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Description  |
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FIELD OF THE INVENTION
This invention relates to anionic polymerization of monomers, to
functionalized polymers used as components in adhesives, sealants and
coatings, and to lithium alkyl reagents used as initiators for the
synthesis of these polymers.
BACKGROUND OF THE INVENTION
Anionic polymerization of conjugated dienes with lithium initiators, such
as sec-butyllithium, and hydrogenation of residual unsaturation has been
described in many references including U.S. Pat. No. Re. 27,145 which
teaches a relationship between the amount of 1,2-addition of butadiene and
the glass transition temperatures of the hydrogenated butadiene polymers.
The capping of living anionic polymers to form functional end groups is
described in U.S. Pat. Nos. 4,417,029, 4,518,753, and 4,753,991. Of
particular interest for the present invention are anionic polymers that
are capped on one or more ends with hydroxyl, carboxyl, phenol, epoxy, or
amine groups.
Anionic polymerization using protected functional initiators having the
structure R.sup.1 R.sup.2 R.sup.3 Si--O--A'--Li is described in WO
91/12277 wherein R.sup.1, R.sup.2, and R.sup.3 are preferably alkyl,
alkoxy, aryl, or alkaryl groups having from 1 to 10 carbon atoms, and A'
is preferably a branched or straight chain bridging group having at least
2 carbon atoms. R.sup.1, R.sup.2, and R.sup.3 are preferably not all
CH.sub.3. The bridging group (A') is most preferably a straight chain
alkyl having from 3 to 10 carbon atoms and is exemplified by the following
compound:
##STR1##
which is readily prepared by lithiation of the reaction product of
1-chloro-6-hydroxy-n-hexane and t-butyldimethylchlorosilane. The use of
such an initiator as Structure (1) to polymerize the desired monomer(s),
followed by capping to produce the second terminal alcohol group, has
several advantages over the preparation of telechelic diols by capping
polymers prepared with difunctional initiators such as 1,4-dilithiobutane
and lithium naphthalide. In addition to providing the option of
polymerizing in non-polar solvents, this route avoids the formation of
ionic gels, which are known to occur when diinitiated polymers are capped
with reagents such as ethylene oxide, generating the polymeric
di-alkoxide. These gels form even in relatively polar solvent mixtures and
greatly complicate subsequent processing steps. By capping to produce the
alkoxide on only one polymer terminus, these gels are avoided.
The initiator of Structure (1) anionically polymerizes unsaturated monomers
like conventional lithium initiators but starts the polymer chain with a
t-butyldimethylsiloxy functional group that can be converted to a primary
alcohol, which is useful in a variety of subsequent reactions. While it
appears that the majority of Structure (1) is active if the initiation
step is performed at a low temperature (-5.degree. C.), at slightly higher
temperatures, a significant fraction of the initiator charge fails to
initiate polymerization; a large portion of the initiator is non-reactive
or "dead". Initiation with sec-butyllithium occurs efficiently well above
room temperature. Nevertheless, the active portion of the initiator of
Structure (1) produces living polymers that can be further endcapped and
hydrogenated like conventional anionic polymers.
The initiator of Structure (1) affords a polymer chain having a
t-butyldimethylsiloxy functional moiety on the end of it. While that
protecting group can be removed (deprotection) to give the desired primary
alcohol functionality, it is somewhat difficult to practice and is costly.
Deprotection of polymers of this type requires contacting with a molar
excess (5X stoichiometry) of a strong organic acid, such as
methanesulfonic acid, and a compatabilizing cosolvent such as isopropanol
(about 20% wt). This mixture is then stirred at elevated temperatures
(about 50.degree. C.) until the polymer is deprotected (several hours
depending on the specific initiator that is used). When the polymer has
been deprotected, it is then necessary to neutralize the acidic hydrolysis
catalyst, wash out the spent acid salt, and distill out the
compatabilizing cosolvent. These additional steps add time and cost to the
process. A functional initiator that contained a protecting group that was
easier to remove would be advantaged in processing efficiency.
The polymers derived from initiators of the type described in Structure (1)
tend to have a non-uniform microstructure. In the early stages of the
polymerization of butadiene using an initiator of this type, 1,4-addition
of monomer is the dominant mode of incorporation of butadiene. Even when a
solvent system that is high in a microstructure modifier is employed, such
as 10% wt diethylether in cyclohexane, the 1,4-addition of butadiene is
over 70%. As the polymer grows longer and the C--Li end of the chain
distances itself from the t-butyldimethylsiloxy functional end, this
effect dissipates and the microstructure of the added units are controlled
by the nature of the solvent; at 10% wt diethyl ether in cyclohexane, it
would be about 50-60% wt 1,4-addition of butadiene. The adverse effect of
this variance in microstructure is manifest in the saturated,
hydrogenated, polymer. The segment of the polymer having a linear
microstructure, high 1,4-addition of butadiene, becomes a polyethylene
segment on hydrogenation and tends to have polyethylene-like
crystallinity. This crystallinity tends to increase the viscosity of
liquid polymers near room temperature and, in the extreme, may induce the
sample to solidify. For the preparation of low viscosity, hydrogenated,
functional polymers, an initiator is needed that has protected
functionality and allows the preparation of a butadiene polymer that has a
uniform microstructure that can be controlled at intermediate levels of
1,4-addition.
It is an object of the present invention to provide improved protected
functional initiators that operate efficiently (with a minimum of dead
initiator) at economical temperatures. These initiators should operate to
afford a butadiene polymer of uniform and controlled microstructure and
should be deprotected under mild and low cost conditions.
SUMMARY OF THE INVENTION
The present invention is the discovery that lithium compounds having the
structure:
##STR2##
wherein A" is cyclohexyl or --CR'R"--, wherein R' is a linear alkyl having
from 1 to 10 carbon atoms and R" is hydrogen or a linear alkyl having from
1 to 10 carbon atoms, initiate polymerization of anionic polymers at
surprisingly higher polymerization temperatures with surprisingly lower
amounts of dead initiator (higher efficiency) than similar initiators
having linear bridging groups connecting the oxygen and the lithium. The
initiators of Structure (2) are also suprisingly easier to deprotect than
similar initiators having branched alkyls bonded to the silicon. The
polymers produced by these initiators are readily endcapped and
hydrogenated to form anionic polymers having one or more terminal
functional groups under commercially-attractive conditions.
DETAILED DESCRIPTION OF THE INVENTION
The polymerization of unsaturated monomers with functionalized initiators
having the structure R.sup.1 R.sup.2 R.sup.3 Si--O--A'--Li is described in
WO 91/12277 wherein R.sup.1, R.sup.2, and R.sup.3 are preferably alkyl,
alkoxy, aryl, or alkaryl groups having from 1 to 10 carbon atoms, and A'
is preferably a branched or straight chain bridging group having at least
2 carbon atoms, preferably linear alkyls having from 3 to 10 carbon atoms.
The present invention is the discovery that lithium initiators having the
structure:
##STR3##
wherein A" is cyclohexyl or --CR'R"--, wherein R' is a linear alkyl having
from 1 to 10 carbon atoms and R" is hydrogen or a linear alkyl having from
1 to 10 carbon atoms, preferably A" is --CR'R"-- wherein R" is methyl,
initiate polymerization of anionic polymers at surprisingly higher
polymerization temperatures with surprisingly lower amounts of dead
initiator (higher efficiency) than similar initiators having linear
bridging groups connecting the oxygen and the lithium. These initiators
are surprisingly effective at affording diene polymers having a uniform
and controllable microstructure by comparison to similar initiators having
a branched alkyl moiety bonded to the silicon center. The initiator of
structure (2) prepares homopolymers of butadiene which have a uniform
distribution of 1,2-addition across the polymer chain when the amount of
1,2-addition is between 5 and 95% wt, more preferably between 30 to 70%
wt.
The efficiency of initiators of this type is readily determined by a
variety of analytical methods. In living polymerizations, each mole of
active initiator is expected to start one mole of polymer, so that the
average molecular weight of the resulting polymer can be predicted from
the following relationship:
MW.sub.ave =(m.sub.mono /m.sub.init)(MW.sub.mono)+MW.sub.init +MW.sub.cap(
1)
where:
m.sub.mono =moles of monomer
m.sub.init =moles of initiator
MW.sub.mono =molecular weight of the monomer
MW.sub.init =MW of the fragment of the initiator that is incorporated into
the polymer chain
MW.sub.cap =MW of the fragment of the capping reagent that is incorporated
into the polymer chain
If a fraction of the initiator charge fails to start polymer, the resulting
product will be higher in molecular weight than predicted by equation (1).
So long as that fraction remains inactive throughout the polymerization,
the molecular weight distribution (MWD) will remain narrow and
monodisperse, typical of a living polymerization having a faster rate of
initiation than of propagation. In practice, molecular weights are often
somewhat larger than predicted by equation (1) due to inactivation of a
small fraction of the initiator charge by protic impurities present in
monomers, solvents, etc.
The initiators of the present invention are similar to s-butyllithium with
regard to economical operating temperature and low amounts of dead
initiator and a uniform, controlled level of 1,2-addition of diene in the
product polymer. However the initiators of the invention have the
advantage of placing a silyl ether group at the start of the polymer chain
which serves as a "masked" or "protected" alcohol, capable of conversion
to a primary, neopentyl-type alcohol group after polymerization is
completed by reaction with acids or bases under mild, low cost conditions
or as described in WO 91/12277. The polymer chains may be terminated,
endcapped, or coupled by conventional means to end the polymerization and
provide one or more terminal functional groups on linear or branched
polymers containing polymerized conjugated dienes.
While the initiator of Structure (1) would, after polymerization and
deprotection, afford a polymer having primary alcohol functionality, a
polymer having primary alcohol functionality of the neopentyl-type should
have improved thermal stability and condensation polymers derived from it
should have improved hydrolytic stability. The improved thermal stability
of neopentyl alcohol and the hydrolytic characteristics of its derivatives
are summarized in Advanced Organic Chemistry, Third Edition, by J. March,
John Wiley & Sons, New York (1985) (see particularly pp. 285, 299, 390,
514, 944, 955, 959, and references therein). It is reasonable that
polymers having this special structure would have similarly improved
properties.
The lithium initiator process is well known as described in U.S. Pat. No.
4,039,593 and U.S. Pat. No. Re. 27,145 which descriptions are incorporated
herein by reference. Typical living polymer structures that can be made
with lithium initiators such as Structure (2) include:
X--B--Li
X--B/A--Li
X--A--B--Li
X--B--A--Li
X--B--B/A--Li
X--B/A--B--Li
X--A--B--A--Li
wherein B represents polymerized units of one or more conjugated diene
hydrocarbons, A represents polymerized units of one or more vinyl aromatic
compounds, B/A represents random polymerized units of the conjugated diene
hydrocarbons and the vinyl aromatic monomers, and X is the residue of the
lithium initiator. The living polymers are terminated as linear polymers,
coupled to form branched polymers, or cappped to form additional
functional groups by conventional means such as addition of methanol,
silicon tetrachloride, divinylbenzene, or ethylene oxide. In the present
invention, X is a trimethylsilyl ether group and cleavage of the
trimethylsilyl ether leaves a neopentyl-like primary alcohol group in this
position. These primary alcohols have different reactivity than other
primary alcohol groups which will lead to different rates of reaction for
the chain ends with diisocyanates and dicarboxylic acids and the like.
This difference in reactivity rates could be very useful in designing
materials where stepwise polymerization is desired.
The initiators of the present invention are very active at room temperature
and polymerization is preferably initiated at a temperature from
15.degree. C. to 60.degree. C., most preferably from 30.degree. C. to
40.degree. C. It is generally advisable to keep the polymerization
temperature below about 100.degree. C.; above this temperature, side
reactions that change microstructure and limit capping efficiency may
become important. Polymerizations can be carried out over a range of
solids levels, preferably from about 5% to about 80% wt polymer, most
preferably from about 10% to about 40% wt. For high solids
polymerizations, it is preferable to add the monomer in increments to
avoid exceeding the desired polymerization temperature. If the initiator
is to be added to the full monomer charge, it is preferable to run the
polymerization between 10% and 20% wt solids.
When the conjugated diene is 1,3-butadiene and when the conjugated diene
polymer will be hydrogenated, the anionic polymerization of the conjugated
diene hydrocarbons is typically controlled with structure modifiers such
as diethyl ether or glyme (1,2-diethoxyethane) to obtain the desired
amount of 1,2-addition. As described in U.S. Pat. No. Re. 27,145 which is
incorporated by reference herein, the level of 1,2-addition of a butadiene
polymer or copolymer can greatly affect the rheology and elastomeric
properties of the polymer after hydrogenation. The hydrogenated polymers
exhibit improved heat stability and weatherability in the final, adhesive,
sealant or coating.
The 1,2-addition of 1,3-butadiene polymers having terminal functional
groups influences the viscosity of the polymers as described in more
detail below. A 1,2-addition of about 40% is achieved during
polymerization at 50.degree. C. with about 6% by volume of diethyl ether
or about 1000 ppm of glyme. Generally, vinyl contents in this range are
desirable if the product is to be hydrogenated, while low vinyl contents
are preferred if the polymer is to be used in its unsaturated form.
Anionic polymerization is often terminated by addition of water to remove
the lithium as lithium hydroxide (LiOH) or by addition of an alcohol (ROH)
to remove the lithium as a lithium alkoxide (LiOR). Polymers prepared from
initiators of the present invention and terminated in this way will be
monohydroxy functional materials (mono-ols) after removal of the
trimethylsilyl protecting group. To prepare polymers having an additional
terminal functional groups, the living polymer chains are preferably
terminated with hydroxyl (--OH), carboxyl (--CO.sub.2 H), phenol (ArOH),
epoxy, or amine groups by reaction with ethylene oxide (--OH), oxetane
(--OH), 2,2-dimethyloxetane (--OH), carbon dioxide (--CO.sub.2 H), a
protected hydroxystyrene monomer (ArOH), ethylene oxide plus
epichlorohydrin (epoxy), or the aziridine compounds listed in U.S. Pat.
No. 4,791,174 (amine). For the preparation of telechelic diols, the
preferred process is to terminate with 1-10 equivalents, most preferably
1-2 equivalents, of ethylene oxide at 30.degree. C.-50.degree. C. This
reaction is quite rapid; reaction times from 5 to 30 minutes yield
acceptable results.
The termination step or neutralization step can result in release of fine
particles of lithium bases as described in U.S. Pat. No. 5,166,277 which
is incorporated by reference herein. The lithium bases may interfere with
hydrogenation of the polymer and preferably are removed, especially if the
hydrogenation is to be carried out at high solids.
Termination with carbon dioxide results in carboxylate salt groups that
reduce hydrogenation catalyst activity as described in U.S. Pat. No.
4,970,254 which disclosure is incorporated by reference herein. Improved
hydrogenation is obtained by converting the carboxylate salt groups to
ester groups prior to hydrogenation and then reconverting to carboxylate
salt or carboxylic acid groups after hydrogenation.
Hydrogenation of at least 90%, preferably at least 95%, of the unsaturation
in low molecular weight butadiene polymers is achieved with nickel
catalysts as described in U.S. Pat. No. Re. 27,145 and U.S. Pat. No.
4,970,254 and U.S. patent application Ser. No. 07/785715 now U.S. Pat. No.
5,166,277 which are incorporated by reference herein. The preferred nickel
catalyst is a mixture of nickel 2-ethylhexanoate and triethylaluminum
described in more detail in the examples. It is preferable to extract the
nickel catalyst after hydrogenation by stirring the polymer solution with
aqueous phosphoric acid (2-30 percent by weight), at a volume ratio of
about 0.5 parts aqueous acid to 1 part polymer solution, at about
50.degree. C. for 30-60 minutes while sparging with a mixture of oxygen in
nitrogen. This step is also described in more detail in the examples.
Saturated or unsaturated conjugated diene polymers having one or more
terminal functional group selected from hydroxyl, carboxyl, phenol, epoxy,
and amine groups can be used without solvents when the viscosity of the
polymer is less than about 500 poise at mixing and application
temperature. Linear hydrogenated butadiene or isoprene polymers having two
terminal hydroxyl groups per molecule and lower viscosity than 500 poise
at mixing and application temperatures are produced by limiting the peak
molecular weight to a range from about 500 to 20,000 and by limiting the
1,2-addition of hydrogenated butadiene to an amount between 30% and 70%,
preferably between 40% to 60%.
After polymerization and, optionally, hydrogenation and washing of the
polymer, the trimethylsilyl group at the front of the polymer chain is
removed to generate the desired primary, neopentyl-type hydroxyl
functional group. This step is often referred to as deprotection. A
variety of processes for removal of the silyl protecting group are known;
for a review, see T. W. Greene, "Protective Groups in Organic Synthesis",
J. Wiley and Sons, New York, 1981. Deprotection preferably involves easily
handled, relatively low toxicity, inexpensive reagents and mild, low cost
process conditions. Reaction with tetrabutylammonium fluoride in THF, as
described in WO 91 112277, is disadvantaged due to the high cost and
toxicity of the reagents. In a preferred process, the trimethylsilyl group
is removed after hydrogenation and during the aqueous acid wash for
removal of the spent Ni/Al hydrogenation catalyst. This technique avoids
the cost associated with a separate process step for deprotection. For the
preparation of an unsaturated polymer where hydrogenation catalyst
extraction is not required, contacting the polymer cement with a dilute
aqueous acid or dilute aqueous base solution is preferred for
deprotection.
For some applications, such as coatings prepared by baked cures of the
polymer with amino resins in the presence of a strong organic acid
catalyst, it may be preferable to use the polymer in its "protected" form.
The viscosity of the protected polymer is lower and conditions such as
those described above should accomplish the deprotection (generate the
alcohol) during the cure.
The conjugated diene polymers produced as described above have the
conventional utilities for terminally functionalized polymers of such as
forming adhesives, coatings, and sealants. Additionally, the polymers may
be used to modify polyurethanes, polyesters, polyamides, polycarbonates,
and epoxy resins.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The most preferred process uses the initiator having the following
structure:
##STR4##
(3-lithio-2,2-dimethyl-1-trimethylsilyloxypropane) to produce
dihydroxylated 1,3-butadiene polymers having a peak molecular weight from
500 to 200,000, most preferably from 500 to 20,000. The dihydroxylated
polymers can be unsaturated with 1,2-addition from 5% to 95% or
hydrogenated with 1,2-addition from 30% to 70%. The polymers preferably
have from 1.75 to 2.0, most preferably from 1.95 to 2.0, terminal hydroxyl
groups per molecule.
After polymerization of the desired amount of 1,3-butadiene, the living
polymer is capped with ethylene oxide and reacted with methanol to give a
terminal primary alcohol group. The silyl group is then converted to a
primary, neopentyl-type hydroxyl group by reaction with dilute aqueous
acid or dilute aqueous base.
The preferred polymers of the present invention are useful in adhesives
(including pressure sensitive adhesives, contact adhesives, laminating
adhesives and assembly adhesives), sealants (such as urethane
architectural sealants, etc.), coatings (such as topcoats for automotive,
epoxy primers for metal, polyester coil coatings, alkyd maintenance
coatings, etc.), films (such as those requiring heat and solvent
resistance), molded and extruded thermoplastic and thermoset parts (for
example thermoplastic injection molded polyurethane rollers or reaction
injection molded thermoset auto bumper, facie, etc.).
A composition of the instant invention may contain plasticizers, such as
rubber extending plasticizers, or compounding oils or organic or inorganic
pigments and dyes. Rubber compounding oils are well-known in the art and
include both high saturates content oils and high aromatics content oils.
Preferred plasticizers are highly saturated oils, e.g. Tufflo.RTM. 6056
and 6204 oil made by Arco and process oils, e.g. Shellflex.RTM. 371 oil
made by Shell. The amounts of rubber compounding oil employed in the
invention composition can vary from 0 to about 500 phr, preferably between
about 0 to about 100 phr, and most preferably between about 0 and about 60
phr.
Optional components of the present invention are stabilizers which inhibit
or retard heat degradation, oxidation, skin formation and color formation.
Stabilizers are typically added to the commercially available compounds in
order to protect the polymers against heat degradation and oxidation
during the preparation, use and high temperature storage of the
composition.
Various types of fillers and pigments can be included in the coating or
sealant formulation. This is especially true for exterior coatings or
sealants in which fillers are added not only to create the desired appeal
but also to improve the performance of the coatings or sealant such as its
weatherability. A wide variety of fillers can be used. Suitable fillers
include calcium carbonate, clays, talcs, silica, zinc oxide, titanium
dioxide and the like. The amount of filler usually is in the range of 0 to
about 65% w based on the solvent free portion of the formulation depending
on the type of filler used and the application for which the coating or
sealant is intended. An especially preferred filler is titanium dioxide.
The dihydroxylated conjugated diene polymers of the present invention may
also be blended with other polymers to improve their impact strength
and/or flexibility. Such polymers are generally condensation polymers
including polyamides, polyurethanes, vinyl alcohol polymers, vinyl ester
polymers, polysulfones, polycarbonates and polyesters, including those,
like polyacetones, which have a recurring ester linkage in the molecule,
and those, like polyalkylene arylates, including polyalkylene
terephthalates, having a structure formed by polycondensation of a
dicarboxylic acid with a glycol. The blends may be made in the reactor or
in a post compounding step.
The present invention is further described by the following examples which
include the best mode known to Applicant for making a dihydroxylated,
saturated polybutadiene (EB Diol). The examples are not intended to limit
the present invention to specific embodiments although each example may
support a separate claim which Applicant asserts to be a patentable
invention.
The peak molecular weights were measured using gel permeation
chromatography (GPC) calibrated with polybutadiene standards having known
peak molecular weights. The solvent for the GPC analyses was
tetrahydrofuran.
The 1,2-additions of polybutadiene were measured by .sup.13 C NMR in
chloroform solution.
Initiator Synthesis
EXAMPLE 1
The initiator of structure (3), designated PFI10, was prepared using the
procedures broadly described in WO 91 112277. The hydroxyl functionality
in 2,2-dimethyl-3-chloropropanol was protected by reaction with
trimethylsilyl chloride. A solution of trimethylsilyl chloride (27.16 g,
0.25 mol) in dry cyclohexane (150 g) was treated with 20.4 g of imidazole
(0.30 mol) under an argon atmosphere. The resulting slurry was stirred
vigorously at room temperature as 2,2-dimethyl-3-chloropropanol (30.93 g,
0.25 mol) was added slowly to the mixture. The rate of addition was
controlled to keep the reaction temperature below 40.degree. C. The
resulting slurry was filtered affording a clear solution of the desired
1-trimethylsilyloxy-2,2-dimethyl-3-chloropropane. Analysis using a Gas
Chromatography-Mass Spectroscopy (GC-MS) technique found essentially no
side products. The trimethylsilyl protected adduct was obtained in
quantitative yield. A repeat of this experiment gave similar results.
The trimethylsilyl adduct of 2,2-dimethyl-3-chloropropanol was lithiated
affording the desired lithium alkyl. For this experiment, Li metal was
obtained as a dispersion (0.5% wt Na) in mineral oil (30% wt Li) and the
dispersion was washed repeatedly, under an argon atmosphere with dry
cyclohexane to remove the mineral oil carrier. A slurry of the freshly
washed Li metal (28 g, 4.03 mol) in cyclohexane (180 g) was contacted with
vigorous stirring with a portion of the cyclohexane solution (73.07 g of
solution) of the trimethylsilyl adduct (about 24 g of adduct, about 0.12
mol of adduct) prepared as described above. The rate of addition of the
chloropropane reagent was controlled to keep the temperature of the
reaction solution below 40.degree. C. When addition of the trimethylsilyl
adduct of 2,2-dimethyl-3-chloropropanol was complete, the resulting slurry
was filtered (5 micron filter) affording a clear solution of
3-lithio-2,2-dimethyl-1-trimethylsilyloxypropane in cyclohexane. An
aliquot of the product solution was titrated with diphenylacetic acid
according to the procedure of Korfron and Baclawski (J. Org. Chem., 41,
1879(1976)). This analysis, which is specific for C-Li moieties, found the
present reagent to have a lithium alkyl concentration of 0,217M (4.65%
wt). A repeat of this lithiation reaction afforded a reagent having a
lithium alkyl concentration of 0.22M (4.74wt %). A third replicate
experiment included additional cyclohexane which gave a reagent solution
having a lithium alkyl concentration of 0.095M (2.03% wt).
EXAMPLE 2
Using the procedure described in Example 1, the hydroxyl functionality in
2,2-dimethyl-3-bromopropanol (83.52 g, 0.5 mol) was protected by reaction
with trimethylsilyl chloride (54.32 g, 0.5 mol) in the presence of an
excess of imidazole (41.8 g, 0.61 mol). The product was isolated and
analyzed as described in Example 1. The trimethylsilyl protected adduct
was obtained in quantitative yield.
Using the procedure described in Example 1, the solution of the
trimethylsilyl adduct of 2,2-dimethyl-3-bromopropanol (31.38 g, 0.13 mol)
was reacted with an excess of Li metal (about 35 g, about 5.04 mol) in
cyclohexane (102 g). The product was isolated and analyzed as described in
Example 2. A solution of 3-lithio-2,2-dimethyl-1-trimethylsilyloxypropane
in cyclohexane (0.13M, 2.72% wt RLi) was obtained.
EXAMPLE 3 (COMPARISON)
Using the procedure described in Example 1, PFI11 was prepared wherein the
hydroxyl functionality in 3-chloropropanol (47.27 g, 0.5 mol) was
protected by reaction with trimethylsilyl chloride (54.32 g, 0.5 mol) in
the presence of an excess of imidazole (40 g, 0.587 mol). The product was
isolated and analyzed as described in Example 1. The trimethylsilyl
protected adduct was obtained in quantitative yield.
Using the procedure described in Example 1, the solution of the
trimethylsilyl adduct of 3-chloropropanol (19.77 g, 0.118 mol) was reacted
with an excess of Li metal (about 28 g, about 4.03 mol) in cyclohexane
(100 g). The product was isolated and analyzed as described in Example 2.
A solution of 3-lithio-1-trimethylsilyloxypropane in cyclohexane (0.101M,
1.8% wt RLi) was obtained.
EXAMPLE 4 (COMPARISON)
Additional comparison initiators, designated PFI2 and PFI3, were prepared
in dry cyclohexane by reaction of 2,2-dimethyl-3-chloropropanol and
3-chloropropanol (respectively) with t-butyldimethylsilyl chloride
(TBDMS-Cl) in the presence of imidazole, followed by reaction with lithium
metal, as broadly described in WO 91 112277. The concentration of active
lithium alkyl was determined by titration with diphenylacetic acid, as
described above (W. G. Korfron and L. M. Baclawski J. Org. Chem, 41(10),
1879 (1976)).
Polymerization
EXAMPLE 5
Reaction of the lithium initiator of structure (3) with butadiene
effectively initiated polymerization and reaction of the living polymer
product with ethylene oxide afforded, after isolation, a high yield of a
telechelic polybutadienyl diol.
A solution of the 3-lithio-2,2-dimethyl-1-trimethylsilyloxypropane
(RLi)(157.85 g of solution, 4.74% wt RLi, 0,045 mol RLi) in cyclohexane,
prepared as described in Example 1, was added, under argon, to a solution
of polymerization grade butadiene monomer (180 g, 3.33 mol) in a mixed
cyclohexane/diethyl ether (202 g cyclohexane/60 g diethyl ether) solvent
with vigorous stirring in a steel autoclave. Not all of the monomer was
present in the reactor at the start of polymerization as a portion of the
monomer was held in reserve and added to the reactor at a rate that
allowed control of the reaction temperature during the exothermic
polymerization reaction. Polymerization was initiated at 15.degree. C. and
the resulting exothermic reaction raised the solution temperature to
21.7.degree. C.
Immediately after the addition of the lithium initiator to the reactor when
polymerization had just begun, an aliquot of the living polymer solution
was removed for analysis and quenched immediately by addition of an excess
of MeOH. (Just Initiated Sample). The remainder of the solution was
allowed to react to essentially complete consumption of the butadiene (85
min). An aliquot of the living polymer solution was taken from the reactor
for analysis and quenched immediately by addition of an excess of MeOH.
(Complete Polymerization Sample). The bulk of the solution which contained
a living butadiene polymer having a trimethylsilyloxy moiety on one end of
the polymer chain was treated with an excess of ethylene oxide (3.4 g,
0.077 mol). The ethoxylation reaction was allowed to proceed for 60 min at
40.degree. C. The cement was treated with 4 g of methanol. An aliquot of
the resulting polymer cement was removed for analysis (EO Capped Sample).
The bulk of the reaction product was reserved for an hydrogenation
experiment which is described in Example 8.
The sample collected just after initiation of butadiene polymerization
(Just Initiated Sample) was found to have a number average molecular
weight (MW.sub.N) of 514 (as measured by a Carbon-13 Nuclear Magnetic
Resonance (NMR) method which compares the ratio of the carbon signal that
is attributed to the alkyl segment of the initiator to the total carbon
signal for the sample). Analysis of this sample for vinyl content, also
using an NMR technique, found that 45.5% wt of the butadiene had added by
1,2-polymerization affording pendant vinyl unsaturation with the remainder
added by 1,4-polymerization giving enchained unsaturation species. When
the sample that was collected after complete polymerization of the
butadiene was analyzed using the same methods, the molecular weight (as
measured by a gel permeation chromatography (GPC) technique) was found to
be 4997 (MW.sub.N) and the 1,2-polymerization content was 45.5% wt. As
both of these samples have the same 1,2-polymerization levels, it is clear
that the microstructure of the polymer prepared using the
trimethylsilyloxy protected initiator is uniform throughout the
polymerization process, a preferred result, and is intermediate in vinyl
content (45.5% wt) when about 10% wt diethyl ether is present in the
polymerization solvent. As the targetted MW for this polymerization was
4000 and the observed MW for the completely polymerized sample was 4997,
it is clear that 80% of the lithium alkyl added to the reactor was
effective in initiating polymerization with the remainder being lost to
deactivation processes ("die-out") prior to or during polymerization.
These results show that the initiators of Structure (2) are effective for
butadiene polymerization at commercially useful temperatures. Further,
these results show that these initiators prepare functionalized butadiene
polymers having a uniform microstructure. A uniform and intermediate
microstructure is preferred during butadiene polymerization for avoiding
crystallinity problems (polyethylene segments) when the polymer is
hydrogenated.
The EO Capped Sample was concentrated at 50.degree. C. under reduced
pressure to afford a sample for High Pressure Liquid Chromatography (HPLC)
analysis (a 250 mm.times.4.6 mm, 5 micro DIOL phase column, using a
stepped heptane/THF solvent gradient with an evaporative light scattering
detector). This method of analysis found principally a butadiene polymer
having 2 hydroxyl functional sites per molecule (a telechelic
polybutadiene diol) with a trace (less than 2% wt) of polymer having 1
hydroxyl functional site per molecule (a polybutadiene having an hydroxyl
functional group on only one end of the chain); there was no evidence for
TMS capped polymer in this sample. Apparently, the TMS protecting group
was removed under the conditions used for concentrating the samples
(methanolic LiOMe at 50.degree. C. for a few minutes). This is a very mild
deprotection condition. The
3-lithio-2,2-dimethyl-1-trimethylsilyloxypropane initiator is preferred
for affording a polymer having masked hydroxyl functionality that is
readily deprotected under mild, basic conditions.
EXAMPLE 6
The polymerization process described above was repeated using another
aliquot of 3-lithio-2,2-dimethyl-1-trimethylsilyloxypropane (89.39 g of
solution, 4.15 g R | | |
