Polyurethane casting material

An improved polyurethane orthopaedic cast bandage is disclosed. The bandage is a polyurethane prepolymer coated on an open-weave, fibrous substrate. The prepolymer contains dimorpholinodiethylether as a catalyst which gives the cast bandage increased shelf stability and excellent set time.

FIELD OF THE INVENTION 
The present invention relates to an improved polyurethane orthopaedic 
casting bandage which is used to form orthopaedic casts. 
BACKGROUND OF THE INVENTION 
Plaster of Paris casts have been used to immobilize body members for some 
time. These bandages are made by depositing plaster of Paris on a 
reinforcing scrim material such as gauze. When the plaster of Paris is 
dipped in water, the alphahemihydrate of calcium sulfate is converted to 
calcium sulfate dihydrate, which results in the hardening of the cast. 
Plaster of Paris casts, however, suffer from a number of disadvantages. 
X-ray transmission through the cast to determine whether a fracture has 
been properly set is extremely difficult. In addition, the cast is quite 
heavy and restricts the mobility of the patient wearing the cast. The 
casts are also very sensitive to water and may seriously lose their 
load-bearing capability if they become wet. In addition, the air 
permeability of the plaster of Paris cast is very limited, and, as a 
result, they do not allow evaporation of moisture from the skin beneath 
the cast, which may result in skin irritation beneath the cast. 
In order to overcome the disadvantages of plaster of Paris casts, numerous 
attempts have been made to develop plastic or plastic-reinforced materials 
as a replacement for plaster of Paris. 
U.S. Pat. Nos. 3,241,501 and 3,881,473 disclose casts which are made with a 
flexible fabric impregnated with a polymer which is capable of being cured 
by ultraviolet light. Although this casting material overcomes some of the 
disadvantages of plaster of Paris cast material, it requires a different 
technique in its application and also requires the use of an ultraviolet 
light source in order to cure the cast. These casts also require 
significantly longer times for the cast to set before they will be load 
bearing. 
More recent attempts to produce substitutes for plaster of Paris include 
the polyurethane polymers disclosed in German Offenlegenschrift Nos. 
2353212 and 2357931, U.K. Pat. No. 1,578,895, and PCT Application No. 
W081/00671. These bandages are open-weave fabrics coated with polyurethane 
prepolymers, that is, reaction products of isocyanates and polyols. The 
bandages are dipped into water in the same manner as the plaster of Paris 
and then applied to the limb of a patient. The water causes the prepolymer 
to polymerize and form a rigid polymer structure. In order to obtain the 
desired rapid hardening or setting of the bandage, it is necessary to have 
a catalyst system incorporated in the prepolymer formulation. The casting 
material disclosed in U.K. Pat. No. 1,578,895 employs amino polyols as 
catalysts and as the polyol components. The casting material disclosed in 
W081/00671 employs dimethylethanolamine (DMEA) or a mixture of DMEA and 
bis(2-dimethylaminoethyl) ether. These catalyst systems provide acceptable 
hardening of the prepolymers by catalyzing the water-isocyanate reaction. 
However, the presence of these catalysts in the prepolymer system also 
causes side reactions which gel the prepolymer in the bandage package. 
These side reactions are generally branching reactions resulting in biuret 
and allophanate formation and some formation of isocyanate trimer. The 
gelatin caused by the side reactions causes premature hardening or setting 
of the bandage in the package and, therefore, poor shelf life or shelf 
stability. The lack of adequate shelf stability can cause numerous 
difficulties in attempting to form a cast from such cast bandages. In 
order for the bandages to have an acceptable set time, it is necessary to 
adjust the polyurethane prepolymer components to the extent that the 
reaction with water is such that the set time of the finished bandage is 
satisfactory. The set time is the time after the bandage is dipped in 
water to the point where the cast made from the bandage is rigid and the 
limb of the patient is immobilized. In order to obtain acceptable set 
times, the polyurethane prepolymer bandages of prior art products had a 
limited shelf life, i.e., less than 12 months, which is not practical 
commercially. 
Although there are numerous catalysts available to catalyze the 
water-isocyanate reaction of the prepolymer, these catalysts are not 
necessarily suitable for use in a cast bandage, as these catalysts do not 
provide adequate shelf life for the cast bandage. The particular catalyst 
employed in the present invention has previously been employed in the 
formation of polyurethane foams (see U.S. Pat. No. 3,645,925) and reaction 
injection molding elastomers (see U.S. Pat. No. 4,273,885). 
SUMMARY OF THE INVENTION 
The present invention relates to a polyurethane cast material which 
comprises a fibrous substrate coated with a polyurethane prepolymer which 
contains a dimorpholinodiethylether catalyst. The use of 
dimorpholinodiethylether as a catalyst avoids the problems of storage 
stability common with other catalyst systems. The cast material is very 
stable, having an extremely long shelf life, and yet it will set after 
being applied to the patient within 10 minutes. The 
dimorpholinodiethylether catalyst used in the present invention catalyzes 
the formation of the side reactions at a much lower rate than the catalyst 
previously used. 
DETAILED DESCRIPTION OF THE INVENTION 
Isocyanates 
The aromatic isocyanates useful in the prepolymer system of the present 
invention may be any of the aromatic polyisocyanates known in polyurethane 
chemistry which are described, for example, in "Polyurethanes, Chemistry 
and Technology," Part I, Interscience Publishers (1962). 
The aromatic polyisocyanates preferred include tolylene diisocyanate (TDI), 
such as the 80/20 or the 65/35 isomer mixture of the 2,4 and 2,6 isomeric 
forms; diphenylmethane diisocyanate (MDI), such as the 4,4', the 2,4' and 
the 2,2' isomeric forms or isomeric mixtures thereof; modified MDI 
containing additional functional groups such as carbodiimide groups, 
urethane groups and allophanate groups and polymethylene 
polyphenylisocyanates (Polymeric MDI) which are derived from phosgenation 
of the condensation products of aniline and formaldehyde. Most preferred 
polyisocyanate is the carbodiimide containing MDI which is readily 
available commercially, e.g., Isonate.RTM.143L and Rubinate.RTM.XI-168. 
Polyols 
The polyols useful in the prepolymer system of the present invention 
include polyether polyols and polyester polyols. The polyether polyols may 
be prepared by the polymerization of epoxides, such as ethylene oxide, 
propylene oxide, butylene oxide, tetrahydrofuran, styrene oxide, or 
mixtures thereof in the presence of the catalysts. The polyester polyols 
include the reaction products of polyhydric alcohols and polybasic 
carboxylic acids. Instead of free carboxylic acids, the corresponding 
polycarboxylic acid anhydrides or the corresponding polycarboxylic acid 
esters of low alcohols or mixtures thereof may be used for preparing the 
polyesters. Polyesters of lactones, such as .epsilon.-caprolactone may 
also be used. 
Most preferred polyols are the poly(oxypropylene) diols and triols, having 
a molecular weight of from 400 to 2,000. Examples of polyols are 
Pluracol.RTM.P1010 and Poly G.RTM.36-232. 
The preferred polyurethane prepolymer is made from 
diphenylmethanediisocyanate containing carbodiimide groups. These 
diisocyanates are reacted with a polyol containing two to three functional 
groups. The polyols may be diols or triols or mixtures of diols and 
triols. The preferred polyols are poly(oxypropylene)glycol having a 
hydroxyl number of 105 and poly(oxypropylene) triol having a hydroxyl 
number of 232. The molecular weight of the polyols is usually below 2,000, 
preferably in the range of 700 to 1,500, and most preferably between 700 
and 1,100. 
The ratio of the polyisocyanate to the polyol in the prepolymer reaction 
mixture is best expressed by the equivalent ratio. Equivalent weight is 
determined by dividing the molecular weight of each particular component 
by its functionality or number of functional groups in the compound. The 
equivalent ratio is the ratio of the equivalency of the isocyanate to the 
polyol. The equivalent ratio in the present system should be between 2:1 
to approximately 15:1 equivalents of the polyisocyanate to the polyol and 
preferably from 2:1 to 10:1. These components are combined so that there 
is an excess of from 5% to 30% NCO groups in the prepolymer. The 
prepolymer also contains from 0.1% to 10% by weight based on the weight of 
the total mixture of the dimorpholinodiethylether catalyst having the 
following structure: 
##STR1## 
The preferredd amount of catalyst is from 1% to 4% based on the weight of 
total mixture. Above 5% by weight of catalyst, the shelf life of the cast 
bandage begins to be reduced. 
It is also possible to use a small amount of a co-catalyst with the 
dimorpholinodiethylether catalyst. Such co-catalyst may be a commonly used 
urethane catalyst such as a tertiary amine or a metal catalyst. 
In addition to the polyisocyanate, the polyol and the catalyst, the 
prepolymer reactants may also include a small amount, 0.01% to 1% by 
weight, of a stabilizer such as benzoyl chloride and a surfactant agent 
such as a silicone liquid used as an antifoam agent. The surfactant or 
antifoam agent would be present in an amount of from 0.01% to 1% by 
weight. 
The prepolymer is reacted under the following conditions: 
A reaction vessel is placed under a vacuum, and the isocyanate component is 
added to the vessel. The vacuum is released, nitrogen is added to the 
vessel, and the antifoam agent is added to the isocyanate component. 
Benzoyl chloride is added to the vessel and mixed thoroughly with the 
reactants. Vacuum dried polyols containing the catalyst are then added to 
the reaction vessel over a period of from 20 to 25 minutes. The reaction 
temperature is maintained between 50.degree. C. and 60.degree. C. for one 
hour. The completion of the reaction can be determined by obtaining a 
sample of the reaction product and testing for the desired level of NCO in 
the prepolymer. 
The prepolymer is then applied in a dry atmosphere to a substrate by 
reverse roll coating or other coating technique to form the cast bandage. 
The substrate may be a knitted or woven fabric having a weight of from 50 
to 350 grams per square meter and preferably between 70 and 290 grams per 
square meter. The fibers in the fabric may be synthetic fibers such as 
polyester, or natural fibers such as cotton or may be fiberglass. Suitable 
fabrics for the substrate include those disclosed in U.S. Pat. Nos. 
3,882,857; 3,787,272 and 4,134,397. The weight of prepolymer on the fabric 
is from about 85 to 200 grams per square meter, preferably between 100-150 
grams per square meter. Immediately after the prepolymer is applied to the 
fabric, the coated fabric is packaged in an inert atmosphere to prevent 
any contact with atmospheric moisture. 
When the bandage is to be used, it is removed from the package and placed 
in water for from 3 seconds to 30 seconds, but preferably between 5 and 10 
seconds. It is removed from the water and applied to the patient, usually 
over a tubular, knitted fabric and a cast padding. The bandage will set 
within less than 10 minutes to a condition where it is capable of 
immobilizing the fracture. 
In the following Examples, the "Gel Time" of the polymer was determined by 
placing 25 ml. of the prepolymer in a 50 ml. tube. The tube is placed in 
an oven at 70.degree. C. The tubes are removed from the oven at designated 
times, and the surface of the prepolymer in the tube is probed with a 
glass rod. The Gel Time is the time when the surface of the prepolymer is 
hard and the rod will not enter or move the prepolymer. The Gel Time has 
been found to be an excellent accelerated aging test useful in predicting 
the shelf stability of the cast bandages when the bandages are stored at 
room temperature. Generally, a Gel Time of 10 days at 70.degree. C. would 
indicate shelf stability of approximately 9 months at 23.degree. C. For 
example, a Gel Time of 30 days would indicate a shelf stability in excess 
of 24 months at 23.degree. C. 
The set time or setting time of the cast in a laboratory is determined by 
dipping the cast bandage in water at 75.degree. F. and squeezing the 
bandage four or five times under the surface of the water. A test cylinder 
is formed by wrapping a layer of the bandage on a 23/4 inch wooden dowel. 
The test cylinder is immediately removed from the dowel. The set time is 
determined by attempting to indent the test cylinder by fingernail 
pressure. When the bandage or test cylinder cannot be indented, the set 
time is recorded.

EXAMPLE I 
A series of prepolymers were prepared with the catalysts indicated in Table 
I. Each of the prepolymers were prepared from a 
diphenylmethanediisocyanate containing carbodiimide groups and mixed 
polyols. The mixed polyols were polyether polyols comprised of 60% by 
weight of a diol having a molecular weight of approximately 1010 and 40% 
by weight of a triol having a molecular weight of approximately 730. The 
prepolymer also contained 0.05% benzyol chloride and 0.075% of a silicone 
surfactant. The diisocyanate and the polyols were reacted in a ratio of 4 
to 1, at a temperature of 50.degree.-60.degree. C. The Gel Time of the 
prepolymer and the set time of a cast made with the prepolymer coated on a 
polyester/cotton substrate are shown in Table I. 
TABLE I 
______________________________________ 
Catalyst Gel Set Time 
Catalyst Conc. Time (Min.) 
______________________________________ 
1. bis(2-dimethylaminoethyl) 
0.3 11 5.0 
ether 
2. triethylenediamine (DABCO) 
0.3 5 6.2 
3. cyclohexylamine (Polycat 9) 
0.4 4 10+ 
4. cyclohexylamine (Polycat 70) 
0.4 6 9.0 
5. cyclohexylamine (Polycat 77) 
0.5 3 10+ 
6. dimethylethanolamine 
1.0 1 4.0 
7. substituted morpholine 
1.0 2 6.5 
8. dimethylpiperazine 0.3 16 14+ 
9. dimethylaminoethyl-3-dimethyl 
1.0 4 15+ 
aminopropylether 
10. dimorpholinoethane 2.0 21 15+ 
11. tetraethylethyleneamine 
0.3 3 slow 
12. DABCO & dimethyl- 0.3 5 slow 
ethanolamine 
13. imidazole 2.0 11 15+ 
14. triethanolamine 0.3 8 no set 
15. 1,3 bis(dimethylamino) 
0.3 7 very slow 
2-propanol 
16. dimethylaminoethoxy- 
1.0 3 4.7 
ethanol 
17. dimorpholinodiethylether 
1.0 34+ 6.0 
18. dimorpholinodiethylether 
2.0 31 4.5 
19. dimorpholinodiethylether 
3.0 28 4.0 
______________________________________ 
It is evident from the results shown in Table I that the 
dimorpholinodiethylether catalyst provides the long Gel Times and the 
short set times that are desirable and required for a polyurethane cast 
bandage. 
EXAMPLE II 
To a 5 liter resin flask equipped with a thermometer, a stirrer, a nitrogen 
inlet and a drying tube, 3007 grams of Isonate.RTM.143L (modified 
diphenylmethane diisocyanate) was charged. Then, 3.62 grams of Dow Corning 
DC-200 (30,000 cs.) and 2.41 grams of benzoyl chloride were added. The 
charge was stirred for 15 minutes to mix thoroughly. To this, 1828 grams 
of Pluracol.RTM.P1010 (60% by weight) and Poly G.RTM.36-232 (40% by 
weight), to which was added 85 grams of dimorpholinodiethylether, was 
added while stirring. The polyols were dried prior to mixing with the 
catalyst. The equivalent ratio of NCO to OH was 4.18:1. The addition of 
the polyols was made through a dropping funnel in 20-25 minutes. After the 
addition was completed, the polymerization was carried out at 
50.degree.-60.degree. C. for one hour. The NCO content of the prepolymer 
obtained was about 13.9%. The Gel Time of the prepolymer at 70.degree. C. 
was 33 days. The set time of the bandage made with this prepolymer on 
polyester/cotton fabric was about 4.7 minutes. 
EXAMPLE III 
To a 1 liter reaction kettle equipped with a thermometer, a stirrer, a 
nitrogen inlet and a drying tube, 665 grams of Papi.RTM.27 (polymeric 
diphenylmethanediisocyanate) was charged. Then, 0.76 grams of Dow Corning 
DC-200 (30,000 cs.) and 0.51 grams of benzoyl chloride were added. The 
charge was stirred for 15 minutes to mix thoroughly. To this, 347 grams of 
the blend of the 208 grams of Pluracol.RTM.P1010, 139 grams of 
Pluracol.RTM.GP 730 and 17.7 grams of dimorpholinodiethylether was added 
while stirring. The polyols were dried prior to mixing with the catalyst. 
The equivalent ratio of NCO to OH was 5.0:1.0. After the addition of the 
blend, the polymerization was carried out at 50.degree.-60.degree. C. for 
one hour. The NCO content of the prepolymer obtained was 15.12%. The Gel 
Time of the prepolymer at 70.degree. C. was about 35 days. The set time of 
the bandage made with this prepolymer on polyester/cotton fabric was about 
4.8 minutes. 
EXAMPLE IV 
To a 1 liter reaction kettle equipped with a thermometer, a stirrer, a 
nitrogen inlet and a drying tube, 522 grams of molten Isonate.RTM.125M 
(pure diphenylmethanediisocyanate) was charged. Then, 0.65 grams of Dow 
Corning DC-200 (30,000 cs.) and 0.44 grams of benzoyl chloride were added. 
The charge was stirred for 15 minutes to mix thoroughly. To this, 347 
grams of the blend of 208 grams of Pluracol.RTM.P1010, 139 grams of Poly 
G.RTM.36-232 and 15.2 grams of dimorpholinodiethylether were added while 
stirring. The polyols were dried prior to mixing with the catalyst. The 
equivalent ratio of NCO to OH was 4.17:1. After the addition of the blend, 
the polymerization was carried out at 50.degree.-60.degree. C. for one 
hour. The NCO content of the prepolymer obtained was 14.42%. The 
prepolymer gelled in 32 days at 70.degree. C. The set time of the bandage 
made with this prepolymer on polyester/cotton fabric was about 5.0 
minutes.