CA1125589A - Method for making orthopedic cast material - Google Patents

Abstract

10,829 METHOD OF MAKING ORTHOPEDIC
CAST MATERIAL

ABSTRACT OF THE DISCLOSURE
Orthopedic cast forming materials are produced by impregnating a porous or permeable substrate, such as gauze or cotton batting with a mixture of a liquid cyclic ester monomer, aluminum secondary butoxide and, optionally, a minor amount of a vinylic polymer, and polymerizing the monomer.

S P E C I F I C A T I O N

Description

l~Z~5-~'9 lo, 829 -This invention relates to improved methods of producing a thermoplastic material in the form of O
a bandage, web, film tape, sheet, or the like which is useful in the formation of orthopedic casts, and to methods of treating injury and disease of the human or animal body.
- BACKGROUND OF THE INVENTION
The use of certain specific plastic materials in splints is known where, as in U.S.

2,616,418, specific crystalline non-polymeric, organic compounds having sharp melting points between 45C. to 100C. are admixed with specific high molecular weight thermoplastic substances such as cellulose acetate, to form cast-forming compositions.
U.S. 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. U.S. 3,420,231 disclosed thermo-plastic cast forming sheet material that is flexible 20 and moldable at about 165F. The sheet contains a fibrous substrate coated with a cast ~orming 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 or polyvinyl methyl ether.

10,829 l~ZS5~.CI

All of these materials and methods for forming orthopedic splin~s, 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 plastici-zers, from the splint, brace, support or cast cont-aining 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 reliably asten to the body portion being corrected and/or is difficult to remove when no longer needed.
U.S. 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.
Such orthopedic cast materials offer various advantages over the previously mentioned orthopedic cast materials, to wit, that they are very easily 1~2S5~9 l0,829 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, without even the slightest injury or irritation to the patient and without serious damage to the cast material whlch may be sterilized and reused, if desired. An important advantage of the cyclic ester polymer or cyclic ester polymer/poly(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 U.S.

3,692,023 for preparing the orthopedic cast material.
For example, the cyclic ester polymer can be dis-- solved in a suitable solvent, applied to a supportive substrate material such as gauze and solidified by evaporating the solvent. Alternatively, ~he cast material can be prepared without a substrate mater-ial 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 1~2S5~9 10,829 substrate with a powder of the cylic 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 pol~-mer 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.
SUMMARY OF THE INVENTION
This invention provides an improved method o~ rapidly forming orthopedic casts and cast materi-als based on cyclic ester polymers. In the improved method of this invention, the orthopedic cast mater-ials are formed directly from cyclic ester monomers, thereby eliminating the need to separately polymerize the cyclic ester monomer prior to forming the ortho-pedic cast material from the polymer. In accordance with the teachings of this invention, a 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 l~ZSS~ o, 829 which is dissolved or dispersed in the cyclic estermonomer and the cyclic ester monomer is polymerized to form a solid orthopedic cast material. The ortho~edic cast material thus formed is applied to a body part in the same manner as described in U.S.
3,692,023. An important difference between our method and the known methods of producing polymeric casts is that it is possible to polymerize the cyclic ester monomer using lower te~peratures 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 polymerized at temperatures as low as ~0C. in times as short as 3 minutes. By comparison, commercial scale processes for producing poly(epsilon-caprolactone) often involve reaction temperatures as high as 180 c . 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 10,829 1~2S5~9 reduction of energy, required to produce orthopedic cast forming materials of the type disclosed in U.S. 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, softening or melting point, etc. 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 such 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.
DESCRIPTION OF THE INVENTION
The cyclic ester monomers which are useful in this invention are illustrated by the formula:

10,829 1~255~9 C--O--_l_R)x (R-C-R)y --- (A)z wherein each R, individually, is selected from the class consisting of hydrogen, alkyl or alkoxy having up to about 12 carbon atoms and halo; A is the oxy gro~lp; x is an integer from 1 to 4; y is an integer from 1 to 4; z is an integer of zero or one; with the - 10 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 doe not exceed 3, and preferably does not exceed 2.
Illustrative R variables include methyl, ethyl, isopropyl, n-butyl, sec-butyl, t-butyl, hexyl, chloro, bromo, iodo, methoxy, ethoxy, n-butoxy, n-hexoxy, 2-ethylhexoxy, dodecoxy, and the like. It is preferred that each R, individually, be hydrogen, lower alkyl, e.g. methyl, ethyl, n-propyl, isobutyl or lower alkoxy, e.g., methoxy, ethoxy, prepoxy, n-butoxy, and the like. It is further preferred that the total number of carbon atoms in the R substituents does not exceed 20. Representative cyclic ester monomers which are contemplated include, for example, delta-valerolactone, epsilon-caprolactone; zeta-enantholactone;
etacaprylolactone; the monoalkyl-delta-valerolactones, 1 ~Z~ S~9 10,829 e.g., the monomethyl-, monoethyl-, monohexyl-, delta-valerolactones, and the like; the dialkyl-delta-valerolactones; e.g.S the dimethyl-, diethyl-, and di-n-octyl-delta-valerolactones, and the like; the monoalkyl-, dialkyl-, and tri-alkyl-epsilon-capro-lactones,e.g., the monomethyl-, monoethyl-, monohexyl-, dimethyl-, diethyl-, di-n-propyl, di-n-hexyl-, trimethyl-, triethyl-, and tri-n-propyl-epsilon-caprolactones, and the like; the monoalkoxy-and dialkoxy-delta-valerolactones and epsilon-caprolactone, e.g., the monomethoxy-, monoisopropoxy-, dimethoxy-, and diethyoxy-delta-valerolactones and epsilon-caprolactones, and the like; 1,4-dioxane-2-one; dimethyl-1,4-dioxane-2-one; and the like. A
single cyclic ester monomer or mixtures of such monomers may be employed. The preferred cyclic ester monomer is epsilon-caprolactone, because it poly-merizes 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 permeable substrate in the method of this invention. The term "major portion", _g_ 1 ~ 2 S L~`9 10 ~ 829 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 polymerization of the cyclic ester monomer at relatively low polymerization temperatures. All~m~num secondary butoxide is employed at conc~ntrations between about 0.001% and 10%, based on the weight of the monomer, and preferably between 1% and 4%. 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, carboxylic acids, etc., 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 mixture 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 wt. av.
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 '-10-1~255~29 lo,829 or vinylidene groups or an interpolymer of two or more such monomers. Illustrative of the many suitable vinylic polymers one can mention polyethylene, poly-propylene, polyvinyl chloride, polystyrene, polyvinyl acetate, poly(vinyl alkyl ethers), e.g., poly(vinyl methyl ether), poly(vinyl ethyl ether), poly(vinyl isopropyl ether), poly(vinyl t-butyl ether), vinyl chloride/vinyl acetate copolymers, vinyl chloride/
vinylidene chloride copolymers, acrylonitrile/ but-adiene styrene terpolymers, styrene/methylmethacrylate copolymers, vinyl chloride/hydroxypropyl methacrylate copolymers, styrene/acrylonitrile copolymers, and the like. 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. Such blends of cyclic ester polymers and vinylic polymers are known in the art, certain of them being disclosed,

5~ o,829 for example, in U.S. 3,592,877. As used throughout this specification, 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, alpha cellulose, and the like, thixotropic agents, such as fibrous asbestos or medication of the desired type for a variety of purposes, e.g., to soothe the skin and/or reduce bacterial or ~ungal activity.
The substrate which is impregnated with the - cyclic ester monomer/catalyst mixture is a flexible web, sheet, tape, film, or the like 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.
Illustrative of suitable substrates one can mention 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 terephalate) fibers, polyacrylonitrile 1 ~ 2 S 5a 9 1o~829 fibers, nylon fibers and the like; fabrics andtextile products made from wool fibers, nylon fibers, poly(ethylene terephalate) fibers, polyacrylonitrile fibers and blends of two or more such fibers; glass fiber fabric; fabrics woven from elastomeric fibers, such as natural and synthetic rubbers, including butyl rubber, nitrile rubber, polybutadiene rubber, polyiso-butylene 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 inven-tion, the porous or permeable substrate is impregnated with a sufficient quantity of a mixture of cyclic ester monomer, catalyst and, if desired, vinylic polymer to completely permeate and wet the individual fibers or particles of the substrate. The impreg-nation 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 1 ~2'5 S~ 10,829 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 sub-strate material or by polymerizing the cyclic ester monomer impregnated in the substrate, as described herein, nd subsequently fusing two or more super-posed layers of material thus produced by the use ofheat and/or pressure. If desired, the cyclic ester monomer impregnated in the substrate can be polymer-ized 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 about 0C.
to 120C., and is preferably carried out at a temp-erature of from 25C. to 85C. 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, i ~ 2 S S ~ ~ 10,829 a 2-mils thick strip of cotton gauze bandage impreg-nated 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 50C. When a vinylic polymer is additionally present in the cyclic ester monomer mixture we have found that a somewhat higher temper-ature 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 gener-ally be achieved at temperatures below 85C. 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 treat-ment of the human and animal body for the maintenance of immobilization-and fixation following réduction of fractures and dislocations, the maintenance of approximation of bone fragements following reduction of fractures, the maintenance of fixation and immob-ilization to promote healing in instances of compound i~255~9 10,829 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 accelerate healing; as a support splint in paralysis or weakness of muscles; and as a means to maintain correction of deformities, either congen-ital 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 place 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, legs, and the like, the cast material can be preformed into a tubular shape or other preformed shape. The cast material can be heated by means of 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 1 ~ Z ~ Sl~9 10,829 successively wrapping it around the body part in anoverlapping manner. Heat applied before or after wrapping causes the overlapping 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 break-ing. When in tubular shape the oriented material canbe placed on a limb and heated, whereupon the material shrinks into place about the limb. Of course, care must be ~aken 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 1 ~Srj~ 10,829 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, bring-ing 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 substrate materials for impregnation by the cyclic ester monomer/catalyst mixture. The orthopedic cast material can also be bonded to a non-porous sheet or web of a polymeric material such as cellulose acetate, nylon, polyethelene terephthalate, thermoplastic polyurethane, acrylic polymers and the like.
The thickness of the orthopedic cast material is not narrowly critical. It can be from about 1 mil to about 500 mils thick. Those skilled ~ ~ 2 5 5 ~ ~ 1O~829 in medical arts will know the preferred thickness ofcast for treating various types of injuries and infirmities, and the desired thickness may be obtained in any of the ways disclosed 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 50C. to 90C. For example, poly(epsilon-caprolactone) melts at about 55C. to 65C. ~hen a vinylic polymer is dissolved or dispersed in the cyclic ester monomer/catalyst mixture the resulting polymer blend in the orthopedic cast material has a melting or softening point from 30C. to 70C. 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 further illustrate the invention and are not intended to limit the scope of the invention in any way.
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 25C.

1 ~ 2 5'S~ ~ 10,829 Example 1 Two-inch wide cotton gauze bandage was placed in an oven at 50C. to dry any moisture which it may have contained. Into a 4-oz. 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 epsilon-caprolactone 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 50C. for three minutes. When cooled, the impregnated gauze composite became solid and non-tacky, and was suitable for use as an ortho-pedic cast material. At this thickness, the ortho-pedic cast material was bendablea although not soft,thus it could be wrapped around an appendage 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 S~ o,829 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 65C., 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 epsilon-caprolactone 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 50C., to form 2-mils thick wet composites. These strips were placed in an oven at 80c. for 10 minutes. When cooled, the strips became hard and non-tacky in a manner similar to the orthopedic cast material ~S 5~3 10,829 produced in Example 1.
Example 4 To each of three open-top, 8-~unce bottles, which had been dried in an oven at 50C. 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 methacrylate 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%
glycidyl methacrylate, and having a viscosity of 11 cps.

Vinyl polymer C-- A terpolymer of 91:3:6 parts, respectively, of vinyl chloride, vinyL acetate and vinyl alcohol having a viscosity 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 epsilon-caprolactone. To each of three 2-ounce bottles, which had been dried in an oven at 50C., 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 a 4-mils thick wet composite.

l~'SS~ o, 829 The wet composite containing vinyl polymer A was placed in an oven at 50C. and had not polymer-ized 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 80C. It polymerized in 7 minutes to form a material which was hard and non-tacky at room temperature, and which was suitable as an orthopedic cast material. The wet composite containing vinyl polymer B polymerized sufficiently in 5 minutes at 50C. to form a suitable material for use as an orthopedic cast and the wet composite containing vinyl polymer C polymerized sufficiently in 3 minutes at 50C. 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 the break. The wrapped pencil was placed in an oven at 50C. 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.

1 1 2 S Si~ 9 10,829 EgAMPLE 5 To a 4-ounce bottle there were charged 85 parts of epsilon-caprolactone and 15 parts of polystyrene having a wt. a~. molecular weight o~
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 catalyst was stirred into the sol-ution for about 1 minute with a high speed stirrerunder 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 60C., however, similarly prepared composites cured to a solid, non-tacky state after 5 minutes in an oven at 75C. The cured material was suitable for use as an orthopedic cast material. Pot life of the soLution containing the catalyst, determined as the time required for the solution to gel at room te~yerature, was 1-2 minutes in one instance and 3 minutes in another instance.

Wet composites were produced in a manner 11 ~5 ~ )~ 10,829 similar to that of Example 5 substituting for polystyrene, poly(vinyl acetate) having a No. 4 Ford cup viscosity of 14-16 seconds (45% solids in acetone at 25C.). The wet composites cured to a solid, non-tacky state after 5 minutes in an oven at 75C. 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.

Claims (13)

10,829 WHAT IS CLAIMED IS:

1. A method of making an orthopedic cast forming material which comprises the steps of:
(a) impregnating a porous or permeable substrate with a mixture comprising:
i) as the major portion thereof, a cyclic ester monomer of the formula wherein each R, individually, is selected from the class consisting of hydrogen, alkyl having up to 12 carbon atoms, alkoxy having up to 12 carbon atoms, and halo; A is the oxy group;
x is an integer from 1 to 4; y is an integer from 1 to 4; z is an integer from 0 to 1; x+y+z is from 4 to 7 and 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 per cent of a vinylic polymer having a wt. av.

10,829 molecular weight of from 5,000 to 600,000;
and then (b) polymerizing the cyclic ester monomer.

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 said mixture.

3. A method as claimed in claim 1, wherein said cyclic ester monomer is epsilon-caprolactone.

4. A method as claimed in claim 1, wherein the cyclic ester monomer in said mixture is polymerized at a temperature of from 0°C. to 120°C.

5. A method as claimed in claim 1, wherein the said cyclic ester monomer in said mixture is polymerized at a temperature of from 25°C. to 85°C.

6. A method as claimed in claim 1, wherein said vinylic polymer has a wt. av. molecular weight of from 10,000 to 400,000.

7. A method as claimed in claim 1, wherein said vinylic polymer has a wt. av. molecular weight of from 10,000 to 300,000.

8. A method as claimed in claim 1, wherein there is from 0 to 30 weight per cent of said vinylic polymer in said mixture.

9. A method as claimed in claim 1, wherein said vinylic polymer is a copolymer of vinyl chloride and hydroxypropyl methacrylate.

10,829

10. A method as claimed in claim 1, wherein said vinylic polymer is a copolymer of vinyl chloride and glycidyl methacrylate.

11. A method as claimed in claim 1, wherein said vinylic polymer is a terpolymer of vinyl chloride, vinyl acetate and vinyl alcohol.

12. A method as claimed in claim 1, wherein said vinylic polymer is polystyrene.

13. A method as claimed in claim 1, wherein said vinylic polymer is poly(vinyl acetate).