Note: Descriptions are shown in the official language in which they were submitted.
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REVERSIBLE CROSSLINKED POLYMERS,
BENZYL CROSSLINKERS AND METHOD
FIELD OF THE INVENTION
The invention involves crosslinked polyurethanes and other polymers
1o not conventionally known as polyurethanes, with added urethane crosslinks
where the , crossiinkers are based on compounds having one or more
benzylic hydroxyl groups, and methods of making the polymers and
crosslinkers. The polymers are useful to make fibers, sheets, moldings,
coatings and other articles typically produced from polymers.
BACKGROUND. OF THE INVENTION
Organic polyisocyanates have been used with compounds having active
hydrogen groups, such as hydroxyl groups, to praduce a wide variety of
useful materials such as coatings, hot-melt adhesives, moldings. The
2o materials have been used in injection molding applications and in composite
or laminate fabrications. Typical of the art is the patent to Markie et al, US
5,097,010.
Urethane bonds are used ubiquitously in polymer chemistry to produce
a wide variety of useful compositions.
The urethane bond is conveniently obtained by the addition reaction of
an isocyanate group (either an aliphatic or an aromatic isocyanate) and an
aliphatic alcohol or an aromatic (also known as aryl) hydroxyl group (a
phenolic group). This reaction is reversible at sufficiently high temperatures
as indicated by showing the following reaction as an equilibrium process.
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lc ~
+ HOR' ~ RNHCOR'
RN=C=O
1c2
Isocyanate Alcohol or Urethane
Phenol
In this equation, R is alkyl or aryl and R' independently is alkyl or aryl.
The
equilibrium constant K is defined as ki/k2 where k1 is the rate constant of
the
forward, or urethane forming reaction, where k2 is the rate constant of the
s reverse reaction involving reformation of RNCO and R'OH. These rate
constants each vary as a function of the temperature, with k1 and k2 both
increasing as the temperature increases. However, k1 will dominate (i.e.,
k1»k~) over some temperature range between ambient temperature and
some intermediate higher temperature since the forward reaction typically has
to a lower activation energy than the reverse reaction. As a result of these
activation energy differences, k2 will increase more rapidly than k1 as the
temperature is increased. Thus, at some higher temperature, k2 may equal k1
(where the equilibrium constant K = 1) and may in certain cases become
appreciably greater than k1 at still higher temperatures. Hence, the
is equilibrium constant will range from quite high values at ambient
temperature
but can become relatively smaller at sufficiently high temperatures so that
significant and useful concentrations of isocyanate groups will be present.
The forward, or urethane forming reaction, can be affected by simply
heating an equimolar mixture of isocyanate and hydroxyl groups to the
2o temperature at which k1 is large enough that urethane formation occurs in
an
acceptable, or practical, period of time (from a few minutes to several
hours).
Catalysts, such as tertiary amines or certain organotin compounds, can speed
both the forward and reverse processes but that are not necessary to bring
about the urethane forming reaction or the establishment of equilibrium. If
2s both compound types are difunctional, that is, if they are diisocyanates
and
dialcohols or diphenols, the forward reaction will produce polymeric products
(polyurethanes) of very high molecular weights. The achievable molecular
weight of fully reacted (i.e., of essentially non-reversed) pairs will be
limited
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by the presence and concentration of monofunctional isocyanates or
monofunctional alcohols; by the isocyanate concentration and the dialcohol or
the diphenol concentrations not being equal to each other; or, by the
intervention of adventitious impurities which deplete the amount of either
s NCO or OH by side reactions. However, as the temperature of the
polyurethane is further increased and k2 increases faster in comparison to the
increase in k1, significant and measurable reverse reaction to isocyanate and
either alcohol or phenol will occur. The approximate reversal temperatures of
urethanes derived from representative combinations of aliphatic or aryl
.o isocyanates and alkyl or aryl hydroxyl groups (as defined earlier) have
been
previously reported by Z.W. Wicks, 7r., "Blocked Isocyanates" Progress in
Organic Coatings, 3, pp. 73-99 (1975) as shown in Table l below:
Table 1
Approximate Urethane
Onset
soc anate T a lcohol T a of Reversal
Tem erature C
A I e. . MD1 A I e. . Phenol 120
Alk I e. . HD1 A I e. . Phenol 180
A I e. . MD1 Alk I e. . n Butanol200
Alk I e. . HD1 Alk I e. . n Butanol250
These temperatures are or approximate values which represent the
onset of reversal or a temperature where the practical effect of reversal,
such
as the onset of distillation or evaporation of phenol or butanol from a heated
zo mixture, or where infrared spectroscopy of heated samples can record the
onset of isocyanate and alcohol or phenol formation from a previously
unreversed urethane compound.
In the work described herein, it was sought to identify combinations of
particular diisocyanates or polyisocyanates and dialcohois or diphenols, or
z5 polyalcohols or polyphenols, which v~rould possess reversibility of
practical
utility (described further below) in terms of some relatively high temperature
at which onset of reversibility would occur. This would allow the preparation
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of polymers with bath backbone urethane bonds (i.e. urethane bonds as part
of the structure of the long molecular strands constituting a polymer chain),
and crosslinking urethane bonds (i.e. urethane bonds connecting two of the
long molecular strands constituting a polymer chain with bridging bonds,
s which result in dramatic increases in average molecular weight, such. as for
example a doubling thereof) which might be expected to have practical utility
up to, or very close to, the temperature of onset of significant reversibility
as
described above. If suffiicient reversible bonds, including latent crosslinks,
are
incorporated into such a reversible bond-containing polymer structure,
~.o polymers may be formed at some elevated temperature, by first heating the
mixture of reactive components to some temperature above the practical
onset of reversibility temperature such that a mixture of molten, or
dissolved,
partially assembled, urethane bond-containing, polymer fragments is
established. As this mixture is cooled below this reversibility onset
15 temperature, the polymer forming isocyanates and hydroxyl functional groups
will fully form (or reform) urethane bonds providing a high molecular weight,
crossiinked, polymer structure. Depending on the degree of crosslinking, the
polymer product wilt be insoluble in a known solvent for the uncrosslinked
polymer. But will swell in such a solvent to various degrees ranging from nil
2o at high levels of crosslinking to moderate to high swell (e.g. 10 or more
times
increase in volume) at low levels. Low to high crosslinking levels, or
crosslinking density, may range from about one crosslink per 100 to 200 or
more polymer backbone repeat units, to one crosslink per 3 to 5 backbone
repeat units. The higher levels of crosslinking are expected to show great
25 utility in terms of mechanical (such as tensile or flexural) strength,
rigidity
(i.e. very high modulus values0 scratch or abrasion resistance, resistance to
organic solvents or water or various pH aqueous solutions, and other
important properties, when used in such practical applications as molded
parts, composite structures (e.g. glass fiber or fabric, carbon fiber or
fabric,
3o various particulate, and the like, filled structures),coatings on various
substrates such as metals, glass reinforced moldings or composites, ceramics,
silicon wafers or electronic components, and so on, very strong, including
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structural strength, adhesives for use to bond substrates such as described
for coatings, and in other useful applications. These useful properties are
expected to be obtained from subambient temperatures up to temperatures
of 150°C or higher, or in some cases up to about 180°C or
higher.
The need exists for new materials having both improved processing
and end use characteristics. The present invention seeks to address those
needs.
BRIEF DESCRIPTION OF THE INVENTION
to Broadly the invention discloses a polymer having a crosslinked
structure wherein the crosslinked structure comprises one or more urethane
bonds made by the reaction of a benzylic hydroxyl group and an isocyanate
group. A further embodiment provides for one or more urethane bonds made
by the reaction of a benzylic hydroxyl group and an isocyanate group that are
is also present in the polymer backbone of individual polymer chains.
Typically
the one or more of the urethane bonds begins to dissociate at a temperature
above about 150°C
A further embodiment of the invention includes a polymer described
above, wherein the crosslinked structure is:
R2 O
i -O-C-NH-Y
Rt
and wherein R1 is H, and R2 represents a group selected from -H,
hydrocarbon groups containing up to ten carbon atoms, and halogen groups;
z5 and Y represents a group selected from an isocyanate residue. Typically the
isocyanate residue is selected from the group consisting of monoisocyanate,
diisocyanate, and triisocyanate residues. The isocyanate residue may also be
selected from the group consisting of aromatic monoisocyanate, aromatic,
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diisocyanate, aromatic triisocyanate, benzylic monoisocyanate, benzylic
diisocyanate, benzylic triisocyanate, aliphatic monoisocyanate, aliphatic
diisocyanate, and aliphatic triisocyanate residues. In some typical
embodiments the polymer is a polyurethane and 0.01 to 99% of the urethane
bonds in the polyurethane are obtained by reaction between a benzylic
hydroxyl group and an isocyanate group. In other typical embodiments the
polymer is a polyurethane and 0.1 to 50% of the urethane bonds in the
polyurethane are obtained by reaction between a benzylic hydroxyl group and
an isocyanate group
~o A yet further embodiment of the invention includes a polymer having a
crosslinked structure including a polyol with a high molecular weight; a
polyicocyanate; a polyol with a low molecular weight; and trifunctional
crosslinking compound selected from the group: (1) a compound having one
benzylic hydroxyl group and two aliphatic hydroxyl groups; (2) a compound
having two benzylic hydroxyl groups and one aliphatic hydroxyl group; (3) a
compound having three benzylic hydroxyl groups; and wherein 0.01 to 99 mol
of bonds in the crosslinked structure comprise urethane bonds obtained by
the reaction between a benzylic hydroxyl group and an isocyanate group.
A yet further embodiment includes a polymer having a crosslinked
2o structure of a polyol; a polyicocyanate; a trifunctional crosslinking
compound
selected from the group: (1) a compound having one benzylic hydroxyl group
and two aliphatic hydroxyl groups; (2) a compound having twa benzylic
hydroxyl groups and one aliphatic hydroxyl group; (3) a compound having
three benzylic hydroxyl groups; and wherein 0.01 to 99 mol % of bonds in
the crosslinked structure comprise urethane bonds obtained by the reaction
between a benzylic hydroxyl group and an isocyanate group.
An additional embodiment includes a compound such as:
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.R5 RI.6 RS
.Ha-CH- 7~. ~ C- X~ ~I~-OH
I
wherein Rl and R2 are identical or different and represent a group selected
from -H, hydrocarbon groups containing up to ten carbon atoms, and halogen
groups; wherein Rs and R~ are identical or different and represent a group
selected from -H, and hydrocarbon groups containing up to ten carbon atoms;
S Rs represents hydrogen, methyl, ethyl, or propyl; Rs represents hydrogen,
methyl, or ethyl; Xi (left arm), Xz (right arm) and Z may be the same or
different and represent none (no additional segment present), methytene,
ethylene, or p-phenylene; the benzylic hydroxyl moiety may be positioned the
para, meta or ortho position. In a preferred embodiment the compound is
1o Z-~[(4-hydroxymethyl)t~nzyl3oxy}-1,3-propanedial. Another embodiment
Includes the use of this compound to crossllnk neighboring polymer chains.
An additional embodiment includes a compound of a poly-benzyHc
hydroxyl group capped polymer or oligomer obtained by reacting compounds
containing one primary aliphatic hydroxyl group and one or more benzylic
15 hydroxyl groups with low molecular weight polyiscx;yanates in a molar ratio
of
one primary aliphatic hydroxyl group per isocyanate group in the
palyisocyanate.
cJther embodiments include erc~sslinker compositions ounsisting of bis-
isocyanate capped low molecular weight polyols, which structures result from
ZQ the reaction of 2-20 moles of diisocyanates as represented by OCN-I~-NCt~O
where R is aliphatic, cycloaliphatic, bisbenzylic, or aromatic, with 1 mole
t~f
low molecular weight diols which include aliphatic dlols with from Z to 11~
carbon atoms, tycloaliphatic diols with from 5 to 1Z carbon atoms and bis-
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(beta-hydroxyethyl) or bis-(beta-hydroxyethoxy) substituted aromatic rings,
including benzene, napthalene, pyridine or pyrazine rings. This embodiment
likewise includes the use of the crosslinker compositions to crosslink
polymers
containing 1 or more pendant benzylic hydroxyl groups on the backbone of
the polymer.
Another embodiment includes. a crosslinker composition consisting of
isophorone diisocyanate or TMXPI diisocyanate capped 1,4-butane diol such
that a short oligomeric product described by the formula or expression
OCN-IPDI[-NH-CO-0-BD-0-OC-HN-IPDI-]"-NH-CO-0-BD-0-IPDI-NCO
where n = 0, 1, 2, 3, 4, 5, etc. but is predominately 0.
is provided, and in which IPDI may be replaced with TMXDI, and is useful as
a crosslinker of polymers containing pendant benzylic-hydroxyl groups.
BRIEF DESCRIPTION OF THE DRAWINGS
The Figure illustrates a method for producing Compound 1 including
chemical structures associated with starting materials, intermediates,
2o byproducts, and final product.
DETAILED DESCRIPTION OF THE INVENTION AND BEST MODE
This invention meets the needs for new polymers by providing
thermally reversible polymer compositions having reversible polyurethane
2s linkages in crosslinks between neighboring chains. The number of crosslinks
can be controlled so as to obtain polymers with desired properties. The
polyurethane crosslinks are based on bonds from benzylic hydroxyl groups
and isocyanate groups. New compounds having such groups are also
disclosed herein so as to achieve the desired reversible characteristics.
3o Broadly the invention discloses new materials and methods for
preparing and crossiinking polymers to form pofyurethanes, and other
polymers not conventionally known as polyurethanes that consist of polymers
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with added urethane crosslinks, having enhanced properties. One broad
embodiment of the invention discloses new crosslinkers useful for obtaining
polymers with enhanced properties. Another broad embodiment of the
invention discloses new polymers obtained with the new crosslinkers. Other
s broad embodiments of the invention include methods and processes for
preparing the polymers and crosslinkers. Yet another embodiment discloses
selective preparation of new oligomeric chain extenders and crosslinkers
derived from a simple compound type containing only one benzylic hydroxyl
group and one primary aliphatic hydroxyl group.
~.o
Preliminar)r Tests
In order to identify more specific types of isocyanate groups and
alcohol or phenol groups which might be expected to provide reversibility
temperatures to meet these criteria and needs, some preliminary work was
1s carried out using model compounds. These were based on the benzylic
hydroxyl group (an aralkyl hydroxyl group intermediate, between a normal
aliphatic hydroxyl group and the pure aromatic hydroxyl group of a phenol) as
represented by p-hydroxymethylbenzoic acid (HMB), the phenol group of p-
hydroxylbenzoic acid (PHBA) and the cycloaliphatic isocyanate groups of
2o isophoronediisocyanate (IPDI) and the araalkyl isocyanate groups of TMXDI
(1,3-bis(1-isocyanato-1-methyl-ethyl) benzene). The isocyanate groups of
IPDI and TMXDI are both expected to result in an onset reversibility
temperature intermediate between an aromatic diisocyanate (such as MDI)
and an aliphatic diisocyanate such as HDI, with any given hydroxyl group.
2s Likewise, the benzylic hydroxyl group is expected to result in an onset
reversibility temperature intermediate between a normal aliphatic alcohol such
as n-butanol (or a n-aliphatic diol such as 1,4-butanedrol) and a phenol
hydroxyl group. Hence, the following three pairings to be used in infrared
spectroscopy determinations of approximate reversibility onset temperature
3o were studied:
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1. Phenolic-OH (from excess PHBA reacted with BD, Example Al)
and IPDI-NCO (from an IPDI-BD-IPDI product with terminal
NCO groups) Example Ci.
2. Benzylic-OH (from HMB reacted with i-octadecanol or C18
s alcohol) to give a nonvolatile, ester-linked hydroxylmethyl
benzoate, Example A2 and the same IPDI-NCO as above,
Example C1.
3. Benzylic-OH (Example A2) and TMXDI-NCO (from a TMXDI-BD
TMXDI product with terminal NCO groups, Example C2.
to
The preparation of the PHBA-BD andHMB-C18 alcohol products is
described in Example A1 and Example A2. The preparation of the three sets
of products listed above for infrared spectroscopic (IR) interrogation as a
function of temperature, to determine the approximate reversibility onset
~.s temperature and the quasi-midpoint of reversibility temperature is
described
in Example A3.
For the IR analysis, the samples were scanned in transmission mode
using a Digi(ab FTS-60A, FT-spectrometer at 4 crri 1 resolution. The sample,
as prepared as described in Example A3, and placed in the sample holder,
2o between two 2 mm thick KBr salt plates. The IR samples were estimated to
be about 0.1 mm thick. The sample holder was custom made by Harrick and
is equipped with a resistance heater and coolant circulation connections for
cooling the cell. The cell was.heated and cooled with Therminol 59, a heat
transfer fluid. For the IR measurements, the sample was heated from room
2s temperature to 230°C (~5°C/min) and then cooled to room
temperature
(N82°C/min). After data collection, the peak intensities of the
isocyanate
(N2257 cm-1) and aromatic substitution absorption bands (700-760 cm-1)
were measured and this ratio was then shown plotted versus the
temperatures at which the isocyanate ratios occurred. The
3o isocyanate/aromatic substitution absorption ratio was used to compensate
for
the potential change in sample thickness during the temperature increases
and decreases.
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The first heatup of samples from room temperature to 230°C showed
isocyanate absorptions already present even at room temperature, before
heatup was started. This was presumed to be due to incomplete reaction of
the NCO-OH pairs prepared in Example A3. However after this first heating
s and cooling cycle, the room temperature isocyanate absorption at 2259 cm-1
was gone, indicating that the reaction was completed.
Based on the models in these tests, it was expected to see reversible
temperatures ranging from about 160 to 210°C. As expected, the TR
analysis
of the system Pair 1, Pair 2 and Pair 3 pairs indicated midpoint reversion
~o temperatures of about 175°C, 195°C, and 197°C
respectively (Table 2). Most
importantly in these tests, both Pair 2 and Pair 3 have a midpoint reversion
temperature in the target range of 190-200°C and both are higher than
the
reversion temperature of Pair 1. This means the benzylic hydroxyl formed a
more stable urethane bond than the phenol groups as expected. In fact,
i5 based on the pre-defined process temperature range (i9~-200°C), both
Pair 2
and Pair 3 have acceptable reversible temperatures for fiber spinning at
195°C. Hence, Compound 1, having three functional groups, a reversible
benzylic hydroxyl group available for crosslinking and two primary aliphatic
groups available for incorporation into the polymer backbone, was
2o synthesized for incorporation in a polymer via urethane linkages, in
particular
a thermoplastic elastic polyurethane. It was expected that Compound i
would polymerize with a diisocyanate like MDI by forming very stable
urethane bonds via the two primary aliphatic hydroxyl groups, but with a
pendant unreacted benzylic hydroxyl group.
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Table 2. Approximate Onset and Quasi-Midpoint Reversibility
Temperature for the Urethane Types
ApproximateQuasi-
Alcohol Onset Midpoint
or
IsocyanatePhenol Urethane ReversibilityReversibility
PairsOli omers Oli omersT es Tem . C Tem . C
1 IPDI-BD PHBA-BD Secondary 105 175
Cycloaliphatic
(phenolic)Isocyanate
-
Phenolic
2 IPDI-BD HMB-C18 Secondary 150 195
Cycloaliphatic
(benzylic)Isocyanate
-
Benzylic
Alcohol
3 TMXDI-BD HMB-C18 Aromatic 140 197
Substituted
(benzylic)Tertiary
Isocyanate
-
Benzylic
Alcohol
EXAMPLE A1 - PHBA-BD Oligomers
p-Hydroxy benzoic acid (PHBA, Aldrich H2,005-9, as received) (60g,
0.435 mole) and butanediol (BD, Aldrich 24,055-9, vacuum distilled) (19.5g,
0.217 mole) were added to a round bottom flask flitted with a refluxing
1o condenser. The contents were heated to 260°C for two hours. The
water
produced from the reaction was removed with a constant flow of nitrogen.
To remove phenol which was formed as a byproduct, the oligoester was
extracted with methanol and the methanol insoluble PHBA-BD portion was
isolated. Then, the methanol soluble PHBA-BD was precipitated twice in
i5 water. The methanol soluble PHBA-BD was redissoived in acetone and
reprecipitated in water. Both the methanol soluble and insoluble materials
were analyzed by H-NMR which did not detect the presence of phenol. The
methanol insoluble phenolic product was used in the model reversibility
studies.
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EXAMPLE A2 - HMB-C18 Oligomers
4-Hydroxymethyl benzoic acid (HMB) (6g, 0.0-3mole) and n
octadecanol (C18)(10.67g, 0.039mo1e) were added to a round bottom flask
fitted with a refluxing condenser. The contents were heated to 260°C
for two
s hours. The water produced from the reaction was removed with a constant
flow of nitrogen. After the reaction,,the HMB-C18 crude product was
dissolved in 10 ml acetone and reprecipitated from 100 ml of methanol to
remove the unreacted HMB. The H-NMR of this product indicated 20 mole
percent of unreacted n-octadecanol. The unreacted n-octadecanol was
to removed by dissolving the HMB-C18 in methylene chloride and precipitating
from hexane, which is a solvent for 1-octadecanol, before it was used for the
reactive blending study.
EXAMPLE A3 - IPDI-BD and PHBA-BD
15 The isocyanate containing oligomers and hydroxyl containing oligomers
were weighted into dry test tubes. They were combined in weight ratios such
that equal molar amounts of NCD and OH groups were present. The mixtures
were then heated to 160°C under a blanket of Argon with the test tube
immersed in a heated Wood's metal bath. The reaction mixtures were
2o maintained at 160°C for about 20 minutes with intermittent stirring
under an
argon gas purge. After the reaction, thin films were prepared from the
oligomer reactive blended materials by pressing at about 180-190°C
between
mil sheets of Teflon on a surface temperature controlled hot plate. The
films were then analyzed by FT-IR by pressing between the IR plates. Two
25 showed incomplete reaction after blending. That is some unreacted
isocyanate was still present in the IR spectrum at room temperature.
However, urethane formation was driven to completion by heating rapidly
from room temperature to 230°C, and then cooling back to ambient
temperature, as evidenced in the infrared spectroscopy (IR) performed in a
3o scanning cell having heat-up and cool-down capability. IR spectra at the
end
of cycle one then showed that no free isocyanate remained. Hence, the IR
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spectra for cycle 2 were taken as representative of the onset of the urethane
reversing reaction and were used for the analysis.
In a general embodiment, the invention discloses new polymers
that contain urethane based crosslinks that start to reversibly dissociate at
s temperatures at about 150°C so as to obtain appropriate melt
viscosities
which allow melt preparation of various materials such as fibers, sheets, etc.
Another embodiment of the invention also includes a trifunctional
crosslinking compound which contains one to three benzylic hydroxyl
functions and none to two primary or secondary aliphatic hydroxyl functions.
to All hydroxyl functions are either benzylic hydroxyl functions or primary or
secondary aliphatic hydroxyl functions.
A further embodiment of the invention includes a tetrafunctional
crosslinking compound containing from two to four benzylic hydroxyl groups
and from none to two aliphatic and primary or secondary hydroxyl groups. All
15 hydroxyl functions are either benzylic hydroxyl functions or primary or
secondary aliphatic hydroxyl functions.
Definitions:
The term "backbone" or "polymer backbone" as used herein indicates
2o the extended linear repeating chain of an oligomer or polymer.
A benzylic hydroxyl group is a hydroxymethyl (-CH~OH) group
substituted on a benzene ring, or a benzene ring containing other substituent
groups.
A polyol with a high molecular weight useful according to the teachings
2~ of the invention typically includes polyester polyols represented by all of
the
below: Polyethylene butylene sebacate and the like; polybutylene adipate;
polycaprolactone diol; aliphatic polycarbonate polyols such as those obtained
by transesterification of polyhydroxyl compounds such as 1,4-butanediol, 1,6-
hexanediol, 2,2-dimethyl(-1,3-propanediol, 1,8-octanediol and the like, with
3o an aryl carbonate, for example, diphenyl carbonate; polyester polycarbonate
polyois, for example reaction products of alkylene carbonates and polyester
glycols such as polycaprolactone or products obtained by conducting a
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reaction of ethylene carbonate with a polyhydric alcohol (such as ethylene
glycol, propylene glycol, butyfene glycol, neopentyl glycol and the like; and
polyether polyols represented by polytetramethylane ether glycol,
polypropylene glycol, polyethylenepropylene glycol and the like.
s
A polyol with a low molecular weight useful with the invention typically
includes difunctional, trifunctional and tetrafunctional benzylic hydroxyl
compounds as represented by 1,2-ethanediol; 1,3-propanediol; 1,4-
butanediol; 1,5-pentanediol; 1,6-hexanediol; i,8-octanediol; 2,2-dimethyl-1,3-
1o propanediol and the like, and also 1,4-cyclohexanedimethanol; 1,4-bis(beta-
hydroxymethoxy) benzene; 1,3-bis-(beta-hydroxyethoxy) benzene; 1,4-bis-
(hydroxyethyl) ester of terephthalic acid; 1,3-bis(beta-hydroxyethyl) ester of
isophthalic acid, and the like.
Additional polyisocyanates useful with the invention include: aromatic
15 diisocyanates such as 4,4'-diphenylmethane diisocyanate (MDI); 1,5-
naphthalene diisocyanate' (NDI); 1,4-phenylene diisocyanate (PDI); 2,4 and
2,6-Toluene diisocyanate (commonly available as an 80/20 mixture of
2,4/2,6) and the like; benzylic diisocyanates such as TMXDI, p-xylyiene
diisocyanate, m-xylene diisocyanate; aliphatic diisocyanates such as 1,6-
2o hexamethylene diisocyanate (HDI) and alicyclic diisocyanates such as 1,4-
cyclohexane diisocyanate 4,4'dicyclohexylmethane diisocyanate, isophorone
diisocyanate, and the like. Isocyanates with more than two isocyanate
groups per molecule are also available and include the trimerized products of
the simple diisocyanates listed above in which three isocyanate groups are
25 symmetrically located on an isocyanate nucleus, these are exempliiaed
herein
by the HDI Trimer (Tolonate~°HDI) from Rhone Poulenc. There are also
polyisocyanates with varying functionality greater than 2 from Upjohn, such
as Isonate 143L and the PAPI series.
Typically, the difunctional benzylic hydroxyl compounds are used in the
3o polymer backbone to obtain special properties. Typically, the trifunctional
and
tetrafunctional benzylic hydroxyl compounds may be used both in the
backbone of the polymer chains and in the crosslinks between neighboring
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6acicbarne or polymer chains. Useful difunctionai benzylic hydroxyl
compounds include: those in the benzene series represented by 1,4-
benzenedimethanol, ~.,3-benzene-dimethanal; and ~.,2-benzenedimethanol;
those in the pyridine series represented by 2,6-bis(hydraxymetbyl)pYridine;
those in the pyrazlne Series represented by ~,5-bis(hydroxymethyl)pyrazlne;
2,3- bis(hydraxymethyi) pyrazine; an~i 2,6-bls(hydro~cymethyl)pyrazine.
Useful trifunctional benzyiic hydroxyl compounds Include those having one
benzylic hydroxyl group and two primary or secondary aliphatic groups
represented by Compound 1 and its analogues; thr~se having three benzylic
io hydroxyl groups represented by ~.,~,4-benzenetrimethanol; 1,3,5-
benzenetrimethanol; and z,4,6-benzenetrimethanol. Useful tetrafunctional
benzyf~c hydroxyl compounds include those having four benayiic hydroxyl
groups represented by i,~,4, 5,-tetra(hydroxymethyl)benzene
New compounds having a benzylic hydroxyl group useful for forming
urethane and ester Linkages are represented by the formula:
Rs Rs R~
HO-CH-~-~.--C--X-CH-(~~T
Z
i
l
R3-C.-.R4
~ R~
R1' C'
OH
wherein R1 and I~z are idenbcai or different and repre$ent a group selected
from -H, hydrocarbon groups containing up to ten carbon atoms, and halogen
zo groups; i~ and R4 are identical or different and represent a grou~r
selected
from -H, and hydrocarbon groups captaining up to ten carbon atoms; R5
represents hydrogen, methyl, ethyl or propyi; Rs represents hydrogen,
methyl, or ethyl; ; xl (left army, x~ (right army and Z may be the same or
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different and represent none (no additional segment present), methylene,
ethylene, or p-phenylene; the benzylic hydroxyl moiety may be positioned in
the para, meta or ortho position
Particularly useful benzylic hydroxyl compounds for making urethane
s bonds according to the present invention are represented by the formula:
Rs ~ Rs
HO-CH-X-C-X-CH-OH
Z
O
R3--C-R4
R2
Rlr C\
OH
wherein R1 is H, and R2 represents a group selected from -H, hydrocarbon
groups containing up to ten carbon atoms, and halogen groups; R3 and R~ are
identical or different and represent a group selected from -H, and
io hydrocarbon groups containing up to ten carbon atoms; R5 represents
hydrogen, methyl, ethyl, or propyl; R6 represents hydrogen, methyl, or ethyl;
X and Z may be the same or different and represent none (no additional
segment present), methylene, ethylene, or p-phenylene; the benzylic hydroxyl
moiety may be any isomer in the para, meta or ortho position. Preferably the
15 hydrocarbon groups of R2 through R~ are no more than eve hydrocarbon
groups and the benzylic hydroxyl moiety may be positioned in the ortho or
para position, most preferably the para position.
These benzylic hydroxyl compounds have three functional groups, a
reversible benzylic hydroxyl group available for crosslinking and two primary
2o aliphatic groups available for incorporation into the polymer backbone. The
compound owes its unique characteristics to the fact that the benzylic
hydroxyl groups are more readily reversible than the aliphatic groups.
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A polyisocyanate useful with the invention typically includes
diisocyantes and other polyisocyanates. Diisocyanates are represented by
isophorone diisocyanate (IPDI), TMXDI, phenylenediisocyanate (PDI),
toluenediisocyanate (TDI), hexanediisocyanate (HDI); methylenediphenyl-
s diisocyanate (MDI), naphthalene diisocyanate (NDI), and others disclosed US
patent 4,608,418 to Czerwinski et al,,which is hereby incorporated by
reference. Additional useful isocyanates are disclosed in US patent 5,097,010
to Markle et al, which is hereby incorporated by reference.
Diols useful for making crosslinkers containing benzylic hydroxyl
1o according to the invention include 1,2-ethanediol; propanediols represented
by 1,2-propanediol or 1,3-propanediol; butanediols represented by 1,3-
butanediol or 1,4,-butanediol; pentanediols represented by 1,5-pentanediol;
hexanediols represented by 1,6-hexanediol; and the like.
Triols useful for making crosslinkers containing benzylic hydroxyl
15 groups according to the invention include 1,2,3-propanetriol (glycerin),
1,2,3-
or 1,2,4-trishydroxybutane, and higher aliphatic triols with at least two of
the
hydroxyls in the 1,2- position.
Preferred crosslinking compounds containing benzylic hydroxyl groups
useful with the invention typically include a tetrafunctional crosslinking
2o compound containing from two to four benzylic hydroxyl groups and from
none to two aliphatic and primary hydroxyl groups, and a trifunctional
crosslinking compound containing from one to three benzylic hydroxyl groups
and from none to two aliphatic and primary hydroxyl groups. A typical and
preferred benzylic hydroxyl compound is 2-~[(4-hydroxymethyl)benzyl]oxy~-
2s 1,3-propanediol (Compound 1).
The following examples and earlier examples are merely exemplary
and illustrative of the invention and are not meant to limit the invention in
any way.
3o EXAMPLE B1
This example illustrates a method for the preparation of a typical
benzylic hydroxyl crosslinker useful with the invention. The method produces
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a trifunctional crosslinking compound containing one benzylic hydroxyl group
and two aliphatic and primary hydroxyl groups (2-~[(4-hydroxymethyl)-
benzyl]oxy~-1,3-propanediol - labeled as Compound i). Compound 1 was
synthesized for incorporation into the backbone of polyurethanes by using its
s aliphatic hydroxyl groups while leaving its benzylic hydroxyl group
available to
form reversible urethane-based crosslinks. Intermediate E was prepared to
determine if blocking of the benzyiic hydroxyl group by a readily removable
group (a methoxyacetic acid ester) in Compound 1 was necessary to allow its
appropriate incorporation into the urethane backbone. The synthetic route
1o that was developed involves the initial synthesis of Intermediate E which
was
then deblocked to form Compound 1.
Preparation of Tntermediate A
Intermediate A is composed of two isomers and is named as follows by
is IUPAC: cis- and traps-2-phenyl-1,3-dioxan-5-ol.
A one liter, three neck, round bottom flask was equipped with a Barrett
tube attached to a reflux condenser which was attached to an argon inlet via
a mineral oil bubbler. This flask, which contained a magnetic stir bar and was
positioned in a heating mantle, was flushed with argon and then charged with
20 200 m) of benzene, 160.0 grams (1.51 moles) of benzaldehyde, 150.0 grams
(1.63 moles) of glycerin and 1.00 grams of p-toluenesulfonic acid
monohydrate. A blanket of argon was kept over the flask during the reaction
period. The reaction mixture was refluxed until close to the theoretical
amount of water had collected in the Barrett tube and transferred to a one
z5 liter separatory funnel. One hundred ml of O.iM sodium hydroxide was added
to achieve pH 9-10 and the mixture was extracted with 350 ml of diethyl
ether. The ether extract was first treated with a saturated solution of sodium
hydrosulfite (32.75 grams/ 100 ml water) causing the formation of some solid
in the ether layer, then washed with water (150 ml), followed by a 5%
3o sodium bicarbonate (100 ml) treatment. After a water wash (2 x 150 ml), the
ethereal layer was dried over sodium sulfate overnight. The solvent was
stripped on a rotating evaporator (bath at 30C) to obtain 199.70 grams of
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liquid. This material was dissolved in 400 ml low boiling petroleum ether and
refrigerated to give a solid which weighed 186.28 g after filtration and
drying
under vacuum. Since proton NMR analysis indicated that a significant amount
of benzaldehyde was,still present, this material was dissolved in diethyl
ether
(800 ml) and washed with 2 x 125 ml of sodium hydrosulfite (61.0 grams in
200 ml water). The white solid that formed during this period was dissolved
by the addition of 100 ml of water. The ether layer was washed with 5 x 120
ml water (pH 2), passed through cotton, dried over sodium sulfate overnight,
and then stripped to obtain a yellow-orange liquid (139.1 grams). This
to material produce a low melting solid when placed in a refrigerator. When
brought to ambient temperature, the liquid phase was decanted and the
remaining solid was dissolved in a total of 400 ml of dry toluene at room
temperature. After addition of 400 ml of hexane, a copious amount of white
solid precipitated at room temperature. After this mixture was placed in a
refrigerator overnight, a fine white solid was filtered and dried which
weighed
74.33 grams (27.4% yield).
Sodium bisulfate can also be used to advantage in removing unreacted
benzaldehyde. The procedure for this reaction is found in: C. Piantadosi, C.E.
Anderson, E.A. Brecht and C.L. Yarbro, J. Am. Chem. Soc., 80, 6613-6617
(1958).
The proton and carbon-13 nuclear magnetic resonance (NMR) spectra
of this material indicated that it was a mixture of cis- and trans-1,3-
benzylidene glycerin and that 1,2-benzylidene glycerin had been completely
removed by recrystallization.
Preparation of Intermediate B
Intermediate B is composed of tow isomers and is named as follows by
IUPAC: cis- and trans-5-{~4-bromomethyl)benzyl]oxy)-2-phenyl-1,3-dioxane.
A two liter, three neck, round bottom flask equipped with an argon
3o inlet and mechanical stirrer was first flushed with argon and then charged
with 1167 ml dimethylsulfoxide (dried over molecular sieves) and 26.10 grams
powdered potassium hydroxide (0.466 moles). This mixture was stirred for
CA 02411001 2002-11-21
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five minutes. and then 21.00 grams 1,3-benzylidene glycerin (0.1165 moles)
was added followed by addition (aH at once) of 92.26 grams a,a'-dibromo-p-
xylene (0.3495 moles). The lemon yellow reaction mixture was stirred while
maintaining it under an argon blanket (via a miheral oil bubbler) for an
s additional eighty minutes at ambient temperature.
The reaction mixture was then added to a six liter separatory funnel
containing 250 grams of ice and 2250 ml of water and considerable yellow
solid formed at this point. The aqueous layer was extracted with methylene
chloride (a 2000 ml portion followed by 2 x 1300 ml portions). The combined
xo organic layers were split in half, filtered through cotton to remove the
yellow
solid, and each half was washed with 3 x 1800 ml water, The methylene
chloride was passed through a cotton plug and dried over sodium sulfate. The
solvent was stripped on a rotating evaporator and the resulting solid was
dried in a vacuum oven with phosphorous pentoxide to obtain 88.50 grams
m yellow solid. The excess a,a'-dibromo-p-xylene was removed by sublimation
and the residue was used directly to prepare Intermediate C (see below). To
illustrate, one sublimation was performed with 52.43 grams crude
Intermediate B in a large sublimation chamber requiring dry ice within the
cold finger. This apparatus was maintained at 0.035 Torr and 80°C in a
Zo controlled temperature oil bath for a total of 47.5 hours until minimal
further
sublimate was formed. The residue (non-sublimed material) weighed 13.83
grams (26.4 % of the starting weight).
The proton NMR spectrum of this material indicated the presence of
both traps- and cis-Intermediate B. Preparative scale High Performance
z5 Liquid Chromatography (HPLC) was used to fractionate this mixture (using a
normal phase HPLC column with tetrahydrofuran (THF)/isooctane (15:85)) to
obtain these isomers in a pure state whose structures were confirmed by
proton NMR spectroscopy and gas chromatography/mass spectroscopy
(GC/MS) (in the electron impact mode).
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Preparation of Tntermediate C
Intermediate C is composed of two isomers and is named as follows by
IUPAC: cis- and trans-4-{[(2-phenyl-1,3-dioxan-5-yl)oxy]methyl}benzyl
methoxyacetate.
Potassium methoxyacetate was prepared by dissolving 52.47 grams
methoxyacetic acid (0.5800 moles) is 150 ml of distilled water in an
Erienmeyer flask and initially adding 32.50 grams potassium hydroxide
(nominally 0.580 moles). Addition of 2 drops of a i% ethanolic
phenolphthalein solution indicated that the end paint had not been reached,
1o so this solution was titrated with a 10 % aqueous solution of potassium
hydroxide until a pink color persisted. This solution was freeze dried and
dried further in a vacuum oven, in the presence of phosphorous pentoxide, to
yield 71.94 grams of a white solid.
A 300 ml, three neck, round bottom flask containing a magnetic stir
is bar and equipped with a reflux condenser and gas inlet tube was positioned
in
a heating mantle and flushed with argon. This flask was maintained under an
argon blanket using a bubbler filled with mineral oil. The flask was charged
with 0.9147 grams 18-crown-6 (3.461 mmoles) and 134 ml acetonitrile was
transferred from an anhydrous source using syringe techniques. Potassium
2o methoxyacetate (18.85 grams; 0.1471 moles) was added and the milky white
suspension was stirred at ambient temperature for 50 minutes to allow
coordination of the 18-crown-6 with the potassium ion. Crude Intermediate B
(26.75 grams and 0.07364 moles) was added and the yellow mixture was
refluxed for 110 minutes. After cooling slightly, the mixture was filtered
z5 through a Buchner funnel (Whatman # 1 paper) and the filter cake was
washed with 4 x SO ml acetonitrile and then with 3 x 50 ml benzene. This
washing was performed to remove residual Intermediate C from the filter
cake. The filtrate was stripped on a rotating evaporator and the resulting
material was placed in a vacuum oven containing phosphorous pentoxide to
30 obtain 29.15 grams of a brown solid.
Column chromatography was used to purify Intermediate C. A column
having an internal diameter of approximately 7.5 cm was filled with 292
z2
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grams of silica gel slurried in excess benzene. Crude Intermediate C (29.15g)
was dissolved in 155 ml of benzene and applied to this column using benzene
as the eluent. A total of 19 fractions were collected ranging in size from 125
ml to 250 ml for fractions 1-7 and 300 ml to 500 ml for fractions 8-19. These
s fractions were stripped on a rotary evaporator and dried overnight at
ambient
temperature in a vacuum oven in the presence of phosphorous pentoxide to
obtain a total of 11.41 grams in total fraction weight. Select fractions were
analyzed by gas chromatography (GC) and by gel permeation
chromatography (GPC). GC results indicated that Intermediate C was the
1o major component. GPC analyses indicated that Intermediate C and Byproduct
D were present in all fractions but the relative ratio of Intermediate C
steadily
increased with increasing fraction number. Thus, the latter chromatography
fractions afforded Intermediate C in highest purity containing the smallest
quantities of Byproduct D. Byproduct D is composed of several isomeric
15 forms and is named as follows by IUPAC: (cis, cis-); (cis, traps-); or
(traps,
traps)-bis-1,4-f [(2-phenyl-1,3-dioxan-5-yl)oxy]methyl}benzene.
Preparation of Intermediate E
Intermediate E is named as follows by IUPAC: 4- f [(2-hydroxy-1-
~o (hydroxymethyl)ethoxy]methyl}benzyl methoxyacetate.
Fractions 6-15 from Intermediate C (8.15 grams) obtained by column
chromatography (described above) were transferred to a one liter Morton
flask equipped with a mechanical stirrer and 489 ml of 90/10 (v/v) acetic
acid/water were added. After stirring for thirty minutes, an additional 81.5
ml
z5 of acetic acid/water (90/10) was added. After stirring rapidly for 18.5
hours
at ambient temperature, a sample was removed which was found to be
depleted in Intermediate C by proton NMR spectroscopy. After the reaction
mixture had been stirred approximately 22 hours, the material was stripped
on a rotary evaporator with vacuum pump pressure using a bath temperature
30 of approximately 34°C. Portions of acetonitrile were added to aid
the removal
of residual acetic acid and water by azeotropic distillation. The resulting
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material was dried further at ambient temperature in a vacuum oven using a
vacuum pump to obtain 6.25 grams of a yellow solid.
Byproduct F was found to be present. Byproduct F is named as follows
by IUPAC: bis-1,4- f ~2-hydroxy-1-(hydroxymethyl)ethoxy]methyl} benzene was
s found to be present. In order to remove Byproduct F, this material was
magnetically stirred with 345 ml methylene chloride for three hours and this
mixture was then filtered through a 0.45 micron filter. The frlter cake was
washed with methylene chloride and dried at ambient temperature under high
vacuum to give 0.975 grams Byproduct F. The proton and carbon-13 NMR
~o spectra of Byproduct F were in agreement with its structure. The filtrate
was
stripped to give 5.09 grams material which was determined by GC (after
trimethysilylation with trimethylsilyl chloride and hexamethyldisilazane in
pyridine) to contain 85.8 % Intermediate E and 2.8 % Byproduct F, with the
remainder being unknown components (percentages express the relative area
1s percentages of GC peaks). The proton and carbon-13 NMR spectra, infrared
(IR) spectrum, and GC/MS spectrum (after trimethylsilylation with
trimethylsilyl chloride and hexamethyldisilazane in pyridine) were in
agreement with the structure of Intermediate E.
The entire procedure described above for hydrolysis of Intermediate C
2o was repeated with Fractions 16-19 of impure Intermediate C (1.07 grams)
obtained from the same column chromatography described above. Using
essentially the same procedure described above in a scaled fashion, 0.72
grams of a product was obtained that was indicated by GC analysis (after
trimethylsilylation) to contain 92.2 % Intermediate E and 1.5 % Byproduct F,
zs with the remainder being unidentii=<ed.
These fractions were purified by recrystallization from isooctane/THF
solvent mixtures which led to only small reductions in Byproduct F in low
recrystallization yields. However, semipreparative HPLC, using a normal
phase column and gradients of isooctane and THF as the mobile phase, gave
3o Intermediate E in which Byproduct F was reduced to below detectable limits
(determined by GC after trimethylsilylation).
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Preparation of Product Compound ~.
Compound 1 is named as follows by IUPAC: 2-{[4-(hydroxymethyl)
benzyl]oxy} propane-1,3-diol.
Intermediate E (0.558 grams) was dissolved in 10 ml dry methanol
s (distilled in glass) and this solution was transfierred to a thick walled
glass
bottle containing a magnetic stir bar After bubbling argon through this
solution for 15 minutes to remove dissolved oxygen while cooling the solution
to 0 C, ammonia gas was bubbled into this solution through a hypodermic
needle for approximately 0.5 hour, The ammonia gas was initially passed
1o through a tower of sodium hydroxide pellets to remove residual water from
the gas. The bottle was then capped with a TeflonT""-lined crown seal and
allowed to stir for ten hours white warming to ambient temperature. The
bottle was then opened and the ammonia was removed by an argon purge.
The methanolic solution was then stripped in a rotary evaporator to obtain a
15 brown gummy solid.
This solid was dissolved in approximately 0.5 ml dry methanol and
approximately 5 ml dry diethyl ether was added. The solution became turbid
after storing overnight in a freezer at approximately -30°C and a
crystalline
solid formed. The supernatant liquid was decanted and the solid was washed
zo with ether and dried under vacuum to obtain 0.164 grams yellow-white
crystalline solid. The proton NMR spectrum of this material was in accord
with the structure of Compound 1 but GC analysis (after trimethylsilylation)
indicated this material to be only approximately 80 % pure. This once-
recrystallized material was then recrystallized two more times from 10/1 (v/v)
z5 diethyl ether/methanoi to obtain a white crystalline material. Proton and
carbon-13 NMR spectra obtained from the second crop were in accord with
the structure of Compound 1. Two crops of crystals were obtained from the
third recrystallization, the first crop weighing 71 mg and the second crop
weighing 35 mg. GC analysis of the first crop (after trimethylsilylation)
so indicated that this material was approximately 97 % pure with one slightly
later eluting peak representing approximately 2 % of the total peak area.
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The proton NMR spectrum of the first crop was essentially identical to the
spectrum of the second crop obtained by recrystallization described above.
EXAMPLE Ci - Crosslinker Making
s This example illustrates a method for making an
isophoronediisocyanate capped 1,4-butanediol (IPDI-BD-IPDI) crosslinker
useful with the invention. The acronym IPDI-BD-IPDI is used to represent a
structure more completely described as
1o OCN-[IPDI-NHC00-BD-OOCNH]n-IPDI-NHC00-BD-OOCNHIPDI-NCO
where n = 0, ~, 2 with n = 0 greatly predominating.
Vacuum distilled (center cut), dry, 1,4-butanediol (BD, Aldrich 24,055-
9), 4.5 g (0.050 mole) was added to a previously flame dried, and cooled
15 while flushing with dry argon, 2 liter Pyrex Erlenmeyer flask. A tared 1000
u1,
Teflon plunger, microsyringe was used for transfer. Dry chloroform (CHCI3,
Burdick and Jackson B&D, distilled in glass, 478.4 g, 318.9 cc) was added to
the BD using a flame dried 1-liter Pyrex graduate while a mild argon flush was
maintained. About 20 grams of Fluka nondusting 3A molecular sieve was
2o added to the solution to ensure that no water was present or picked up.
Separately a 2-liter, three-neck (standard taper size 24/40 necks) reaction
flask containing a football-shaped Teflon coated magnetic stir bar was flame
dried and cooled while flushing with dry argon. The flask and stir bar were
then tare weighed (296.16 g) and clamp mounted on a rack in a fume hood
Z5 for conducting the reaction. A 1-liter Pyrex dropping funnel with a bottom
24/40 male joint and a drip tip, and a pressure equalizing side arm, was
placed into one of the side 24/40 female joints. A pre-flame-dried, water
cooling equipped reflux condenser was placed in the other side joint. The
assembled apparatus was all re-flame-dried and cooled while argon flushing.
3o The argon was passed through the top of the dropping funnel, which had a
side-arm gas inlet adapter affixed, through the reaction flask, and exited
from
a gas outlet adapter at the top of the water cooling equipped condenser. The
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outlet gas was then passed through a mineral oil bubbier to allow adjustment
and visual observation of the gas flow rate. The center port of the reaction
flask was closed with a z4/40 stopper. Then, the reaction flask assembly was
removed from its mounted position on the rack, while maintaining a slow
s argon flush, and 222.5 g (1.00 Mole) of center cut vacuum distilled
isophorone diisocyanate (Aldrich 31,2-4, IPDI) was added to the unmounted
reaction flask assembly, which was placed on a large torsion balance to
accurately weigh the IPDI. The IPDI was poured from the argon flushed 1
liter Pyrex round bottom distillation receiver into which it had been
distilled
(under argon in a flame dried Pyrex distillation assembly). The theoretical
yield of IPDI-BD-IPDI crosslinker was calculated to be z6.9 g (0.0105 Mole BD
x 538.74 g/Mole molecular weight of the expected IPDI-BD-IPDI product).
Similarly 167 grams (111cc) of dry B&D CHCI3 solvent was added to
the reaction flask and the assembly was then remounted on the rack in the
5 hood. Then the separately prepared BD in CHCl3 solution (Erlenmeyer flask)
was transferred directly to the dropping funnel and rinsed in with three small
portions (N10 cc each) of CHCI3 to insure that all BH was transferred, leaving
the 1=luka 3A molecular sieve in the z liter Erlenmeyer flask. The reaction
flask was then heated to 50°C using a thermostatically temperature
controlled
2o mineral oil bath mounted on a lab jack, which was raised until the
preheated
mineral oil lave! was wail above the level of the magnetically stirred clear,
colorless IPDI/CHCIs solution. The CHCI3 solvent quickly boiled and refluxed
gently. The CHCI3/BD solution in the dropping funnel was then added in
rapid-dropwise fashion over a 2.5 hour period, while maintaining a steady,
z5 slow (1 bubble per 2 or 3 seconds) argon purge. The reaction was
maintained at 50°C for 24 hours after BD addition was complete. Then
the
heat was turned off and the reaction mixture cooled to ambient temperature
by removing the 50°C mineral oil bath and letting the mixture stand
over the
weekend, while maintaining the slow argon purge. The CHCI3 was then
3o vacuum distilled (stripped) from the reaction flask, while stirring was
maintained, by replacing the reflux condenser with a vacuum pump
connected through a large capacity, dry ice cooled, trap to collect the
z7.
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distillate. The dropping funnel was also removed and replaced with just the
argon inlet adapter. Argon flow was adjusted to nil when vacuum was
applied. The mineral oil bath was replaced around the reaction flask and
heated only very slightly to maintain a temperature near ambient (N 25-
27°C). The CHCI3 was stripped carefully, to avoid foaming, until 175.9
g of a
fairly thin, clear, very light yellow, presumably CHCI3 free liquid was
obtained.
Apparently 51.1 g of IPDI had codistilled with CHCI3 since the total weight of
BD + IPDI originally was 227.0 grams.
One (1.0) gram of the liquid product was added to 25 cc of bone-dry
1o hexane (Aldrich 22,706-4, water < 0.002%) in a dry 100 cc Pyrex Erlenmeyer
flask to test the use of hexane as a purifying medium. A white, emulsion-
looking, mixture was obtained, which separated after several hours into a thin
layer of clear viscous liquid on the bottom and a clear, colorless upper
layer.
Since IPDI is very soluble in hexane and the product, with two internal,
highly
hydrogen bonding urethane bonds, was expected to be hexane insoluble, it
was assumed that the thin bottom layer was the desired product and the
upper layer was a hexane solution of unreacted IPDI. Hence, the entire batch
of product was added to a total of 3.6 liters of the dry hexane in two equal
portions in two liter, flame-dried, Pyrex Erlenmeyer flasks. The same
2o precipitation phenomenon occurred on the larger scale. After phase
separation was complete the clear, supernatant hexane-IPDI layers were
decanted, and the viscous, clear, but very slightly yellow product layers were
rinsed with about 50 cc of dry hexane, the product redissolved in about 10 cc
of bone dry methylene dichloride (CH2CI2) (Aldrich 27,099-7, < 0.005%
2s water) and reprecipitated with about 200 cc of dry hexane in each flask.
When phase separation was complete, this dissolution and reprecipitation
process was repeated.
The two product portions were then combined into a 100 cc, flame
dried, one neck, Pyrex round bottom flask using several small (N 10 cc)
3o amounts of the bone dry CHZCI2 solvent. The CHZCIZ was carefully stripped
in
a vacuum oven at ambient temperature, then dried overnight in the vacuum
oven (N 1 Torr) with mild heating (N 35°C), Obtained were 11.87 grams
of a
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clear, very light yellow, extremely viscous oil or liquid. This was a 44.1%
yield based on the theoretical yield of 26.94 grams. A significant portion of
the product was apparently removed during the hexane precipitation
purification process. .This should be recoverably by, for example, separate
s vacuum distillation of the unreacted IPDI, after distilling all of the
precipitation
medium hexane. Although this was not done, it is considered very likely that
the hexane and unreacted IPDI could be collected and recycled, and virtually
all of the product IPDI-BD+IPDI crosslinker product recovered, if this is
desired. The product was analyzed by H-NMR. The product spectrum was
to compared with the HNMR spectra of the starting IPDI and BD. The spectra of
all three materials are fully consistent with the expected HNMR spectra.
EXAMPLE C2 Crosslinker Making
This example illustrates the dibutyltindilaurate catalyzed preparation of
15 TMXDI capped 1,4-butanediol crosslinker (TMXDI-BD-TMXDI). This acronym
(TMXDI-BD-TMXDI) is understood to represent
OCN TMXDI-(NH-CO-0-BD-0-OC-HN-TMXDI)"-NH-CO-0-BD-0-OC-HN-TMXDI-
NCO
2o where n=0,1, or 2 with n=0 greatly predominating.
The same two liter reaction flask, magnetic stir bar and handling and
flask drying procedures were used as in Example C1. Thus, 244.3 grams
(1.000 mole) of as received 1,3-bis(1-isocyanato-1-methyl-ethyl) benzene
2s (TMXDI, CYTEC industries) were added to the dried and argon flashed
reaction flask. Then 4.506 grams (0.050 moles) 1,4-butanediol (BD) were
added. The two reactants were immiscibie. Then i00 grams (127 cc)
anhydrous acetonitriie (Aldrich 27,100-4, water < 0.001%) were added to the
flask and a clear, colorless, one phase, reaction mixture was quickly
obtained.
3o Then 0.0365 grams (6.115 x105 mole) of dibutyltindilaurate catalyst were
added. This is 0.122 mole percent of catalyst based on the 0.050 moles of
BD present. The clear, thin mixture was then stirred at ambient temperature
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(N 23°C) under a constant argon flush for 9 days. The acetonitrile
solvent
was then vacuum stripped at N 23-25°C using the mineral oil bath and a
very
low heat input. After distillation ceased, 211 grams of a clear, slightly
viscous
solution of the TMXDI-BD product dissolved in unreacted TMXDI were
obtained. This is.37.8 grams less than the expected weight of 248.8.
Presumably this amount of TMXDT cQ-distilled with the acetonitrile. The
theoretical amount of TMXDI-BD-TMXDI product present, if no dimerization,
trimerization, or higher oligomerization occurred, was 28.94 grams. Hence,
the percentage by weight of expected product in the final mixture was
to (28.94/211.4) x 100 = 13.69%. A 30.0 gram aliquot of the final mixture was
taken for product recovery and purification. The theoretical yield of TMXDI-
BD-TMXDT product from this aliquot was (0.1369 x 30.0) = 4.11 grams.
The solution was added to 300 grams (455 cc) of the anhydrous,
reagent grade hexane in a dry 500 ml Erlenmeyer flask, under argon. As in
Example C1, a white, emulsion-Pike suspension was obtained, which gradually
separated into two distinct phases. These were a thin layer of clear, viscous
liquid on the bottom of the flask and a large amount of clear, thin
supernatant
liquid. This upper layer consisted of hexane and presumably most of the
unreacted TMXDI, which is readily soluble in hexane, as well as some portion
of the product codissolved in the hexane/TMXDI mixture. It was decanted
and the thin, clear product layer rinsed with about 10 cc of anhydrous hexane
twice. The viscous, clear, colorless liquid was redissolved in about 10 cc of
dry methylene chloride (CH2C12~ and reprecipitated in 100 cc anhydrous
hexane as before. The supernatant layer was decanted, the viscous, clear
2s product washed with 10 cc hexane and again dissolved in 10 cc CHCIZ and
precipitated in100 cc anhydrous hexane. The final supernatant layer was
decanted, the product layer rinsed with more of the anhydrous hexane and
the product vacuum dried overnight at N 1 Torr and 30-35°C to obtain
3.15
grams of clear, practically solid, colorless product. This was 76.6% overall
3o yield based on a theoretical 4.11 grams of product from the aliquot. H-NMR
analysis of this three times precipitated product indicated 99+% purity.
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EXAMPLE C3
4-Hydroxymethyl-beta-(hydroxyethoxy)benzene, hereafter referred to
as Compound G, is reacted with MDI in a mole ratio of two moles of
compound G and one mole of MDI. This constitutes an equimolar ratio of
s aliphatic primary hydroxyl and isocyanate groups. The reaction is carried
out
by melting together under anhydrous and air-excluded conditions the two
component reactants. They are heated while stirring and kept under a very
slow purge of inert gas such as dry nitrogen or dry argon. They are heated to
a temperature of at least about 180°C and perhaps beneficially to a
1o temperature of about 200°C. After maintaining this temperature for
about
10-30 minutes, the mixture is cooled slowly to the temperature at which the
mixture solidifies. This will be done over about a 30-60 minute time period.
Obtained will be the bis-hydroxymethyl-capped-diurethane coupled product
from the formation of stable urethane bonds between the two primary
1s aliphatic hydroxyethyl groups and the two MDI isocyanate groups. The
benzylic hydroxyl groups will be essentially uncombined and will constitute
the
end of groups of this bis-urethane.
EXAMPLE C4
2o Compound G of the previous example is reacted with the tri-isocyanate
compound available commercially. This compound is Compound H from
Rhone-Poulenc known as Tolonate~ (HDT) Trimer. Compound G is reacted
with Compound H in a mole ratio of three moles of Compound G and one
mole of Compound H. This constitutes an equimolar ratio of aliphatic primary
2s hydroxyl and isocyanate groups. lThe reaction is carried out following the
procedure of Example C3 obtained will be the tris(hydroxymethyl)-capped-tri-
urethane coupled product obtained from the formation of stable urethane
bonds between the three primary hydroxyethyl groups of Compound G and
the three isocyanate groups of Compound H. The three benzylic hydroxyl
3o groups will be essentially uncombined and will constitute available
reactive
groups for the formation of reversible urethane crosslinking bonds when
combined in a minor amount (less than or equal to 50 mole percent of the
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hydroxyl groups used) polymer with a major amount (less than or equal to 50
mole percent of the hydroxyl groups used, from di-benzylic hydroxyl
compounds or oligomers such as 1,4-benzenedimethanol and/or the di-
hydroxymethyl compound product of Example C3.
EXAMPLE P1 Polymer Making
A control polyurethane was prepared without using any Compound 1.
Diphenylmethane diisocyanate, commonly referred to as methylenediphenyl-
diisocyanate (MDI), polybutylene adipate (PBA) with a molecular weight of
1o about 1986 (a high molecular weight polyol with two end group aliphatic-
hydroxybutyl-hydroxyl groups), and 1,4-butanediol (BD) were used. The MDI
and BD were reagent grade chemicals obtained from Aldrich (MDI, Aldrich
25,643-9; BD, Aldrich 24,055-9) but were vacuum distilled before use. The
PBA is a commercially available polyurethane polymerization quality aliphatic
polyester diol. All reactants were handled under dry argon gas. The
polymerization was performed in a silylated Pyrex reactor tube (N50 cc heavy
walled test tube) equipped with a standard taper 24/40 top joint. Sylilation
of
the Pyrex glass surface was carried out using an octadecyltrialcoxsilyl
functionalized silane (Siliclad~), Gelest Product No. SIS 6952-0, lot-964-
3014,
zo 20% active). A 1% solution of this product is made up in distilled water.
The
glass is rinsed with 5% aqueous NaOH followed by several distilled water
rinses, then the 1°to Siliclad~. It is then rinsed with water again and
dried at
about 100°C for one hour to provide an extremely stable hydrophobic
surface.
A simple head adapter with a small opening on top just large enough for a
2s thin stainless steel spatula to fit through, and a side argon inlet tube,
was
placed in the top standard taper joint during the polymerization. The head
adapter was removed from the Pyrex reaction tube and 8.937 grams (4.50
mMole) of PBA and then 2.463 (9.842 mMole) of MDI were weighed into the
dry (silylated) tube. The head adapter was reinstalled and an argon flush was
3o immediately started. The tube was lowered into a Woods metal bath
preheated to 97°C. The contents melted and were carefully stirred at 90-
100°C for one hour. Care was taken not to splash any reaction mixture
on
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the upper walls of the tube. A moderate viscosity increase occurred during
the one hour of heating, with essentially all of the increase occurring in the
first 30-45 minutes.
Then 0.4908 g. (5.446 mMoles) of 1,4-BD was quickly added directly
s onto the top of the melt via a pre-tared 1000 ml syringe while maintaining
the
argon flush. The Woods metal bath Was then heated rapidly to approximately
200°C while stirring was continued. The heat up from 100°C to
200°C only
required about 6-7 minutes. Stirring was continued while heating at 197-
200°C for about 30 minutes. During the first 10-15 minutes of this
period the
~.o melt viscosity increased rapidly until a quite viscous but still readily
hand
stirrable melt was obtained. This melt viscosity did not noticeably change
over the last 10-15 minutes of stirring at 197-200°C. A fiber was drawn
from
this melt. The fiber was quite strong and elastic at room temperature. The
hot molten polymer was then rapidly removed from the small reaction vessel,
15 into a Teflon dish, and allowed to cooi. The product was a tough, strong
elastic thermoplastic.
A post polymerization treatment to insure that polymerization was
complete was carried out by heating the polymer mass overnight at 80°C
in a
vacuum oven set at about 1 Torr.
2o The product, both before and after this vacuum oven treatment was a
strong, tough, elastic thermoplastic. A small piece readily dissolved in dry
dimethyl formamide (DMF) in several hours at room temperature. A small
piece was also submitted for gel permeation chromatography (GPC) molecular
weight analysis. This was done using a Waters GPC instrument and columns
z5 with tetrahydrofuran (THF) solvent. The GPC was calibrated using four
narrow molecular polystyrene standards. The GPC molecular weight of a
commercial Spandex-type, melt processible, elastic thermoplastic
polyurethane was also measured at the same time. The number (Mn), peak
(Mp), and weight Mw average molecular weights for the commercial TPU are,
so respectively, Mn=57,539; Mp=126,884; and Mw=147,283. The same
molecular weight data for the laboratory prepared control TPU are,
respectively, Mn=52,200; Mp=131,525; and Mw=144,381. This shows that a
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TPE based on an aliphatic polyesterdiol, MDI and 1,4-Butanediol can readily
be carried out to make a polyurethane with molecular weight parameters
within a few percent of those desired in a commercial product.
EXAMPLE P2
This example illustrates the production of a thermoplastic polyurethane
elastomer (TPE) with pendant benzylic hydroxyl groups using Compound 1.
The polymerization was performed in silylated Pyrex reaction tubes
(N50 cc volume) equipped with 24/40 joints and using a molten Woods metal
io bath for heating. A 24/40 adapter with an argon inlet was inserted into the
top of the Pyrex reaction tube. Dry argon was slowly, but constantly, flushed
through a small opening in the reactor tube during the reaction. The reaction
mixture was stirred with a thin stainless steel spatula inserted through a
small
opening in the top of gas inlet adapter. Constant, slow stirring was
i5 performed due to the small scale used and the requirement that ingredients
be mixed but not spread upward on the tube surface. This assured that all
material was available for reaction.
Next, 2.2343 grams (1.125 m Mole) of polybutylene adipate
(MW=1986, Eq. wt. =993) and 0.6356 g (2,540 mMole) of MDI were weighed
2o to four decimal places directly into the reaction tube using an analytical
balance placed in a glove bag which was flushed and filled with argon. All
reactants were carefully placed onto the bottom of the reaction tube. The
reactor tube was then removed from the glove bag with the head adapter
already in place the mixture was heated while stirring at 100-110°C for
one
2s hour during which time it became moderately viscous. The reaction tube was
lifted just out of the molten metal bath, which was then heated rapidly up to
197-200°C. Then, 0.1177 g (1.3063 mMole) of 1,4-BD was quantitatively
carefully added directly onto the still argon flushed prepoiymer mixture from
a
preweighed 1000 microliter syringe, which was also reweighed after addition
30 of 1,4-BD to insure accurate weight addition by difference. Immediately
after
this 0.0146 g (0.0688 mMole) of Compound 1 was added, also carefully
placing it on top of the reaction mixture. The end capper, diethyleneglycol
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WO 01/92366 PCT/US00/14722
ethyl ether, 0.0107 g (0.0797 mMole) was then added from a microsyringe,
again weighing the syringe before and after the addition. These additions
were performed while maintaining the argon flow. As soon as the additions
were complete, the reactor tube was lowered back into the Woods metal bath
and the mixture was heated at 197-200°C while carefully stirring for 30
minutes.
The total hydroxyl content of the reaction mixture was 5.0793 mMole,
while the total isocyanate content was 5.0796 mole. The Compound 1
hydroxyl content represented 5 mMolar % replacement of butanediol mMolar
1o hydroxyl content. Table 3 shows the quantities of all components used to
prepare the polymer.
Table 3
Component Weight Component Hydroxyl Isocyanate
(g) Amount Amount Amount
(mMole) (mMole) (mMole)
PBAa 2.2343 1.125 2.250 0
MDI 0.6356 2.540 0 5.0796
1,4-BD 0.1177 1.3057 2.6115 0
Compound 1 0.0146 0.0688 0.1376 0
.
End Capper~ 0.0107 0.0797 0.0797 0
Total: 3.0129 N/A 5.0788 5.0796
a - polybutyleneadipate
b - this number of moles includes only the two primary hydroxyl groups and
not the benzylic hydroxyl group
c - diethylene glycol ethyl ether (MW=134.18; dried over Fluka 3A molecular
2o sieves.
EXAMPLE P3
The reactor tube of Example P2 was then removed from the hot
Woods metal bath and 2.2250 g of the thermoplastic polyurethane elastomer
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with pendant benzylic hydroxyl groups was removed (73.85% of the
calculated total weight of 3.0129g), thus leaving a calculated quantity of
0.7878 g of the thermoplastic polyurethane (26.15°!°) (TPE) with
(presumably
mostly unreacted) pendant benzylic hydroxyl groups in the reaction tube.
s This polymer contained a calculated quantity of 0.0180 mMole of Compound
1. Great care was taken while removing this control polyurethane portion of
Example P2, to not leave any polymer deposits on the walls of the reactor
tube, above the polymer melt line. A crosslinker made from an excess of
isophorone diisocyanate with 1,4-butanediol (with a presumed IPDI-BD-IPDI
1o structure; molecular weight = 534.7, from Example C1 was then added to the
melt in an amount based on the presumed presence of 90% of the theoretical
amount of benzylic hydroxyl groups. This quantity corresponded to 0.90 x
(0.0180/2) = 0.0081 mMole or 4.3 mg crosslinker, which was carefully added
to the top surface of the remaining melt. The total quantity of MDI derived
15 carbamate groups in the TPE remaining in the reactor tube was 5.08 x 0.2615
= 1.33 mMoles. It should be noted that the maximum quantity of urethane
groups derived from the benzylic hydroxyl groups of Compound 1 and the
IPDI-based crosslinker (0.0081 mMole) was 2 x 0.0081 x 100 = 0.0162
mMole of urethane groups. This quantity of urethane groups corresponds to
20 1.20% of the total urethane groups in this sample 0.0162 mMole x 100/(1.33
mMole + 0.0162 mMole) = 1.20 %. The reactor tube was then placed back
in the molten metal bath (maintained at about 200°C) and the
crosslinker was
very carefully and thoroughly mixed into the quite viscous melt over a five
minute period.
a5 The viscosity of the molten polyurethane was essentially the same as
the final melt viscosity of the control TPU in Example P1 and the experimental
TPU product final melt viscosity in Example P2, both before and after adding
the IPDI-BD-IPDI crosslinker. Hence essentially no crossfinking was in
evidence at the 200°C reaction temperature.
so This product, a quite viscous but still readily hand-stirrable melt, was
then cooled. Very importantly, a small piece of this material when placed in
dimethylformamide (DMF) at ambient temperature swelled slightly over 3-4
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hours. It did not change (swell) any additional amount after 24 hours more
at room temperature. The fact that it did not dissolve showed that it was
crosslinked, as desired. In contrast, the control material, which was removed
from the reactor tube before the isophorone-based crosslinker was added,
s dissolved readily in DMF over a 3-4 hour period at ambient temperature. The
solution was clear and qualitatively free of gel (i.e. undissolved polymer).
This showed that it was not crosslinked. These solubility test results provide
strong evidence that Compound 1 was largely copolymerized into the hard
segment of the backbone structure of the TPU with pendant benzylic -OH
1o groups that were largely not reacted with isocyanate groups, until the IPDI-
BD-IPDI crosslinker isocyanate groups were added. Interestingly then, when
the crosslinked TPE was reheated back to 200°C under argon gas, fibers
could readily be drawn from the melt. These fibers were quite strong and
elastic at room temperature. Films were then prepared from both the IPDI-
15 crosslinked material and the control material by pressing these materials
between sheets of Teflon in a heated press (at 200-300 Ibs. of force at about
180-190°C). Thin clear, tough, elastic films having a thickness of 1-2
mils
were readily obtained. These films were used for the IR reversion studies
described below. '
20 Although the control material appeared to completely dissolve in
dimethyl formamide (DMF) it is believed that a small number of crosslink sites
were made with the material of Compound 1. It is noted that there was an
excess of 0.0008 mMole of isocyanate added. Due to the ratios of the
materials added, however, the number of crosslinked sites was too small to
2s interfere with apparent solubilization of the polymer.
EXAMPLE P4
This example illustrates the production of a reversible thermoplastic
polyurethane elastomer (TPE) but which contains, at room temperature
3o crosslinked MDI urethane bonds, by using Compound 1 at 5 mole percent
replacement of 1,4-BD and an amount of MDI sufficient to provide an
isocyanate content that is equivalent to the total hydroxyl content, including
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the benzylic hydroxyl content. The benzylic urethane crosslinks will be
present at room temperature and up to at least about 150°C, but will
reverse
when heated above this temperature to about 200°C, allowing the TPE to
melt
s The polymerization is performed in silylated Pyrex reaction tubes (N50
cc volume) equipped with 24/40 joints and using a molten Woods metal bath
for heating. A 24/40 adapter with an argon inlet is inserted into the top of
the Pyrex reaction tube. Dry argon is slowly, but constantly, flushed through
a small opening in the reactor tube during the reaction. The reaction mixture
1o is stirred with a thin stainless steel spatula inserted through a small
opening
in the top of gas inlet adapter. Constant, slow stirring is performed due to
the small scale used and the requirement that ingredients be mixed but not
spread upward on the tube surface. This assures that all material is available
for reaction.
15 Next, 2.2343 grams (1.125 m Mole) of polybutylene adipate
(MW=1986, Eq. wt. =993) and 0.6442 g (2.5741 mMole) of MDI is weighed
to four decimal places directly into the reaction tube using an analytical
balance placed in a glove bag which is flushed and filled with argon. All
reactants are carefully placed onto the bottom of the reaction tube. The
zo reactor tube is then removed from the glove bag with the head adapter
already in place the mixture is heated while stirring at 100-110°C for
one hour
during which time it becomes moderately viscous. The reaction tube is lifted
just out of the molten metal bath, which is then heated rapidly up to 197-
200°C. Then, 0.1177 g (1.3063 mMole) of 1,4-BD is quantitatively
carefully
z5 added directly onto the stiN argon flushed prepolymer mixture from a
preweighed 1000 microliter syringe, which is also reweighed after addition of
1,4-BD to insure accurate weight addition by difference. Immediately after
this 0.0146 g (0.0688 mMole) of Compound 1 is added, also carefully placing
it on top of the reaction mixture. The end capper, diethyleneglycol ethyl
3o ether, 0.0107 g (0.0797 mMole) is then added from a microsyringe, again
weighing the syringe before and after the addition. These additions are
performed while maintaining the argon flow. As soon as the additions are
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complete, the reactor tube is lowered back into the Woods metal bath and the
mixture is heated at 197-200°C while carefully stirring for 30 minutes.
The total reactive hydroxyl content of the reaction mixture is 5.1476
mMole, while the total isocyanate content is 5.1484 mole. The Compound 1
hydroxyl content represents 5 mMolar °lo replacement of butanediol
mMolar
hydroxyl content. Table 4 shows the,quantities of all components that will be
used to prepare the polymer.
Table 4
Component Weight Component Hydroxyl Isocyanate
(g) Amount Amount Amount
(mMole) (mMole) (mMole)
PBAa 2.2343 1.125 2.250 0
MDI 0.6442 2.5742 0 5.1484
1,4-BD 0.1177 1.3057 2.6115 0
Compound 1 0.0146 0.0688 0.2064 0
End Capper' 0.0107 0.0797 0.0797 0
Total: 3.0215 N/A 5.1476 5.1484
a - polybutyleneadipate
b - this number of moles includes the three hydroxyl groups of Compound 1
c - diethylene glycol ethyl ether (MW=134.18); dried over Fluka 3A molecular
sieves.
While the forms of the invention herein disclosed constitute presently
preferred embodiments, many others are possible. It is not intended herein
2o to mention all of the possible equivalent forms or ramifications of the
invention. It is to be understood that the terms used herein are merely
descriptive, rather than limiting, and that various changes may be made
without departing from the spirit of the scope of the invention
39
