Bismuth catalyst system for preparing polyurethane elastomers

Processes are provided for preparing polyurethane elastomers by reacting a polyether or polyester polyol with a polyisocyanate in the presence of a catalytic amount of a bismuth salt of a carboxylic acid having from 2 to 20 carbon atoms. The catalysts of these processes are relatively non-toxic, yet they promote rapid polymerization for a wide variety of polyurethane elastomeric applications.

BACKGROUND OF INVENTION 
Urethane polymers or polyurethanes are a large family of polymers with 
widely varying properties and uses, all based on the reaction product of 
an organic isocyanate with compounds containing a hydroxyl group. 
Polyurethane polymers are generally classified into two broad categories: 
A. foam or urethane foam, and B. elastomers or polyurethane elastomers. 
Polyurethane foams are polyurethane polymers produced by the reaction of 
polyisocyanates with an hydroxyl group from a polyol and a polymerization 
catalyst, in the presence of water and/or an auxiliary blowing agent, such 
as monofluorotrichloromethane, which allows the polymeric mass to expand 
into a cellular mass upon reaction. In preparing a polyurethane elastomer, 
no blowing agent or mechanism for producing gas which would lead to cell 
development is present. Therefore, the polymer is produced by the reaction 
of the isocyanate with a hydroxyl group to form urethane linkages in the 
presence of a polymerization catalyst. 
Polyurethane elastomers have been widely used in a variety of applications. 
They have been used as protective coatings, in the insulation of 
electrical elements, as caulks, sealants, gaskets, etc. Because of 
favorable rheology of an elastomer formulation, they can be used to cast 
intricate forms such as found in the toy industry. They have also been 
widely used in the preparation of sporting goods, fabric coatings and shoe 
soles wherein the cured urethane elastomer comes in repeated intimate 
contact with human beings. The prior art catalysts used to prepare 
elastomers frequently contained toxic mercury and lead compounds and the 
toxicity was carried over into the cured elastomer. If less toxic 
organotin compounds are employed as catalysts, elastomers having physical 
properties less than optimum are obtained. 
There are several patents relating to various catalysts for reacting 
isocyanates with polyether polyols. U.S. Pat. No. 3,245,957 to Henderman 
et al describes a process for reacting an isocyanate with an active 
hydrogen compound in the presence of an antimony containing catalyst. 
U.S. Pat. No. 3,203,932 to Frisch et al relates to a process for preparing 
urethane-urea elastomers using metal organic catalysts such as lead, 
cobalt and zinc napthenates. 
U.S. Pat. No. 4,468,478 to Dexheimer et al discloses polyurethanes prepared 
from polyoxyalkylenes containing alkali metal or alkaline earth metal 
catalyst residues chelated with benzoic acid derivatives. 
U.S. Pat. No. 3,714,077 to Cobbledick et al relates to a urethane foam 
catalyst system consisting of a combination of polyol-soluble organic 
stannous compounds with polyol-soluble organic bismuth and or antimony 
compounds with certain sterically hindered tertiary amines. 
BRIEF DESCRIPTION OF THE INVENTION 
The instant invention relates to a process for preparation of polyurethane 
elastomers by reacting polyether or polyester polyols having molecular 
weights of between 1000 and 10,000, possibly in conjunction with smaller 
percentage of lower molecular weight glycols, which provides for a balance 
of physical properties required, with an organic polyisocyanate, wherein 
the ratio of NCO groups to hydroyl groups is from 0.70 to 1 to 1.35 to 1, 
in the presence of a catalytic amount of a bismuth salt of a carboxylic 
acid having from 2 to 20 about carbon atoms in the molecule. The catalyst 
is present as about 0.01 to 1.5 weight percent based on the weight of the 
reactants. 
Polyurethane elastomer can be prepared utilizing three methods: 1. Full 
Isocyanate Prepolymer, 2. Quasi-Prepolymer; and 3. One-Shot Method. 
In the Isocyanate Prepolymer Method: The isocyanate is reacted with high 
molecular weight polyol producing an NCO terminated prepolymer. At the 
time of use, a chain extender (if used) and catalyst is added by the 
processor. 
Quasi-Prepolymer Method--Part of the high molecular weight polyol is 
reacted with an isocyanate. The processor blends the remaining polyol, 
chain extender (if used) and catalyst together with the quasi-prepolymer 
prior to elastomer manufacture. 
One-Shot Method--The isocyanate stands alone. The polyol chain extender (if 
used) and catalyst are mixed and added to the isocyanate by the processor. 
DETAILED DESCRIPTION OF THE INVENTION 
The catalysts of the instant invention are prepared by reacting a bismuth 
salt with a carboxylic acid having 2 to 20 carbon atoms in the molecule, 
preferably 8 to 12 carbon atoms in the molecule. More specifically, 
bismuth tris(neodecanoate) has been determined to be a particularly 
effective catalyst for two component urethane elastomer systems. The 
useful carboxylic acids are represented by the formula RCOOH wherein R is 
a hydrocarbon radical containing 1 to about 19 carbon atoms. R can be 
alkyl, cycloalkyl aryl, alkaryl such as methyl, ethyl, propyl, isopropyl, 
neopentyl, octyl, neononyl, cyclohexyl, phenyl, tolyl or napthyl. 
The primary use of the catalyst is to accelerate the reaction between the 
isocyanate and the hydroxyl groups. The catalyst can be employed in a wide 
range of elastomer formulation systems where reduced catalyst toxicity is 
desirable. The catalyst provides an alternative to the use of catalysts 
based on lead, tin or mercury. 
Catalysts in use prior to this invention all had the capability of 
promoting reaction between a hydroxyl group and isocyanates to produce 
urethane linkages and, ultimately, polyurethane products. The major 
disadvantage of organomercury based catalysts is that, as supplied, they 
must be handled with extreme caution due to their classification as 
poisons and the shipping containers must be managed under the Resources 
Conservation and Recovery Act as hazardous waste. Organolead catalysts 
must also be handled with a great deal of caution due to their toxicity 
classification as a hazardous substance under the Resources Conservation 
and Recovery Act. Primarily due to these questions of toxicity and 
handling, the use of organotin catalysts in non-cellular urethane systems 
has occurred. As a class, organotin compounds do not provide the same type 
of catalytic performance as organomercury and organolead compounds, since 
organotin compounds also promote the reaction between moisture and 
isocyanates in addition to the hydroxyl group-isocyanate reaction. The 
non-specific nature of the tin catalysts makes their use difficult, with 
the processor required to go to extreme measures to reduce the presence of 
moisture in order to eliminate bubbling or pinhole formation in the 
elastomers obtained. 
In addition, when using catalysts based on mercury, lead or tin, monitoring 
of the work place environment must be done in order to ascertain ambient 
air quality compliance with Occupational Safety and Health Administration 
Standards ("OSHA"). 
The catalyst of this invention provides optimum performance based on 
tailored gel times, rapid release or demold times and will not contribute 
to embrittlement of the cured elastomer. The catalyst of the instant 
invention, as a polymerization catalyst, has minimal effect on the 
water/isocyanate reaction with moisture levels normally found in a 
wet/undried formulated urethane system. Most importantly, the catalyst has 
an excellent acute toxicity profile. No occupational exposure limit 
standard must be met when using the catalyst. 
In contrast to the organomercury compounds, the lead salts of organic acids 
and organotin compound catalysts of the instant invention have the 
following toxicity profile: 
Oral LD.sub.50 : 3 Grams/Kilogram 
Dermal LD.sub.50 : 2 Grams/Kilogram 
Inhalation LC.sub.50 : 3 Milligrams/Liter 
It is apparent, therefore, that, when contrasting these toxicity indicators 
with organomercury compounds and lead salts of organic acids, the bismuth 
compounds of this invention are orders of magnitude less toxic. The 
toxicity profiles of organotin based chemicals are somewhat poorer, but 
within the same order of magnitude as the compounds of this invention, but 
when considering their limitations based on moisture sensitivity and OSHA 
monitoring requirements, the safety and ease of use of the compounds of 
this invention are evident. 
The primary hydroxy containing reactants used in the preparation of the 
polyurethane elastomers of the present invention are primary and secondary 
hydroxy terminated polyalkylene ethers and polyesters having from 2 to 4 
hydroxyl groups and a molecular weight of from about 1000 to 10,000. They 
are liquids or are capable of being liquified or melted for handling. 
Examples of polyalkylene polyols include linear and branched polyethers 
having a plurality of ether linkages and containing at least 2 hydroxyl 
groups and being substantially free from functional groups other than 
hydroxyl groups. Typical examples of the polyalkylene polyols which are 
useful in the practice of the invention are the polyethylene glycols, 
polypropylene glycols and polybutylene ether glycols. Linear and branch 
copolyethers of ethylene oxide and propylene oxide are also useful in 
preparing the elastomers of this invention. Those having molecular weights 
of from 2000 to 5000 are preferred. Polyethers having a branch chain 
network are also useful. Such branch chain polyethers are readily prepared 
from alkylene oxides and initiators having a functionality greater than 2. 
Any organic di or tri isocyanate can be used in the practice of the present 
invention. Diisocyanates are preferred. Examples of suitable organic 
polyisocyanates are the trimethylene diisocyanate, tetramethylene 
diisocyanate, pentamethylene diisocyanate and hexamethylene diisocyanate. 
Examples of aromatic diisocyanates include 2,4 tolylene diisocyanate, and 
2,6 tolylene diisocyanate. In addition, methylene diphenyldiisocyanates 
and polymeric isocyanates based on methylene diphenyldiisocyanates can be 
employed. 
The amount of polyisocyanate employed ranges from about 0.7 to 1.3 mole of 
NCO in the polyisocyanate per mole of active hydrogen in the polyols. 
In certain instances it may be desirable to add a chain extender to 
complete the formulation of polyurethane polymers by reacting isocyanate 
groups of adducts or prepolymers. Examples of some types of polyol chain 
extenders include 1,4 butanediol, diethylene glycol, trimethylol propane 
and hydroquinone di(beta hydroxyethyl ether). 
The chain extender when present is added as 1 to 20 weight percent, 
preferably 3 to 6 weight percent based on the weight of the reactants. The 
invention is illustrated by the following specific but nonlimiting 
examples.

Example I is a description of the preparation of bismuth salts of the 
instant invention. 
EXAMPLE I 
A typical laboratory preparation of a Bismuth Salt of an Organic Acid is as 
follows: 
0.215 moles of purified Bismuth Trioxide, and 1.3 moles of an organic acid 
were charged to a 500 ml. three neck flask equipped with agitator, 
condenser, and thermometer. These materials were reacted at 90-100 Degrees 
Centigrade for seven hours, at which time the reactants were heated to 124 
Degrees Centigrade under vacuum to remove water of reaction. 
The resulting product was vacuum filtered at 90 Degrees Centigrade with the 
use of a filter-aid. The finished product weighed 196 grams for a yield of 
74.7%. It was assayed at 17.1% Bismuth, had a Gardner Viscosity of V and a 
Gardner Color of 4. 
Typical acids employed singly or in combination were Acetic, Propionic, 
2-Ethyl Hexanoic and Isononanoic at mole ratios equivalent to 
approximately 6 moles of acid to mole of 1 Bismuth. 
EXAMPLE II 
A series of runs were completed to determine gel time and hardness of 
elastomers prepared with catalysts of this instant invention. In each of 
the runs, 91 grams of polyol and 0.5 grams of catalyst were weighed into a 
container. The components were mixed in a Hamilton Beach Mixer until a 
temperature of 100 Degrees F. was reached. At that time, 9 grams of a 
commercially available TDI based isocyanate was added and the time for the 
liquid composition to be converted into a gel was recorded. The hardness 
of the vulcanizates was determined following a 72 hour room temperature 
post-cure. 
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CATALYST ORGANIC ACID GEL SHORE 
% ON BISMUTH 
UTILIZATION BASED 
TIME A 
COMPOSITION 
CONTENT 
ON 1 M BISMUTH 
SECONDS 
DUROMETER 
__________________________________________________________________________ 
0.50 16.3% 6 m Neodecanoic Acid 
7 73 
0.50 16.4% 1 m 2-Ethyl Hexanoic Acid 
12 68 
5 m Neodecanoic Acid 
0.50 17.2% 3 m 2-Ethyl Hexanoic Acid 
35 65 
3 m Propionic Acid 
0.50 17.2% 3 m 2-Ethyl Hexanoic Acid 
33 65 
3 m Neodecanoic Acid 
0.50 19.2% 6 m 2-Ethyl Hexanoic Acid 
35 65 
0.50 24.0% 3 m 2-Ethyl Hexanoic Acid 
77 48 
0.50 28.9% 3 m Neodecanoic Acid 
26 60 
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The Shore A value is a standard Durometer test under ASTM Method D676. An 
instrument (Shore A Durometer) is used to determine hardness of an 
elastomer by measuring penetration (or resistance to penetration) of a 
point pressed on the surface. The instrument has hardness scales ranging 
from 0 (very soft) to 100 (very hard). 
The above data show clearly that the products of this invention provide 
cures for room temperature cured polyurethane systems which are in large 
part independent of the bismuth concentration. 
EXAMPLE III 
Another procedure used to evaluate the performance of listed polyurethane 
catalysts in cast elastomers is as follows: 
Liquid prepolymers were heated to 60 Degrees Centigrade to obtain flow 
viscosity. Higher temperatures were required to melt solid prepolymers. 
The chain extender, 1-4 butanediol, was warmed slightly to facilitate 
mixing. The chain extender, catalyst and prepolymer were thoroughly mixed 
together by hand for sixty seconds. Castings were press cured for twenty 
minutes at 250 Degrees Fahrenheit followed by post-cure for sixteen hours 
at 180 Degrees Fahrenheit. Vulcanizates were allowed to equilibrate at 
room temperature for twenty-four hours minimum before testing. 
Dumbells were cut from the slabs, and Shore A Durometers were determined. 
Dumbells were elongated on the Dillon Testing Machine at 2.11 
inches/minute to determine tensile and elongation. 
__________________________________________________________________________ 
% ON lb./in.sup.2 
percentage 
CATALYST PREPOLYMER 
SHORE A 
TENSILE 
ELONGATION 
__________________________________________________________________________ 
COMMERCIAL PREPOLYMER A/100 TS 
CHAIN EXTENDER 1-4 BUTANEDIOL/6.8 TS 
dibutyltin dilaurate 
0.025 85 877* 840* 
bismuth tris 
0.025 81 2150* 840* 
(neodecanoate) 
Phenyl Mercury 
0.10 84 1870* 840* 
Carboxylate 
COMMERCIAL PREPOLYMER B/100 TS 
CHAIN EXTENDER 1-4 BUTANEDIOL/6.3 TS 
dibutyltin dilaurate 
0.025 81 730* 800* 
bismuth tris 
0.10 83 730* 800* 
(neodecanoate) 
Phenyl Mercury 
0.10 82 835* 800* 
Carboxylate 
COMMERCIAL PREPOLYMER C/100 TS 
CHAIN EXTENDER 1-4 BUTANEDIOL/6.7 TS 
dibutyltin dilaurate 
0.05 84 1570* 840* 
bismuth tris 
0.10 80 1550* 840* 
(neodecanoate) 
Phenyl Mercury 
0.10 82 2100* 840* 
Carboxylate 
__________________________________________________________________________ 
*Specimen Unbroken 
It is apparent from the data that the catalysts of the instant invention 
compare favorably with dibutyltin dilaurate and phenyl mercury carboxylate 
in preparing polyurethane elastomers. 
EXAMPLE IV 
A series of runs were conducted to characterize the viscosity build of an 
MDI based polyurethane composition as influenced by various catalysts, 
including bismuth, mercury, tin and lead compounds. 
The formulation consisted of a commercial high molecular weight polyol (249 
grams), chain extender 1, 4 butanediol (39 grams) and catalyst as 
required. The polyol blend (72.0 grams) was mixed with MDI (33.75 grams). 
Cures were conducted at 25 Degrees Centigrade. 
After the polyols and isocyanates were mixed together, the viscosities were 
measured continuously through gellation. Viscosities were determined by a 
Brookfield Viscosimeter, Model RV, Number 6 Spindle, at 1 RPM. 
______________________________________ 
MDI SYSTEM 
PHENYL 
ELAPSED MERCURY 
TIME/ CARBOXY- 
SECONDS LATE BISMUTH ORGANOTIN LEAD 
______________________________________ 
0 5000 5000 5000 5000 
60 5000 5000 5000 5000 
180 5000 5000 5000 5000 
250 5000 5000 20,000 500,000 
300 5000 5000 500,000 500,000 
360 5000 5000 500,000 500,000 
420 5000 5000 
600 5000 500,000 
750 500,000 
______________________________________ 
These data show that the working time (flow time) of bismuth cured systems 
most nearly approaches that of phenyl mercury compounds and, therefore, in 
areas where catalyst toxicity must be given consideration, the products of 
this invention most closely provide the gel profile of a long induction 
time at uniform viscosity prior to gellation which is the desired gel 
curve characteristic. 
EXAMPLE V 
In areas where catalyst toxicity is not of paramount importance, the use of 
organomercury catalysts is extensive. The only negative physical 
characteristic which these catalyzed systems exhibit is the potential for 
cured systems to exhibit polyurethane degradation or, in effect, for the 
mercury to act as a depolymerization agent. This phenomenon is related to 
the temperature and/or humidity of the environment into which the cured 
polyurethane is exposed. Another major advantage to the use of the 
products of this instant invention is the lack of polymer degradation 
which the cured elastomer exhibits upon exposure to conditions which would 
render mercury catalyzed polyurethane elastomer unfunctional. The use of 
polyurethane elastomers to fill tires is an area which has received much 
attention. It has been a practice in the industry that the addition of 
sulfur to a mercury containing polyurethane formulation would chemically 
bind the mercury catalyst so that depolymerization would not take place. 
The data below indicate that the use of the catalyst of this invention is 
superior to that currently being employed. The same formulation as 
discussed in Example I above was utilized in the run described below. 
__________________________________________________________________________ 
SHORE A 
HARDNESS AFTER 
SHORE BEING EXPOSED 
GEL TIME/ 
HARDNESS 
TO BOILING WATER 
CATALYST SECONDS 
INITIAL 
FOR 32 HOURS 
__________________________________________________________________________ 
Phenyl Mercury 
113 65 Soft Paste 
Carboxylate 
Phenyl Mercury 
74 61 42 
Carboxylate Plus 
Equivalent Weight 
Of Sulfur 
Phenyl Mercury 
90 62 50 
Carboxylate Plus 
Five Times Weight 
Of Sulfur 
Phenyl Mercury 
96 65 53 
Carboxylate Plus 
Ten Times Weight 
Of Sulfur 
Bismuth tris (neodecanoate) 
180 67 60 
Catalyst 
Bismuth tris (neodecanoate) 
177 68 61 
Catalyst Plus 
Equivalent Weight Of 
Sulfur 
Bismuth tris (neodecanoate) 
157 71 60 
Catalyst Plus 
Five Times Weight 
Of Sulfur 
Bismuth tris (neodecanoate) 
83 75 63 
Catalyst Plus 
Ten Times Weight 
of Sulfur 
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