 methane) and it was heated to 70C- After 5 days the pad was 2 removed and foamed in silicone oil at 275C. The foam is 13 rigid at room temperature and shows no collapse when held at 14 125C. for ~ hour. This foam is solvent resistant unlike con-ventional commercial polystyrene foam; the latter almost im-l6 mediately collapses when toluene is added to it, while the 17 foam of the instant i~vention only shrinks slightly. This ex-18 periment demonstrates that the foams of the instant invention 19 have improved heat stability and solvent resistance as com-pared to thermopla~tic foams, due to the physical cross-links.
21 ExamPle 4 22 ~ne hundred parts of a powder of lightly sulfonated 23 polystyrene having approximately 3 mole percent sulfonation 2~ content with barium as the counter ion (lOOX neutrslized) was 2s mixed wi~h 15 phr of a fine powder of 3,4-dimethyl benzoic 26 acid. A pad 0.030 inches thick was pressed from this mixture 27 at 260C. The pad was immersed in Freon 12 in a pressure 28 vessel at 70C. After 5 days the pad was removed and foamed 29 in silicone oil at 250C. A foam having good cell structure and a density of 4.25 pcf was produced.
31 ~xamPle 5 32 Decanol was mixed with 3 mole percent sulfonated .' - ' ,. .. .

1 polystyrene with sodlum a~ the counter ion (100% neutralized).
2 The mixture contained 0.01 ml of decanol per gram of polymer.
3 This material wa~ molded at 180C. into a 0.040 inch thick 4 pad. The pad was immersed in Freon 12 at 70C. in a pressure ves~el. After 2 days the pad was removed and foamed in sili-6 cone oil at 150C. A foam having a good quality cell struc-7 ture and 8 density of 5.56 pcf was produced.
8 Example 6 9 100 parts of a powder of lightly sulfonated poly-styrene having approximately 3 mole % sulfonation with sodium 1 as the counter ion was mixed with two phr of a fine powder of 2 pentaerythritol Sthe polymer was 100% neutralized). A pad 13 0-035 inches thick was molded from this mixture at 260C- The 14 pad was immersed in isopentane in a pressure vessel at 70C.
for two days. Then the pad was removed and weighed. It had 16 increased in weight by 13.5%. The pad was then foamed in si~i-17 cone oil at 245C. A foam having good cell structure was pro-18 duced, having an average density of 3.05 pcf.
19 ExamPle 7 A molded pad 0.035 inches thick of lightly sulfonated 21 polystyrene having approximately 3 mole percent sulfonation 22 with sodium as the counter ion was immersed in Freon ~ in a 23 pre88ure ve98el at 70C. for 3 days (the polymer was 100% neu-24 tralized). Piece9 of the pad were then foamed in silicone oil 25 at 150C. and 200C. The resulting foams had densities of 26 greater than 20 pcf. This shows that the polar substance is 27 necessary for the production of moderate or low density foam 28 from this sulfonated polystyrene polymer.
29 Ex~mPle 8 One hundred parts of a powder of lightly sulfonated 31 polystyrene having approximately 3 mole percent sulfonation 32 with godium as the counter ion was mixed with two phr of a fine powder of pentaerythritol (the polymer was 100% neutral-2 ized). A ~ad 0.35 inches thick wss molded from this mixture 3 at 260C. The pad was immersed in 1,2-dichlorotetrafluoro-4 ethane in a pressure vessel at 70C. for three days. Then the pad was removed and weighed. It showed no measurable 6 weight pickup of the blowing agent, and it did not foam appre-7 ciably when placed in hot silicone oil. This example shows 8 that the conditions of the incorporation of the blowing agent 9 must be such that the blowing agent is able to penetrate into the polymer mixture. Under the conditions of this experiment the rste of diffusion of this blowing agen~ into the polymer

12 mixture was too small due to low solubility and low diffusion

13 rates. Higher temperature and pressure should increase both l4 the solubility and diffusion rate of the 1,2-dichlorotetra-fluoroethane in the polymer mixture, so uptake of this blowing 16 agent into the polymer mixture should increase, and good qual-17 ity fo~ms should be possible.
l8 When the temperature was raised to 100C. and the 19 above experiment repeated, a foam with a solid core was obtain-20 ed, thus indicating that the permeation rate wa~ too low. It 21 is appsrent that with longer times or higher temperatures 1,2-22 dichlorotetrafluoroethane can be used as a foaming agent, with-23 In the scope of the instant invention.
24 Example 9 One hundred parts of a powder of lightly sulfonated 26 polystyrene having approximfltely 3 mole percent sulfonation 27 with ~odium as the counter ion was mixed with two phr of a 28 fine powder of pentaerthritol (the polymer was 100% neutrsl-29 ized). A pad 0.35 inches thick was molded from this mixture 30 at 260C~ The pad was immersed in the blowing agent in a 31 prossure vessel at 70C. After 2 or 3 days the pad was re-32 moved and foamed in hot silicone oil. ~he following are 1 results obtained with several different blowing agents.
2 Blowin~ Ag~t Tempera~ure Density 3 of Foamin~ (lbs/ft3) 4 Butane 245C. 3.4 Pentsne 200C. 5.4 6 Chlorodifluoro- -7 methane 198C. 3.0 8 1,1,2-trichloro-9 trifluoroethane 200C. 3.1 Example 10 11 Lightly sulfonated polystyrene having about 3 mole 12 percent sulfonate groups (with respect to the polystyrene mon-13 omer subunits) with sodium as the counter ion was used. (The

14 polymer was 100% neutralized.) Pieces of this material which were about one mm thick were put in 3 ml of methanol and 10 16 ml of Freon 12 in a pressure vessel and heated to 70C. After 17 four days the impregnated lightly sulfonated polystyrene was 18 removed from the pressure vessel and exposed to microwave 19 radiation. When exposed for about 1/2 second to an incoming power of 325 watts in a microwave oven, the material foamed.
21 The density of the core of the foam was about 9.8 lbs./cu.ft., 22 while the overall piece had a smooth hard surface which gave 23 an overall density of about 20.7 lbs./cu.ft. for the foam.
24 Thus, this invention may employ microwaves as the source of energy to foam multiphase polymer systems in which 26 one phase (the ionic domains) is preferentially plasticizPd 27 by a polar species. The polar plasticizer may be the primary 28 microwave ab~orbing component, or an additional microwave 29 absorbing component could be added to the material.

Claims (44)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE
IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for making a foamed polymeric product of uniform cell structure which comprises mixing a non-volatile polar substance, a foaming agent and an ionic polymer said ionic polymer containing pendant ionic groups consisting of neutralized acid moieties, said non-volatile polar substance being a preferential plasticizer for said ionic polymer, and said foaming agent being characterized as being sparingly soluble in said ionic polymer, at an elevated temperature and pressure whereby said plasticizer and said non-volatile polar substance are impregnated into said ionic polymer, and foaming said impregnated ionic polymer.

2. The process of Claim 1 which further includes a non-volatile liquid chain plasticizer.

3. The process of Claim 1 wherein the pendant ionic groups are neutralized to a degree of greater than 90%.

4. The process of Claim 1, 2 or 3 wherein said ionic polymer comprises from about 0.2 to 20 mole percent pendant ionic groups.

5. The process of Claim 1, 2 or 3 wherein said pendant ionic groups are selected from the group consisting of sulfonate and carboxylate groups, said groups being neutralized with a neutralization agent.

6. The process of Claim 1, 2 or 3 wherein said pendant ionic groups are neutralized with an agent selected from the group consisting of (1) ammonia, (2) C1 to C30 amines, and (3) basic compounds whose cation is selected from Groups IA, IIA, IB and IIB of the Periodic Table of the Elements lead, tin, antimony and aluminum.

7. The process of Claim 1, 2 or 3 wherein said non-volatile polar substance is selected from the group consisting of compounds having a dipole moment of at least 0.9 Debyes and a boiling point of greater than 100°C.

8. The process of Claim 1, 2 or 3 wherein said non-volatile polar substance 18 selected from the group consisting of organo compounds having hydroxyl, carboxyl, thio and amino functional groups, wherein said organo compound comprises no more than 30 carbon atoms per functional group.

9. The process of Claim 1, 2 or 3 wherein the molar ratio of non-volatile polar substance to the pendant ionic groups is from about 0.1 to about 50.

10. The process of Claim 1, 2 or 3 wherein said ionic polymer comprises from about 20 to 99 weight percent of said mixture.

11. The process of Claim 1, 2 or 3 wherein said foaming agent comprises from about 1 to 300 weight percent of said ionic polymer.

12. The process of Claim 1, 2 or 3 wherein said pendant ionic groups are sulfonate groups.

13. The process of Claim 1, 2 or 3 wherein said non-volatile polar substance has a dipole moment of from 1.2 to 5.5 Debyes.

14. The process of Claim 1, 2 or 3 wherein said foaming agent is selected from the group consisting of alkanes having 4 to 6 carbons, and fluorocarbons and fluorochlorocarbons having 1 or 2 carbons.

15. The process of Claim 1, 2 or 3 wherein said ionic polymer is a sulfonated polystyrene.

16. The process of Claim 1, 2 or 3 wherein said ionic polymer is a sulfonated styrene-t-butyl styrene copolymer.

17. The process of Claim 1, 2 or 3 wherein said foaming agent is selected from the group consisting of compounds having a solubility parameter of less than 7.9.

18. The process of Claim 1, 2 or 3 wherein said non-volatile polar substance is selected from the group consisting of decanoic acid, p-toluic acid, pentaerythritol and 3,4-dimethyl benzoic acid.

19. The process of Claim 1, 2 or 3 wherein said pendant ionic groups are neutralized with an agent selected from the group consisting of hydroxides, oxides, carboxylates and C1 to C20 alkoxides of barium, calcium, magnesium, potassium and sodium.

20. The process of Claim 1, 2 or 3 wherein said pendant ionic groups are neutralized with an agent which is a hydroxide or carboxylate of sodium or barium.

21. The process of Claim 1, 2 or 3 wherein said pendant ionic groups are neutralized with an agent which is a hydroxide or carboxylate of sodium or barium and said non-volatile polar substance is pentaerythritol.

22. The process of Claim 1, 2 or 3 wherein said mixture also comprises a nucleating agent.

23. The process of Claim 2 wherein said ionic polymer is a sulfonated polystyrene, and said non-volatile liquid chain plasticizer is selected from the group consisting of di-n-hexyl adipate, dicapryl adipate, di-(2-ethyl hexyl) adipate, dibutoxyethyl adipate, benzyloctyl adipate, tricyclohexyl citrate, butyl phthalyl butyl glycolate, butyl laurate, n-propyl oleate, n-butyl palmitate, dibutyl phthalate, dihexyl phthalate, dioctyl phthalate, tributyl phosphate, dioctyl sebacate and mixtures thereof.

24. The process of Claim 2 wherein said ionic polymer is a sulfonated polystyrene and said chain plasticizer is dioctyl phthalate, dihexyl phthalate, or a combination of these.

25. The process of Claim 2 wherein said ionic polymer is a sulfonated copolymer of t-butyl styrene and styrene and said chain plasticizer is a hydrocarbon oil.

26. The process of Claim 2 wherein said neutralizing agent is a hydroxide or carboxylate of sodium or barium.

27. A foamed polymeric product having a density of less than 10 lbs./ft3, an average cell volume of less than 0.3 x 10-3 cm3, and less than 5% of the foamed volume is occupied by cells of volumes greater than 0.5 x 10-2 cm3, comprising an ionic polymer, said ionic polymer containing pendant ionic groups consisting of neutralized acid moities and a non-volatile polar substance which is a preferential plasticizer for said ionic polymer.

28. A foamed polymeric product as claimed in Claim 27 which further includes a non-volatile liquid chain plasticizer.

29. A foamed polymeric product as claimed in Claim 27 wherein said pendant ionic groups are neutralized to a degree of greater than 90%.

30. A foamed polymeric product as claimed in Claim 27, 28 or 29 wherein said ionic polymer comprises from about 0.2 to 20 mole percent pendant ionic groups.

31. A foamed polymeric product as claimed in Claim 27 wherein said pendant ionic groups are selected from the group consisting of sulfonate and carboxylate groups, said groups being neutralized with a neutralization agent.

32. A foamed polymeric product as claimed in Claim 27, 28 or 29 wherein said pendant ionic groups are neutralized with an agent selected from the group consisting of (1) ammonia, (2) C1 to C30 amines, and (3) basic compounds whose cation is selected from Groups IA, IIA, IB and IIB of the Periodic Table of the Elements, lead, tin, antimony and aluminum.

33. A foamed polymeric product as claimed in Claim 27, 28 or 29 wherein said non-volatile polar substance is selected from the group consisting of compounds having a dipole moment of at least 0.9 Debyes and a boiling point of greater than 100°C.

34. A foamed polymeric product as claimed in Claim 27, 28 or 29 wherein said non-volatile polar substance is selected from the group consisting of organo compounds having hydroxyl, carboxyl, thio and amino functional groups, wherein said organo compound comprises no more than 30 carbon atoms per functional group.

35. A foamed polymeric product as claimed in Claim 27, 28 or 29 wherein the molar ratio of non-volatile polar substance to the pendant ionic groups is from about 0.1 to about 50.

36. A foamed polymeric product as claimed in Claim 27, 28 or 29 wherein said ionic polymer comprises from about 20 to 99 weight percent of said mixture.

37. A foamed polymeric product as claimed in Claim 27, 28 or 29 wherein said pendant ionic groups are sulfonate groups.

38. A foamed polymeric product as claimed in Claim 27, 28 or 29 wherein said non-volatile polar substance has a dipole moment of from 1.2 to 5.5 Debyes.

39. A foamed polymeric product as claimed in Claim 27, 28 or 29 wherein said ionic polymer is a sulfonated polystyrene.

40. A foamed polymeric product as claimed in Claim 27, 28 or 29 wherein said ionic polymer is a sulfonated styrene-t-butyl styrene copolymer.

41. A foamed polymeric product as claimed in Claim 27, 28 or 29 wherein said non-volatile polar substance is selected from the group consisting of decanoic acid, p-toluic acid, pentaerythritol and 3,4-dimethyl benzoic acid.

42. A foamed polymeric product as claimed in Claim 27, 28 or 29 wherein said pendant ionic groups are neutralized with an agent selected from the group consisting of hydroxides, oxides, carboxylates and C1 to C20 alkoxides of barium, calcium, magnesium, potassium and sodium.

43. A foamed polymeric product as claimed in Claim 27, 28 or 29 wherein said pendant ionic groups are neutralized with an agent which is a hydroxide or carboxylate of sodium or barium.

44. A foamed polymeric product as claimed in Claim 27, 28 or 29 wherein said non-volatile polar substance is pentaerythritol.