Note: Descriptions are shown in the official language in which they were submitted.
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ALKOXY SILYL CAPPING AGENTS FOR MAKING
TERMINALLY FUNCTIONALISED POLYMERS
This invention relates to preparation of
functionalised polymers used as components in
adhesives, sealants and coatings. More specifically,
this invention relates to capping of living anionic
polymers to add term; n~ 1 functional groups.
Anionic polymerisation of conjugated dienes with
lithium initiators, such as sec-butyllithium, and
hydrogenation of residual unsaturation has been
described in many references. The capping of mono-
initiated and di-initiated living anionic polymers to
form functional end groups is described in British
Patent Application No. GB 2270317.
Anionic polymerisation using protected functional
initiators having the structure RlR2R3Si-o-A'-Li is
described in US 5,331,058 wherein Rl, R2, and R3 are
preferably alkyl, alkoxy, aryl, or alkaryl groups haing
from l to l0 carbon atoms, and A' is preferably a
branched or straight chain bridging group having at
least 2 carbon atoms. Polymerisation with such a
protected functional initiator, followed by capp ng to
produce a second terminal functional group, p~oduces
telechelic polymers which otherwise can be prepared by
capping polymers prepared with difunctional initiators
such as l,4 dilithiobutane and lithium naphthalide.
The use of a protected functional group avoids the
formation of ionic gels which occur when diinitiated
polymers are capped with reagents such as ethylene
oxide. These gels form even in relatively polar
solvent mixtures and hinder subsequent processing
steps.
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One way to prepare difunctional telechelic polymers
without forming a gel is to use a protected functional
initiator such as the structure:
ICH3
CH3-Si-O-CH2-A"-CH2-Li (A)
CH3
wherein A" is cyclohexyl or -CR'R"-, wherein R' is a
linear alkyl having from l to l0 carbon atoms and R" is
hydrogen or a linear alkyl having from l to l0 carbon
atoms. The compounds of structure (A) initiate
polymerisation of anionic polymers at high
polymerisation temperatures. The protected functional
group survives hydrogenation of conjugated diene
polymers and is readily removed by hydrolysis in the
presence of methanesulfonic acid. The initiators of
structure (A) can be used to make telechelic polymers
by capping with ethylene oxide or oxetane. However,
oxetane is not readily available on a commercial scale
and ethylene oxide can be hazardous due to its
reactivity and toxicity.
A recent publication by M.A. Peters and J.M.
DeSimone (Polym. Prepr. (Am. Chem. Soc. Div. Poly-
Chem.), 1994,35(2), 484) describes the prepara.lc~ of
mono- and di-functional polymers by capping mono-
initiated and di-initiated living anionic polymer with
a chlorosilane of the following structure:
CH3 CIH3 CH3
CH3-1C Si-O-(CH2)3-Si-Cl (B)
CH3 CH3
instead of ethylene oxide or oxetane. In this process,
LiCl is eliminated and the protected alcohol group is
added to the polymer chain end, avoiding gel formation.
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~ - G~ ( p ~ - 3 -
The present invention is the discovery that
mono-initiated or di-initiated anionic polymers are
efficiently capped with silyl alkoxy ~ompounds LcR p~e~
possessing acidic alkoxy ~adicals as leaving groups and
a variety of protected functional groups, resulting in
terminal protected functional groups that are stable
under a variety of conditions. The protected
functional group is preferably an acetal group, but can
be any group that readily converts to more reactive
terminal functional groups useful for making adhesives,
sealants and coatings.
The anionic polymerisation of unsaturated monomers
with mono-lithium initiators such as s-butyllithium or
di-lithium initiators such as the diadduct of
s-butyllithium and m-diisopropenylben~ene is described
in British Patent Application Serial No. 2270317.
Polymerisation results in one or more terminal lithium
atoms which readily react with ethylene oxide or
oxetane to cap the polymers with one or more terminal
hydroxyl groups per molecule. The terminal hydroxyl
groups tend to form weak associations between
molecules, which has no adverse effects if these chains
are mono-initiated. However, the di-alkoxide folymer
anions formed by capping di-initiated polymers
associate to form an ionic gel w~ch is very~difficult
to process.
The use of the protected-functional capping agent
of structure (B) avoids gel formation and avoids the
problems presented by capping with cyclic ethers.
However, the use of this reagent to cap low molecular
weight polymer anions results in the generation of
large amounts of lithium chloride, which introduces new
difficulties. For example, the preferred method for
converting the silyl ether to the alcohol involves
contact with aqueous methanesulfonic acid. The
presence of high levels of halide in such a mixture
f o ~ e~o ~
.
AMENDE~ SHEET
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~ v~c~l ~c ~ _ 4 _
presents severe corrosion problems. Also, the polymers
are preferably hydrogenated with a Ni/Al catalyst (to
be described in detail below) that is poisoned by high
levels of halide. In order to hydrogenate polymers
capped with structure (B), an aqueous acid wash would
likely be required to remove the LiCl. A drying step
would probably also be required, since the catalyst is
also deactivated by water.
The advantages gained by using a protected-
lo functional capping agent are realized without
introducing halide ions by capping mono-initiated or
di initiated polymers with silyl alkoxides ~aving
acidic alkoxy ~eaving groups and stable protecting
groups as shown by the following structure:
CH3 ~ p~ cl~
I
Y-(CH2)3-Si-Z (1) ~v
I o ~ e~c,c,
CH3
15 wherein Y is a protected functional group, preferably
an acetal group, which is stable during the
polymerisation step and converts to more reactive
terminal functionality as described below, and Z is an
acidic alkoxy ~roup, preferably phenoxy radicals or
trifluoroethoxy radicals. The acetal group is
preferred as the protecting group since it is easily
introduced and cleaved, and has more favorable raw
material costs than the t-butyl dimethylsilyl ether
group of structure (B) or the trimethylsilyl ether
25 group of structure (A).
The alkoxy ~ilyl capping agents of equation (1) are
prepared by hydrosilation of the appropriate
dimethylsilane (Z-Si(CH3)2H) with an allyl species
containing the protected functional group
(CH2=CH-CH2-Y). Hydrosilation was accomplished using a
Pt catalyst, as is generally described by M. A. Peters
~E\IDEI~ SH~Er
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and J. M. DeSimone (Polym. Prepr. (Am. Chem. Soc.Div.
Polym. Chem.), 1994,35(2), 484). After capping of the
polymer, the protecting group is removed by reaction
with methanesulfonic acid, as described in U.S. Patent
5,391,663.
A variety of processes for removal of the
protecting groups are known; for a review, see T. W.
Greene, "Protective Groups in Organic Synthesis", J.
Wiley and Sons, New York, 1981. A preferable process
would involve easily handled, relatively low toxicity,
and inexpensive reagents. In a preferred process, the
acetal group is removed by reaction of the polymer
solution with 1 - 10 equivalents (basis acetal end
groups) of a strong organic acid, preferably
methanesulfonic acid (MSA), in the presence of 0.1% -
2% by weight of water and 5% - 50% by volume of
isopropanol (IPA) at about 50C.
Mono-initiation is preferentially performed using
s-butyllithium. Di-initiation is preferentially
performed using the diadduct of s-butyllithium and
m-diisopropenylbenzene, as described in British Patent
Application Serial No. GB 2270317. Polymerisation is
preferably initiated at a temperature from 20C to 60C,
most preferably from 30C to 40C. It is generally
advisable to keep the polymerisation temperature below
about 100C; above this temperature, side reactions that
change microstructure and limit capping efficiency may
become important. Polymerisations can be carried out
over a range of solids, preferably from 5% to 80%, most
preferably from 10% to 40%. For high solids
polymerisations, it is preferable to add the monomer in
increments to avoid exceeding the desired
polymerisation temperature. If the initiator is to be
added to the full monomer charge, it is preferable to
run the polymerisation between 10% and 20~ solids.
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The protected group is introduced by reacting l.05
- 2 equivalents of the capping agent of structure (1)
per lithium site (2 per chain in the case of
di-initiated polymers) at a temperature of 40C - 80C
for at least 30 minutes. If no polar microstructure
modifier was present during the polymerisation, it may
be desireable to add a non-reactive coordinating agent,
such as diethyl ether or glyme, during this step.
The polymers of the present invention preferably
comprise a polymerised unsaturated monomer selected
from the groups consisting of styrene, l,3-butadiene,
and isoprene. When the anionic polymer comprises
polymerised l,3-butadiene which contains residual
monomer unsaturation which is to be saturated by
hydrogenation, the anionic polymerisation of the
conjugated diene hydrocarbons is typically controlled
with structure modifiers such as diethyl ether or glyme
(l,2-diethoxyethane) to obtain the desired amount of
l,4-addition. As described in Re 27,145, the level of
l,2-addition of a butadiene polymer or copolymer can
greatly affect elastomeric properties after
hydrogenation. The hydrogenated polymers exhibit
improved heat stability and weatherability in the
final, adhesive, sealant or coating.
The l,2-addition of l,3-butadiene polymers having
terminal functional groups influences the viscosity of
the polymers as described in more detail below. A
l,2-addition of about 40% is achieved during
polymerisation at 50C with 6% by volume of diethyl
ether or lO00 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.
Hydrogenation of at least 90%, preferably at least
95%, of the unsaturation in low molecular weight
butadiene polymers is achieved with nickel catalysts as
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described in U.S. Patents Re. 27,145 and 4,970,254 and
U.S. No. 5,166,277. 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 ~20 - 30 percent by weight), at
a volume ratio of about 0.5 parts aqueous acid to 1
part polymer solution, at about 50C for 30 - 60 minutes
while sparging with a mixture of oxygen in nitrogen.
This step is also described in more detail in the
examples.
Sufficient IPA must be present during deprotection
to prevent the formation of a discrete aqueous phase.
Excess acid is then removed by washing with dilute
aqueous base, preferably O.lN - 0.5N sodium hydroxide,
followed by water. 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.
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
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are highly saturated oils, e.g. TUFFLO 6056 and 6204
oil made by ARCO and process oils, e.g. SHELLFLEX 371
oil made by SHELL. The amounts of rubber compounding
oil employed in the invention composition can vary from
s 0 to 500 phr, preferably between 0 to 100 phr, and most
preferably between 0 and 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 weather-ability. 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
2s 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
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.
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 preferred process of the present invention
caps di-initiated 1,3-butadiene polymers with alkoxy
silyl capping agents having acetal protecting groups
represented by the structure:
~ IL ~Q~Q
F~3 ICH3
CH3-CH2-O-C~-O-CH2-CH2-CH2-Si-Z (2)
CH3
wherein Z is a phenoxy group or a trifluoroethoxy
group. The alkoxy ~ilyl capping agents of equation (2)
are prepared by hydrosilation of the appropriate
dimethylsilane (Z-Si(CH3)2X) with the vinyl acetal
resulting from the reaction of ethyl vinyl ether and
allyl alcohol in the presence of an acid catalyst.
Hydrosilation was accomplished using a Pt catalyst, as
is generally described by M. A. Peters and J. M.
D DeSimone (Polym. Prepr. (Am. Chem. Soc.Div. Polym.
Chem.), 1994,35(2), 484). After capping of the polymer,~
the protecting group is removed by reaction with
methanesulfonic acid, as described in U.S. Patent No.
5,391,663.
The preferred process ultimately produces
dihydroxylated, saturated 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,
~MENDE!)SHEE~
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most preferably from 1.95 to 2.0, terminal hydroxyl
groups per molecule.
The preferred process initially makes a novel
intermediate polymer which has a protected acetal
functional group on each end of a linear 1,3-butadiene
polymer. The intermediate polymer can be sold in a
saturated or unsaturated version for making adhesives,
sealants, and coatings wherein either the supplier or
the customer deprotects the functional groups by a
reaction that converts the protected functional groups
to hydroxyl groups. L~ P~ ~7
The preferred process comprises di-initiation with
the diadduct of s-butyllithium and m-diOisopropenyl-
benzene, polymerisation of 1,3-butadiene, and capping
with an .acidic alkoxy ~ilyl acetal having structure
(2). The reaction results in exclusion of lithium
alkoxide and the silyl acetal protecting group replaces
the lithium at both ends of the living anionic polymer
molecule.
The intermediate polymers of the present.invention
are useful for making adhesives (including pressure
sensitive adhesives, contact adhesives, laminating
adhesives and assembly adhesives), sealants (such as
J urethane architectural sealants, etc.), coatings (such
as topcoats for automotive, epo~-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, étc.).
The present invention is further described by the
following examples which include the best mode known to
Applicant for making a saturated, linear polybutadiene
polymer having one or two terminal silyl acetal groups.
The examples are not intended to limit the present
Al~1ENDED ~HEET
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~ c~d~ ~
The examples are not intended to limit the present
invention to specific embodiments.
Examples
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
13C NMR in chloroform solution.
Three protected-functional capping agents,
ethyl(dimethylethoxysilylpropyl) formaldehyde acetal
(CAl), ethyl(dimethylphenoxysilylpropyl) formaldehyde
acetal (CA2), and ethyl(dimethyl-3,3,3-trifluoroethoxy-
~
silylpropyl) formaldehyde acetal (CA3), were preparedby hydrosilation of the appropriate dimethylsilane
(dimethylethoxysilane, dimethylphenoxysilane, and
dimethyl-3,3,3-trifluoroethoxysilane, respectively) as
described previously. Reaction conditions are
summarized in Table 1 for these agents.
Example 1
Poly(butadiene) "mono-ols" were prepared by
initiation with s-butyllithium while poly(butadiene)
"diols" were prepared by initiation with the product of
diisopropenyl benzene and 2 equ-i~alents of s-butyl-
lithium. Unless otherwise specified, polymer examples
1-1 through 3-2 were prepared in cyclohexane/diethyl
ether(10%) and methanol was added to terminate any
uncapped ch~; nS . For the alkoxy~silyl acetal capping
agents of structure (2) (i.e. CAl, CA2, and CA3), the
characteristic yellow color of the polymer anion faded
considerably after adding the capping agent. Samples
were deprotected using methanesulfonic acid, dried
(rotary evaporator), and analyzed by GPC, 13C NMR, and
HPLC. Samples taken prior to deprotection were
contacted with concentrated phosphoric acid to remove
La~ ~47
~ ENDED ~HEET
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~ p ~ - '2 -
or neutralize lithium salts prior to drying; except in
one case, described below, this did not result in
significant hydrolysis of the acetal groups.
To simplify the analysis, screening studies were
carried out using "mono-initiated" polymers although
di-initiated polymers are preferred. The results are
summarized in Table 2. HPLC could not unambiguously
resolve acetal-capped polymer from proton-terminated
polymer, so only NMR data was used to assess the
io capping efficiency prior to deprotection. The results
of the analysis of the deprotected products are also
summarized in Table 2; 13C NMR results are consistent
with quantitative hydrolysis of the acetal group. The
more acidic alkoxy ~ apping agents were much more ~ p ~e~
reactive than the ethoxy analog, yielding capping
efficiencies on the order of 90% without adding THF or
any other reaction promoter.
GPC analysis indicated that a small fraction of the
polymer anions were coupled (twice original MW). This
may be due to oxygen coupling or the presence of a
small amount of silane impurity with two "active"
ligands; the capping agents were added without further
purification. These experiments also suggest that both
capping agents react readily at moderate temperatures.
Analysis by NMR could detect no~ignificant improvement-
in capping efficiency between samples capped for 30
minutes at 40C and samples taken after heating to 80C
and holding at 80C for an hour.
Example 2
In order to assess the utility of this approach for
preparing diols, a diinitiated butadiene polymer
(Example 2-1) was capped with the phenoxy silyl acetal
compound (CA2) at 40C, and an aliquot of the same
cement was reacted with excess ethylene oxide (Example
2-2). The analytical results are summarized in Table
3. The silyl acetal capped product remained a viscous
~`E~DF~H~ET
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G,~ p~ ~ - 13 -
liquid while the ethylene oxide capped product formed a
gel. After deprotection, the silyl acetal capped
product was analyzed by HP~C as well as 13C NMR. The
NMR results indicate slightly higher capping efficiency
with the phenoxy silyl acetal than with ethylene oxide.
The HPLC chromatograms are consistent with this
conclusion. The ethylene oxide capped product contains
substantially more unfunctionalized and
mono-functionalized material and less diol. A
substantial amount of material, tentatively identified
as tri-ol (resulting form initiation by trifunctional
lithium species), was also observed. The relatively
high levels of both mono-ol and tri-ol in this
polymerisation suggest that the optimum yield of
diinitiator may not have been achieved, but it is clear
that products comparable to those obtained by EO
capping were produced without the complications of the
gel using the alkoxy~ ilyl approach. ~ p ~G~
~xam~le 3
A sample (3-1) prepared by capping a monoinitiated
polymer with the phenoxy silyl acetal compound (CA2),
followed by methanol termination was hydroge~ated tsing
300 ppm of a 2.5:1 Al:Ni catalyst, added in three 100
ppm aliquots over 3 hours. About 95.6% o' the ~_ vmer
double bonds were hydrogenated~ sample c' ~ s
cement was isolated without methanol additio~ (3-2).
Surprisingly, the acetal seems to have been hydrolyzed
by the phosphoric acid neutralization; an unusually
high level of suspended salts was also noted in the dry
sample. On standing, a significant amount of
precipitate, presumably lithium phenoxide, settled out
of the solution. After decanting from the precipitate,
the sample was hydrogenated as described above; the
extent of hydrogenation achieved was quite low, only
about 56%. The reason for the decreased yield is
unclear, but it seems safe to conclude that it is
A~END~r;~HE~
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p ~ - 14 -
preferable to terminate with met~anol prior to
- hydrogenation.
Table 1
Summary of Alkoxy ~ilyl Capping Reaction Conditions
Sample Initiator CA# CA:Li Rxn Time Txn Temp
1-1 s-BuLi CAl 1.5:1 60 min.l 80
1-2 s-BuLi CA12 1.5:160 min. 1 80
1-3 s-BuL CA13 1.5:160 min. 1 80
1-4 - s-BuLi CA2 1.5:130 min. 40C
1-5 s-BuLi CA2 1.5:160 min.4 80C
1-6 s-BuLi CA3 1.5:130 min. 40C
1-7 s-BuLi CA3 1.5:1 , 60 min.4 80C
2-1 DiLi5 CA2 1.05:1 80 min. 40C
3-1,3-26 s-BuLi CA3 l:l60 min. 40C
1 CA added at 40C, then heated to 80C for 60 min.
2 100 ppm glyme added with CAl.
3 Tetrahydrofuran added until 5% by volume, prior to
CAl.
4 Prepared by heating preceding 30 min/40C sa~.ple to
80C and holding for 60 min. ~
5 Product of 2 moles s-butylithium and 1 mole
diisopropenyl benzene (DIPB).
6 Sample 3-2 was not terminated with methanol.
[ ~ r ~--
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Table 2
Summary of Analytical Data for Mono-ols
Prepared by Capping with CA1 and CA2
SampleMW Capping % hydro- % mono-
(GPC) Effic'y carb(1) ol(1)
(NMR) (NMR(2)/ (NMR(3)
HPLC) HPLC)
1-1 2,000 65% 40/34 60/66
1-2 5,000 70% ---- ----
1-3 4,800 83% 28/15 72/85
94% ____
1-5 4,100(4) 99% 22/8 78/92
1-6 4,160(4) 89% ---- ----
1-7 4,160(4) 90% 25/15 75/85
3-1 4,320(4) 80%205/1o(5,6) 80/go(5,6)
3-2 4,320(4) 79%21(5~7)/10(5)79(5,7)/90(5)
(1) Unless otherwise specified, after deprotection.
(2) No acetal resonances detected by 13C NMR,
consistent with quantitative hydrolysis of all capped
chains.
(3) Lower value relative to HPLC and theoretical
(complete conversion of capped chains) may be due to
error in backing out the contribution of interefering
resonances.
(4) 2%-3% polymer of twice this MW (coupled product).
(5) Hydrogenated sample.
(6) Sample deprotected during isolation; did not
require treatment with MSA/IPA to effect deprotection.
(7) Capping efficiency prior to deprotection;
hydrogenation obscures s-bu resonance so that the
s-bu:C-OH ratio cannot be determined.
.~
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- 16 -
Table 3
Analytical Data for Diols Prepared by Capping with
Phenoxy Silyl Acetal (CA2) or Ethylene Oxide (EO)
Sam- Cap- MW NMR % % % %
ple ping (GPC) C.E.HC M-ol Diol Triol
Agent (1)(HPLC) (HPLC) (HPLC) (HPLC)
2-1 CA2 4,700 96%0.5 18 50 31.5
2-2 EO 4,500 86~5 23.5 44.5 27
(1) MW of 4,400 prior to adding capping agent (MeOH
termin.).
