GB1560179A - Method for making orthopedic cast material - Google Patents

Description

(54) METHOD FOR MAKING ORTHOPEDIC CAST MATERIAL (71) We, UNION CARBIDE COR PORATION, a Corporation organised and existing under the laws of the State of New York, United States of America, of 270 Park Avenue, New York, State of New York.

10017, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to improved methods of producing a thermoplastic material in the form of a bandage, web, film, tape, or sheet which is useful in the formation of orthopedic casts, and to methods of treating injury and disease of the human or animal body.

The use of certain specific plastic materials in splints is known where, as in United States Patent No. 2,616,418, specific crystalline nonpolymeric, organic compounds having sharp melting points between 450C. to 1000C. are admixed with specific high molecular weight thermoplastic substances such as cellulose acetate, to form cast-forming compositions.

United States Patent No. 2,385,879 discloses plastic cast material comprising a particular plasticizer and a conjoint polymer of a vinyl ester of an aliphatic acid and a vinyl halide.

United States Patent No. 3,420,231 discloses thermoplastic cast-forming sheet material that is flexible and moldable at about 1650F. The sheet contains a fibrous substrate coated with a cast-forming material comprising a specific elastomeric type resin, such as, a trans 1,4 chloroprene polymer and a specific inversely soluble resin, such as, methyl cellulose, hydroxy propyl methyl cellulose of polyvinyl methyl ether.

All of these materials and methods for forming orthopedic splints, braces, supports or casts have involved various disadvantages attending their use. In some cases they are difficult to apply or mold and involve complicated heating and water treatments or other manipulating steps. In other cases, separation of components, such as plasticizers, from the splint, brace, support or cast containing same can cause discomfort and in some instances extreme irritation to the skin of the patient.

In still other cases the splint brace, support or cast is water sensitive, lacks sufficient strength or rigidity, is difficult to fasten reliably to the body portion being corrected and/ or is difficult to remove when no longer needed.

United States Patent No. 3,692,023 discloses an orthopedic cast material comprising a supported or unsupported web or sheet of a cyclic ester polymer or a blend of a cyclic ester polymer and poly (vinyl alkyl ether). The orthopedic cast material, in the form of a sheet, tape, film or preformed contour-fitting shape, can be applied to the human or animal body to form a splint, brace, support.

protective shield or cast. These orthopedic cast materials offer various advantages over the previously mentioned orthopedic cast materials, to wit, that they are very easily and rapidly applied to the human or animal body to form rigid, non-irritating, strong durable, water-resistant, soil-resistant, close-fitting splints, braces, supports, shields and casts which are very easily removed when no longer needed, withot even the slightest injury or irritation to the patient and without serious damage to the cast material which may be sterilized and reused, if desired. An important advantage of the cyclic ester polymer or cyclic ester polymerlpoly(vinyl alkyl ether) blend over certain other polymeric cast materials is that they are completely non-irritating to the skin.

A number of methods are disclosed in United States Patent No. 3,692,023 for preparing the orthopedic cast material. For example, the cyclic ester polymer can be dissolved in a suitable solvent, applied to a supportive substrate material such as gauze and solidified by evaporating the solvent. Alternatively, the cast material can be prepared without a substrate material by fluxing the polymer on a two-roll mill and then extruding it through a sheet-forming die. If desired, the extruded sheet can then be affixed to a substrate by bringing the extruded sheet and substrate together under pressure and/or heating. Yet another method of preparing the cyclic ester orthopedic cast material involves dusting a substrate with a powder of the cyclic ester polymer and heating to fuse the powder to the substrate.The orthopedic cast material, in the form of a supported or unsupported sheet or web, is generally applied to a body part by heating the sheet or web to the softening point of the polymer and manipulating it to the contour of the body part. At this elevated temperature, the polymer becomes self-adherent and therefor is easily affixed around a body part such as an arm or leg by wrapping the warm material around the arm or leg and joining the ends under pressure.

This invention provides an improved method of rapidly forming orthopedic casts and cast materials based on cyclic ester polymers. In the improved method of this invention, the orthopedic cast materials are formed directly from cyclic ester monomers, thereby eliminating xhe need separately to polymerize the cyclic ester monomer prior to forming the orthopedic cast material from the polymer.

In accordance with the teaching of this invention, a flexible permeable or porous substrate such as gauze or cotton batting is impregnated with a mixture of a liquid cyclic ester monomer, aluminum secondary butoxide as catalyst, and, optionally, a minor portion of a vinylic polymer which is dissolved or dispersed in the cyclic ester monomer and the cyclic ester monomer is polymerised to form a solid orthopedic cast material.

In accordance with the present invention there is provided a method of making an orthopedic cast-forming material which comprises the steps of: (a) impregnating a flexible porous or perme able substrate with a mixture comprising: i) as the major portion thereof (as here inafter defined), a cyclic ester mono mer of the general formula:

wherein each R, individually, is a hydrogen or halogen atom, or an alkyl group containing up to 12 carbon atoms, or an alkoxy group containing up to 12 carbon atoms;A is an oxy group; x is an integer from 1 to 4; y is an integer from 1 to 4; and z is 0 or 1; with the proviso that the sum of x+y+z is from 4 to 7 and that the number of R variables which are substituents other than hydrogen is from 0 to 3; ii) from 0.001 to 10 weight per cent of aluminum secondary butoxide; iii) from 0 to 45 weight percent of a vinylic polymer having a weight aver age molecular weight of from 5,000 to 600,000; and then (b) polymerizing the cyclic ester monomer substantially in the absence of moisture.

The invention also provides a method of treating a non-human animal which comprises aDplying to the animal a cast-forming material of the present invention and thermally setting the material on the animal to form an orthopedic cast thereon.

The orthopedic cast material thus formed is applied to a body part in the same manner as decribed in United States Patent No.

3,692,023. An important difference between the present method and the known methods of producing polymeric casts is that it is possible to polymerize the cyclic ester monomer using lower temperatures and shorter reaction times than those which must be employed in commercial polymerization reactions.

In some instances, the cyclic ester monomer impregnated in the substrate can be polyerized at temperatures as low as 50oC. in times as short as 3 minutes. By comparison, commercial scale processes for producing poly (epsilon - caprolactone) often involve reaction temperatures as high as 1800C. and reaction times as long as 12 hours. Moreover, since the polymerization of the cyclic ester monomer and the formation of the orthopedic cast material are accomplished in a single step, there is no need to melt the cyclic ester polymer or dissolve the cyclic ester polymer in a solvent to form the orthopedic cast material; as there is in prior art methods wherein the orthopedic cast material is formed from a solid cyclic ester polymer.Thus, the method of this invention effects a substantial reduction of energy required to produce ortho pedic cast forming materials of the type disclosed in United States Patent No. 3,692,023.

In one embodiment of this invention, the cyclic ester monomer has admixed therewith a minor portion of a vinylic polymer. By the inclusion of the polymer, the skilled chemist can adjust various properties of the unpolymerized or polymerized cyclic ester material, such as potlife, viscosity and softening or melting point. The material which is formed in this embodiment, exclusive of the supporting substrate, is a blend of the polymer of the cyclic ester monomer (e.g., polycaprolactone) and the vinylic polymer which is admixed with the cyclic ester monomer. while these polymer blends are known in the prior art, the method of preparing them which comprises the steps of forming a mixture of cyclic ester monomer, the polymer which is soluble or dispersible therein, and aluminum sec butoxide and polymerizing the cyclic ester monomer is not disclosed in the prior art.

The cyclic ester monomers which are used in this invention are illustrated by the general formula:

wherein each R, individually, is a halogen or hydrogen atom or an alkyl or alkoxy group containing up to 12 carbon atoms; A is an oxy group; x is an integer from 1 to 4; y is an integer from 1 to 4; z is zero or one; with the further provisos that (a) the sum of x+y+z is at least 4 and not greater than 7, and (b) the total number of R variables which are substituents other than hydrogen does not exceed 3, and preferably does not exceed 2.

Examples of the group R are the methyl, ethyl, isopropyl, n-butyl, sec-butyl, t-butyl, hexyl, chloro, bromo, iodo, methoxy, ethoxy, obutoxy, n-hexoxy, 2-ethylhexoxy, and dodecoxy groups. It is preferred that each R, individually, is a hydrogen atom, a lower alkyl group, e.g. a methyl, ethyl, n-propyl or isobutyl group, or a lower alkoxy group, e.g. a methoxy, ethoxy, propoxy, or n-butoxy group. It is further preferred that the total number of carbon atoms in the R substituents does not exceed 20.Examples of the cyclic ester monomers which are contemplated in dude delta-valerolactone, epsilon-caprolactone; zeta - enantholactone; etacaprylactone; the monoalkyl - delta - valerolactones, e.g. the monomethyl,- monoethyl-, monohexyl-, and delta - valerolactones; the dialkyl - delta valerolactones; e.g., the dimethyl-, diethyland di - n - octyl - delta - valerolactones; the monoalkyl-, dialkyl-, and tri - alkyl - epsilon caprolactones, e.g., the monomethyl-, mono ethyl-, monohexyl, dimethyl-, diethyl-, di n - propyl, di - n - hexyl-, trimethyl-, triethyl, and tri - n - propyl - epsilon - caprolactones; the monoalkoxy and dialkoxy delta - valerolactones and epsilon - capri lactone, e.g., the monomethoxy-, monoisopropoxy-, dimethoxy-, and diethoxy - delta valerolactones and epsilon - caprolactones; 1,4 dioxane - 2 - one; and dimethyl - 1,4 - di oxane - 2 - one. A single cydic ester monomer or mixtures of these monomers may be employed. The preferred cyclic ester monomer is epsilon - caprolactone, because it polymerizes to form a material with a relatively low melting point which has the ability to crystallize and harden at a reasonable rate at room temperature well within the times involved in applying the cast, and it is relatively inexpensive.

The cyclic ester monomer described above constitutes the major portion of the mixture which is impregnated into the porous or per meable substrate in the method of this inven tion. The term "major portion", as used in this specification and the claims, means at least 50 weight per cent thereof.

Aluminum secondary butoxide is employed as the catalyst herein because it is somewhat unique in its ability to promote rapid poly merization of the cyclic ester monomer at rela tively low polymerization temperatures. Alu minum secondary butoxide is employed at con centrations between 0.001% and 10% by weight, based on the weight of the monomer, and preferably between 1 and 4% by weight.

In addition to the catalyst, there can also be present in the cyclic ester monomer/catalyst mixture a small amount of any of the active hydrogen-containing initiators which are known to have utility in polymerizing cyclic ester monomers, such as alcohols, amines, thiols, and carboxylic acids in the usual known amounts. However, an initiator is not necessary to achieve efficient polymerization by the method of this invention.

There can optionally be present in the mix ture of cyclic ester monomer and catalyst up to 45 weight per cent, and preferably not more than 30 weight per cent, of a vinylic polymer having a weight average molecular weight of from 5,000 to 600,000, preferably from 10,000 to 400,000, and most preferably from 10,000 to 300,000. The polymer can be a homopolymer of a single monomer containing polymerizable vinyl or vinylidene groups or an interpolymer of two or more of these mono mers.Examples of the many suitable vinylic polymers are polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyvinyl ace tate, poly(vinyl alkyl ethers), e.g. poly(vinyl methyl ether), poly(vinyl ethyl ether), poly (vinyl isopropyl ethers), poly(vinyl t - butyl ether), vinyl chloride/vinyl acetate copolymers, vinyl chloride/vinylidene chloride copolymers, acrylonitrile/butadiene styrene terp olymers, styrene/methyl methacrylate copolymers, vinyl chloride/hydroxypropyl methacrylate copolymers, and styrene/acrylonitrile copolymers.

The vinylic polymer can be dissolved in the cyclic ester monomer or, if a vinylic polymer is employed which is not soluble in the cyclic ester monomer, uniformly dispersed therein, preferably in particle sizes not exceeding about 500 microns in diameter.

When a vinylic polymer is dissolved or dispersed in the cyclic ester monomer as described the orthopedic cast material obtained by the method of this invention is a composite of the substrate material and a blend of the corresponding cyclic ester polymer and the vinylic polymer. These blends of cyclic ester polymers and vinylic polymers are known in the art, certain of them being disclosed, for example, in United States Patent No.

3,592,877. As used throughout this specifica tion, the term "cyclic ester monomer/catalyst mixture" is meant to include mixtures of cyclic ester monomer and catalyst containing the vinylic polymer which is optionally present.

If desired, there can additionally be present in the cyclic ester monomer/catalyst mixture a small amount, preferably less than 10%, of a conventional filler, such as calcium carbonate, finely divided silica, clay, asbestos, or alpha cellulose, a thixotropic agent, such as fibrous asbestos or a medication of the desired type for a variety of purposes, e.g., to soothe the skin and/or reduce bacterial or fungal activity.

The flexible substrate which is impregnated with the cyclic ester monomer/catalyst mixture is preferably a web, sheet, tape, or film which is permeable to the cyclic ester monomer/catalyst mixture and compatible therewith, and which has no harmful effects upon skin when maintained in contact with it.

Examples of suitable substrates are knitted or woven fabrics which can be made from cellulosic materials, such as flannel or gauze made from cotton, rayon, blends of cotton and rayon, blends of cotton or rayon with synthetic fibers, such as poly(ethylene terephthalate) fibers, polyacrylonitrile fibers, or nylon fibers; fabrics and textile products made from wool fibers, nylon fibers, poly(ethylene terephthalate) fibers, polyacrylonitrile fibers and blends of two or more of these fibers; glass fiber fabric; fabrics woven from elastomeric fibers, such as natural and synthetic rubbers, including butyl rubber, nitrile rubber, polybutadiene rubber, polyisobutylene rubber and silicone rubbers; and flexible foamed plastic, such as polyurethane foam, or other flexible foam material, such as foam rubber or natural sponge.

In accordance with the method of this invention, the porous or permeable substrate is impregnated with a sufficient quantity of a mixture of cyclic ester monomer, catalyst and, if desired, vinylic polymer completely to permeate and wet the individual fibers or par ticks of the substrate. The impregnation may be achieved by any convenient means, such as dipping the substrate in the mixture of brushing, pouring, spraying, or coating the mixture onto the substrate. Also included within the scope of this invention is a procedure wherein individual fibers of the substrate material are coated with the mixture and then woven into a fabric. Since the cyclic ester monomers are generally free flowing and levelling liquids at room temperature, the thickness of the orthopedic cast material produced will depend largely on the thickness of the substrate employed.One can achieve any desired thickness of orthopedic cast material either by using a substrate material of the suitable thickness, by simultaneously polymerizing two or more superposed layers of impregnated substrate material or by polymerizing the cyclic ester monomer impregnated in the substrate, as described herein, and subsequently fusing two or more superposed layers of material thus produced by the use of heat and/or pressure. If desired, the cyclic ester monomer impregnated in the substrate can be polymerized and a sheet or strip of the orthopedic cast material thus produced can be wound several times around the limb or body member and the several layers thereafter fused by heat to achieve the desired thickness.

The monomer which has been impregnated into the substrate is polymerized to a solid state to form the orthopedic cast material.

The polymerization can be carried out at a temperature of from OOC. to 1200C., and is preferably carried out at a temperature of from 250C. to 850C. We have found that by employing aluminum sec-butoxide as the polymerization catalyst, the polymerization reaction proceeds rapidly, even at relatively low temperatures. For example, a 2-mils thick strip of cotton gauze bandage impregnated with a mixture of epsilon-caprolactone and 4 weight per cent aluminum sec-butoxide was converted to a solid sheet of orthopedic cast material by polymerizing the epsilon-caprolactone for 3 minutes at a temperature of 50 C. When a vinylic polymer is additionally present in the cyclic ester monomer mixture we have found that a somewhat higher temperature of polymerization is sometimes required to achieve the desirably short polymerization time.This temperature varies, depending on the particular vinylic polymer employed and the amount of vinylic polymer employed, however, polymerization can generally be achieved at temperatures below 850C. in a few minutes.

Care should be taken that moisture does not contact the cyclic ester monomer/catalyst mixture during the polymerization, since moisture is known to impede the polymerization reaction.

The solid orthopedic cast material formed by the method described above is useful in the treatment of the human and animal body for the maintenance of immobilization and fixation following reduction of fractures and dislocations, the maintenance of approximation of bone fragments following reduction of fractures, the maintenance of fixation and immobilization to promote healing in instances of compound fractures and bone disease, the immobilization of inflamed or injured joints in disease or trauma, and the support and immobilization of ligamentous and muscular structures in instances of sprains and strains.

The improved cast materials also may be used as an occlusive dressing for wounds of the extremities by encasing the limb or part to reduce motion and accelerated healing; as a support splint in paralysis or weakness of muscles; and as a means to maintain correction of deformities, either congenital or acquired.

The orthopedic cast material can be applied to a body part by warming the orthopedic cast material to its softening point and then manipulating it to the contour of the body part. The cast can be fixed in Dlace by overlapping the ends while soft, thus fusing the orthopedic cast material to itself, and cooling the material below its softening point. To form many casts, e.g., those for fingers, toes, arms and legs, the cast material can be preformed into a tubular shape or other preformed shape.

The cast material can be heated by means an ordinary home hair dryer, a specially designed heat gun or simply by immersing it in a pan of hot water drawn from an ordinary hot water tap. The cast material can also be used in the form of a tape or elongated sheet by successively wrapping it around the body part in an overlapping manner. Heat applied before or after wrapping causes the over lapping tape to bond together into a unitary cast which sets upon cooling.

The orthopedic cast material can be oriented by stretching it while it is warmed to a temperature below its melting point and cooling it while it is in its stretched condition, provided that the substrate material is one which can be stretched without breaking. When in tubular shape the oriented material can be placed on a limb and heated, whereupon the material shrinks into place about the limb. Of course, care must be taken that the tubular material is large enough and/or the extent of shrinkage is so controlled that the circulation is not cut off. The oriented material, in tube, sheet or strip form, can also be placed over and shrunken on a previously hardened cast to give a neater, smoother surface, if desired.

The cast material can be perforated to permit diffusion of air or moisture to and from the skin covered by the cast material, although it is not usually necessary since the orthopedic cast materials produced by the method of this invention are inherently moisture and gas permeable.

If desired, either one or both faces of the orthopedic cast material can be bonded to a different flexible sheet or web-like material.

For example, one may desire to interpose a soft comfortable material, such as flannel or terry cloth between the rigid cast material and the skin of the wearer. This can be achieved by warming the cast material, bringing it in face-to-face contact with the flexible sheet or web-like material and cooling it whereupon the two materials will adhere.

Alternatively, the flexible sheet or web-like material can be maintained in face-to-face contact with cyclic ester monomer/catalyst impregnated substrate material during polymerization of the cyclic ester monomer and a bond will be formed as the monomer is polymerized. The flexible sheet or web-like materials to which the orthopedic cast material can be bonded include, but are not limited to, the porous or permeable materials which were previously described as being suitable substate materials for impregnation by the cyclic ester monomer/catalyst mixture. The orthopedic cast material can also be bonded to a nonporous sheet or web of a polymeric material such as cellulose acetate, nylon, polyethylene terephthalate, thermoplastic polyurethane and acrylic polymers.

The thickness of the orthopedic cast material is not narrowly critical. It can be from 1 mil to 500 mils thick. Those skilled in medical arts will know the preferred thick ness of cast for treating various types of in juries and infirmities, and the desired thick ness may be obtained in any of the ways dis closed above.

When the cyclic ester monomer/catalyst mixture employed has no vinylic polymer therein, the melting point of the resulting polyester in the orthopedic cast material is from 500 C. to 900 C. For example, poly (epsilon-caprolactone) melts at from 550C. to 650C. When a vinylic polymer is dissolved or dispersed in the cyclic ester monomer/cata lyst mixture the resulting polymer blend in the orthopedic cast material has a melting or softening point from 300 C. to 700C. depending on the melting, or softening point of the particular vinylic polymer employed and the amount thereof which is dissolved in the cyclic ester monomer/catalyst mixture.

The following Examples are presented to illustrate the invention further. Unless otherwise indicated, all parts and percentages are by weight and all viscosities are measured at a concentration of 20% solids in methyl ethyl ketone at 250C.

Example 1 Twoinch wide cotton gauze bandage was placed in an oven at 500C. to dry any moisture which it may have contained. Into a 4oz. open top bottle there were placed 20 grams of epsilon-caprolactone which had been dried with molecular sieves. To this monomer 0.8 gram of aluminum sec-butoxide was added and the mixture was thoroughly mixed.

Several 12-inch long strips of the dried gauze bandage were attached to a glass plate. Two minutes after the epsiloncaprolactone and aluminum sec-butoxide were mixed, they were applied to the gauze strips, using a Baker coating knife, to form a 2-mils thick wet composite and thoroughly wet the gauze. The impregnated gauze strips were then removed from the glass plates and placed in an oven at 500 C. for three minutes. When cooled, the impregnated gauze composite became solid and nontacky, and was suitable for use as an orthopedic cast material. At this thickness, the orthopedic cast material was bendable, although not soft, thus it could be wrapped around an appendange such as a finger.

Example 2 A pencil was broken to simulate a broken finger. The broken ends of the pencil were held together and five turns of the orthopedic cast material produced in Example 1 were wrapped around the pencil at the point of the break. Using a hot air gun, the cast material on the pencil was heated to 650C., at which point the individual layers around the pencil flowed together. Upon cooling, the poly (epsilon - caprolactone) crystallized to form a rigid unitary material. The two portions of the broken pencil were held rigidly together as a broken limb would be by an orthopedic cast.

Example 3 There were placed in a bottle 16 grams of epsilon - caprolactone, which had been dried with molecular sieves, and 4 grams of a copolymer of vinyl acetate and vinyl chloride.

The copolymer contained 86% vinyl chloride mer units and 14% vinyl acetate mer units and had a viscosity of 50 cps. The epsiloncaprolactone and copolymer were agitated to effect solution and 0.64 gram of aluminum sec-butoxide was then added to the solution and mixed for about 2 minutes. Using a Baker coating knife, the solution was drawn down onto four 2-inch wide strips of cotton gauze, which had been dried in an oven at 500 C., to form 2-mils thick wet composites. These strips were placed in an oven at 800C. for 10 minutes. When cooled, the strips became hard and non-tacky in a manner similar to the orthopedic cast material produced in Example 1.

Example 4 To each of three open-top, 8-ounce bottles, which had been dried in an oven at 500C.

were charged 22 grams of one of three vinyl polymers, identified as vinyl polymers A, B and C and described below: Vinyl polymer A A vinyl chloride/hydroxypropyl meth acrylate copolymer containing 80% vinyl chloride mer units and having a viscosity of 300 cps (measured at 27% solids in an 80/20 volume per cent mixture of toluene/methyl isobutyl ketone).

Vinyl polymer B- A vinyl chloride copolymer contain ing 80% vinyl chloride and 20% gly cidyl methacrylate, and having a vis cosity of 11 cps.

Vinyl polymer C A terpolymer of 91:3:6 pans, res pectively, of vinyl chloride, vinyl ace tate and vinyl alcohol having a vis cosity of 60 cps.

There were then added to each bottle 125 grams of epsilon-caprolactone and the bottles were purged with nitrogen, sealed and agitated to effect solution of the polymer in the epulon-caprolactone. To each of three 2ounce bottles, which had been dried in an oven at 500C., were charged 20 parts of one of the solutions produced above and 0.68 parts aluminum sec-butoxide and the mixture was stirred for 4 minutes. Each of the three solutions was applied with a Baker coating knife to a 2-inch by 12-inch strip of cotton gauze to form a6-mils thick wet composite.

The wet composite containing vinyl poly.

mer A was placed in an oven at 500 C. and had not polymerized sufficiently after 10 minutes to produce a material suitable for use as orthopedic cast material. A second wet composite containing vinyl polymer A was prepared and placed in an oven at 800 C. It polymerized in 7 minutes to form a material which was hard and non-tacky at room tem perature, and which was suitable as an ortho pedic cast material. The wet composite con taining vinyl polymer B polymerized suffi ciently in 5 minutes at 500C. to form a suit able material for use as an orthopedic cast and the wet composite containing vinyl poly mer C polymerized sufficiently in 3 minutes at 500C. to form a suitable material for use as an orthopedic cast A wooden pencil was broken to simulate a broken finger.The broken ends of the pencil were held together and three turns of the orthopedic cast material incorporating vinyl polymer A were wrapped around the pencil at the point of break. The wrapped pencil was placed in an oven at 500 C. for one minute, after which the layers of cast material had bonded together to form a unitary cast which held the pencil rigidly after being cooled to room temperature.

Example 5 To a 4-ounce bottle there were charged 85 parts of epsilon-caprolactone and 15 parts of polystyrene having a wt. av. molecular weight of 300,000. The mixture was blended on a roller until the polystyrene was completely dissolved. There were then placed in a bottle 40 parts of the solution and 1.6 parts of aluminum secondary butoxide. The catalystwas stirred into the solution for about 1 minute with a high speed stirrer under a nitrogen blanket The solution containing the catalyst was drawn down onto 2-inch wide cotton gauze strips using a Baker coating knife to form 2-mils thick wet composites. The wet composites did not cure after 3 minutes, in an oven at 600C., however, similarly prepared composites cured to a solid, non-tacky state after 5 minutes in an oven at 750C. The cured material was suitable for use at an orthopedic cast material. Pot life of the solution containing the catalyst, determined as the time re quired for the solution to gel at room temperature, was 1-2 minutes in one instance and 3 minutes in another instance.

Example 6 Wet composites were produced in a manner similar to that of Example 5 substituting for polystyrene, poly(vinyl acetate) having a No. 4 Ford cup viscosity of 1G16 seconds (45% solids in acetone at 250C.). The wet composite cured to a solid, non-tacky state after 5 minutes in an oven at 75 C. The cured material was suitable for use as an orthopedic cast material. Pot life of the solution containing the poly(vinyl acetate), epsilon-caprolactone and catalyst was about 40 minutes.

WHAT WE CLAIM IS:- 1. A method of making an orthopedic castforming material which comprises the steps of: (a) impregnating a flexible porous or perme able substrate with a mixture comprising: i) as the major portion thereof (as hereinbefore defined), a cyclic ester monomer of the general formula:

wherein each R, individually, is a hydrogen or halogen atom, or an alkyl group containing up to 12 car bon atoms, or an alkoxy group con taining up to 12 carbon atoms;A is an oxy group; x is an integer from 1 to 4; y is an integer from 1 to 4; and z is 0 or 1; with the proviso that the sum of x+y+z is from 4 to 7 and that the number of R variables which are substituents other than hydrogen is from 0 to 3; ii) from 0.001 to 10 weight per cent of aluminum secondary butoxide; iii) from 0 to 45 weight percent of a vinylic polymer having a weight aver age molecular weight of from 5,000 to 600,000; and then (b) polymerizing the cyclic ester monomer substantially in the absence of moisture.

2. A method as claimed in claim 1 wherein the aluminum secondary butoxide is employed at a concentration of from 1 to 4 weight per cent of the mixture.

3. A method as claimed in claim 1 or claim 2 wherein the cyclic ester monomer is epsiloncaprolactone.

4. A method as claimed in any one of the preceding claims wherein the cyclic ester monomer in the mixture is polymerized at a temperature of from OOC. to 120 C.

5. A method as claimed in claim 4 wherein the cyclic ester monomer is polymerized at a temperature of from 250C to 850C.

6. A method as claimed in any one of the preceding claims wherein the vinylic polymer has a weight average molecular weight of from 10,000 to 400,000.

7. A method as claimed in claim 6 wherein the vinylic polymer has a weight average molecular weight of from 10,000 to 300,000.

8. A method as claimed in any one of the preceding claims wherein up to 30 weight per cent of the vinylic polymer is present in the mixture.

9. A method as claimed in any one of the preceding claims wherein the vinylic polymer is a copolymer of vinyl chloride and hydroxypropyl methacrylate.

10. A method as claimed in any one of claims 1 to 8 wherein the vinylic polymer is a copolymer of vinyl chloride and glycidyl methacrylate.

11. A method as claimed in any one of claims 1 to 8 wherein the vinylic polymer is a terpolymer of vinyl chloride, vinyl acetate and vinyl alcohol.

12. A method as claimed in any one of claims 1 to 8 wherein the vinylic polymer is polystyrene.

13. A method as claimed in any one of claims 1 to 8 wherein the vinylic polymer is poly(vinyl acetate).

14. A method as claimed in any one of the preceding claims wherein an active-hydrogen-containing polymerization initiator is addi optionally present in the mixture.

15. A method as clamed in any one of the preceding claims wherein a filler, thixotropic agent or medication is additionally present in the mixture.

16. A method as claimed in any one of the preceding claims wherein the flexible permeable or porous substrate is in the form of a web, sheet, tape or film.

17. A method as claimed in claim 16 wherein the substrate is a woven or knitted fabric, or a natural or synthetic sponge.

18. A method as claimed in claim 1 substantially as hereinbefore described.

19. A method as claimed in claim 1 substantially as hereinbefore described in any one of Examples 1 or 3 to 6.

20. An orthopedic cast-forming material when made by a method as claimed in any one of the preceding claims.

21. A method of treating a non-human animal which comprises applying to the animal an orthopedic cast-forming material as claimed in claim 20 and thermally setting

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (22)

**WARNING** start of CLMS field may overlap end of DESC **. quired for the solution to gel at room temperature, was 1-2 minutes in one instance and 3 minutes in another instance. Example 6 Wet composites were produced in a manner similar to that of Example 5 substituting for polystyrene, poly(vinyl acetate) having a No. 4 Ford cup viscosity of 1G16 seconds (45% solids in acetone at 250C.). The wet composite cured to a solid, non-tacky state after 5 minutes in an oven at 75 C. The cured material was suitable for use as an orthopedic cast material. Pot life of the solution containing the poly(vinyl acetate), epsilon-caprolactone and catalyst was about 40 minutes. WHAT WE CLAIM IS:-

1. A method of making an orthopedic castforming material which comprises the steps of: (a) impregnating a flexible porous or perme able substrate with a mixture comprising: i) as the major portion thereof (as hereinbefore defined), a cyclic ester monomer of the general formula:

wherein each R, individually, is a hydrogen or halogen atom, or an alkyl group containing up to 12 car bon atoms, or an alkoxy group con taining up to 12 carbon atoms;A is an oxy group; x is an integer from 1 to 4; y is an integer from 1 to 4; and z is 0 or 1; with the proviso that the sum of x+y+z is from 4 to 7 and that the number of R variables which are substituents other than hydrogen is from 0 to 3; ii) from 0.001 to 10 weight per cent of aluminum secondary butoxide; iii) from 0 to 45 weight percent of a vinylic polymer having a weight aver age molecular weight of from 5,000 to 600,000; and then (b) polymerizing the cyclic ester monomer substantially in the absence of moisture.

2. A method as claimed in claim 1 wherein the aluminum secondary butoxide is employed at a concentration of from 1 to 4 weight per cent of the mixture.

3. A method as claimed in claim 1 or claim 2 wherein the cyclic ester monomer is epsiloncaprolactone.

4. A method as claimed in any one of the preceding claims wherein the cyclic ester monomer in the mixture is polymerized at a temperature of from OOC. to 120 C.

5. A method as claimed in claim 4 wherein the cyclic ester monomer is polymerized at a temperature of from 250C to 850C.

6. A method as claimed in any one of the preceding claims wherein the vinylic polymer has a weight average molecular weight of from 10,000 to 400,000.

7. A method as claimed in claim 6 wherein the vinylic polymer has a weight average molecular weight of from 10,000 to 300,000.

8. A method as claimed in any one of the preceding claims wherein up to 30 weight per cent of the vinylic polymer is present in the mixture.

9. A method as claimed in any one of the preceding claims wherein the vinylic polymer is a copolymer of vinyl chloride and hydroxypropyl methacrylate.

10. A method as claimed in any one of claims 1 to 8 wherein the vinylic polymer is a copolymer of vinyl chloride and glycidyl methacrylate.

11. A method as claimed in any one of claims 1 to 8 wherein the vinylic polymer is a terpolymer of vinyl chloride, vinyl acetate and vinyl alcohol.

12. A method as claimed in any one of claims 1 to 8 wherein the vinylic polymer is polystyrene.

13. A method as claimed in any one of claims 1 to 8 wherein the vinylic polymer is poly(vinyl acetate).

14. A method as claimed in any one of the preceding claims wherein an active-hydrogen-containing polymerization initiator is addi optionally present in the mixture.

15. A method as clamed in any one of the preceding claims wherein a filler, thixotropic agent or medication is additionally present in the mixture.

16. A method as claimed in any one of the preceding claims wherein the flexible permeable or porous substrate is in the form of a web, sheet, tape or film.

17. A method as claimed in claim 16 wherein the substrate is a woven or knitted fabric, or a natural or synthetic sponge.

18. A method as claimed in claim 1 substantially as hereinbefore described.

19. A method as claimed in claim 1 substantially as hereinbefore described in any one of Examples 1 or 3 to 6.

20. An orthopedic cast-forming material when made by a method as claimed in any one of the preceding claims.

21. A method of treating a non-human animal which comprises applying to the animal an orthopedic cast-forming material as claimed in claim 20 and thermally setting

the material on the animal to form an orthopedic cast thereon.

22. A method as claimed in claim 21 substantially as hereinbefore described.