Note: Descriptions are shown in the official language in which they were submitted.
7~3~
Significant advances have been made in recent
years in development of vascular prosthesis. For example,
U. S. Patent 4,131,604 to Szycher entitled Polyurethane
Elastomer for Heart Assist Devices discloses a family of
polyurethanes with excellent properties which can be used
to form moldable prosthetic devices. One deficiency of
the polyurethan~ disclosed in that patent however is that
those polyurethanes are not extrudable. There are many
proschetic devices as well as other devices, which must be
blood compatible which can only be manufactured efficiently
by extrusion or blow molding.
It should be apparent that devices such as pace-
maker leads, blood bags, catheters, and I.V. tubing must
be ~ormed of a material that meets a number of criteriaO
The most significant criteria is that the material from
which such devices are fabricated must be hemocompatible.
That is, the material should not induce the formation of a
thrombus which can embolize into the peripheral bloodstream.
Of course, the material must be non-toxic. In addition to
the foregoing, it is desirable that materials for devices
to be used in manufacturing vascular prosthesis po~sess a
high degree of resiliency~ strength and an ability to Elex
without breakage. As is mentioned above for the formation
of certain devices, it is desirable that the material be
extrudable.
This invention relates to an extrudable polyure-
thane polymer specifically developed for use in molding
devices for use in the human body and requiring a high degree
of blood compatability. The polymer is a polyurethane elas-
tomer andthe reaction produc-t of: (a) dicyclohexyl methane
diisocyanate; (b) a polytetramethylene ether polyol having
a molecular weight in the range of 1000/2000; and (c~ 1,4
butane diol, wherein for each diol there are two dicyclohexyl
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~g~ 3~
me~hane diisocyanates and one glycoli and the average
molecular weight of the polymer is 120,000 units, and a
weight average molecular weight of 315,000 molecular weight
uni~s. This polymer being alip~atic and polyether-~ased with
100~ urethane linkages in the molecular backhone, exhibits
superior flexuxal life, outstanding hydrolytic stability,
and a high degree of blood compatibility. In addition to
the foregoing, the polymer can be pelleti~ed and extruded
to form a variety of shaped devices such as cardiac pace-
maker leads, blood bags, catheters and I.V. tubing. Thisunusual combination of properties makes the polymer useful
in devices requiring blood contact surfaces.
The sole figure of the drawing is a diagram
illustrating the process for extruding articles from the
elastomer of the present invention.
At the outset, the invention is described in its
broadest overall aspects with a more detailed description
followingO The polyurethane elastomer of the present inven-
tion is a rubbery reaction product of an aliphatic organic
diisocyanates, a high molecular weight polyether polyol
and a specific low molecularweight glycol (cha.in extender).
The low molecular weight glycol is 1,4 butane diol.
In addition to the foregoing required constituents,
the reaction constituents preferably include a catalyst and
optionally an antioxidant and a lubricant for extrusion.
1~97~)37
¦ In general, polyurethane polymer~ are the c4ndensation
¦I product of reactions between diisocyanates and compounds con-
taining active hydrogen ~ites such as hydroxyl groups.
Ij A diisocyanate is an isocyanate compound having a func-
¦¦ tionality of two. The polymerization takes place in the pre~enceof a difunctional hydroxyl compound (thifi can be either a ~imple
glycol or a macromolecular glycol)O
1, catalyst
Il n 0- C~ ~ R-M - C~O + n HO Rl OH ~ >
(diisocya~ate~ (glycol)
~ R-~ - C -O - Rl - 0
j (polyurethan~3
Examples of ~liphatic diisocyanates useful in this
invention are: hexamethylene diisocyanate ~DI),
NCO
~ I CH ~
i c~3 CH2~CO
OCN (CH2)6NCO;
¦ i~ophorone diisocyana~e (IPDI~;
tri methyl he~amethyle~e diisocyanat~ (TMHDI),
CH3
OC~ CH2- F~-~H2 ~fH CH2 CH2 NCO;
CH3 CH3
_4_
~9'7~3~
dicyclohexyl methane diisocyanate (HMDI),
OCN - C } 2 ~ } NCO
CH2(C6HloNco)~
and dimer acid diisocyanate (DDI)
(CH2)9--NCo
H - f ~ CH = CH - (CH2)9--NCO
H ~ (CH2)4CH3
(CH2~9--CH3
The preferred diisocyanate for forming polymers
in accordance with this invention is dicyclohexyl methane
diisocyanate IHMDI)~
Although a number of aliphatic diisocyanates can
be utilized in pre~aring a polymer of the general type under
discussion, numerous tests have indicated that the selection
of the high molecular weight polyol is limited to poly tetra
methylene ether glycol (PTMEG) H - (O--CH2--CH2--CH2--CH2) --OH.
Stated ano-ther way, this high molecular polyol is the only
polyol which has been found to produce a polyurethane which
is hemocompatible and possesses the other properties dis-
cussed above. In general~ this gl~col should have ~n avexage
molecular weight between about 1000 and 2000~ In the pre~
ferred emhodiment of this invention PTMEG having a molecular
weight of 2000 is utili%ed.
As was s~ated above, the chain extender for the
polymer of the present invention is 1,4 but~ne dioi
(HO~CH2--CH2--C~2~H2
s~
1~'7037
¦ Th~ prefexred polyur~thane ha~ the following etructural
¦ formula:
__
- ~{--~2--~ff d~--Cd2 ~ ~ C~2 ~ ~ ~12~d2Cd
1,4 butane diol Diisocyanate MacroglycDl _
(~MDI) ~ n
~ l
where n~lis an integer ~elected to give a molecular
weight between 500-5000
¦ x is an integer from 1 to 5~
¦ and n i~ an integer selected to give a number average
¦~ molecular weight of 120,000 units, and a weight average molecular
¦~ weight of 315,000 molecular weight Uni~B~
¦¦ As can be ~een from the above formula, the polymer of
~ the present invention i6 compos~d of three repeating unitst the
¦ dio~, ~he diisocyanate and ~he macroglycol. ~he relationship of
these r~peating uni~ to each other is determined by the physical
characteristics de ired. For example, for tubing which should be
soft and elas~omeric (70 5hore A), ~or each diol there are two
diisocyanate repeating units ~nd one macroglyco~. To produce
hard~r ma~erial, the ratio uf diol o dii~ocyana~e and m~crogly-
col can be increa~ed thereby re~ultin~ in a harder materialO For
~xæ~ple, for catheters ~50 Shore D~ two butane diol units ~re
rupeated for each i~ocyanate and each m~cr~glycol.
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~L9703 t'
The reactant& ar~ pro~ided in approximately the molar
amounts necessary to produce the foregoing polymerO
To obtain fully cured polyurethane ca~ting~ in a
reasonably hort period of time, it i~ cu~omary to incorporate
into the mixture a ~uitable cataly~t ~o promote the
polymerization reaction. Suitable ca~alysts include N~methyl
morpholine, trimethyl amine, triethyl amine, zinc octoate,
dibutyl tin dilaurate and dioctyl tin dilaurateO Dioctyl tin
dilaurate i~ the p~eferred ca~aly6t.
The proce6s in accordance with the present invention i8
represen~e~ diagramma~ically in the ~ole figur~ of th~ drawing.
Il
The polyurethane i8 prepared from two component~ which
, can be referxed to a~ part A and part B. Part A i the aliphatic
¦ dii~ocyanate, Part B i~ comprised of ~he other con~ti~uen~s: a
¦I macroglycol ~the polyether base), the low molecular weight chain
extender, the cataly~t, the antioxidant and t~e lubricant. Of
¦¦ couræe the cataly~t, antioxid~nt and lubricant do not combine
¦¦ chemically as part of the polymer~
¦ To form a polyurethane element, the proper
stoichiometric proportion6 of part A and part B ~re emul~ified by
a mixer at room t~mperature to form a moderately reactive
¦ thixotropic mixture having a vi~cocity below about 2500 cps.
~ ince the emulsiPica~ion introduces air into the reac
tive mixture, ~he air mu~t be removed. The air bubble~ are
removed by placing a ve~sel containing the emul~ion under a bell
jar and evacuating the air from the bell jar wi.h a ~uction
device. The bell jar i~ evacuated to a pre~ ure of about 0O3
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7~
~"
¦I micron~ and the mixture i8 Xept under ~he bell jar about 8
¦I minute~ causing ~he mixture to appear to boil. After the
emulsion is taken from the bell jar, it i8 allowed to stand until
¦ the exothermic reaction that i8 ~aking place brings it to a tem-
perature of abou~ 400C.
At this point, the emul~ion is preferably poured into a
pan where i~ i8 allowed to flow to form uncured ~heets. The pan
with the heet~ is then placed in an oven and heated a~ a tem
perature of ~t least llOaC~ or four hours or more un~il the
I elastomer i~ cured~ The sheets are then chopped up or pelletized
in a s~andard pelletizer resulting in pellet~ approximately V4
, inch in lengtha These p~llet~ are then used in machinery
sui~able for an extrusion of the de~ired product.
In an optional embodiment of the invention, it .is al o
po6sible to di~ olve the pellets in a ~olvent uch as dime~hyl
¦ acetamide, tetrahydxofuran, 1,4 dioxan~ and m-pyrrol. The 801u
tion can then be used to make an article by the solvent casting
_ methodO
The invention iæ further illustrated by the following
non-limiting example.
67.75 gr~ms of dicyclohexyl methane diisocyan~te (HMDI)
was reacted wi~h a mi~ture o~ the following ive constitu~nt~.
229.2 grams of 2000 molecular weigh~ poly ~ra methylene ether
glycol, 12.35 grams of 1,4, bu~ane diol. Thi8 reaction ~i~tur~
~l~o contai~ed 3~0 gram~ of a anti-o~idant. Th2 antiroxidant
? UBed i8 sold under the trade-~a~ IRGA~0~ 1010 by Ceiba GeigyO
The chemical name of the anti-oxid~n~ is tetraki~ tme~hylene
~ )3~7
(3,5-di-tert~bu~yl-4-hydroxyhydrocinn2ma~e)J methan~. A180
included in thi reactio~ mixture was 0-5 grams of a lubricant
`''''~`!,~
l~ scld under the trade ~e of GLYCOLUBE VL obtained from the Glyco
Chemical Company of N~w York. 0.006 grams of a tin based cata-
lyst ~old by Co&an Chemical Corporation of Carl~tadt, ~ew Jer ey
~ Jp~
under their trade ~am~ COTI~ 430 was al~o includeda
The above consti~uent~ were mixed wi~h the HMDI,
deaerated until all entrained gases were removed~ The mixture
was ~hen cured at 110~C for three hour~ under a nitrogen
~tmosphere in the form of sheetsD The sheet~ were ~hen chopped
up in the standard pelleti~er to form pellets 6uitable for extru-
sion~ The phy~ic 1 properties of ths cured elastomer wa~ a~
follows: ten~ile ~trength 4500 pRi minimum, elongation 650
hardness (Shore A) 70~7S.
The p~llets were then processed in a laboratory
extruder. Processing conditions were determined on a 1"
diameter, 24/1 gen~ral purpose s~rew, ae shown below:
Rear aF 300
Middle F 320
Front F 20
Di~ 330
ThroatWatex cooling
Tubing, in 8ize8 appropriate for u~e in pacemaker
leads, was extruded. ~he tubing exhibited all the desirable
physical ~haracteri~tics required in the6e application6O
The invention ~ay be ~mbodied in other ~pecific form=
withou~ departing from the spirit or essential characteristics
~ f~3~7
j thereof. The prefient embodiments are therefore ~o be con6idered
¦ in all respec~s as illu~trative and not restrictive the scope of
¦ the invention being indicated by the appended claims ra~her than
¦ by the foregoing descrip~ion, and all change~ which come within
the meaning and xange of equivalency of the claims are therefore
intended to be embr~ced therein.
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