WO1990003036A1

WO1990003036A1 - Homogeneous radiopaque polymer-organobismuth composites

Info

Publication number: WO1990003036A1
Application number: PCT/US1989/003966
Authority: WO
Inventors: Johannes Smid; Yadollah Delaviz; Israel Cabasso
Original assignee: Johannes Smid; Yadollah Delaviz; Israel Cabasso
Priority date: 1988-09-12
Filing date: 1989-09-12
Publication date: 1990-03-22
Also published as: EP0387348A1; EP0387348A4

Abstract

Novel radiopaque materials and a method for their preparation are described. The radiopaque materials comprise composites of polymers and heavy metal-containing organic compounds, which heavy metal containing compounds have formula (I), wherein X is a heavy metal; R1, R2 and R3 may be the same or different and are individually selected from the group consisting of phenyl, halogen substituted phenyls, alkyl substituted phenyls, aryl substituted phenyls, ester substituted phenyls, alkene substituted phenyls, silyl groups and methylmethacrylate and R3 can additionally be selected from the group consisting of halogen, alkyl, alkene, ester and carboxylic acid when R3 is not the same as R1 and R2. The composites, which are permanent and nonleachable, do not adversely affect the mechanical and physical properties of compositions. They are useful as medical and dental resins, in fabricating medical and dental appliances, prosthetic devices, radiation shielding devices and radiopaque polyester fabrics for clothing.

Description

HOMOGENEOUS RADIOPAQUE POLYMER-ORGANOBISMUTH COMPOSITES

1 BACKGROUND OF THE INVENTION

2 The present invention relates to new and useful

3 polymers, and more specifically, to improved nonleachable,

4 optically transparent, homogeneous radiopaque heavy

5 metal-containing polymers, compositions of matter, their meth

6 of preparation and articles prepared therefrom.

7 Translucent polymeric materials, and particularly, 3 acrylic type resins have been widely used for years in both 9 medical and dental applications. In dentistry, for example,

10 resins have been used to produce removable dentures, temporar H crown and bridge materials, restorative materials, impression^" 12 materials, and the like. Polymeric resins also find many 12 applications in medicine, such as surgical and body implants ^ and other prosthetic devices, (e.g., heart valves, blood •_jr vessels, etc.). Translucent plastics are also widely used in ₆ medical appliances, such as catheters.

U The desirability of imparting radiopacity to plastics

18 used in dentistry and medicine has long been recognized. In

19 dentistry for example, it has been difficult to detect

20 secondary cavities or underlying decalcified dentin resulting

«-i from the placement of unreinforced direct restorative resins

22 because these materials are relatively radiolucent, and are no

23 opaque to x-rays. Surveys have also shown that dental

24 instruments, materials and nonfixed appliances have fractured

₂c and become embedded in soft tissues, ingested or inhaled

26 inadvertently by patients. Although incidents of ingestion or

27 inhalation of dental plastics are relatively rare compared wit 2g other foreign objects, the occurrence may result in a severe 2_Q medical emergency or even death. The potential severity of 30 such an incident makes it imperative to diagnose and remove such foreign bodies rapidly. /03036 2-

In medicine, it would be desirable to monitor the positioning of bone cement used in hip joint replacements without surgical procedure. Similarly, it would be desirable to use x-rays to monitor replacement heart valves, replacemen arteries, or the path of catheters traversing blood vessels a organ systems. Hence, there is a need for polymeric material with increased radiation absorption potentials which also possess the requisite nonleachable properties for safe and acceptable use in dentistry and medicine. Heavy metal salts, such as, for example, those of bismuth or barium have been used as contrast medium in diagnostic radiography. They have properties which would suggest their suitability for increasing the radiation absorption potential of medical and dental resins. As a result, substantial effort has been made to incorporate bariu sulfate and other radiopaque salts, such as, for example, bismuth bromide, bismuth chloride or bismuth subnitrate into polymers to render them opaque to x-rays. However, early radiopaque polymers containing heavy metal salts have not bee totally satisfactory. One type of known heavy metal-containing radiopaque materials are radiopaque glass containing embedded heavy metals. In these materials, the metal is not molecularly bou to the polymer matrix and, therefore, has a tendency to weake the composite. Moreover, because glass filler based resins lack homogeneity a further weakening of regions in the matrix results. Those regions of a composite having little or no glass are radiolucent. In addition, a light scattering effec is produced by radiopaque glasses which alters optical properties and renders them optically opaque. 1 Polymers with added inorganic heavy metal salts in an

2 essentially physical mixture, are also known. In these

3 materials the heavy metal is present as fine powders locked in

4 a matrix. Their preparation results in an uneven distribution

5 of the salt, which has an adverse affect on the mechanical

6 properties of the plastic material. The salt tends to

7 gradually leach out of the matrix causing discoloration of the

8 polymer and release of heavy metal toxins. The salt and

9 polymer remain as separate distinct phases in these mixtures

10 producing an opaque, cloudy, light scattering material. Mixin

11 does not impart homogeneity between the salt and polymer.

12 More recently, heavy metal salts have been complexed

13 with a polymer. Such composites require that the complexing polymer contain at least one monomer which is capable of

•_j_5 donating a pair of electrons, i.e., acting as a Lewis base.

•_j_6 These materials are, therefore, limited in structure since onl

1~ polymers containing appropriate interaction sites, especially

1g carbonyl moieties, are useful. These heavy metal-salt-polymer

•19 complexes are usually moisture sensitive. That is, an

20 initially clear complex will cloud or turn milky upon exposure 1 to moisture, making them inappropriate for certain

22 applications. These heavy metal salt-polymer complexes may

23 also be heat sensitive, and interfere with room temperature

24 curing accelerators used in dental and other applications.

25 OBJECTS OF THE INVENTION 26 27 It is therefore an object of this invention to provid

28 a means for imparting radiopaque characteristics to a wide

29 range of polymers. 1 It is a further objective of this invention to prov

2 radiopaque composites containing heavy metal atoms which are

3 evenly distributed within a polymer.

4 A further objective of this invention is to provide

5 radiopaque composites wherein a heavy metal containing orga

6 compound is incorporated into the polymer chain thereby

7 imparting radiopaque characteristics to the polymer.

8 It is also an objective of this invention to provi g non-leachable, moisture insensitive and heat insensitive 0 radiopaque composites which do not interfere with room

11 temperature curing accelerators of the types used in dental

12 applications.

13 It is also an objective of this invention to provi -^ composites which are non-toxic and non-carcinogenic.

^• _j_ A still further objective of this invention is to

•_j_ provide composites in which the radiopacifying or x-ray η contrast additive may also act as a bactericide, fungicide,

18 antioxidant or stabilizer.

19 These and other benefits will be apparent to those

20 skilled in the art from the following description and Examp

21 DETAILED DESCRIPTION OF THE INVENTION

22

23 It has now been found that these objectives can be

24 attained by carrying out polymerization of a monomer or mix

25 of monomers in the presence of a heavy metal containing org

26 compound. The heavy metal containing organic compound has

27 general formula:

28 ^R- ^-^R2

29 ?

30 ^R3 1

2 wherein X is a heavy metal; R_1; R and R₃ may be the same or

3 different and are individually selected from the group

4 consisting of phenyl, halogen substituted phenyls, alkyl

5 substituted phenyls, aryl substituted phenyls, ester substituted phenyls, alkene substituted phenyls, silyl groups

7 and methylmethacrylate and R₃ can additionally be selected fr

8 the group consisting of halogen, alkyl, alkene, ester and

9 carboxylic acid when R₃ is not the same as R-^ and R₂.

10 Heavy metals useful in this invention have atomic 1 numbers of 50 to 92, an more preferrably, atomic numbers of 7

12 to 92. Lanthanide series metals having atomic numbers of 57 t 12 71, although satisfactory, are less preferred than the higher ^• _j_4 atomic weight metals like mercury, lead and bismuth. Rare

1~ transition metals with atomic numbers of 72 to 77 are also

•_jώ acceptable, but are less preferred because of lower atomic

•17 weights, high cost and their ability to form multinuclear

•_jo complexes. Most preferred heavy metals include barium,

■_jo bismuth, lead, mercury and uranium.

20 The heavy metal containing organic compounds useful i

2 the present invention are relatively non-polar and are thus

22 hydrophobic. This provides radiopaque composites that are

23 moisture insensitive. These organometallic compounds are also

₂Λ miscible up to 70 weight percent with many polymers.

25 A preferred organo etalJLic compound useful in this

₂₆ invention is triphenyl bismuth. Known uses for triphenyl

27 bismuth include bactericide, fungicide, antioxidant and

28 stabilizer. While the addition of triphenyl bismuth to

29 polymers to form composites having radiopaque characteristics

30 is a novel aspect of the present invention, the triphenyl > O 90/03036

1 bismuth component of the novel composite may also impart so

2 bactericide, fungicide, antioxidant or stabilizing

3 characteristics to the composite.

4 In one aspect, the present invention provides

5 radiopaque materials which comprise a heavy metal containin

6 organic compound as a radiopacifying agent miscible with a

7 polymer at the molecular level. That is, instead of a

8 physical, incompatible mixture of radiopacifying agent and g polymer resulting in uneven distributions of radiopacifying 0 agent which adversely affect mechanical and physical 1 properties, according to the present invention a heavy meta 2 containing organic compound, such as an organobismuth compo

13 is homogeneously solubilized into a polymer during

14 polymerization of the corresponding monomer in which the 5 radiopacifying compound is also soluble. The hydrophobic

^*L nature of the compound prevents its leaching out from a pol matrix of the polymer into an aqueous environment. •_j_3 In another aspect, this invention provides radiopa

IQ . materials comprising a, heavy metal containing organic compo

20 incorporated directly into a polymer chain. For example, b

2"_j employing organometallic compounds in which one or more of

22 Rl, R , R3 substituents is a polymerizable group, such as,

23 example, a styryl substituent, the polymerization of a mono

2 in the presence of such a compounds in accordance with thi

25 invention produces a material in which the organometallic

2 compound is incorporated directly into the backbone of the

27 polymer chain to provide distribution of the organobismuth 2g compound on the molecular level, thereby producing a

29 homogeneous composite. Since the organometallic compound

30 actually part of the polymer chain, the heavy metal radio-pacifying agent is non-leachable. The polymer composite may be formed from any monome or mixture of monomers into which the selected organometallic compound can be solubilized. It may also be formed by castin a homogeneous mixture of the polymer and the radiopacifying agent from an appropriate solvent. The method of imparting radiopaque characteristics of this invention has a much wider range of structures and applications than the heavy metal sal previously mentioned. The latter are essentially only useful with carbonyl-containing monomers and polymers, while the mor hydrophobic organobismuth and related compounds are soluble i a much wider range of monomers and polymers. Useful polymers and mixtures of polymers include those derived from styrene, vinyl halides, alkenes, (e.g., polypropylene), dienes vinylpyridines, those derived from, acrylonitrile, vinyl acetate, acrylates and the like. The organometallic compound can also be mixed, or incorporated into condensation polymers. They include linear and cross-linked types formed from dicarboxylic acids and dio or triols. Specific representative examples of polyesters include polyethylene terephthalate, poly (isophthalic acid-co-maleic anhydride), poly (lauric acid-co-glycerol) , an the cross-linked resin poly (phthalic anhydride-co-glycerol) (glyptal) • The polyester composite fibers of this invention are especially of interest for making fabrics for clothing to be worn by workers exposed to potentially harmful levels of radiation, such as radiologists and x-ray technicians. The heavy metal containing organic compound should b present in an amount sufficient to impart a desired radiopaci to the polymer. The relative amounts of the components of composites of this invention depend largely upon the speci heavy metal containing organic compound utilized, the speci polymer or mixture of polymers, the dimensions of the final product and the amount of radiopacity to be imparted to the polymer. As previously mentioned, the heavy metals of the present invention are homogeneously distributed in the pol at the molecular level to form optically lucent radiopaque materials. The hydrophobic nature of the heavy metal comp renders them virtually nonleachable from the resin into an aqueous environment to which the composites of this invent may be exposed. Non-leachability into many other solvents be achieved by incorporating a polymerizable radiopacifyin agent into the polymer backbone, either by addition polymerization or by condensation polymerization. The present invention also contemplates the addit of cross-linking agents. This will provide even greater resistance to leaching of the heavy metal compound from th polymer. Suitable representative examples of cross-linkin agents include tetraethylene glycol dimethacrylate (TEG) , divinylbenzene, bisphenol-A-glycidyl methacrylate (BisGMA) the like. The linear radiopaque polymeric materials have molecular weights generally ranging from 10,000 to about

1,000,000, and more specifically, from about 25,000 to abo 500,000. Generally, the methods for preparing the homogene radiopaque polymers of the present invention include: a) polymerization at high temperatures; b) room temperature polymerization; c) suspension or emulsion polymerization; d) solvent casting; and e) compounding followed by melt processi Bulk polymerization involves dissolving the heavy metal compound in the monomer(s) and polymerizing in the ^" presence of an initiator like benzoyl peroxide, azobisisobutyronitrile (AIBN), etc. More specifically, in th preparation of radiopaque polymers having carbon to carbon unsaturation, such as a vinyl group, the heavy metal compound and an initiator are dissolved in the monomer, such as, for example, styrene, and bulk polymerized at elevated temperatures. This high temperature bulk method is especiall adaptable for industrial uses. In polymerizations for molds in vitro applications, for example, the heavy metal organic compounds can be dissolved in styrene and polymerized with AI at the desired temperature. Room temperature polymerization can be utilized in this invention since, unlike the bismuth salts previously use to impart radiopacity, the radiopacifying organometallic compounds of this invention do not interfere with the room temperature polymerizations in which a peroxide initiator is

1 used jointly with a ine accelerators such as

2 c/imethyl-p-toluidine. Room temperature polymerization can al

3 be initiated without accelerators by using a strong visible Λ light source. As an alternative to dissolving the heavy metal g organic compound in monomer(s) followed by polymerization, th 7 homogeneous organometallic-polymer composites may be formed b g film casting methods and solvent evaporation. Incorporation Q triphenyl bismuth, for instance, in poly(methyl methacrylate) 0 to form films or transparent radiopaque shields can be 036 I O

performed by dissolving the polymer and heavy metal compoun a common solvent like THF. Thus, for example 40 percent by weight solution of triphenyl bismuth in THF containing dissolved poly(methyl methacrylate) can be cast as a film a the solvent allowed to slowly evaporate. Another alternative for making homogeneous, radiop composites is by thoroughly mixing the heavy metal organic compound with the polymer, followed by melting processing o this mixture. For example, mixtures of triphenyl bismuth a powdered polypropylene, when heated above the melting point the polymer produce homogeneous, radiopaque composites. Radiopaque polyesters of the present invention may prepared by dissolving the heavy metal organic compound in polyol, such as, for example, ethylene glycol. The dissolv organometallic compound is then mixed with a dicarboxylic a such as terephthalic acid or phthalic anhydride, and polymerized at elevated temperatures in the presence of a k catalyst.

As previously mentioned, the radiopaque heavy meta compound polymer composites have a wide variety of applicat especially in the dental and medical field. In the latter, radiopaque polymers may be employed in resin systems having levels of cross-linking which, for purposes of the present invention, range from 0 to about 5 percent, and denser more rigid structures having a higher degree of cross-linking ranging from more than 5 to about 15 percent. Such systems include "self-curing¹¹ type resins which react at ambient temperatures of between 25 and 30"C, and systems which cure elevated temperatures with the application of heat. Generally, for preparing radiopaque bio edical resin i.e., polymer compositions having useful applications in restorative dentistry and medicine, the heavy metal-polymer composite would be ground to a fine powder and used as a ^' component of a two-part system. More specifically, in the two-part system the composition is furnished in two separate containers. The first container would comprise a powder containing a mixture of the radiopaque polymer complex previously described, fillers and an initiator, such as benzo peroxide or AIBN. The second container comprises a liquid containing methyl methacrylate monomer, an amine acelerator a a cross-linking agent such as ethylene glycol dimethacrylate. When the solutions are mixed, or when in the absence of amine accelerator they are exposed to a strong visible light, the radiopaque polymer complex will swell in the methyl methacrylate monomer and polymerize into a solid homogeneous polymeric mass. Applications for the radiopaque polymer composites having low levels of cross-linking include removable dental devices like dentures, bite splints, night guards, orthodontic space maintainers, maxillofacial devices and other nonfixed devices where there is a risk of accidental impaction into the respiratory or digestive tracts. These radiopaque polymer composites having low levels of cross-linking can also be formulated into bone cements for bonding implanted devices to bone tissues so as to permit monitoring by noninvasive methods The second category for biomedical resins include highly cross-linked structures where radiopacity is also a desirable property. They include fixed structures like restorative resins, veneering facings for dental crowns and

bridges, dental and surgical implants, root canal sealants other dental, surgical and implants applications. These materials are generally provided to the user as a two-part system which upon mixing cures at ambient temperatures eith by combining the initiator with a light source or with an a accelerator. In the highly cross-linked structures, howeve no preformed polymer is used. Instead, each component cons of a solution of monomers. Many of such applications can a employ a hard, inert reinforcing ^■•filler¹¹ consisting of a finely divided material such as silica. In addition to the foregoing medical/dental applications, the radiopaque polymer composites may be used with all body implants, prosthetic devices and appliances w are presently used with radiolucent plastics, such as, for example, catheters, bone implants, heart valves or arteries Industrial applications for the radiopaque composi of the present invention include x-ray and other radiation shielding devices. Optionally, the transparent radiopaque polymers, which are also opaque to U/V radiation, can be us in such areas as aircraft windows and cabins for shielding pilots and astronauts from high energy ϋ/V and x-radiation found at high altitudes. Transparent shielding devices mad sheets of radiopaque plastics for workers exposed to x-rays other forms of potentially harmful radiation are also inten utilities. The radiopaque polyester fibers are especially useful in textiles and fabrics for making specialized radiopaque garments to be worn by workers exposed to radia in the job place. Additionally, the radiopaque polymers can be incorporated into any plastic device which requires detect by x-rays. For example, the composites of this invention ca be incorporated into plastic firearms to ensure detection by airport security x-ray devices. The following specific examples demonstrate the radiopaque polymers and resin compositions, and are representative of the various methods for producing them. However, it is to be understood that these examples are for illustrative purposes only and do not purport to be wholly definitive as to conditions and scope.

EXAMPLES I-VII

Seven samples of the composites of this invention w prepared by dissolving varying concentrations of triphenylbismuth in methyl methacrylate monomer. The compositions are reported in Table A. AIBN or BPO was added an initiator in an amount of 0.5% by weight based on the monomer. Each sample was placed in a test tube with a serum cap, flushed with nitrogen, sealed and bulk polymerized for 4 hours at 65"C. All samples of methyl methacrylate- triphenylbismuth formed a hard, transparent, colorless, clea and homogenous polymer. The radiopaque polymers of Examples I-VII were teste to develop data on the possible presence of free triphenylbismuth and the effects of dissolved triphenyl bismu on the glass transition temperature of poly(methyl methylacrylate) by differential scanning calorimetry using a Perkin-Elmer DSC-4 instrument. Scans were run from 50 to 150 with a scan rate of 20°C per minute. A sample of poly(methyl methylacrylate) containing no triphenylbismuth was used as a control for comparison purposes. The results of the DSC 036 analyses are also reported in Table A.

TABLE A

The data in Table A show a gradual decrease in the glass transition temperature on increasing the triphenylbismuth content. The 78.5"C melt peak of triphenyl bismuth was not evident in any sample. Thus, a homogenous dispersion of triphenylbismuth in polymer was formed.

The radiopacity of the composites of EXAMPLES I-VI was tested as follows: Samples of EXAMPLES I-VII were cut cylindrical pellets of 1 mm and 2 mm thickness. The pellet were polished and placed on a Kodak X-ray film along with a aluminum stepwedge with 1mm steps. The pellets were place inches below the cathode ray tube of an X-ray apparatus an VA*^ exposed to 90 kv 6 nja-s X-rays. Using a microfilm densitom the X-ray absorption of the pellets was then compared with of the aluminum stepwedge. It was found that 23 percent b weight triphenyl bismuth was required in a 2 mm pellet to provide the same radiopacity as a 2 mm pellet of aluminum, radiopacity standard adopted for dental applications. Studies were also performed to determine the leachability, heat stability, and air and moisture sensiti of the samples prepared in Examples I-VII. The composite samples were placed in a tube which was sealed. Vacuum was applied and the samples were heated up to 150-160"C, which temperature was maintained for several hours. No change in ^" color, transparency or homogeneity was observed in the samples. In addition, samples of the composites of EXAMPLES I-VII were placed in water for more than 4 months. No change in color, transparency, homogeneity, radiopacity or weight o the samples was observed. No detectable amount of triphenylbismuth was found in^'the water. All the experiments show non-leachability, heat stability, moisture and air insensitivity of the polymer-triphenylbismuth system made in accordance with the present invention.

EXAMPLE VIII

Room temperature polymerization in accordance with this invention was performed by dissolving the organometallic compound in the monomer, followed by addition of an initiator and an amine accelerator to form the polymer-organometallic composite. As a specific example, the composite of EXAMPLE VIII was prepared according to the following procedure: in a test tube 0.25 grams of triphenylbismuth was dissolved in 0.9 grams of methyl methacrylate to form a clear, homogeneous and transparent solution. Benzoylperoxide, an initiator, was the added to the mixture in an amount of .025 grams or 2.5 weight percent based on the monomer. By adding 0.015 grams of an ami accelerator, specifically, N,N-dimethyl p-toluidine, a hard, polymerized, homogeneous, transparent product was formed afte a few minutes. The composites of Examples VIII had the same mechanical and thermal stability, and the same air and moistu insensitivity as the composites formed in Examples I-VII .

EXAMPLES IX and X

Another way of incorporating organometallic compound into polymers is by solvent casting and formation of transparent and clear homogeneous films. In Examples IX and the incorporation of triphenylbismuth into poly(vinyl chlorid was achieved by dissolving polyvinylchloride in hot THF (50-55 ° C) in a test tube. After complete dissolvation, triphenylbismuth was added and the solution stirred for about hour. The colorless, clear, homogeneous solution formed was poured into a glass dish. The THF was removed first under a flow of N for 48 hours and then in a vacuum oven until a constant weight for the film was achieved. PVC used in this experiment had a molecular weight of about 93,000.

Formulation of EXAMPLES IX and X

Example IX t %

Polyvinylchloride Triphenylbismuth THF

Example X

Polyvinylchloride triphenyl bismuth THF

The films formed by this method were transparent, clear and homogeneous. IR spectra of the samples of Examples IX and X show no trace of solvent (THF) left in the film. The solvent casting procedure may be used to incorporate organometallic compounds into many other polymer The choice of solvents is dependent on the solubility of the polymers and organometallic compounds in the solvents. For example, an appropriate solvent for incorporating triphenylbismuth into polyacrylonitrile by solvent casting i dimethyl formamide (at 70°C), and for preparing polyethylene-triphenylbismuth composites hexane is an appropriate solvent.

EXAMPLES XI-XIV

Radiopaque characteristics may also be imparted to polymers according to this invention by compounding polymer a an organometallic compound followed by melt processing to incorporate heavy metal organometallic compounds into polymers. The composites of EXAMPLES XI-XIV were prepared by first mixing (compounding) the triphenylbismuth into isotacti polypropylene and then transferring the mixture to a test tube. The mixture is sealed and the test tube is evacuated._, The mixture is heated above its melting point and kept at tha temperature for a few hours to give a homogeneous, clear and transparent mixture. The mixture on cooling becomes opaque, is pure isotactic polypropylene. The weight percent of triphenylbismuth in isotactic polypropylene for EXAMPLES XI-X are shown in TABLE B. The isotactic polypropylene-triphenylbismuth samples of EXAMPLES XI-XIV were cut in cylindrical pellets of 1 mm an 2 mm thickness. The radiopacity of the samples was measured the same way as described above in regards to EXAMPLES I-VII this invention. It was found that 35 percent by weight triphenyl bismuth was required in a 2mm pellet to provide th same radiopacity as a 2mm pellet of aluminum. The thermal properties of the samples of EXAMPLES XI-XIV were tested using the procedures described above in regard to EXAMPLES I-VII. The control in this case is pure isotactic polypropylene. The results are also shown in TABL TABLE B

Weight percent of Triphenyl "bismuth T_m'C Control θ70^" Ϊ52 EXAMPLE XI 10 151 EXAMPLE XII 15 150 EXAMPLE XIII 25 146 EXAMPLE XIV 30 146

DSC measurements of the blends show no melting point for triphenylbismuth indicating a homogeneous composite was achieved. Other than radiopacifying properties of these blends, the composites of EXAMPLES XI-XIV are heat stable, non-leachable and moisture and air insensitive.

EXAMPLE XV

Diphenyl p-styryl bismuth, synthesized according t known procedures, was copolymerized with methyl methacrylat bulk with AIBN at 65*C to give a transparent, hard and clea copolymer. Because the monomer-containing heavy metal is p of the backbone of the product, it improves the thermal and mechanical properties of polymers in comparison to material containing heavy metal components as additives only. Its permanent, chemical incorporation into the polymer structur prevents the leaching out of the heavy metal X-ray contrast agent in any kind of solvent ,

Formulation of EXAMPLE XV

Diphβyi p-styryl bismuth 0.54gram Methyl methacrylate 1.26gram AIBN .009gram

As should be apparent to those skilled in the art, the same procedure may be followed to achieve copolymerization with other monomers.

Other copoly ers were formed using the same procedu given for EXAMPLE XV to ^"yield poly(methylmethacrylate-co- diphenyl p-styryl bismuth) with different weight percent (or molar ratio) of heavy metal monomer. These copolymers were c in cylindrical pellets of 1mm and 2mm thickness. The radiopacities of the pellets, were measured the same way as mentioned above in regard to Part C Examples I-VII of this invention. It was found that for this copolymer a 2mm thick pellet containing 26 wt% of the bismuth-containing monomer ga the same radiopacity έ 2 mm thick aluminum. The Tg of his copolymer was 110*C, close to that of pure poly(methylmethacr late) , a considerable improvement of the Tg of 85^*C (Table A, Example VI) for a composite of poly (methyl methacrylate) and fawe triphenylbismuth.

EXAMPLE XVI

The organometallic radiopacifying compounds includin the radiopacifying monomers of this invention do not interfer with room cured polymerization procedures utilizing amine accelerators. EXAMPLE XVI was prepared by the room temperatu polymerization of methyl methacrylate which contained 30 wei 036 ^«

percent of diphenyl p-styryl bismuth in accordance with the procedure described above with regard to EXAMPLE VIII of th invention.

Formulation of EXAMPLE XVI Diphenyl p-styryl bismuth 0.54g methyl methacrylate 1.26g Benzoyl peroxide 0.045g N,N-dimethyl p-toluidine 0.027g

The copolymer formed by this method has the same transparen homogeneity, and mechanical and thermal properties as that formed in EXAMPLE XV of this invention.

Although particular illustrative embodiments of th present invention have been described herein, the present invention is not limited to these particular embodiments.

Various changes and modifications may be made thereto by th skilled in the art without departing from the ^pi il or sco of the invention, which is defined by the appended claims,

Claims

We claim:

1. A method for imparting radiopaque characterist to a polymer, the method comprising polymerizing a monomer o mixture of monomers in the presence of a compound having the following formula:

wherein X is a heavy metal; Ri, R₂ and R₃ may be the same or different and are individually selected from the group consisting of phenyl, halogen substituted phenyls, alkyl substituted phenyls, aryl substituted phenyls, ester substituted phenyls, alkene substituted phenyls, silyl group and methylmethacrylate and R₃ can additionally be selected f the group consisting of halogen, alkyl, alkene, ester and carboxylic acid when R₃ is not the same as R^ and R .

2. A method for imparting radiopaque characterist to a polymer, the method comprising solvent casting the poly from a solvent into wh'ich the polymer is dissolved, said solvent also having dissolved therein a compound having the following formula:

R3

wherein X is a heavy metal; Ri, R₂ and R3 may be the same or different and are individually selected from the group consisting of phenyl, halogen substituted phenyls, alkyl substituted phenyls, aryl substituted phenyls, ester substituted phenyls. alkene substituted phenyls, silyl group and methylmethacrylate and R₃ can additionally be selected f the group consisting of halogen, alkyl, alkene, ester and carboxylic acid when R₃ is not the same as R_]_ and R₂.

3. A method for imparting radiopaque characterist to a polymer, the method comprising melt processing a mixtur of the polymer and a compound having the following formula:

Rl *2

I R3

wherein X is a heavy metal; Ri, R₂ and R₃ may be the same or different and are individually selected from the group consisting of phenyl, halogen substituted phenyls, alkyl substituted phenyls, aryl substituted phenyls, ester substituted phenyls, alkene substituted phenyls, silyl group and methylmethacrylate and R3 can additionally be selected f the group consisting of halogen, alkyl, alkene, ester and carboxylic acid when R₃ is not the same as R*_]_ and R₂.

4. A composition comprised of a radiopaque organ polymer resin and a sufficient amount of an organometallic compound having the structure:

Ri y R2

/

X^'

I

R3

wherein X is a heavy metal; R^, -R and R3 may be the same o different and are individually selected from the group consisting of phenyl, halogen substituted phenyls, alkyl substituted phenyls, aryl substituted phenyls, ester substituted phenyls, alkene substituted phenyls, silyl grou and methylmethacrylate and R3 can additionally be selected the group consisting of halogen, alkyl, alkene, ester and carboxylic acid when R3 is not the same as R^. and R₂.

5. The composition of claim 4 wherein the amount o organometallic compound incorporated in the polymer chain is from .5 weight percent to 60 weight percent.

6. The composition of claim 4 wherein the organometallic compound is triphenylbismuth

7. The composition of claim 4 where the organometallic compound has a polymerizable substituent, for example, diphenyl-p-styrene bismuth.

8. The method of claim 1 wherein said polymerizati

is carried out in the presswee of a cross-linking agent.

9. The method of claim 1 wherein said compound is dissolved in a polyol and said polymerization is carried out said polyol.